School Science Lessons
2024-07-09
Please send comments to: j.elfick@uq.edu.au
(UNBiology6)
Plant physiology
Contents
9.2.0 Hydroponics
9.3.0 Plant growth
9.4.0 Seed germination
9.5.0 Tropisms
9.2.0 Hydroponics, soil-less culture solutions
9.2.1 Hydroponics
9.2.2 Containers for hydroponics
9.2.3 Knop's solution
9.2.4 Mineral deficiency experiment, hydroponics, EDTA
9.2.5 Plants need mineral salts, maize
9.2.6 Soil-less culture solutions, maize
9.2.7 Use of freshwater algae for hydroponics
9.3.0 Plant growth
9.3.1 Effect of copper on the growth of algae
Experiments
9.3.2 Allelopathy of Lantana leaves
9.3.3 Best conditions for plant growth using data loggers
9.3.4 Growth of plants in the classroom without soil
9.3.5 Growth of radicle, zone of elongation, broad bean root
9.3.6 Growth of young shoot, sunflower, castor oil seedlings, mung bean
9.3.7 Growth of first internode, runner bean seedlings
9.4.18 Plant embryo development, shepherd's purse
9.3.9 Seedlings growing in the light and in the dark, e.g. pea
9.3.10 Zone of elongation of growing root
9.4.0 Seed germination
9.4.1 Breakdown starch during germination
9.4.2 Conditions necessary for germination, After-ripening
9.4.3 Cotyledon functions
1.27 Drinking glass garden (Primary)
9.4.4 Drinking glass garden
9.4.5 Endospermic and non-endospermic seed
9.4.6 Enzyme activity during germination
9.4.7 Epigeal germination
9.4.8 Epigeal germination of bean
9.4.9 Germination and air, germination and the need for oxygen
9.4.10 Germination and light
9.4.11 Germination and temperature
9.4.12 Germination and water
9.4.13 Germination from seed to plant
5.27 Germination test (Primary)
1.28 Grow plants from seeds (Primary)
9.4.14 Hypogeal germination, broad bean, pea, wheat
9.4.16 Natural growth inhibitors
9.4.17 Parts of a seed, morphology of the seed
9.4.18 Plant embryo development, shepherd's purse
9.2.6 Soil-less culture solutions, maize
9.4.20 Plants need water, daisy, potted plants
5.28 Seed depth (Primary)
9.4.22 Swelling of seeds, imbibition, during germination
9.4.21 Viability of seed before planting, germination test
9.5.0 Tropisms, nastic movements
9.5.1 Chemotropic responses in germinating pollen, pollen tube
9.5.2 Circumnutation, winding plants
9.5.3 Dispersal of pine seed by swelling movements
9.5.4 Geotropism responses in shoots
9.5.5 Geotropism responses in soaked seeds
9.5.6 Geotropism responses using a clinostat
9.5.7 Gravity affects the growth of stems and roots
9.5.8 Heliotropism of sunflowers
9.5.9 Phototropism
9.5.10 Sprouting potato tuber
9.5.11 Thermonastic responses, nastic movements
9.2.1 Hydroponics
Hydroponics means growing plants without soil.
The technology of culture with hydroponics is to use chemical culture solution that includes contain elements essential for plants.
It is mainly used in vegetables, flowers and plants and tree seedlings.
It is used to beautify the environment and home.
You can plant with hydroponics in places, e.g. desert, city roof and balcony.
Then you can provide nutrient elements according to what the plant is essential.
Water is used in a circle, so it saves fertilizer and water.
9.2.2 Containers for hydroponics
Prepare a series of plastic troughs in which root systems can grow.
Line the interfaces of the trough's both ends plastic cement to avoid leaks or use black plastic to avoid being corroded by culture solution and secretion of root system.
Grow two plants in a plastic bottle wrapped in shading material.
To cultivate small sized vegetables put culture tanks on the windowsill or assemble hanging models.
To link plastic trough and metal net or stand with bolts and fixed articulates.
According to the variety of vegetables and the size of plant regulate the distance between every layer trough.
The end of the plastic trough inclines faintly and slopes criss-cross between every layer trough.
The lower end has the drain hole to drop culture solution, or divert through the thin plastic pipes, into the next layer trough.
In the end, culture solution is dropped can be used repeatedly when the plastic bucket is retrieved.
You can invert over the highest trough a plastic flat bucket whose capacity is 5 to 7 litres.
The outside is packed with black paper or is painted by black and white to cover the light.
To control the velocity at which culture solution moves into the upper trough with the thin pipes and the regulating knob.
The advantage is that it does not take up much land to use space enough, after vegetables grow, it may keep out the burning sun in the summer.
So the plant can give out oxygen to purify the air in the day and let off carbon dioxide to reduce the respiratory consumption in the night.
Open the window when the temperature is not low, and, because this way need not be controlled by electrical machinery and water pumps, managing it is easy.
9.2.3 Knop's solution
In 1865, Johann August Ludwig Wilhelm Knop, 1817-1891, Germany, proposed one of the first culture solutions containing the essential elements.
The ten elements essential for the growth of a green plant are carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium, and iron.
Plants take in carbon as carbon dioxide from the air and hydrogen and oxygen from the water in the soil and air.
Plants absorb other elements with the soil water as salts.
Prepare Knop's solution, in one litre of demineralized or deionized water:
Dissolve: 0.8 g of calcium nitrate, 0.2 g of magnesium sulfate, 0.2 g of acid potassium phosphate, 0.2 g of potassium nitrate, 3 drops of ferric chloride solution.
Prepare the following variations of Knop's solution:
1. Knop's solution omitting nitrogen, calcium sulfate instead of calcium nitrate, potassium sulfate instead of potassium nitrate
2. Knop's solution omitting phosphorus, omit potassium phosphate
3. Knop's solution omitting potassium, sodium phosphate instead of potassium phosphate, sodium nitrate instead of potassium nitrate
4. Knop's solution omitting calcium, sodium nitrate instead of calcium nitrate
5. Knop's solution omitting magnesium, sodium sulfate instead of magnesium sulfate
6. Knop's solution omitting iron, omit the ferric chloride
7. Knop's solution omitting sulfur, magnesium nitrate instead of magnesium sulfate
8. Knop's solution: control
Use 1 litre containers fitted with waxed corks bored with holes to take the plants.
Fix seedlings into the corks with cotton wool, e.g. barley, wheat, broad bean.
Wrap the glass jars with black paper to exclude the light.
Label the jars and record the growth and appearance of the plants.
9.2.6 Soil-less culture solutions, maize
Use 1 litre containers fitted with waxed corks bored with holes to take the plants.
Fix seedlings into the corks with cotton wool, e.g. barley, wheat, broad bean.
Wrap the glass jars with black paper to exclude the light.
Label the jars and record the growth and appearance of the plants.
4.0 Prepare three containers to hold the following solutions:
4.1 Aerated deionized water
4.2 Good garden soil and aerated deionized water
4.3 Aerated deionized water + 2 parts calcium nitrate, 1 part each of potassium nitrate, monobasic potassium phosphate and magnesium sulfate, trace of iron (II) sulfate.
Plant 50 maize grains in a large pot containing old sawdust.
When the maize plants are 3 cm high, select 21 plants of equal size and wash their roots.
Punch seven holes in each of three cork discs.
Insert seven maize plants in each of the holes so that their roots hang down below the holes.
Put a cork disc with attached plants in each container.
After two weeks, note any difference in development of the maize plants.
The plants in 4.1 do not grow well, but the plants in 4.2 and 4.3 grow well.
Compare the growth of plants in 4.2 and 4.3.
9.2.7 Use of freshwater algae for hydroponics
Instead of using higher plants, freshwater green algae, e.g. Scenedesmus, can be used in hydroponics experiments using the solutions above or special mineral deficiency water culture sets of solutions, e.g.Sach's water culture set.
These experiments can be done using indirect sunlight or fluorescent light.
The health of the algae can be gauged by the greenness of the culture.
Excess growth can be used to study the phenomenon of algal bloom leading to deoxygenation of water and production of hydrogen sulfide.
Use copper (II) sulfate, bluestone, to kill algae (< 30g in 35, 000 L potable water).
9.3.1 Effect of copper on the growth of algae
18.7.15 Algicides, control of algae in swimming pools
In swimming pools a copper-based algicide (algae killer) may be used to controls algae, because the copper ion, Cu2+ is a very effective algicide.
A concentration of 0.03 to 1.0 mg / L (0.03 to 1.0 ppm) of free copper ion is needed.
The algicide must contain "free" copper, because "bound" copper, in an insoluble form, does not work.
A concentration in excess of a continuous level of 1.0 ppm is wasteful and may damage surfaces and equipment.
Although copper is toxic to algae at high concentration it is an essential micronutrient for algae at very low concentrations.
Non-copper based algicides may contain the disinfectant benzalkonium chloride, also present in Dettol.
1. Test the growth of algae in solutions with different copper ion concentrations from 0 to 1 ppm.
Measure the amount of algae by measuring the depth at which you can just see a black cross appear or disappear, like the Secchi Disk method for turbidity, or use a simple nephelometer tube.
Copper is a heavy metal ion so handle with care.
9.3.2 Allelopathy of Lantana leaves
9.3.2 Allelopathy of Lantana leaves
Allelopathy usually means the harmful biochemical effects of one plant on another plant.
(Greek allelo, pathy mutual harm).
Extract the juice from chopped up leaves of Lantana camara and observe the effects on the germination of crops species, including the inhibition of germination, root and shoot elongation, and development of lateral roots.
9.3.3 Best conditions for plant growth using data-loggers
1. Use sensors to get quantitative data about plant growth and behaviour, e.g. sensors for oxygen, CO2, relative humidity, gas pressure, colorimeters, pH and conductivity.
2. Use sensors to design and do experiments on rates of photosynthesis, respiration, transpiration and germination.
3. Use sweet basil, chervil, Impatiens, radish in punnets to investigate the factors, e.g. hormones, fertilizer, wavelength or intensity of light, water, carbon dioxide.
4. Problems
How to quantify growth without killing the plant, e.g. height, number of leaves, size of leaves.
How to quantify the % light to the plant, e.g. use shade cloth.
How to quantify intensity of light and colour (wavelength).
How to quantify the growth of tissue-cultured plants with different concentrations of hormones, e.g. horticultural rooting powder.
How to quantify consistently.
Use the same person as an observer for any one variable.
9.3.4 Growth of plants in the classroom without soil
See diagram 9.3.46: Grow plants without soil.
Put a potato, sweet potato, arrowhead vine, and tops of carrot, beet, turnip, pineapple in a container and keep the lower third covered with water or mineral water.
Press toothpicks or matches into the sides to rest the plant parts on the rim of the container.
The tops produce foliage, but not new plants.
9.3.5 Growth of radicle, zone of elongation, broad bean root
See diagram 9.111: Epigeal germination.
See diagram 9.102: Hypogeal germination, Growth of broad bean radicle.
The increase in root length results from growth in the zone of elongation between the root tip and where the root hairs begin.
Germinate a broad bean seed.
When its radicle is 2 cm long, mark with Indian ink from the tip upwards at intervals of exactly a millimetre, for about 10 mm.
Use a wide-necked jar with a cork lid and half full of water.
Push a long pin through the cork and the seed to suspend the seedling in the jar with the root in the water.
Wrap aluminium foil around the jar to keep the root in the dark.
The next day, note how the ink marks have moved apart, because of the growth of the root.
The ink marks have moved different distances apart.
The marks near the root tip have not parted much.
The marks further away have parted further, but the top marks and may not have parted at all.
9.3.6 Growth of young shoot, sunflower, castor oil seedlings, mung bean
See diagram 9.0: Castor seedling.
Grow the seedlings on damp sawdust or potting mix and measure the growth rate under different conditions of watering, fertilizers, exposure to white light, exposure to coloured light.
9.3.7 Growth of first internode, runner bean seedlings
See diagram 9.129.1: Growth-measuring apparatus.
When they are sufficiently developed, take daily measurements of the increase in length of the first internode.
Record these measurements for 2 weeks then plot the data on a graph.
9.3.9 Seedlings growing in the light and in the dark, e.g. pea
Soak same size seeds, e.g. pea or bean, in water and sow in same size flowerpots.
Put one pot in a well light place and the other pot in the dark.
After the seedlings in the light grow to a height of 3 centimetres, compare the seedlings grown in the light and in the dark.
Remove the plants from the pots, wash and dry them and weigh them.
The etiolated plants grown in the dark are taller, but their dry weight per plant is less than the plants grown in the light.
9.3.10 Zone of elongation of growing root
See diagram 9.9.14: Bean plant on floating cork sheet.
See diagram 9.102: Growth of broad bean radicle.
The increase in root length results from growth occurring a small zone, the extension zone, which is situated just behind the tip of the root.
It is only a few millimetres long and usually ends just where the root hairs begin.
Use four bean seedlings having straight roots 3 cm long, and apply, with a fine hair brush, 15 to 20 horizontal ink lines, each 1 mm apart, on the root, starting immediately behind the tip.
A glass container is filled to a depth of 2 cm with water.
The bean seedlings are placed on the cork disc, with 7 holes in it, the roots are stuck through the holes, and, with help, the disc is hung from the hooks in the glass container and the glass plate is placed on top.
So that the roots will continue to grow, as far as possible, under normal light conditions, a blackout cover is placed over the glass container.
After 24 hours a marked increase in root length can be seen.
The ink lines have been pulled different distances.
The lines at the bottom, immediately behind the tip of the root, have not parted very much, the following lines have a much greater distance between them.
The top lines are closer still and may not have moved at all.
When the roots grow, the ink marks are pulled apart, the distance corresponding to the amount of extension growth in that particular root section.
9.4.1 Breakdown starch during germination.
Experiments
1. Use needles to take some starch from the following: 1.1 a cotyledon of a bean seedling, with a root 2 cm long, 1.2 the endosperm near the embryo of a wheat seedling with coleoptile 3 to 5 mm long, 1.3 as a control, similarly take starch from an ungerminated bean seed and a wheat grain.
Examine the starch samples under high power.
Only the starch grains from the germinated plants show clear corrosion patterns.
2. The starch stored in the cotyledons or in the endosperm is converted to sugar during germination by amylases that becomes available to the developing seedling as a building material and fuel.
The corrosion of the starch grains can be clearly seen if a specimen is examined under the microscope.
Exercise using a dissecting needle take some starch from one of the cotyledons of a bean seedling, a root 1 to 2 cm long, and mount them on a microscope slide in a drop of water.
Make another specimen in the same way using starch taken from the endosperm in the vicinity of the embryo from a wheat seedling with a coleoptile 3 to 5 mm long.
For control purposes, mount two more starch specimens from an ungerminated bean seed and wheat grain respectively and examine all the specimens under a microscope, magnification 600 X compared with the starch from the ungerminated dry seeds, the grains from the germinated plants show clear corrosion patterns.
9.4.2 Conditions necessary for germination, After-ripening
1. A seed can germinate only if the following conditions are present:
* presence of water,
* presence of oxygen,
* presence of adequate temperature.
* the after-ripening period has elapsed.
After-ripening may be a period of usually several months of dry storage at room temperature of freshly harvested, mature seeds, to release dormancy and to promote germination of fully-developed seeds.
For example, white light promotes dormancy in freshly harvested cereal grains, but dark and after-ripening have the opposite effect.
After-ripening prevents germination prior to the completion of seed maturation.
2. To show that water is necessary for the germination of seeds, fill two flat glass dishes with dry garden soil to a depth of 1 cm.
Ensure that the soil is dry by spreading it out on a sheet of paper and letting it dry until it can be crumbled into dust.
Then put it in the dishes.
In each of two other flat glass dishes put three circular filters and smooth them out on the bottom of the dishes.
In each of the four flat glass dishes put 10 dry bean or pea seeds.
In the dishes containing garden soil, the seeds should just peep out of the soil.
Into one of the two dishes with the circular filters pour just enough water to cover the seeds.
Into one of the two dishes containing soil pour just enough water for the soil to be well and evenly moistened.
Put the lids on the dishes so that the water does not evaporate too quickly from the dishes that have been kept moist.
After 24 hours, the seeds that have been lying in water in the flat glass dish without soil have soaked up most of the water.
Keep on pouring more water into this dish, but only enough for the filters on which the seeds are resting to be very moist.
Note in which dishes the seeds germinate.
Experiment
"Comment from teacher:
Students set up a prac to investigate the conditions needed for germination.
They often confuse light as always being necessary.
I then taught more ecology and covered dryland salinity.
I then directed the students in this direction.
Modifications were simple to implement (salt %, change of growth media, containers and conditions, measurements etc).
There was also a move to peas, snow peas and beans as there is a better effect with these seeds.
We gathered sufficient data just by measuring a germination percentage and then shoot length."\
Examine the conditions necessary for germination.
Use: Lettuce seeds, Petri Dishes, Water, Paper Towel.
1. Label 4 Petri Dishes with your name and the date.
2. Label 1 Petri Dish RTL (room temperature, light), 1 RTD (room temperature, dark), 1 FRI (fridge, dark) and 1 RTNW (room temperature, no water, dark).
3. Fill each Petri Dish with paper towel (2 layers thick).
4. Water 3 of the dishes so the paper towel is damp.
5. Place 10 seeds evenly on the top of the paper towel in each container.
6. Cover each dish with the lids.
7. Place each Petri Dish in the correct environment.
9.4.3 Cotyledon functions
See diagram 9.103: Castor seedling.
Place six similar bean seedlings on which sprouting primary leaves are just emerging, in test-tubes so that the roots are immersed completely in water.
Hold the seedlings in place with cotton wool plugs, but the water must not contact the cotton wool.
Keep two seedlings with both cotyledons.
Remove one cotyledon from each of two other seedlings, and remove both cotyledons from the last two seedlings.
After two weeks compare the growth of the bean plants.
The plants with both cotyledons have developed best, and those without cotyledons have developed worst.
Note that the cotyledons that were not cut off have shrivelled.
When you remove a cotyledon the seedling gets less nutrients and it may starve.
9.4.4 Drinking glass garden
See diagram 9.3.50: Drinking glass garden.
Put rolled paper towels into the drinking glass.
Fill the centre with peat moss, cotton, sawdust, or wood shavings.
Put a piece of graph paper with water insoluble ink, cut to size, between the glass and the paper.
Plant bean seeds between the paper and the glass.
Water the centre of the glass.
Make frequent observations of growth, using the graph paper lines as reference points.
Results may be presented by constructing graphs that show time on the horizontal axis and the root and stem elongation in millimetres along the vertical axis.
9.4.5 Endospermic and non-endospermic seed
See diagram 9.109: Non-endospermic seed and endospermic grain.
A fertilized ovule becomes a seed.
The seed consists of 1. outer seed coats to protect the embryo, 2. an embryo, 3. stored food as endosperm in endospermic seeds, e.g. castor bean, or 4. stored food as swollen cotyledons in non-endospermic seeds, e.g. pea.
The ovum (egg) inside the ovule becomes the embryo (baby plant).
The calyx, corolla, stamens, stigma and style later usually shrivel and fall off.
The ovary forms a fruit.
Endospermic seeds (albuminous seeds) have food stored in a separate endosperm tissue, e.g. castor bean, coconut, coffee, date, lupin, maize, pine, shepherd's purse, wheat.
The development of the embryo is slowed to allow it to remain surrounded by the endosperm that forms the bulk of the seed.
Non-endospermic seeds (exalbuminous seeds) have food stored in the cotyledons, e.g. apple, bean, broad bean, pea, peanut, pumpkin, sunflower.
The embryo enlarges at the expense of the endosperm, absorbs its contents and crushes its cells.
The food reserves from the endosperm are stored in the cotyledons that become the main bulk of the embryo.
Examine the flowers on a plant and follow the fate of the different parts of the flowers until mature fruit forms.
Experiments
1. Examine grains of wheat, barley and maize, and the seeds of onion.
Soak seeds in water, remove the seed coats and examine the internal parts.
Endospermic seeds have food stored in a separate endosperm tissue, e.g. castor oil, pine, wheat, barley, maize, coconut, date, lupin, coffee.
Non-endospermic seeds have food stored in the cotyledons, e.g. peas, beans, pumpkin, sunflower, peanut, apple.
2. A fertilized ovule becomes a seed.
The seed consists of the following:
2.1 Outer seed coats to protect the embryo
2.2 Stored food as endosperm in endospermic seeds, e.g. castor bean, or as swollen cotyledons in non-endospermic seeds, e.g. pea.
Wheat, barley and rye endosperm consists of starch (amylum) and gluten, (gliadin and glutenin).
However, maize and rice gluten is glutenin only.
2.3 An embryo.
The ovum (egg) inside the ovule becomes the embryo (baby plant).
3. The calyx, corolla, stamens, stigma and style later usually shrivel and fall off.
The ovary forms a fruit.
Endospermic seeds (albuminous seeds) have food stored in a separate endosperm tissue, e.g. castor bean, coconut, coffee, date, lupin, maize, pine, shepherd's purse, wheat.
The development of the embryo is slowed to allow it to remain surrounded by the endosperm that forms the bulk of the seed.
Non-endospermic seeds (exalbuminous seeds) have food stored in the cotyledons, e.g. apple, bean, broad bean, pea, peanut, pumpkin, sunflower.
The embryo enlarges at the expense of the endosperm, absorbs its contents and crushes its cells.
The food reserves from the endosperm are stored in the cotyledons that become the main bulk of the embryo.
Examine the flowers on a plant and follow the fate of the different parts of the flowers until mature fruit forms.
9.4.6 Enzyme activity during germination
At the start of germination, the substances stored in the seeds must be converted into a form that can be utilized by the seedling which, at first, is not nutritionally and physiologically independent.
To do this it is necessary to activate the enzymes that cause these conversions.
About 10 bean seeds and 10 maize seeds are placed in flat glass dishes half filled with water and left to swell for 2 days.
The contents of four tubes containing starch agar are liquefied by warming the water bath and poured out into four half flat glass dishes.
The swollen seeds are halved longitudinally and placed, separately according to species, with the cut surface downwards into two half flat glass dishes containing starch agar.
For control purposes halved unswollen bean and maize seeds are similarly placed in the two remaining dishes containing starch agar.
All the dishes are placed in the glass tank, it is filled to half the height of the dishes with water and then covered with the glass disk, forming a moist chamber.
In order to inhibit, as far as possible, the development of bacteria or mildew, the test assembly is left at a temperature of 15oC.
After 2 days, dilute iodine potassium iodide solution is dropped onto the starch agar in all the dishes.
The starch agar turns blue violet.
However, a fairly bright halo is to be seen around the swollen seeds, which is not present around the unswollen seeds.
On swelling, and with it the incipient germination, the amylase contained in the seeds is activated.
It transforms starch into sugar that becomes available to the seedling.
9.4.7 Epigeal germination
See diagram 9.111: Epigeal germination 1.
See diagram 9.112: Epigeal germination 2.
Castor bean, lettuce, tomato, marrow, onion, common bean (dwarf bean and climbing bean, French bean)
Epigeal germination means that these seeds germinate with the cotyledons expanding above ground as the first green leaves, seed leaves.
The food supply for the growth of the embryo is stored in the cotyledons.
The embryo root, the radicle, emerges through the micropyle and grows down due to geotropism (growth repositioning in response to gravity) to form a tap root and lateral roots.
The seedling stem, hypocotyl, the part of the axis below the attachment of the cotyledons, but above the radicle, emerges from the seed coats by elongating and bending.
Then it straightens to carry the seed above the surface of the soil.
When the food reserves are exhausted, the seed coats drop off leaving the cotyledons to spread out horizontally each side of the plumule, turn green and function as the first leaves, seed leaves.
Later the plumule grows to become the shoot and form leaves and the cotyledons drop off leaving cotyledon scars on the stem.
Experiment
1. Plant common bean or castor bean seeds in damp sawdust to examine the stages of germination.
2. Plant 10 seeds of the castor oil plant in boxes containing damp sawdust.
Place in a window and allow them to germinate.
Examine the various stages of germination.
Note the epigeal germination of the castor oil.
Examine the specimen of an early stage of this dicotyledon.
The food supply for the growth of the embryo is stored in a nutritive tissue called endosperm.
The membranous cotyledons rise above ground during germination and function as the first pair of leaves.
This is accomplished by the elongation of the hypocotyl, the part of the axis below the attachment of the cotyledons, but above the radicle.
Test the endosperm for starch and oil.
3. To tests for oil, crush a small piece of endosperm on a slide, add a drop of Sudan III, mount under a coverslip and examine for pink-stained oil droplets.
9.4.8 Epigeal germination of bean
See diagram 9.3.52: Epigeal germination of bean.
9.3.50 Drinking glass garden.
Germination of common bean plant
Put 10 bean seeds in an open 100 mm diameter flat glass dish and cover the seeds completely with water.
Note how have they changed by the following day.
Now fill a glass tank with garden soil up to 2 cm from the top and sow the swollen bean seeds in it.
Plant the seeds evenly along the four sides of the tank close to the glass.
Fix black cardboard or cloth around the tank up to the soil level.
Each day, water the plants and note how the bean seeds develop.
Replace the black cardboard or cloth after each observation.
Note the following:
1. How long it takes for the seeds to germinate.
2. In what direction the beanstalk grows.
3. In what direction the roots grow.
4. The first leaves on the stalk, the very thick seed leaves or cotyledons.
5. How do the seed leaves change in time.
6. When the next leaves appear and how do they look compared to the seed leaves
7. The changes in the root and the purpose they serve.
8. The daily growth of a bean plant.
Attach a strip of graph paper to a wood splint and place next to one of the bean plants just as it comes out of the soil and begins to sprout.
Mark the height of the bean plant on the graph paper every day at the same time.
9.4.9 Germination and air, germination and the need for oxygen
See diagram 9.3.49: Germination test.
Experiments
1. Put absorbent paper in the bottom of two dishes.
Add 10 dried beans in each dish.
Add tap water to the first until the beans are only just covered.
Fill the second dish with water to deeply cover the beans.
By the next day the beans in the first dish have absorbed most of the water, have swollen and are now lying exposed to the air on the damp absorbent paper.
The beans in the second dish have also swollen, but remain covered with water.
After two days, most of the beans in the first dish have germinated.
The beans in the second dish are still immersed in water and have swollen with no further change.
Eventually they will die and decompose.
2. Take two pieces of foam rubber small enough to float freely in a preparation glass, 150 mm tall and diameter 80 mm.
Using scissors make a hole in both pieces of foam rubber and pull a piece of thin string through each hole.
Attach each piece of foam rubber by means of the string and a strip of sticking plaster to the lower side of the lids of the preparation glass.
With the lid in place the pieces of foam rubber should hang halfway down in the glasses.
Put 100 mL water into one of the preparation glasses and 50 mL 20% pyrogallol and 20% sodium hydroxide solution in the other, to absorb the oxygen, the pieces of foam rubber are well soaked with water, on each put 15 unswollen garden cress, seeds, smear the rim of the preparation glasses with glycerine to aid sealing and then put the lids in place with the foam rubber pieces hanging down.
The pieces of foam rubber with the cress seeds should not come into contact with the fluids underneath them.
Leave the preparation glasses to stand at room temperature.
Within 2 days the cress seeds in the preparation glass with water have germinated, they have developed into small plants.
The cress seeds in the preparation glass with the pyrogallol sodium hydroxide solution, however, have not germinated.
The pea seeds that were completely covered with water, experiment 1, could not come into direct contact with the air.
They suffered from lack of oxygen, and germination could not take place.
Experiment 2 shows that oxygen is the determining factor.
3. Investigate whether germinating seeds need air (oxygen) and water.
Explain why the seed does not sprout in flooded fields and may not germinate in very wet garden beds.
Put absorbent paper in the bottom of two dishes, dish A and dish 2. Put 10 dried beans in each dish.
Add tap water to dish A until the beans are just covered and to dish B up to the rim.
Label each dish and leave them in the classroom.
Cover the dishes to make exchange of air possible.
Keep adding water to dish B to ensure that the surface of the water is always a few millimetres above the beans.
By the following day, the beans in dish A, which was not filled to the rim, have absorbed most of the water.
These beans have swollen and are now lying exposed to the air on the damp filter paper.
The beans in dish B have also swollen, but remain covered with water.
After two days, most of the beans in dish A still lying on the damp paper and exposed to the air have germinated.
The beans in dish B are still completely immersed in water and have are still only swollen with no further change.
Seeds need air (oxygen) and water for germination.
However, the beans in dish B that were completely covered with water had no direct contact with the air.
They did not obtain enough oxygen to germinate.
4. Take two wide tubes of equal length, about 10 cm.
Holding them vertically, fix a wad of moist cotton wool in each, about 2 inches from the top end.
Drop in 6 pea seeds or 50 wheat grains so that they lie on the wool.
Insert a stopper in each.
Now immerse the open lower end of one of the tubes in a beaker of water and the other in a beaker of pyrogallic acid and support in a vertical position.
Record the number of grains that have germinated each day, and, realizing that pyrogallic acid absorbs the oxygen from the atmosphere, deduce the role of oxygen in germination.
"9.4.10 Germination and light
Experiments
1. Test the effect of light on the germination of different seeds, e.g. watercress, onion.
Note which seeds show that germination is promoted by light, hindered by light or are indifferent to light.
Such seeds are called "light germinators", "dark germinators" and "seeds unaffected by light".
The germination of many plant seeds is not affected by light.
Some seeds, however, can only germinate if they are exposed in their swollen condition for some length of time to light, while the germination of others is prevented by exposure to light.
So plants may be light germinators or dark germinators.
2. To examine the effect of light on seeds, set up saucers containing seeds, but having duplicate sets.
Place one set in the light and another set in a dark room or box.
Do the same with examples of light hard and light-sensitive seeds.
Record the results as percentages, and from them discuss the effect of light on germination.
3. Examine the effect of light on the germination of seeds of watercress, onions, and love-in-a-mist.
In each of six flat glass dishes of 100 mm diameter put two circular filters of 90 mm diameter and smooth them out on the bottom of the dishes.
In each of two of the dishes put 20 watercress seeds, in each of another two 20 onion seeds, and in each of the remaining two 20 seeds of love-in-a-mist.
Pour in just enough water to cover the seeds in all the dishes, close each dish with its lid.
Keep one of each of the dishes with the same seeds in the light, and put the other immediately next to it, both with the same temperature under a light proof cover, pasteboard carton.
After a few days compare the extent of germination of the seeds in the dishes kept in the light and in the dark respectively.
Note in which seeds germination is promoted by light and in which seeds is it hindered by light, i.e. which plants are light germinators and which plants are dark germinators.
Also, note in which seeds germination is unaffected by light.
9.4.11 Germination and temperature
Like every other living process, germination is greatly affected by temperature, and the heat needs of different species of seeds can vary greatly.
Each species has an optimum temperature for germination.
Experiment
Put moist absorbent paper in two flat dishes.
Add dry seeds to each dish, e.g. garden cress.
Close the lids on the dishes and leave one dish at room temperature and the other dish at 12oC.
Within 24 hours most of the cress seeds at room temperature have germinated, but the cress seeds at 12oC have not developed.
9.4.12 Germination and water
See diagram 9.3.49: Germination test.
Experiments
1. Use a dish with absorbent paper in the bottom and another dish containing dry, finely divided garden soil.
Put 10 dry beans in each dish.
Fill the first dish with tap water until the beans are just covered.
Leave the dishes to stand at room temperature.
Within 24 hours only the beans covered with tap water have swollen considerably and have absorbed much water.
Most beans germinate after two days.
The beans in the other dish have not changed.
2. Seeds absorb water through the surface of the seed coats and through their micropyle.
Weigh 10 dry bean seeds, then block their micropyles with collodion or rubber solution, e.g. the solution used to stick soles on shoes.
Be careful! Rubber solution can be toxic when inhaled so work in a fume cupboard, fume hood.
Leave the solution to dry then put the seeds in water.
Compare the weight and volume of the treated seeds with untreated seeds.
3. Half fill measuring cylinders and add equal volumes of seeds, e.g. pea, common green bean and broad bean.
Observe the swelling seeds and calculate how much water they absorb.
At first, water is absorbed by imbibition through the seed coats that swell and wrinkle.
Then water passes through the micropyle causing the embryo to swell inside the seed coats and make them smooth again.
Starch food reserves are hydrolysed to glucose sugar to enable the embryo to grow first by cell enlargement then by cell division.
Later growth occurs mainly at the two meristems:
3.1 The dividing cells in the embryo shoot, plumule.
3.2 The dividing cells in the embryo root.
4. Seeds can only germinate when they absorb water and swell.
Take two flat glass dishes and put a circular filter into each, a third dish is filled almost up to the edge with completely dry, finely-divided garden soil.
Put 15 to 20 dry pea seeds in each of the dishes.
In the dish filled with soil they should project only a little above the soil, one of the other dishes is filled with water until the pea seeds are just covered.
All three dishes are then left to stand at room temperature with the lid placed on them obliquely, to allow exchange of air.
Within 24 hours the pea seeds covered with water have swollen considerably.
They have absorbed a lot of the water.
After a further 1 to 2 days they have almost all germinated, the pea seeds in the other two flat glass dishes on dry filter paper and in dry garden soil have not changed.
Seeds only germinate after absorbing water and after the resultant swelling.
Dry seeds cannot germinate whether they are in open air or in dry soil.
9.4.13 Germination from seed to plant
Experiments
Sow seeds of pea, broad bean, common dwarf bean or climbing bean, at the same distances apart and at equal depths, almost touching the sides of a glass or plastic container, so you can see them through the walls.
Fix black paper or aluminium foil around the container to keep the seeds in the dark.
Water the seeds regularly and note daily how they develop.
Replace the black paper or aluminium foil after every observation.
Measure the daily growth of a bean plant.
Mark the height of a bean plant on the graph paper every day at the same time or attach the top of a bean plant to a clinostat.
See: 6.4.1 Clinostat.
9.4.14 Hypogeal germination, broad bean, pea, wheat
See diagram 9.110.1: Hypogeal germination 1.
See diagram 9.110.2: Hypogeal germination 2.
In the diagram:
1. The skin wrinkles due to imbibition (absorption of fluid by a solid).
2. The embryo swells and the wrinkles are lost.
3. The radicle emerges through the micropyle.
4. The plumule (embryo shoot) emerges.
5. The plumule straightens.
Hypogeal germination means that these seeds germinate with their cotyledons remaining under the ground, within the seed coats.
The embryo root, the radicle, emerges through the micropyle and grows down to form a tap root and lateral roots.
The petioles of the cotyledons elongate and bend, pulling the embryo shoot, the plumule, out of the seed coats.
The plumule then straightens to grow upwards and emerge from the soil then form the shoot system, the stem with leaves.
The growing point is covered by young unexpanded leaves.
Experiment
Plant pea or broad bean seeds in damp sawdust to examine the stages of germination.
9.4.16 Natural growth inhibitors
See diagram 9.3.49: Germination test.
1. The formation of growth inhibitors in the immediate vicinity of the embryos, e.g. in the endosperm, in the seed coats, in the pulp, may prevent the premature germination of seeds.
Put seeds of garden cress, in a Petri dish with water for ten minutes and allow them to swell.
Put absorbent paper moistened with water in 4 Petri dishes and add the following:
Dish 1: a thin slice of apple,
Dish 2: a thin slice of orange,
Dish 3: a thin slice of tomato,
Dish 4: absorbent paper only (control).
2. Put ten swollen cress seeds on each of the fruit slices and also on the filter paper in the Dish 4, the control.
Put lids on the dishes and leave at room temperature After 48 hours the cress seeds laid on the slices of fruit have hardly altered.
However, the seeds on the filter paper in the control dish have germinated.
They have grown a small root 10 to 20 mm long.
In most instances the first tiny leaves can also be seen.
The flesh of apple, tomato and orange all contain growth inhibitory substances.
To ensure germination, seed must be separated from the old surrounding fruit tissue.
9.4.17 Parts of a seed, morphology of the seed
See diagram 9.76: Parts of a seed.
A seed is a megasporangium containing an embryo and food.
It is the post fertilization transformation of an ovule.
The embryo is the new diploid generation.
The endosperm, the female gametophyte, and the nucellus and seed coats are the parent diploid generation.
1. In an open 100 mm diameter flat glass dish put five bean seeds for swelling.
Next day pick out a seed that has swollen nicely for close observation.
The first thing that strikes you is that the bean seed is enclosed in a relatively tough skin.
Because of the swelling this skin nearly always bursts and can be easily removed with a pair of forceps.
The skin is called the seed pod.
The seed pod encloses two whitish, thick, fleshy formations.
Their outline is kidney shape.
These are the two seed leaves, cotyledons.
With the forceps take one seed leaf, without crushing it, and bend the second a little to one side with a dissecting needle.
By doing this you can see that both seed leaves hang together at one end.
At this spot there are two whitish, small leaflets.
They lie folded in between the two seed leaves.
They are the first leaves of the subsequent bean plant.
They rest on a very short, delicate stalk that merges at its other end into a pointed peg, the root.
The seed contains a complete miniature model plant, called the embryo.
State the parts that go to make up the bean seed.
Do a simple drawing showing the parts and their position in relation to each other.
How many seed leaves has the bean seed?
In seed plants you can distinguish between one seed leaf, monocotyledon, and two seed leaves, dicotyledon, plants.
9.4.18 Plant embryo development, shepherd's purse.
See diagram 9.99.1: Capsella embryo, Early stages A and B.
See diagram 9.99.2: Capsella embryo, Later stages C to G.
See diagram 9.99.3: Capsella seed, VS.
1. As there are often considerable differences in the time for development between embryos of the same age, grow many more than you need for the experiment.
Put the seeds in a flat glass dish, add water, and allow the seeds to swell.
For embryos in an early stage of development, put the swollen seeds in a flat glass dish on moist absorbent paper and leave until the desired stage has been reached.
For seedlings of a greater, put the swollen seeds in a flowerpot filled with sawdust or sand.
Stand the pot in one half of a flat glass dish and water regularly.
For erect seedlings, rotate the flowerpot occasionally so that all seedlings get an equivalent amount of light, or use a clinostat.
When the plants have reached the desired stage of growth, remove them from the sawdust and rinse under water.
The plant embryo develops from the fertilized ovule of the egg cell as the result of numerous cell divisions.
During this process it passes through various stages of development, from the scarcely differentiated state with a small number of cells to the form where the cotyledons and the roots are clearly distinguishable.
2. Investigate the development of embryos of shepherd's purse.
Use forceps and a dissecting needle to open carpels of shepherd's purse taken at different ages and remove several ovules.
Put a drop of 5% potassium hydroxide solution on a slide using a glass rod, put the ovules in the drop and put a cover slipover them.
The tissue of the ovules is disintegrated, disaggregated, to some extent by the potassium hydroxide.
Press down on the cover slip with the handle of the dissecting needle to squeeze the embryos out of the ovules.
Do this operation with the utmost care to avoid crushing the embryos.
Press down several times and check through the microscope after each application of pressure.
Examine the preparation under 50 x, objective 10 x, eyepiece 5 x, and then under 200 x, objective 40 x, eyepiece 5 x, microscopic magnification.
If, by luck, ovules of differing ages were transferred to the slide, embryos in almost all stages of development will be present.
Draw embryos in different stages of development and arrange them according to age.
9.2.5 Plants need mineral salts, maize
1. Plants need nutritive salts from the soil to develop normally.
Prepare three glass containers using large beakers or buckets or small aquaria as follows:
1.1 Put good garden soil and deionized water in the glass container to 2 cm below the brim.
Stir the contents of the vessel and leave to settle.
1.2 Fill a third glass container with aerated water and add two measures of calcium nitrate, one measure each of potassium nitrate, monobasic potassium phosphate and magnesium sulfate, and a trace of iron (II) sulfate.
1.3 Fill a glass container with deionized water to 2 cm below the rim.
2. Plant 50 maize grains in a large pot containing old sawdust.
Water them regularly.
When the young maize plants are 3 cm high, select 21 of equal size, pull them out of the sawdust and wash their roots under the tap.
Punch seven holes in each of three cork discs.
Insert seven maize plants in each of holes so that their roots hang down below the holes.
Put a cork disc with attached plants in each of the glass containers.
After two weeks note any difference in development of the maize plants in the different glass containers.
The plants in the glass container 3. do not grow well, but the plants in glass containers 1. and 3. grow well.
Compare the growth of plants in glass containers 1.1 and 1.3.
9.4.20 Plants need water, daisy, potted plants
Plants wither and die if not supplied with water to absorb.
Plants need water for dissolving and transporting nutritive substances, and maintaining turgor excess pressure in plant cells.
Use dyes to show the conduction of water to all parts of the plant.
1. Put a fresh daisy in each of two test-tubes.
Fill one test-tube two thirds full with tap water and put no water in the other test-tube.
The next day, the daisy standing in water has remained fresh, but the other one is limp and faded.
2. Put a daisy flower in a test-tube two thirds full of acid fuchsine solution.
Within 15 minutes, the originally white petals of the daisy have turned a reddish colour.
Also, you can also see the colour change in other parts of the plant.
3. To show that water is necessary for photosynthesis, place a potted plant in a dark room for 48 hours, so that at the end of that time there is no starch present in the leaves.
Then remove two leaves.
Stand one leaf in water and place in the light, put the other leaf in the light also, but do not supply it with water.
After about eight hours, test both leaves for starch.
9.4.22 Swelling of seeds, imbibition, during germination
See diagram 3: Soaked bean seed.
1. After soaking dry bean seeds in water the seed coats swell and wrinkle.
Water also enters a tiny hole in the seed coats, the micropyle.
The cotyledons absorb water and swell pushing out the wrinkles in the seed coat.
So the bean seed becomes larger and the seed coats become smooth again.
2. Fill a small cheap glass tube with dry peas.
Fill the tube with water, plug with wet cotton wool, leaving no air in the tube and attach a cork stopper.
Secure the stopper in position with wire.
Put the tube in a closed plastic container.
By the next day the tube breaks, because the peas enclosed in the test-tube have swollen with water and exerted a strong pressure inside the tube.
The seeds become larger by imbibition.
3. Measure the increase in size of pea seeds by imbibition.
Half fill a measuring cylinder with water, add fifty dry pea seeds and shake the measuring cylinder to remove air bubbles.
Record the level of the water in the graduated cylinder.
Pour the seeds into a flat dish of water.
After two days, pour out the water from the flat dish, take the pea seeds out and dry their surfaces between the absorbent paper.
Half fill a measuring cylinder with water, add the fifty swollen pea seeds, shake the measuring cylinder to remove air bubbles.
Calculate the percentage increase in volume of the seeds.
Some students leave the peas in the measuring cylinder, but seeds can swell to jam and even break the measuring cylinder!
4. Swelling seeds exert pressure on their surroundings.
Pushing dry peas or beans into their nose or ear is dangerous for children, because these seeds swell and cause pain in the nose or ear.
Fill a test-tube with dry peas.
Cover the mouth with a triple layer of muslin tied tightly below the flanged rim.
Fill a Petri dish with tap water to 1 cm below the rim.
Hold the test-tube containing the peas obliquely in the Petri dish.
Its mouth must be below the surface of the water so the water can run into the test-tube.
Move the tube to and fro until all the air between the peas is displaced by water, and leave lying in the water in the Petri dish.
The next day the test-tube in the Petri dish breaks.
The peas enclosed in the test-tube have swollen in the water.
They have expanded and exerted so strong a pressure on the test-tube that it has shattered.
Seeds absorb water before germinating.
This process, by which the seeds become appreciably larger is called swelling or imbibition.
When the seeds imbibe water, they swell.
5. Fill a glass with dry peas.
Shake the glass and keep adding peas until no more can fit in without forcing them in.
Add water to the glass until no more can be added without it spilling over.
Put a light lid over the glass and peas and place the glass over a baking tray.
During the next hours, as the peas swell some peas will be pushed over the rim and fall with a sound on the baking tray.
6. Determine the increase in size of pea seeds through swelling.
Fill a graduated cylinder of 100 mL capacity with water up to the 50 mL mark.
Add 50 dry pea seeds and shake the graduated cylinder several times to remove any air bubbles that may have been locked in between the seeds.
Read the level of the water in the graduated cylinder.
By how many millilitres has it risen through the addition of the so dry seeds?
What can be deduced from this rise in the water level?
Shake the pea seeds with the water into the beaker of 100 mL capacity and cover it with an open flat glass dish of 100 mm diameter.
After three days, pour out the water from the beaker, take the pea seeds out and dry their surfaces between the filter papers.
The pea seeds have swollen.
Again fill the graduated cylinder up to the 50 mL mark with water.
Put the fifty swollen pea seeds in the graduated cylinder and shake it several times to remove any air bubbles that may have been locked in between the seeds.
Read the level of the water in the graduated cylinder again.
By how many millilitres has it risen this time, as a result of adding the 50 swollen pea seeds?
What can be deduced from this rise?
What was the volume of the 50 dry pea seeds?
What is their volume after swelling?
By how much has the volume increased?
9.4.21 Viability of seed before planting, germination test
See diagram 9.3.49: Germination test.
Experiments
1. Do a germination test on your seeds before planting.
Soak seeds in water until they are swollen then put them seeds on wet absorbent paper or newspaper in a closed container.
Each day, record the number of seeds that have germinated and calculate the percentage germination, i.e. the number of germinated seeds / the number of seeds planted × 100.
Note the diversity of time taken to germinate among seeds that look the same.
Also, germinate seeds in rolled absorbent paper or paper towels in a drinking glass.
2. Place a piece of absorbent paper or cotton wool in a saucer.
Thoroughly moisten it with water.
On this absorbent paper, sow a hundred wheat grains.
Do the same with other seeds, preferably garden seeds, e.g. cress (garden cress), radish, onion, beet, carrot.
Each day record the number that have germinated and calculate the percentage.
More water may be added to keep the absorbent paper moist.
Note the diversity of time taken to germinate.
3. Fold 1 m2 muslin twice in the same direction.
Near one end mark out with a pencil 8 or 10 squares 5 × 5 cm.
Number the squares, and on each square place ten seeds from a particular packet.
Note the arrangement of the different seeds.
Fold the opposite end of the muslin over the seeds.
Roll up the tester and tie it loosely with string.
Saturate the rest with water.
Keep it moist and in a warm place for several days.
The unroll it and see how many of each kind of seeds have germinated.
Report the viability as a percentage or by constructing graphs.
9.5.1 Chemotropism responses in germinating pollen, pollen tube
See diagram 9.123: Germinating pollen grain.
A tropism is a response affected by the direction of the origin of the stimulus.
For example, geotropism is a response to gravity and in the direction of gravity.
Experiments
1. Shake fresh pollen from several kinds of flowers on absorbent paper soaked in a 10% sugar solution.
Put a cover over the pollen and leave it for 12 hours.
Use a magnifying glass to see little tubes growing from the pollen grains, the pollen tubes.
Shake fresh pollen from flowers onto stigmas of the same kind of flower and look for germinating pollen on the stigmas.
Observe pollen stained with methylene blue under low power.
2. Dissolve 2.5 g of sucrose and 1 g of gelatine in 50 mL of demineralized water in a beaker.
Put one drop of the solution to a microscope slide.
Cut a piece of stigma or style from a female marrow flower and squash it in the drop on the microscope slide.
Pick some mature stamens and cut the anthers over the drop so that the pollen falls near the squashed piece of stigma or style.
Keep the microscope slide in a damp place and examine it the next day.
Note the pollen grains that have germinated to form pollen tubes.
Most of the pollen tubes are growing towards the squashed stigma or style.
The pollen tubes respond to a chemical that diffuses into the sugar gelatine from the female parts of the flower.
In a similar way, the pollen tube would normally grow down the style to reach the ovary and fertilize the ovule.
Be careful! Do not break the coverslip, because the broken pieces are very sharp and dangerous.
9.5.2 Circumnutation, winding plants
1. The growing tip of a stem does not grow directly vertically, but moves upwards in a helical path, but there is a difference in the magnitude of the winding movement, circumnutation, in shrubs and twining climbers.
The direction of winding is under genetic control of a microtubule protein, tubulin, in the cells.
Most plants exhibit circumnutation, the irregular spiral or elliptical rotation of the apex of a growing stem, root, or shoot.
The difference is caused by caused by differences in the rate of growth of the opposite sides.
However, winding plants show extreme circumnutation.
Shoot circumnutation is controlled by gravity-sensing plant cells.
Inflorescence stems of thale cress may show differences in circumnutation that follows a circadian rhythm.
Experiments
2. Investigate the environmental factors that affect this movement, e.g. light and darkness, wind.
Investigate whether phototropism can affect the experiment.
3. Place a piece of vertical fencing wire in the path of a twining stem of leaf tendril and note the subsequent movement.
4. Mount a sheet of glass 10 cm above the plant than line up the apex with a spot on the glass.
Observe the plant every few hours to get a record of the plant movement.
5. Investigate whether a twining plant can climb around supports of different sizes.
Find the critical cylinder radius above which a plant can no longer twine.
6. Examine clockwise winding plants (CW):
* Hops, Humulus, Cannabaceae
* Honeysuckle, Lonicera, Caprifoliaceae
Examine counter clockwise winding plants (CCW).
* Morning glory, Ipomoea, Convolvulaceae
* Wisteria, Fabaceae
Uncoil them from their support and recurl them in the opposite direction to see if they can change direction of winding.
9.5.3 Dispersal of pine seed by swelling movements
The swelling of biological material is caused by molecules of water penetrating between the carbohydrate chains, cellulose, starch, or molecules of protein, forming aqueous films.
As a result of this process the molecules or groups of molecules, the micelles, which are stored without much space between them before swelling, are forced apart.
Infiltration of water, and with it swelling, takes place predominantly in a vertical direction to the longitudinal axis of the micelle.
If the structure of a micelle, consisting of strongly bound layers of a membrane, differs, then the direction of the greatest swelling between these layers is different.
As soon as the swelling changes in shape, curvature must occur.
Swelling movements of this kind play a role in the dispersal of seeds and spores.
Experiments
See diagram 9.50.1: Swelling movements.
1. Cut strips 15 cm long and 3 cm wide from a sheet of writing paper.
Using a soluble adhesive each of the strips is smeared over its whole surface and they are then bonded together as follows: strip a on strip b, strip c on strip d and strip e on strip f, the double strips obtained in this way are dried, using forceps, at a suitable height over a Bunsen burner flame.
The double strip e / f turns into a corkscrew.
Double strip c / d bends into a circle.
Double strip a / b remains unaltered.
When manufacturing paper, most of the cellulose fibres end up mainly facing in one direction after the milling process to make large pieces.
Because a soluble adhesive is used to bond the paper strips together, water penetrates between the fibres and leads to swelling, mainly vertically to the direction in which the fibres run, double strips c /d and e / f, where the direction of the fibres in the individual strips differs, both resemble a biological membrane consisting of two layers of different micellar structure, on drying, shrinkage, these strips must warp.
2. Plants have special mechanisms for the widest possible dissemination of their seeds and these mechanisms for seed dissemination have adapted to different conditions.
Put an open dry pine cone in a 250 mL beaker, filled with water.
By next morning, the cone has closed.
If it is taken out of the water, the scales reopen again when it dries.
Put the closed cone in a warm place, in the sun or on the radiator.
As it dries, the cone opens again.
The scales that cover the cones are composed of two layers that swell at different rates when exposed to moisture.
In this way, "swelling movements" occur.
In dry weather, when conditions are favourable for widespread dissemination of the seeds, the cones open.
The seeds can fall out and be carried away by the wind.
During wet or damp weather the cones close, because the released seeds would stick to the moist soil close to the street and could not be disseminated by the wind.
Pull a seed out of an open pine or spruce cone with sharp forceps.
Each seed has a large, thin, membrane-like appendage, called a "wing".
It increases the capacity for flight of the seed.
9.5.4 Geotropism responses in shoots
Use broad bean, Pelargonium (geranium).
Cut shoots from herbaceous plants and fix in a large test-tube of water with a rubber stopper.
Seal the hole in the stopper with wax.
Fix the specimen so that the shoot is horizontal, preferably in a fairly warm place where uniform light is provided.
Examine periodically for negative geotropic curvature in the stem and diageotropic responses in the leaves.
9.5.5 Geotropism responses in soaked seeds
Use any small seedlings, e.g. rapid-cycling Brassica rapa (fast plants), Sinapis alba (white mustard), Raphanus sativus (radish).
The seedlings should have straight hypocotyls.
1. Soak broad bean seeds in water overnight and sow with the hilum downwards in sand or sawdust.
Use a wide-necked glass jar, half fill with water, and close the top with a cork or a piece of cardboard.
Insert several long blanket pins through the latter.
When the radicles have attained a length of about half an inch, fix several seedlings to the pins inside the jar, with the radicles pointing in various directions.
Seedlings with straight radicles should be selected, and they should be fixed clear of the water.
Place the jar at a temperature of 15oC to 25oC and inspect from time to time for positive geotropic curvatures in the radicles.
2. Arrange 20 radish seeds across the centre of a Petri dish and cover the seeds with damp cotton wool.
Place four thin strips of clear Sellotape in a square at the edges of the Petri dish to hold the cotton wool and seeds in place.
Replace the lid of the petri dish.
Attach the Petri dish vertically to the wall, with double-sided "Sellotape".
Roots appear within 1 to 2 days and seedlings appear within 7 days.
For a control, place a similar Petri dish of seeds on the table without a lid, in a similar light.
3. Repeat the experiment by placing a black box with no bottom over the Petri dish attached to the wall, but allow a light source to illuminate the seeds directly upwards.
Observe whether this light source has affected the direction of growth of the seeds.
9.5.6 Geotropism responses using a clinostat
See diagram 9.3.59: Geotropism.
1. Grow maize or wheat on a rotating turntable, axis horizontal.
Tropisms take the form of movement, or turning, in relation to the direction from which the stimulus comes.
Geotropism is the tropism that occurs in response to the stimulus caused by the earth's gravitational field.
Tip a pot plant on its side.
After about a week, the growing point of the stem turns upwards as auxin accumulates on the lower side and makes these cells grow longer than cells on the upper side.
2. Leave seeds to swell in water.
The next day sow them in a flowerpot filled with sawdust.
Fix a wire gauze square over the flowerpot.
Invert the flowerpot and fix it over a container of water with the water touching the rim of the flowerpot.
Keep the sawdust dump by watering through the hole in the bottom of the flower pot.
After a few days roots grow through the wire gauze down towards the damp air in the container of water.
After 10 days remove the sawdust from the flower pot and note that the shoots have grown upwards from the seed into the sawdust.
3. Plant seeds in a two flowerpots, e.g. oats, radish, or mustard.
When the seedlings emerge, attach the first flowerpot horizontally to the vertical disc of a clinostat turntable or record player.
Switch on the clinostat so that it turns slowly.
Lay the second flowerpot on its side.
After a few days the plants in the flowerpot on its side have become curved with their shoots pointing up.
The plants rotating on the clinostat continue to grow forward horizontally.
The gravitational pull affects the plants attached to the clinostat evenly, so no geotropic curvature occurs.
Shoots show negative geotropism.
They grow against the pull of the gravitational field.
Roots show positive geotropism.
They grow towards the direction of the gravitational pull.
Leaves show diageotropism (diagravitropism), i.e. orientation at right angles to the vertical in response to gravity.
4. Soak broad bean seeds in water overnight then sow them in flower pots filled with damp sawdust.
Make a lid for a wide neck jar with cardboard or cork and insert long pins through the lid.
Put water in the jar.
When radicles of broad bean seeds are 1 cm long, fix seedlings to the pins inside the jar, with radicles pointing in different directions.
Select seedlings with straight radicles and fix them clear of the water in the jar.
Observe positive geotropic curvatures in the radicles.
5. Fill a flowerpot and a culture pot of a clinostat with sawdust and put 10 bean sprouts with 1 cm roots in each pot.
When the seedlings break through, put the clinostat on a window sill so that its disc is vertical.
Attach the culture pot with the bean plants to the disc and switch on the clinostat.
Put the flowerpot with the bean plants in the wooden holder on its side next to the clinostat.
After a few days the bean plants in the flowerpot have become curved while growing and their shoots point upwards.
The plants rotating on the clinostat continue to grow forward horizontally.
The shoots are negatively geotropic.
They grow against the pull of the gravitational field.
However, the roots behave in a positively geotropic manner.
They grow towards the direction of the gravitational pull.
This behaviour is independent of the orientation of the air and the soil.
The gravitational pull affects the plants attached to the clinostat evenly, so no geotropic curvature can occur.
6. Use a clinostat to show that geotropic responses are no longer shown if roots and shoots are placed horizontally and slowly revolved about their long axes.
9.5.7 Gravity affects the growth of stems and roots
1. Sprout seeds and select one that is straight.
Pierce the seed with a long pin or needle and stick this into a cork.
Put damp cotton or absorbent paper in a bottle.
Put the cork and seedling in the bottle.
Put the bottle in dark cupboard and look at it every four hours.
2. Put seeds that grow rapidly, oats, radish, or mustard seeds on moist absorbent paper between two glass plates secured with rubber bands.
After germination, turn the apparatus vertically through 90o and leave to remain undisturbed.
Repeat the turning at intervals and observe the effect on the roots.
3. A technique used in some laboratories is to put developing plants in a shaking machine.
Without a sense of gravity the plants the tissue, e.g. orchid tissue plantlets, does not differentiate into roots and shoots.
This process allows undifferentiated tissue to grow bulkier and prepare for transplanting.
9.5.8 Heliotropism of sunflowers
by Gregory Moore, Doctor of Botany, The University of Melbourne, (edited for this website)
Many of us probably first got to know of heliotropism by watching the enormous yellow and black flowering heads of aptly name sunflowers, which moved as they grew.
These flowers track the course of the sun spectacularly on warm and sunny, spring or summer days.
Sometimes they move through an arc of almost 180⁰ from morning to evening.
The mechanics of tracking the sun.
A number flowering species display heliotropism, including alpine buttercups, arctic poppies, alfalfa, soybean and many of the daisy-type species.
This is Heliotropium arborescens, named for its heliotropism.
They were very popular in gardens a century or more ago, but have fallen from favour as they can be poisonous and weedy.
Flowers are really in the advertising game and will do anything they can to attract a suitable pollinator, as effectively and as efficiently as they can.
There are several possible reasons why tracking the sun might have evolved to achieve more successful pollination.
By tracking the sun, flowers absorb more solar radiation and so remain warmer.
The warmer temperature suits or even rewards insect pollinators that are more active when they have a higher body temperature.
Optimum flower warmth may also boost pollen development and germination, leading to a higher fertilisation rate and more seeds.
For many heliotropic flowering species, there’s a special layer of cells called the pulvinus just under the flower heads.
These cells pump water across their cell membranes in a controlled way, so that cells can be fully pumped up like a balloon or become empty and flaccid.
Changes in these cells allow the flower head to move.
In 2016, scientists discovered that the sunflower movement is due to significantly different growth rates on opposite sides of the flowering stem.
Sunflowers move differently to other heliotropic flowers.
On the east-facing side, the cells grow and elongate quickly during the day, which slowly pushes the flower to face west as the daylight hours go by — following the sun.
At night the west-side cells grow and elongate more rapidly, which pushes the flower back toward the east over night.
Everything is then set for the whole process to begin again at dawn next day, which is repeated daily until the flower stops growing and movement ceases.
9.5.9 Phototropism
See diagram 9.125: Phototropism.
1. Cover seedlings growing in pots or a sprouting potato with a black box with a hole in one side.
Observe the change in direction of growth as the plants turn towards the light from one side.
Repeat the experiment by removing the growing tip from some plants.
These plants do not turn towards the light.
Repeat the experiment with the hole in the box covered with red, then yellow then blue cellophane.
Phototropism is caused by increased concentration of the growth hormone auxin on the dark side of the growing tip of the shoot.
So the plant cells grow more on the shaded side.
Plants growing in the dark grow faster than plants growing in the light, but they become etiolated, pale yellow, due to lack of sunlight.
Phototropism is more responsive to blue light than any other colour.
2. Find a plant that grows in the shade and put it in a flowerpot.
Turn the flowerpot on its side and observe the resulting direction of growth of the shoot and the leaves.
The shoot turns towards the light and the leaves turn to be at right angles to the source of light.
Leaves are diaphototropic, orientated at right angles to the vertical in response to light.
3. Demonstrate phototropic response of seedlings of mustard, wheat, barley, with uniform illumination.
When the seedlings have grown to 5 cm, place the pots under a box or black cloth so that light reaches the shoots from one side.
4. Place the plants in a darkroom about 60 cm to the side of a 40 watt lamp.
Note the time taken for positive phototropic curvature to appear.
Instances of diaphototropic responses in leaves can be found in plants grown in living rooms or against the wall.
5. Grow plants, e.g. Pelargonium (geranium), in uniform light partly screened with a black cloth so that light now reaches it from the side.
In a few hours time the leaves begin to adjust their position.
A positive response will also develop in the stem.
6. Plant seeds that grow rapidly, e.g. oats, radish, bean or mustard seeds, in two flowerpots.
When the seedlings are 2.5 cm high, cover one pot with a box that has a hole cut near the top.
From time to time lift the box and observe the direction of growth.
Turn the box so that light comes from a different direction and observe again after a few days.
7. Observe plants that turn towards the sun, e.g. sunflower.
9.5.10 Sprouting potato tuber
See diagram 9.85: Sprouting potato tuber.
1. Put two light baffles in a long, narrow box and cut a hole in the end.
Plant a sprouting potato in a small pot that will fit in the box.
Put the pot behind the baffle farthest from the hole.
Cover the box and put near a window.
Observe the direction of growth from time to time.
2. Plant some fast growing seeds in four flowerpots.
Keep the pots in a darkened room until the seedlings are 2.5 cm high.
Put one pot near a sunny window and observe the effect.
Turn the plants away from the light and observe.
Leave the pot in a place away from direct light for a few days and observe the results.
3. Put each of the three remaining pots of seedlings in a different box.
Cut a window in each box and cover each window with a different colour of cellophane, red, yellow and blue.
Put the three boxes containing the pots of seedlings in good light with the window facing the light.
Observe any difference in the effect produced by different coloured light on the growth of stems.
9.5.11 Thermonastic responses, nastic movements
See diagram 9.126: Thermonastic movement of daisy, e.g. four o'clock flower, crocus, tulip
A nastic movement is a response not affected by the direction of origin of the stimulus.
Movements made in response to a stimulus, tropic movements, where the direction of the movement is not controlled by the stimulus, are called nastic movements.
These stimuli often consist only of a general change in some external factors, temperature, light.
A thermonastic response is movements caused by temperature changes, e.g. opening and closing of flowers.
In addition to temperature and light, the diurnal rhythm of the plant and other autonomic stimuli may control the opening and closing of flowers.
The "four o'clock flower", does not close its flowers, because the time is four o'clock, but because of drop in temperature.
Experiments
1. Transplant two flowering plants with many petals, e.g. daisy, to two tubes containing water.
Put one tube in a beaker of cold water and the other tube in a beaker of warm water.
After 30 minutes the flower in the beaker containing warm water has opened further, but the flower in the beaker containing cold water has closed.
2. Half fill two beakers with water.
Heat the water in one beaker to 30oC.
Fill two collecting tubes to a height of 2 cm with water.
Put one daisy with half opened petals in each collecting tube and put the tubes in the beakers containing warm and cold water.
The tubes must float so use glass beads to balance the tubes.
Observe the behaviour of the petals.
After 30 minutes the flower in the beaker containing warm water has opened further, but the flower in the beaker containing cold water has closed.
The different temperatures cause a differing degree of expansion in the upper and lower side of the petals, which causes thermonastic movements.
In addition to temperature and light, the diurnal rhythm of the plant and other autonomic stimuli play a role in opening and closing flowers.
3. If you bring flowers in the closed condition into the warm laboratory, opening usually commences promptly even if the flowers are placed in a dark cupboard.
The movements are reversed if you put the specimens into a refrigerator.
Use daisy or dandelion flowers to illustrate the photonastic properties of these flowers.
They may be performed outdoors or daisy plants can be transplanted into pots in the greenhouse.
If certain plants are covered over with a box in the afternoon, examination next day will show that at a time when exposed plants have opened their flowers, the flowers in darkness are still closed.
The sleep movements of leaves should be studied in suitable examples in the garden and field.