School Science Lessons
2024-10-28
(UNBiology1)
Plant Kingdom
See: Websites: Plants
Please send comments to: j.elfick@uq.edu.au
Contents
9.10 Magnoliophyta, Angiosperms, flowering plants
9.1 Angiosperms, flowering plants, Magnoliophyta Division
9.2 Monocotyledons and dicotyledons (angiosperms)
9.3 Monocotyledons, grass (cereals), bamboo, sugar cane, maize
9.4 Grass family, Poaceae
9.5 Bromeliaceae, bromeliads
9.6 Dicotyledons (angiosperms), herbs, shrubs, trees
9.7 Angiosperms, asexual reproduction
9.8 Heterotrophic angiosperms
9.9 Stems
9.10 Plant body
9.10 Angiosperms, flowering plants, Magnoliophyta Division
9.1 Angiosperms, flowering plants, Magnoliophyta Division
Tracheophyta (vascular plants), monocotyledons and dicotyledons
Angiosperms, have seeds enclosed in an ovary, they are the "flowering plants".
Angiosperms have endosperm inside the seeds which are enclosed in a fruit.
Nowadays the term "angiosperm" is not used in plant classification.
1. Angiosperms have the following characteristics:
* The ovules are enclosed in a carpel.
The carpel with three parts, the stigma where pollen germinates, the style that allows pollen tubes to reach the ovary, and an ovary that encloses the ovules and where fertilization occurs.
The three parts together are called the pistil.
* Double fertilization produces a zygote that becomes the embryo plant and endosperm nutritive tissue in the seed for the developing plant embryo.
* Stamens with pollen sacs produce pollen.
* Phloem tissue consisting of sieve tubes and companion cells for the transport of nutrients and hormones.
* The shoot system consists of stem, leaves and buds.
The leaves are attached to the stem at the nodes.
The internode is the part of the stem between two nodes.
The leaf is attached to the stem by a leaf base.
The petiole, leaf stalk, joins the leaf base to the expanded lamina, the leaf blade.
The leaf venation, pattern of veins, is net-like.
This reticulate venation is typical of dicotyledons.
At the apex of the shoot is the terminal bud with the growing point protected and covered by young unexpanded leaves.
The nodes and young leaves are telescoped together.
Elongation of the short internodes in this region results in growth in length of the shoot.
Axillary buds in the axils of leaves are also embryonic shoot systems that can grow into lateral branches, stems bearing leaves, or they may just remain dormant.
Inflorescences, clusters of flowers, can be produced from axillary or terminal buds.
Examine the external features of a herbaceous flowering plant, e.g. buttercup, wallflower, groundsel.
9.2 Monocotyledons and dicotyledons, (angiosperms)
See diagram 9.53: Parts of a plant.
See diagram 9.52: Grass plant.
Table 9.6.0 Monocotyledons and dicotyledon
Monocotyledons / Dicotyledons
1. Embryo has one cotyledon / Embryo has two cotyledons
2. Mostly herbaceous plants, except palms / Mostly woody plants
3. Tap roots are common / Tap roots are rare
4. Vascular bundles closed, no cambium, secondary thickening rare / Vascular bundles open, have cambium, secondary thickening common
5. Leaves have parallel veins with simple cross connections, midrib is absent / Leaves have network of veins, midrib is present
6. Floral parts usually in threes, typical floral formula: P 3+3 A 3+3 G3./ Floral parts usually in fives, typical floral formula: K5 C5 A5 G5
7. Include grasses, orchids, lilies, palms.
Many have bulbs, corms, rhizomes / Most trees and shrubs
9.3 Monocotyledons, grass (cereals), bamboo, sugar cane, maize
See diagram 9.52: Grass plant.
Monocotyledons include arrowroot, banana, coconut palm, canna, ginger, maize, onion, orchids, pineapple, screw-pine, sisal, taro, yam.
Monocotyledons have the following characteristics:
1. The embryo has one cotyledon.
2. They are mostly herbaceous plants, except palms and the larger bamboo.
3. Tap roots rarely occur.
4. The vascular bundles are closed, cambium is absent, and secondary thickening is rare.
5. The leaves have parallel veins with simple cross connections.
The midrib is absent.
6. The floral parts are usually in threes.
A typical floral formula is as follows: P 3+3 A 3+3, G (3).
7. Many monocotyledons have bulbs or corms, or rhizomes.
8. Monocotyledons include sisal, onion, taro, pineapple, canna, yam, grasses (cereals) arrowroot, banana, orchids, palms, screw-pine and ginger.
Experiments
1. Cut stems transversely, e.g. grass (cereals), bamboo, sugar cane, maize (corn).
Note the similarities in the cross sections.
Note the tubes of vascular bundles scattered through the pith.
9.4 Grass family, Poaceae
9.67 Grass leaf
Poaceae, grass family.
2. Examine a grass and note flowers (inflorescence), ligule, leaf blade, parallel veins, leaf sheath, node, internode, fibrous roots,
9.5 Bromeliaceae, bromeliads
Angiosperms, Monocotyledons, Family Bromeliaceae, usually herbaceous perennials, terrestrial or epiphytic, parallel-veined leaves in rosettes to store water, silica in leaf epidermis, flowers with coloured bracts and calyces of three sepals and three petals, nectaries, capsule or berry fruit, trichomes to capture water, (CAM) photosynthesis, often in arid climates.
Pineapple, (Ananas comosus), Bromeliaceae
Spanish moss, (Tillandsia usneoides), Bromeliaceae
9.6 Dicotyledons (angiosperms), herbs, shrubs, trees
See diagram 9.53: Parts of a plant (diagrammatic).
Dicotyledons have the following characteristics:
1. The embryo has two cotyledons.
2. They are mostly woody plants.
3. Tap roots are common.
4. Vascular bundles are open, cambium is present, and secondary thickening is common.
5. The leaves have a network of veins and a midrib.
6. The floral parts are usually in fives, so a typical floral formula is K5 C5 A5 G5.
7. Dicotyledons include mango, kapok, hemp, sunflower, sweet potato, cress, pumpkin, cassava, avocado, peas and beans, cotton, fig, nutmeg, eucalyptus, passion fruit, sesame, pepper, coffee, citrus, tomato, potato,
cocoa, tea, jute, and many trees and shrubs.
Experiments
1. Examine a dicotyledon and note terminal bud, axillary bud, branch or lateral shoot, roots, root tips, stem, 1st node, 2nd node, axil, 3rd node, leaf, flower, and flower stalk or pedicel.
2. Cut stems transversely, e.g. geranium, tomato, willow.
Note a bright green layer, the cambium layer, under the outside layer of the stem.
Note tubes of vascular bundles arranged in a ring about the central, or woody, portion of the stem.
3. Compare monocotyledon stems with dicotyledon plant stems.
Cut stems downwards under water then put the cut ends in an ink solution.
Later, cut the stems transversely to see which cells are involved in the upward movement of water.
9.7 Angiosperms, asexual reproduction
5.5 Banana rhizome
9.7.1 Bulb, onion, Narcissus, Oxalis
9.7.2 Corm, false stem (pseudostem) banana, taro
9.7.3 Lignotuber, Banksia, Eucalyptus
9.7.4 Rhizome, ginger, iris, banana
9.7.5 Runners, strawberry
9.7.6 Potato stem tuber
9.7.7 Tuberous roots, root tuber, sweet potato
9.8 Heterotrophic angiosperms
Most angiosperms are autotrophic and create compounds by photosynthesis,
except the parasitic and semiparasitic angiosperms, which are heterotrophic.
Experiments
9.8.1 Bird's nest orchid
9.8.2 Bladderwort
9.8.3 Butterwort
9.8.4 Hemiparasites, Nuytsia
9.8.5 Insectivorous plants, pitcher plant, Venus fly trap
9.8.6 Mycorrhizal plants, Eucalyptus, Dipodium
9.8.7 Parasitic angiosperms, mistletoe
9.8.8 Parasitic angiosperms, dodder
9.8.9 Parasitic angiosperms, sundew
9.9 Stems
9.10.2 Stems
Bramble, (blackberry)
9.4.2 Celery stalk
Corm, Gladiolus corm
9.9.1 Creeping stems, moneywort (creeping jenny), ground ivy
9.4.3 Dicotyledon stem, sunflower
9.9.2 Herbaceous dicotyledon stem, buttercup
9.9.3 Herbaceous dicotyledon stem, carnation
9.9.4 Herbaceous stem, forage legume alfalfa (lucerne)
9.9.5 Herbaceous monocotyledon stem, iris
9.4.5 Monocotyledon stems, Cocos nucifera coconut, Dracaena
9.4.4 Monocotyledon stem, maize (corn), Zea mays
Rhizome, ginger, iris, banana
9.7.5 Runners, (strawberry)
9.9.14 Stem with secondary thickening, Linden tree (lime tree), horse chestnut
9.9.6 Stem hooks, bramble (blackberry), rose
9.4.1 Stems, (cut wood)
9.9.7 Stolons, currant, European gooseberry, banana
9.9.13 Terminal bud, linden tree (lime tree), beech, oak
9.9.10 Twigs of trees in winter, horse chestnut, sycamore, beech, oak
9.9.11 Twining stem, climbing bean, yam
9.9.12 Woody stem, hawthorn
9.9.9 Xeromorphic stem, spinifex
9.10 Plant body
9.10.1 Plant body
9.9.8 Leaves
9.10.2 Stems
9.10.3 Roots
9.10.4 Root hairs
9.10.5 Root rhizosphere
9.10.6 Flowers
9.10.7 Flower and fruit formation
9.10.8 Fruit
9.7.1 Bulb, onion, Narcissus, Oxalis
See diagram 9.81: Bulb of Narcissus (daffodil, jonquil).
A inflorescence, B storage scales, C axillary bud, D protective scales, E stem, F adventitious roots
A bulb is an aggregation of fleshy leaf base developed on a short disc-like stem.
It is protected by a series of thin, membranous, scale-like leaf bases.
The scale leaves are the swollen bases of the vegetative leaves.
They are composed of parenchyma cells and are swollen with food stored during the growing season.
A longitudinal section shows a terminal bud or growing point, surrounded by the vegetative leaves, with the flowering stem in one of their axils.
In Narcissus, unlike most bulbs, the flowering shoot is thus lateral to the growing point, is not directly involved in the formation of the shoot, so persists from year to year.
The bases of the vegetative leaves swell to form the new fleshy scales, bulb scales, as their organic material passes down to the base.
Axillary buds in the axils of the outermost scales may form two daughter bulbs.
The innermost scales are the most recently formed, and the outer scales represent the bases of leaves of previous seasons.
The stem is flat with many adventitious roots at its base.
In onion or hyacinth the growing point produces a flowering shoot with leaves that terminates its growth.
Axillary buds arising in the axils of fleshy scales grow at the expense of food synthesized in the green leaves or stored in the bulb scales and enlarge to form the bulbs for the next season.
The surface of the bulb is covered by the thin papery exhausted scales of the old bulb.
The bulb is a very condensed shoot with extremely short internodes and with leaf bases swollen with stored food.
Experiments
1. Cut the bulb of an onion longitudinally through the middle.
Note the stem, the outer membranous and inner fleshy scale leaves, and the large central bud containing the rudiments of foliage leaves and the flower.
Dissect a bulb and note the presence of buds in the axils of the scale leaves.
2. Cut a bulb transversely and note the arrangement of the scale leaves.
Test the fleshy scale leaves for reducing sugars, starch and food reserves with iodine solution.
Compare the bulbs.
Grow bulbs and investigate the origin of new bulbs.
3. Observe the annual top growth and perennial bulbs of (Oxalis pes caprae), Bermuda buttercup, soursop.
The bulbs sprout in autumn to produce a slender underground stem, which thickens to form the vertical rhizome.
The top of the rhizome produces leaves and flowers.
After flowering commences, a new bulb starts to form.
In summer, a contractile tuber forms underneath the new bulb that contracts, drawing the new bulb deeper into the soil.
So oxalis is a bulb that pulls itself down into the soil.
9.7.2 Corm, false stem (pseudostem) banana, taro
See diagram 51.5: Banana corm, VS.
See diagram 51.1: Cultivated and "village" banana plant.
See diagram 62.7: Taro corm.
See diagram 9.82: Gladiolus corm.
1. The true stem of the banana plant is an underground stem, a rhizome.
The swollen stem base is the corm with very short internodes.
The corm makes shoots that grow into branches or other corms.
New plants come from these shoots.
Suckers grow from the dormant buds called "eyes" on the corm.
Each sucker formed is higher than the corm it came from.
If the land is sloping, the suckers are usually formed on the uphill side.
If left alone, generations of banana plants will gradually move up a hill.
2. The taro corm is an underground stem swollen with stored starch.
Like other stems it has these parts: The growing point or a shoot apex.
Many leaves joined to the shoot apex.
Leaf scars are seen as circular marks that go around the corm.
Axillary buds form just above the place where the leaf was joined to the stem.
The axillary buds can grow into little corms or "cormlets" (cormels).
The cormlets can grow into suckers.
3. Corm, Gladiolus, crocus, taro
See diagram 9.82: Gladiolus corm.
A corm is the swollen base of the flowering stem, usually a monocotyledon.
Its surface is sheathed in the bases of withered leaves, forming membranous brown scales.
Remove the scales to see thin depressed scars where axillary buds form.
The upper axillary buds form the next season's leaves and flowering shoot.
The lower axillary buds can form little corms or "cormlets", (cormels), which can grow into suckers, separate, and reproduce vegetatively.
The growth of the vegetative leaves and flowering axis uses all the food stored in the old corm, but the old corm can still be seen below the new corm for some time.
The base of the flowering shoot gradually becomes swollen using the food transferred from the leaves, and the old corm.
This base stem swelling is the young corm, sheathed in the bases of the lower leaves of the flowering shoot.
At the close of the flowering period, the leaves and flowering stem wither and their stored food transfers to the swollen stem base, while buds are produced in the axils of the withered leaves.
See much starch in the outer part of the corm in a vertical section stained with iodine solution.
Also, many scattered vascular bundles pass longitudinally to the uppermost buds and others pass laterally into the leaf bases.
At the top of the corm are scars left by the withered flowering stem and foliage leaves.
The flowering shoot of the next season develops from an upper bud in the axil of a scale leaf.
Each new corm is lateral to that of the previous season. because it arises as a flowering shoot from a lateral bud in the axil of the uppermost scale loaves.
Experiments
1. Cut longitudinally through the middle of a corm, passing through one large bud.
Test the cut surface of the stem for reducing sugars and starch with iodine solution.
2. Observe the corm of crocus.
In the autumn, note the flattened swollen stem, the adventitious roots, the membranous scales encircling the stem, and the axillary buds.
One or more buds near the top of the corm are strongly developed.
Cut longitudinally through the middle of a corm and passing through one large bud.
Examine the cut surface and note the structure of the bud with its axis, scale leaves, foliage leaves and central flowers.
Test the cut surface of the stem with iodine solution.
Grow corms and trace the development of the flowering shoot and of the new corms.
Note that the old corms of are persistent.
Note also that some axillary buds produce widely spreading underground stems that terminate in new corms.
3. Observe the taro corm, underground stem swollen with stored starch.
Like other stems it has the following parts:
1. The growing point or a shoot apex.
2. Many leaves joined to the shoot apex.
3. Leaf scars appear as circular marks around the corm.
4. Axillary buds form just above the place where the leaf was joined to the stem.
The axillary buds can grow into little corms or "cormlets" (cormels).
The cormlets can grow into suckers.
See 5. Parts of the taro plant.
9.7.3 Lignotuber, Banksia, Eucalyptus
Banksia, (Banksia serrata), Proteaceae
Eucalyptus, (Eucalyptus species), Myrtaceae
A lignotuber is a swollen region where the trunk and roots meet.
It enables the plant to survive fires.
9.7.4 Rhizome, ginger, iris, banana
See diagram 9.9.3: Iris rhizome.
See diagram 9.83: Ginger rhizome.
A rhizome is part of a shoot with reduced scale-like leaves.
It usually develops horizontally and underground.
The apex sends up stems or leaves.
The rhizome is composed of a series of segments that have arisen from axillary buds.
At the apex of each segment is the apical bud (terminal bud), that forms the large strap-shaped, vertical, sheathing leaves and flowering axis.
Development of the flowering axis stops further growth of the segment.
Axillary buds just behind form new branches of the rhizome.
They also have terminal buds that later form leaves and a flowering axis.
Each segment is marked by a series of concentric circles that represent the bases of the former sheathing leaves formed at the nodes.
Axillary buds are associated with the circles.
Fibrous adventitious roots develop from the under surface of the rhizome.
The rhizome can be separated into segments.
Each segment can reproduce the plant if it has a growing point.
The rhizome is a food storing organ, accumulating much starch.
Note the position of the aerial shoots and the way in which more growth of the rhizomes can continue.
Note at each node a scale leaf with an axillary bud or branch.
Adventitious roots also arise at the nodes.
Note how the system becomes progressively more extensive.
Note the presence of scale leaves, axillary buds, and adventitious roots.
Experiment.
Ginger rhizome
1. Observe the ginger rhizome.
It is hard and compressed sideways.
Inside it is pale yellow.
It is covered with scales and has fine fibrous roots.
9.7.5 Runners, strawberry
1. A runner is a stolon, i.e. a long lateral shoot producing roots at intervals.
The shoot between the roots dies to form new individual plants.
Plant a well-developed strawberry plant in spring in a dish.
Put the dish on a windowsill and water regularly so that the soil does not become either too moist or too dry.
Note the runners that grow out of the leaf axils.
Note the runners that grow out of the leaf axils.
Small leaves appear at their tips.
Roots develop that anchor the tip of the runner in the soil and the leaves appear.
A new strawberry plan forms.
2. Study the formation of new plants.
The short stem, the crown, produces runners, stolons, from it axillary buds.
The stolons are modified shoots.
The second node on the stolon touches the ground and forms a new plant.
9.7.6 Potato stem tuber
See diagram 9.85: Sprouting potato tuber,
A potato tuber has sprouting axillary buds to form aerial shoots.
See diagram 9.86: Potato cell with starch grains.
A stem tuber starts from a specialized stem called a stolon, which is unlike other stems. because it grows downwards into the soil to form a stem tuber, a potato.
Later, the stolon withers to leave a scar on the potato.
A stem tuber is the swollen end of an axillary underground branch developed at one of the lower stem nodes from dormant axillary buds called "eyes".
There is a terminal bud among the axillary buds.
Each eye can reproduce the plant.
A stem tuber has vestigial leaves as slight bumps.
Axillary buds are clustered at the apical end of the potato, i.e. furthest from the base.
The thin outer cork layer of the potato, the jacket, it pitted with lenticels for gas exchanges.
Hormones and light cause the axillary buds to form shoots, haulms.
Leaving the potato in the light is called "chitting".
However, when potatoes are exposed to light, the skin turns green and produces solanine, C46H73NO15, a poisonous glycoalkaloid.
Experiments
1. Cut the potato and test the cut surface with iodine solution.
Thin layers of cork cells cover the tubers formed from phellogen, cork cambium, layers in which lenticels form.
The eyes are within slight depressions with rims on which the scale leaves form, arranged in a distinct spiral.
At the apex of the tuber is the terminal bud.
At the opposite end is the scar of attachment to the stem that develops the tuber.
Tubers have thin-walled intercellular spaces containing starch grains of characteristic shape and protein.
This stem tuber is different from the root tuber of sweet potato, dahlia, lesser celandine.
2. Scrape a freshly cut surface of a potato tuber with a blunt knife.
Transfer some milky fluid on the knife to a drop of water on a slide, then add a coverslip.
Find isolated grains under low power then high power.
Note the structure of the starch grains.
Each grain has a hilum and eccentric stratification.
9.7.7 Tuberous roots, root tuber, sweet potato
See diagram 9.87: Sweet potato tuber.
A outer periderm, B may produce secondary roots, C the "crown" end that may produce sprouts.
In many biennials and perennials the main taproot, and sometimes the chief lateral roots, is very much swollen with stored food.
When the aerial organs have died down, they preserve the plant until the next season.
In these tuberous roots the new shoot develops at the expense of the reserve foods.
Tubers form by secondary thickening of some adventitious secondary roots near the soil surface.
The cambium in these tuberous roots forms much xylem parenchyma and few lignified elements.
The food surplus is stored in the xylem parenchyma.
Weeds with tuberous roots may be broken up during cultivation, develop adventitious shoot buds and propagate the weed.
Axillary buds at the base of the foliage leaves also propagate the plant readily.
Tuberous roots, root tuber, include carrot, turnip, parsnip, beetroot, sweet potato, dahlia, skeleton weed, dandelion.
Experiments
1. Examine plants at various seasons of the year and trace the origin and mode of development of the root tubers.
2. The sweet potato tuber is a root tuber so it has no nodes or internodes or reduced leaves.
The end neared the main plant, the "crown" end, may produce shoots, stems and foliage.
This end can be cut off and used as planting material.
The end farthest from the main plant may produce secondary roots.
Some botanists in USA refer to the storage organ of the sweet potato as a root, not a tuberous root, because only the swollen end of an axillary underground branch is a tuber, e.g. potato, Irish potato.
In USA, sweet potatoes, Ipomoea batatas, are called "yams" but that name should apply only to plants in the genus Dioscorea.
Examine a sweet potato tuber (tuberous root).
Note the fibrous, normal roots, and the club-shaped root tubers.
3. In the dandelion, a peculiar longitudinal contraction of the tuberous taproots wrinkles its surface, and pulls the radical leaves downwards to the soil surface.
At times the plant may form a shallow saucer-like pit on the surface of the soil.
Crocus, gladiolus, and oxalis develop similar contractile roots.
They drag the bulb, corm, or rhizome from which they arise, more deeply into the soil.
4. In gladiolus, each new corm arises on top of the old one and is higher in the soil, but the contractile roots at the base of the corm pull it down to a lower level.
5. Aerial shoots (suckers) also result in vegetative reproduction.
They arise from adventitious buds on the roots, and produce new aerial shoots as in begonias, plums, apples, poplars.
9.81 Bird's nest orchid
Note the matted underground stems and the fleshy roots.
Sections of the latter will show the endotrophic mycorrhiza.
9.8.2 Insectivorous plants, pitcher plant, Venus fly trap
See diagram 9.66.3: Pitcher plant, Nepenthes.
Butterworts and sundews live on wet acid soils where there is a lack of nitrogenous compounds.
Keep plants damp in the laboratory with the original soil left around the roots.
9.8.3 Butterwort
Note the rosette leaves with incurved margins of the butterwort and the sticky nature of the upper surface.
Mount a piece of leaf with the upper surface uppermost and examine under low power.
Note the stalked capturing glands and the sessile digestive glands.
9.8.4 Hemiparasites, Nuytsia
See diagram Nuytsia floribunda.
West Australian Christmas tree, (Nuytsia floribunda) Loranthaceae, has green leaves and is unable to live without connections with roots of other plants through haustoria.
Experiment on what stimulates roots to make haustoria, which may be attached to non-living things, e.g. electric cables.
Seed-bearing plants, Seed plants, Spermatophytes (gymnosperms and angiosperms)
9.8.5 Bladderwort
The bladderwort lives in pools of brackish water.
This plant has no roots.
The leaves are very finely divided.
The flowers project above the water.
Note the shape of the bladder and the presence of hairs at the orifice.
Open several bladders and look for the remains of animal prey.
9.8.6 Parasitic angiosperms, mistletoe
Parasitic angiosperms include toothworts, broomrapes, mistletoe, sandalwood, devil's twine, olax, sarracenia Rafflesia has the largest flower in the world.
See diagram 9.53.11: Mistletoe, Loranthus.
See sections across a branch in TS or LS and through the haustorium longitudinally.
Greenhouses of botanic gardens often contain examples of tropical carnivorous plants.
9.8.7 Dodder
See diagram 9.53.12: Dodder, Cuscuta.
Cuscuta australis, Australian dodder Agroclavine Convolvulaceae
Observe dodder plants coiling around the stems of clover, heather, gorse and nettle, Urica.
Note the manner in which it coils around its host, its reduced, scale-like leaves and its pink flowers.
Notice the absence of chlorophyll and explain the parasite's method of nutrition in view of this.
Examine the haustoria and cut a transverse section of the stem of the host plant in the region of a haustorium.
Notice the type of host tissue that the haustoria cells penetrate.
9.8.8 Mycorrhizal plants, Eucalyptus, Dipodium
See diagram Eucalyptus tereticornis.
The mycelia of certain fungi assist in absorbing of plant nutrients, especially poor soils.
The relationship between the fungus and the plant is mutualism.
Some fungi live just outside the roots of woody species, e.g. Eucalyptus, oaks, pines, olives.
Other fungi penetrate the root and live between the cells in many grain plants.
The myco-heterotrophic orchids, Dipodium variegatum and Dipodium hamiltonianum are colonized by Russulaceae fungi.
9.8.9 Parasitic angiosperms, sundew
See diagram: Drosera rotundifolia, sundew.
The sundew (Drosera rotundifolia) occurs in bogs.
Observe the creeping rhizomes, rosette arrangement of the leaves and short petioles.
In the field, touch the leaf to get the tentacles to respond as if trying to trap an insect.
Mount tentacles and examine under low power.
Note the stalk and the glandular head.
9.9.1 Creeping stems, moneywort (creeping jenny), ground ivy
Note the long, recumbent habit of the stem, the absence of scale leaves and the position of the adventitious roots.
9.9.2 Herbaceous dicotyledon stem, buttercup
See diagram 9.51: Buttercup, Ranunculus.
See diagram 9.59.1: TS Pumpkin stem, Cucurbita.
Cut by hand TS and LS sections of young buttercup stems.
9.9.3 Herbaceous dicotyledon stem, carnation
Carnation is a perennial herbaceous plant with a complete vascular cylinder.
Observe the following: epidermis covered by a cuticle, cortex comprising chlorenchyma and sclerenchyma, stele is a continuous ring comprising phloem, cambium, xylem, endarch (the first formed xylem next to the pith) medulla parenchyma.
9.9.4 Herbaceous stem, forage legume alfalfa (lucerne)
Herbaceous stems have growth from the cambium limited to one season or part of one season, or lacking.
They have no distinctive anatomical structure, but some features are typical of monocotyledons others of dicotyledons.
Vascular bundles in stems are collateral with endarch xylem.
Alfalfa (lucerne), Medicago sativa, Fabaceae, is a perennial herbaceous plant grown for fodder.
Observe the following tissues:
1. The epidermis is covered by a cuticle.
2. The cortex is narrow compared with the cortex of the root and consists of collenchyma as four corner strands forming longitudinal ridges on the stem and parenchyma.
3. The outer part of the cortex contains chloroplasts.
4. The single peripheral ring of discrete bundles without active cambium.
5. The vascular tissue arranged as discrete collateral bundles with phloem to the outside, xylem to the inside and cambium between the xylem and phloem.
6. The pith consisting of parenchyma in the centre of the stem.
7. The parenchyma rays between the vascular bundles.
9.9.5 Herbaceous monocotyledon stem, iris
Observe the widely spaced discrete vascular bundles arranged peripherally in two rings or scattered throughout the transverse section.
Cambium is not usually formed and most vascular bundles have a sclerenchyma sheath.
In monocotyledons with scattered bundles there is no distinction of ground tissue into cortex and medulla.
Where the vascular strands are confined to the periphery of the stem there is either a medulla cavity or a distinct parenchyma medulla.
9.9.6 Stem hooks, bramble (blackberry), rose
Examine the hooks on the stem and petioles of the bramble or rose.
Compare them with thorns.
Hooks are modified hairs.
Thorns are modified branch shoots.
9.9.7 Stolons, currant, European gooseberry, banana
See diagram 51.13.0: A "stool" of bananas.
Note the curved stems and how adventitious roots are given off from where the stem touches the ground.
Note exactly where the new adventitious shoots form.
9.4.1 Stems, (cut wood)
See diagram 9.57.2: Section of cut wood.
See diagram 9.57.1: Sections, Transverse Section (TS), Radial Longitudinal Section (RLS).
The day before the lesson, stand a young plant in a jar containing enough red or blue ink to cover the roots.
Find a stump of a tree or coconut that has been cut down recently.
Get a piece of sugar cane, a yam, a taro corm, a bit of banana corm and a ginger or tumeric rhizome.
You will need a razor blade for this lesson.
Show the students the young plant standing with roots in red ink.
Take the plant out and wash it.
Then cut the stem and open it with a razor blade to show the ink inside.
What does this prove? [Liquids move up the stem.]
Show the students the cut stump of a tree.
What is the function of the wood? [To let the plant become large and strong]
Eat some sugar cane.
What does this show? [Stems can be used to store food.]
Show the students the yam, taro and bit of banana corm.
Stems have three functions: transport of food from leaves to roots, transport of water and plant nutrients from roots to leaves, support of leaves and branches.
In a young stem only a few leaves can be supported.
In a large tree many leaves and branches can be supported, food storage, e.g. sugar cane.
9.4.2 Celery stalk
Celery (Apium graveolens var. dulce), Apiaceae
Celery for cutting ( Apium graveolens) Apiaceae.
9.169 Celery, Suction potential and tissue tension in celery
See diagram 9.78.0: T.S. Celery stalk.
Celery stalks are enlarged petioles.
A petiole is not a stem.
The stem of the celery plant is reduced to a disc.
Experiment
Wear safety glasses and nitrile chemical-resistant gloves.
Use a one-sided razor blade to cut thin transverse sections and longitudinal sections from a celery stalk.
Be careful! Cut away from the body.
Mount in water and apply a coverslip.
Stain sections with acid phloroglucin.
Observe the following tissues:
Epidermis is a single layer of cells with a thick cuticle covering the outermost surface.
Collenchyma has cellulose thickenings in the corners of the cells.
Parenchyma has large cells with thin cell walls.
Vascular tissue is arranged as discrete collateral bundles.
Each vascular bundle has phloem to the outside, xylem to the inside and cambium between.
Sclerenchyma caps the vascular bundle.
9.4.39.79 Dicotyledon stem, sunflower
See diagram 9.79: T.S. Young sunflower stem.
See diagram 9.78.1: LS Sunflower stem.
1. Mount the section and irrigate with an aniline salt, to stain the woody tissues.
Examine the whole section under low power.
Observe the epidermis, cortex and central cylinder.
Look for any layers of the cortex thickened to give additional strength.
Observe the vascular bundles composed of xylem, phloem and cambium.
Observe the pith and note if the stem is solid or hollow.
2. Observe the stem under high power and note the cellular structure in detail.
Observe the epidermal tissues, cortical tissues and a complete vascular bundle.
3. Examine a similar stem by means of radial longitudinal sections, R.L.S.
Note the appearance of the collenchyma, the annular protoxylem vessels, and the pitted metaxylem vessels.
9.4.4 Monocotyledon stem, maize, (corn), Zea mays
See diagram 9.80: T.S. stem of maize (corn).
Use low power to observe the small size, large number, and irregular arrangement of the vascular bundles.
The outer scattered vascular bundles are surrounded by fibres to strengthen the stem.
Note the complete absence of cambium.
9.4.5 Monocotyledon stems, Cocos nucifera coconut, Dracaena
See diagram 9.78.4: Dracaena.
See diagram 53.4: Cocos nucifera, coconut.
9.9.8 Leaves
See diagram 9.66.2: Shapes of leaves
Collect samples of leaves with different shapes.
Some leaves should be the leaves of your crops.
Show the students the leaves you have collected.
Leaves are usually flat and thin so that they can catch plenty of sunlight and have little holes in the lower side to let gases and water vapour move in and out.
The bushy plant the leaf has three parts: 1. leaf, 2. petiole, and 3. leaf blade.
The grass leaf has three parts: 1. leaf blade, 2. leaf sheath, and 3. ligule.
Draw the leaves of the different crop plants you are growing and describe their shape.
9.9.9 Xeromorphic stem, spinifex
See: diagram 9.6.8: Spinifex stem, TS, (from EBOT, University of Sydney).
Spinifex (Triodia sp), is a grass that grows on sand dunes.
It has a prostrate stem with roots and shoots at the nodes.
The anatomical structure is a typical monocotyledon stem with scattered bundles and no cambium.
Observe the epidermis covered by cuticle, vascular bundles scattered in the parenchyma ground tissue, fibre sheath around each vascular bundle, band of sclerenchyma in the peripheral region where the sheaths merge to give rigidity to the stem.
9.9.10 Twigs of trees in winter, horse chestnut, sycamore, linden tree (lime tree), beech, oak
See diagram 9.51.2: Shoot of horse chestnut, Aesculus.
Note the terminal bud, the leaf scars with associated axillary buds, the ring of bud scale scars and the lenticels.
Dissect a terminal bud.
Arrange the scales and young foliage leaves in series.
The scales are leaf bases.
A large scar between two terminal buds shows the position occupied by an inflorescence in the previous spring.
The formation of an inflorescence by the terminal bud leads to the growth of the branch being carried on by the two axillary buds immediately below.
Examine stages in the opening of the buds in spring.
9.9.11 Twining stem, climbing bean, yam
See diagram 63.4: Yam twining stem.
Swollen rounded underground stem, i.e. stem tuber, e.g. yam.
Twining tendrils: white bryony, passion fruit, sweet pea, garden pea.
Virginia creeper has adhesive tendrils.
9.9.12 Woody stem, hawthorn
See diagram 9.57.0: Tissue sections.
See diagram 9.57.1: Sections.
See diagram 9.57.2: Section of cut wood.
See diagram 9.56.1: Helianthus wood fibres.
Stems have four functions:
1. Transport of food from leaves to roots,
2. Transport of water and plant nutrients from roots to leaves,
3. Support of leaves and branches,
4. Store food.
Note the position of the thorns on the hawthorn stem.
Look also for larger examples that bear foliage leaves.
Compare the structure of a twig of gorse with that of the hawthorn.
9.9.13 Terminal bud, linden tree (lime tree), beech, oak
Examine the apparently terminal bud and note that at the side of a leaf scar another small scar has been formed when the original terminal portion of the shoot falls off.
So the apparently the terminal bud is really an axillary bud.
Dissect a bud and arrange the parts in a series.
Note the pair of outer scales followed by pairs of inner scales that have a small foliage leaf between them.
The bud scales are stipules.
Note the opening of the buds in the spring and note that the stipules soon fall from the foliage leaves.
9.9.14 Stem with secondary thickening, Linden tree (lime tree), horse chestnut
See diagram 9.57.4: Tilia, secondary wood, TS.
1. Examine transverse sections through the stem of various ages as follows:
1.1 near the apex of the shoot.
1.2. the middle of the first year's growth.
1.3. near the bottom of the first year's growth.
1.4. about the middle of a later year's growth.
Note the secondary wood and examine the vessels of the spring and autumn wood.
Look for medullary rays.
On the outside of the cambium, note the secondary phloem, containing thickened cells called phloem fibres.
Note how the medullary rays widen out in the phloem.
Near the periphery, look for cork cambium, and note the layers of cork cells produced on the outside of this.
2. Examine a secondarily thickened stem by means of radial longitudinal and tangential longitudinal sections.
Observe the following tissues:
2.1 The periderm consists of phellem and phellogen.
Phellem (cork) cells have radial rows of cells with suberized walls, formed by division of the phellogen (cork cambium) one row of radially flattened cells with thin walls.
In some plants the phellogen may also produce a farther layer, the phelloderm, towards the inside.
This layer is not apparent in Tilia.
The lenticels, part of periderm, are regions of rounded, loosely packed cells, which allow exchange of gases through the otherwise impermeable tissue
2.2 The secondary phloem, in wedges, consists of alternating bands of fibres and sieve tubes, companion cells and parenchyma.
2.3 The cambial zone
2.4 The secondary xylem, wood, (Greek xylon wood)
2.5 Primary rays extend from the cortex to the pith and are very wide in secondary phloem.
2.6 Secondary rays are in secondary xylem and phloem and do not extend to the centre or to the cortex.
2.7 Primary xylem surrounds the medulla.
The interpolation of secondary vascular tissues between primary xylem and primary phloem creates considerable stress in the stem.
3. The medulla and primary xylem are least affected.
In the outer layers, accommodation to the increasing circumference is accomplished by the following changes:
3.1 The epidermis initially keeps pace with growth by radial cell divisions, but eventually is replaced by a periderm of superficial origin, usually just beneath epidermis.
3.2 The cortex increases in circumference by expansion of cells in the tangential plane, and divisions in the radial plane.
Parenchyma is mostly squashed, but collenchyma retains its form and the new walls from recent cell divisions are evident.
3.3 Parenchyma cells of the primary rays between phloem wedges expand and divide similarly.
Some of these rays become conspicuous by great increase in width towards the periphery.
9.10.1 Plant body
See diagram 9.53: Parts of a plant
You will need some small plants that have flowers, branches and roots.
Bring them to the classroom.
Give one plant to each pair of students.
Point to the parts of the plant body.
The plant body consists of two parts:
The shoot above the ground, and the root below the ground.
The shoot is the stem with the leaves.
The stem is divided by thick parts called nodes.
Leaves grow from the nodes.
Roots may grow from nodes when the nodes touch the wet ground, e.g. sugar cane or para grass.
Roots grow at the root tips.
A bud is a baby shoot.
The terminal bud is at the end of the shoot and either makes the shoot grow or forms a flower.
The axillary buds grow from the nodes.
They grow in the angle (axil) between the leaf and the stem.
Axillary buds can grow to form lateral shoots called branches.
The buds at the ends of the branches can either make the branch grow or form a flower.
Axillary buds make the plant grow short and bushy or they can form flowers.
Leaves make food in the sunlight using air and water.
The stem carries food and water between the leaves and the roots.
The stem holds up the leaves, and may store food, e.g. sugar cane.
Roots take in water and plant nutrients from the soil.
Roots hold the plant in the ground and may store food, e.g. sweet potato.
Plant nutrients are chemicals the plants need.
Flowers can form fruits containing seed.
The seeds can grow to form new plants.
9.10.2 Stems
| See diagram 9.57.2: Section of cut wood
See diagram 9.57.1: Wood sections
The day before the lesson, stand a young plant in a jar containing enough red or blue ink to cover the roots.
Find a stump of a tree or coconut that has been cut down recently.
Get a piece of sugar cane, a yam, a taro corm, a bit of banana corm and a ginger or turmeric rhizome.
You will need a razor blade for this lesson.
Show the students the young plant standing with roots in red ink.
Take the plant out and wash it.
Then cut the stem and open it with a razor blade to show the ink inside.
What does this prove? [Liquids move up the stem.]
Show the students the cut stump of a tree.
What is the function of the wood? [To let the plant become large and strong]
Eat some sugar cane.
What does this show? [Stems can be used to store food.]
Show the students the yam, taro and bit of banana corm.
Stems have three functions: transport of food from leaves to roots, transport of water and plant nutrients from roots to leaves, support of leaves and branches.
In a young stem only a few leaves can be supported.
In a large tree many leaves and branches can be supported, food storage, e.g. sugar cane.
Table 5.08
Stem description
 Swollen stem base
 Swollen horizontal underground stem
 Swollen rounded underground stem
Name of stem
 corm
 rhizome
 stem tuber
Example.
 banana, taro
 ginger, turmeric
 yam
9.10.3 Roots
See diagram 9.57.5 Fibrous roots.
See diagram 9.57.6 Taproot.
Before the lesson, dig up a small bushy plant such as a mung bean and a grass such as para grass.
Wash the soil off the roots.
Show the students the bushy plant roots and grass roots.
1. Bushy plants have a main root called a tap root (or a primary root) and smaller lateral roots.
These roots grow very deep.
Grasses and palms have no main root, only many fibrous roots.
These are thin roots and do not grow deep.
2. Complete columns 2 and 3 of the Table 5.09.
Table 5.09
Kind of Root
 Tuberous root
 Aerial root
 Prop roots
 Swollen tap root
Function
 Stores food
 Breathes above water
 Holds up stem
 Stores food
Example
 Sweet potato
 Mangrove
 Maize
 Radish
9.10.4 Root Hairs
| See diagram 9.73.2: Root hairs 1
| See diagram 9.73.3: Root hairs 2
| See diagram 9.75: Root hairs 3
Remind the students of the need to transplant carefully so as not to damage the roots or root hairs.
Five days before the lesson put some bean seeds on wet paper or cotton wool on a plate.
Cover with a saucer or another plate to keep the seeds damp.
After germination, you will see small root hairs growing from the side of the root.
Use seed packaged in silver packets, because they will be protected from attack by fungus.
Most plants take water and plant nutrients into their roots through tiny root hairs (but coconuts do not have root hairs).
The root hairs are very small, have thin walls and are easily damaged.
If plants do not get enough water the leaves will wilt then dry up and later the plant will die.
If you damage the root or root hairs during transplanting: insects or disease damage the root, e.g. bacterial wilt disease of tomatoes.
If there is not enough water in the soil, the soil water is salty.
If there is too much water in the soil you say that the soil is waterlogged.
Roots will die in waterlogged soil, because they need some air to breathe.
Soils should be well-drained so that there is some air in them to give oxygen to the root hairs.
9.10.5 Root rhizosphere
The rhizosphere is the region just around the root hairs and fine roots that is influenced by root hair secretions and the local micro-organisms.
In the rhizosphere the following processes may occur:
1. Excretion of H+ that exchanges for nutrient Mg2+, Ca2+, NH4+, K+.
2. Release of carbon dioxide from root hair cells by respiration.
3. Oxidation of nitrogen and sulfur to nitrate and sulfate ions.
4. Excretion of organic acids by the root hairs.
The organic acids may complex metals and increase the mobility of Al3+ and Fe3+.
5. Depletion of oxygen gas around the root hairs to reduce the redox potential and so favouring Fe2+ over Fe3+.
6. Removal of water by root uptake.
7. Change in soil permeability.
9.10.6 Flowers
See diagram 9.98.7: Flower parts and flowers
Before the lesson pick enough large flowers so there will be one flower for each pair of students.
Flowers to use:
1. Poinciana Delonix) flower from a large tree, is a legume and forms large pods.
It has five sepals that are thick and green on the outside and red on the inside, five separate petals, (The upper one is more showy.), 10 stamens, and an ovary like a bean pod.
2. Hibiscus flower is a large red flower with five sepals, five red petals, many stamens attached to a red tube separate from the style that is inside it, five stigmas and so five female parts.
The flower does not usually produce seed.
3. Sweet Potato flower (Ipomoea) has five sepals joined, five petals joined to form a purple trumpet, five stamens attached to the petals, and female part.
It can form little black seeds.
4. Other suitable flowers are tomato, wing beans, peanut.
Give the flowers to the students.
What are the shapes, colour and smells of the flowers?
Shake some pollen out of the flowers.
Most flowers contain male parts and female parts.
Insects are attracted to flowers by their shape, colour and smell.
They fly from flower to flower carrying pollen on their bodies and legs.
Pollen comes from the male parts.
Pollen makes the female part form a fruit and seeds.
This is called fertilization.
5. Experiment
Hold the flower by the stalk and touch the following parts:
* Receptacle: Where the stalk gets wider at the base of the flower.
It is a platform for the other flower parts.
*. Sepals: Like little green leaves on the outside of the flower.
They project the young flower in a flower bud.
*. Petals: Coloured parts inside the sepals.
They attract insects.
*. Stamens: The male parts.
Each stamen consists of a little stick called the filament that holds up a bag called the anther.
The anthers produce pollen.
Can you see the pollen coming out of the anthers?
* Stigma: The top of the female part in the middle of the flower.
It is sticky and can catch the pollen.
* Style: The long tube of the female part below the stigma.
Pollen can grow down inside the tube to fertilize the ovary.
* Ovary: The swollen base of the female part that contains ovules.
After fertilization, the ovary will form a fruit and the ovules will form seeds.
Count the number of sepals, petals and stamens.
Then they should pull off some sepals and petals, and open the ovary to see the ovules.
6. Experiment
Functions of the parts of flowers
| See diagram 9.98: Dicotyledon half flower
| See diagram 54.9.2: Chilli flower (dicotyledon)
| See diagram 9.98.1: Lily flower (monocotyledon)
For this lesson you will need chilli or tomato flowers, one for two students, and razor blades.
You will also need a chilli or tomato fruit.
Before the lesson, practice cutting a half flower.
To do this hold the flower upside down and cut down the middle of the stalk between two of the sepals and cut the flower in half.
Now check that the stigma, style and ovary are cut exactly in half.
You will need a magnifying glass to see all the ovules in the ovary.
Can you count them?
Give a flower to each pair of students.
Name each part of the flower as you point to them.
Show the students how to cut a half flower.
Touch each part of the half flower.
Students should also touch each part of their half flower and tell you is name and function:
7. Functions of flower parts
* Sepals: protect flower bud
* Petals: attract insects
* Stigma: female part, pollen sticks to it
* Style: pollen grows down it
* Ovary: pollen fertilizes it to form a fruit
* Ovule: pollen fertilizes it to form seed
* Filament: part of male stamen, holds up anther part
* Anther: part of male stamen, produces pollen
* Pollen: can fertilize the ovary and ovules to produce fruit and seed.
* After fertilization, sepals, petals, stamens, stigma, and style usually die and fall off.
9.10.7 Flower and fruit formation
See diagram 9.4.2: Tomato flower and fruit formation
Collect some green tomatoes and tomato flowers, one of each for each group of four students.
You could also use chilli or eggplant (aubergine) fruit and flowers.
You will need some razor blades and a magnifying glass.
Examine the flowers and fruit, cut them down the middle with razor blades.
BE CAREFUL! Show them the ovary (fruit) and ovules (seed).
The remains of the sepals, petals, stamens, stigma, style, may be seen if they have not dropped off.
After pollen sticks to the stigma and grows down the style into the ovary, the ovary swells to form a fruit.
The ovules in the ovary become seeds.
Pollination is when the pollen touches the stigma and sticks to it.
Big flowers are pollinated by insects.
Small flowers such as grass are pollinated by the wind.
Fertilization is when the male pollen reaches the ovary and ovules.
The pollen grows down the style to the ovary.
Tell the students to draw their cut tomato flowers and fruit.
After fertilization, the flower stalk becomes the fruit stalk, the sepals, petals, stamens, stigma and style usually die, the ovary becomes the fruit, the ovules become seed.
9.10.8 Fruit
| See diagram 9.100.3: Succulent fruit
| See diagram 9.100.4: Berry, drupe legume
| See diagram 9.100.5: Pome, apple
| See diagram 53.7: Coconut fruit
| See diagram 58.1: Papaya fruit
| See diagram 9.113.4: Maize kernel, caryopsis
Collect examples of the eight different kinds of fruit.
When preparing the lesson, use only examples of fruit that the students have seen.
Show the students the different examples of fruits you have collected.
A fruit is a swollen ovary with one or more seeds inside.
Kinds of fruit:
Caryopsis, "grain": single carpel so a single seed is tightly closed in the ovary wall, indehiscent, pericarp fused with thin seed coat, e.g. maize, wheat.
Capsule: A dry fruit that opens to let the seeds out, e.g. cassava, sweet potato, okra.
Pod: A dry fruit that opens on two sides to let the seeds out, e.g. legume (cowpea, wing bean, peanut)
Berry: Fruit wall in two layers - outer layer is a tough skin, inner layer is thick and juicy, e.g. tomato, chilli, papaya, guava, banana.
Citrus fruit: Like a berry with thick peel and oil glands, e.g. orange, lime, pomelo.
Gourd: Like a berry with a hard outer skin, e.g. pumpkin, melon, snake gourd.
Drupe: Fruit walls in three layers: outer thin, middle thick, inner very hard - called a shell or stone, e.g. coconut, mango, coffee.
Multiple fruit: Many fruits stuck together to form one fruit, e.g. pineapple, breadfruit.