UNBiol1

School Science Lessons
Biology experiments
Updated: 2009-09-08
Please send comments to: J.Elfick@uq.edu.au

9.39 Green algae, Phylum Chlorophyta, Chlamydomonas, Sphaerella, (Haematococcus)
9.40 Phylum Chlorophyta, Pleurococcus, (Protococcus)
9.41 Phylum Chlorophyta, Spirogyra, Zygnema
9.42 Phylum Chlorophyta, Volvox
9.43 Desmid, Phylum Chlorophyta, Closterium
9.44 Brown algae, brown seaweed, kelps, Phylum Phaeophyta, Ecklonia
9.45 Brown algae, (Family Fucaceae), common seaweed, Hormosira
9.46 Liverworts, Phylum Hepatophyta, Marchantia
9.47 Mosses, Phylum Bryophyta, Dawsonia
9.48 Ferns, Phylum Pteridophyta, (Pterophyta), (Order Filicales), Dryopteris
9.49 Club mosses, Phylum Lycopodiophyta, (Lycophyta), Selaginella
9.50 Conifers, Phylum Pinophyta, (gymnosperms, naked seeds not enclosed in an ovary), Pinus
9.51 The parts of a flowering plant, (angiosperms, enclosed seed plants), Phylum Magnoliophyta
9.52 Monocotyledons, grass
9.53 Dicotyledons
9.54 The plant cell, cork cells, Robert Hooke
9.55 Human cheek cells
9.56 Leaf scale cells of onion
9.57 Cells and tissue sections, T.S., L.S., R.L.S., T.L.S
9.58 Parenchyma cells of tomato
9.59 Phloem cells of pumpkin, Cucurbita
9.60 Section-cutting by hand
9.61 Microscope staining techniques
9.62 Stamen hair cells of Tradescantia
9.63 Cells of a waterweed, Elodea
9.64 Wood cells, Eucalyptus, poplar
9.65 Leaf of a bushy plant
9.66 Leaves of agricultural plants
9.67 Grass leaf
9.68 Eucalyptus leaf, isobilateral leaf
9.69 Stomates in a leaf
9.70 Leaf with aerenchyma, water lily
9.71 Dicotyledon root and monocotyledon root
9.72 Legume roots, broad bean, clover, Rhizobium
9.73 Apogeotropic roots of mangrove
9.74 Excretion of acids by roots
9.75 Root hairs of a germinating bean
9.76 Root structure of mung bean
9.77 Root function, Tradescantia
9.78 Celery stalk
9.79 Dicotyledon stem, sunflower, Helianthus
9.80 Monocotyledon stem, maize, (corn), Zea
9.80.1 Other monocotyledon stems

9.39 Green algae, Phylum Chlorophyta, Chlamydomonas, Sphaerella, (Haematococcus)
See diagram 9.39: Chlamydomonas, Sphaerella, (Haematococcus)
Look for the cilium, contractile vacuole, cytoplasm, eye spot, cup-shaped chloroplast, nucleus, and cell wall. Find Chlamydomonas as a bright green "water bloom" in freshwater pools, tanks and stagnant water. Chlamydomonas is unicellular, grows quickly and is about 10 microns in diameter.
Put cheese and the white of a hard-boiled egg in a glass container. Add garden soil and washed sand. Fill the container with rainwater and stand it in diffuse sunlight. After a week, the water in the glass container may turn green with Chlamydomonas. Put a drop of the culture water on a microscope slide, apply a coverslip, and examine the culture under low power. Observe the rapid rhythmic rolling movements of Chlamydomonas. Irrigate with iodine solution and observe the cell wall, basin-shaped chloroplast, eye spot and storage granules.
Sphaerella is another unicellular alga that occurs in stagnant pools. It has a brick-red pigment in the vacuoles and so may form brown masses on trees and even brown rain and snow. If cultured in a jar of water, it is attracted by low intensity light.

9.40 Phylum Chlorophyta, Pleurococcus, (Protococcus)
See diagram 9.40: Pleurococcus (Protococcus)
Stain with iodine solution. Observe the cell surrounded by the cell wall. Look for the nucleus, cytoplasm, and the large irregular-shaped chloroplast. Note division into two daughter cells that will become round and separate from each other. Scrape a green encrustation from a piece of damp wood or bark of a tree. Mount in water and examine under low power. The spherical green structures are single cells of the alga Pleurococcus. Look for colonies of cells.

9.41 Phylum Chlorophyta, Spirogyra, Zygnema
See diagram 9.41: Spirogyra cell | See diagram 9.41.1: Chloroplasts of Spirogyra and Ulothrix
Look for the nucleus, cytoplasm, cell wall, and spiral chloroplast.
Spirogyra and Zygnema are unbranched filaments with cylindrical cells arranged end to end. Find these bright green, freely floating algae as clumps on the surface of ponds as "pond scum". Keep them in water from the original site. Spirogyra chloroplasts are in spiral bands. Zygnema has two star-shaped chloroplasts. These filamentous algae live as blue-green patches in rain puddles, on the moist walls of greenhouses and at the water's edge in dirty ponds and pools. Observe its threadlike growth. Lift out a piece of green scum with attached mud and transfer it to a glass container with some water in which it was growing. Keep it in a room in diffuse sunlight. Examine the algae in a drop of the original water to see the blue-green filaments with cross walls.

9.42 Phylum Chlorophyta, Volvox
See diagram 9.42: Volvox and similar species
Volvox looks like a hollow sphere colony of Sphaerella. Each Volvox is composed of many flagellate cells each similar to a Chlamydomonas, about 1000-3000 in total, interconnected by plasmodesmata and arranged in a hollow sphere (coenobium). Each cell has beating cilia that cause the Volvox to roll along through the water. Inside a Volvox colony may be daughter colonies. Reproduces asexually from large gonidia cells and sexually from male antheridia and female oogonia cells.

9.43 Desmid, Phylum Chlorophyta, Closterium
See diagram 9.43: Closterium
Look for the nucleus, pyrenoids, and chloroplasts in two "semi-cells".
Closterium and other desmids occur in acidic clean water, e.g. ponds and drainage ditches. Culture them in the water in which they were living. Examine the crescent-shaped cells. Desmids contain barium sulfate crystals and they indicate clean water with acid pH. l

9.44 Brown algae, brown seaweed, kelps, Phylum Phaeophyta, Ecklonia
See diagram 9.44: Ecklonia
Look for the fronds, stem, and holdfast.
The Sargasso Sea in the Atlantic Ocean is famous for huge areas of the floating brown algae, Sargassum.
Examine a brown seaweed found between low and high tide marks. Observe the holdfast for anchorage, the stem and the expanded frond containing chlorophyll for photosynthesis and the yellow-brown pigment fucoxanthin.

9.45 Brown algae, (Family Fucaceae), common seaweed, Hormosira
See diagram 9.45: Hormosira | See diagram 9.45.1: Cladophora, Dictyota
Look for the repeated forking at the receptacles, inflated internodes form hollow bladders called receptacles, flask-shaped conceptacles sunken into the bladder wall that produce sperm and ova.
Hormosira is a marine alga, also called sea grapes or bubble weed, that grows in the intertidal zone.
Observe the holdfast and body like a string of hollow beads or grapes, receptacles. The bumps on the receptacles are the conceptacles, round little holes containing the sexual organs. At high tides, gas in the receptacles keeps the plant erect. At low tides, the exposed plant collapses but the tough leathery body protects it.

9.46 Liverworts, Phylum Hepatophyta, Marchantia
See diagram 9.46.2: Marchantia life cycle
Look for thethallus, gemma cups, rhizoids, sperm with two flagella, male thallus, antheridium, female thallus, and archegonium.
Liverworts are the most lowly land plants with single-celled rhizoids and no clearly-differentiated stem and leaves. They grow in moist shady habitats on wet rocks or near shallow streams, usually clumped together to save moisture. The plant is the gametophyte generation, a broad branching thallus. Together the plants look like little leaves clumped together and attached to the damp soil by hair-like rhizoids. The antheridia produce swimming sperm that fertilize an ovum in the archegonium to form the zygote that grows into the sporophyte. The sporophyte has no chlorophyll and remains a sort of parasite with no connection to the soil but attached to the archegonium. It releases spores that develop into the next gametophyte generation. Marchantia reproduces rapidly by vegetative buds produced in gemma cups. The sexual organs, the antheridia and archegonia are formed on different plants. Riccia is a floating liverwort.
Collect plants from moist sheltered places, e.g. behind waterfalls, in cooler periods of the year.

9.47 Mosses, Phylum Bryophyta, Funaria, Dawsonia
See diagram 9.47.1: Funaria sporogonium | See diagram 9.47.2: Dawsonia, life cycle
Look for the male and female plant, female plant with attached sporogonium, leaves, stem, rhizoids, sporogonium capsule, sporogonium seta.
Mosses grow 1-10 cm tall in clumps or mats in shady or damp locations. Some grow on trees, fences and walls. Mosses have multicellular rhizoids and distinct stems and leaves. Mosses have an upright or creeping gametophyte with leaves arranged spirally. If the sex organs are developed on different plants, as with Dawsonia, the antheridia are attached to a cup-like receptacle at the apex of the male plant. The antheridia burst to release sperm that use their two cilia to swim in rain water to the archegonia at the apex of the female plants and fertilize the ova. The zygote grows vertically into the sporophyte that remains attached to the female plant and consists of a long stalk, seta and a capsule containing the sporogonium. The mature capsule will release very light spores to be dispersed by the wind and grow into the next gametophyte generation.
Collect common woodland mosses usually found in compact colonies or cushions in damp shady places. Some grow on the damper side or south side of tree trunks and fence posts. Observe the erect stems, small leaves, and the rhizoids that attach the plant to the soil. Look for terminal cups, sexual organs, and tubular capsules that contain asexual spores. Some tufts of plants bear rosette-like antheridia cups containing spores. Dissect out the contents of one of these into water and note the structure of the antheridia and paraphyses, sterile hairs or filaments that bear the spore-making structures, the sporangia. The archegonia cups that house the ovum are less conspicuous, so you may have to dissect more than one apex to find an archegonium.

9.48 Ferns, Phylum Pteridophyta, (Pterophyta), (Order Filicales), Dryopteris
See diagram 9.48.0: Dryopteris | See diagram 9.48.2: Pteridium frond, leaflet, rhizome | See diagram 9.48.3: Pteridium prothallus, sporophyte | See diagram 9.48.4: Fern life cycle
Look for the sori under a leaf, compound leaf or frond, coiled young leaf, rhizome, and roots.
Ferns are vascular plants with xylem and phloem, true leaves, but no seeds. They are mostly terrestrial but Marsilea lives in swamps. Azolla and Salvinia are floating ferns. The stag's horn is a common epiphyte in rainforests. The asexual phase, the sporophyte, is the large fern that develops spores in sporangia. The sexual phase, the gametophyte, develops the sexual organs. It is an insignificant little plant like a little flat leaf, the size of a fingernail.
1. Examine Dryopteris, wood fern. Note the rhizome and adventitious roots, stem and compound leaves, fronds. Note the sori (singular: sorus) under the recurved fronds where spores are formed. Dryopteris has rounded sori. Pteridium has long sori along the margins of the pinnules.
2. Cut a transverse section of a pinnule of Dryopteris to pass through a sorus. Observe the tissues of the leaf, the placenta, sporangia in various stages of development in the indusium.

9.49 Club mosses, Phylum Lycopodiophyta, (Lycophyta), Selaginella
See diagram 9.49: Selaginella
Look for the Selaginella plant, cone, scale leaves, lateral leaves, rhizophores, microsporangia containing many microspores, and megasporangium containing four megaspores.
The club mosses have club-shaped cones that bear spores and are known as ‘fern allies’. Plants of the Selaginella genus, spikemoss, are small prostrate plants with four rows of small leaves on the axis. They live in damp places and Selaginella kraussiana and Selaginella martensii are grown in greenhouses. The Selaginella plant is a sporophyte bearing microsporangia and megasporangia in the same cone. A microsporangium produces microspores to be dropped onto damp soil and later eject a swimming sperm. The larger megaspangium produces megaspores to be dropped onto the soil, germinate in rainy weather, and produce a females prothallus with an ovum inside. The ovum is fertilized by the sperm to form a zygote that grows into the next sporophyte generation. Both types of spores have a tri-radiate ridge from origin in the tetrads following meiosis. Collect the microspores and megaspores from a ripe cone and scatter the spores on moist absorbent paper. Observe the development of young sporophytes.

9.50 Conifers, Phylum Pinophyta, (gymnosperms, naked seeds not enclosed in an ovary), Pinus
See diagram 9.50: Vertical section microspore cone and megaspore cone
Look for a microspore cone, pollen grain, pollen tube, microsporophyll, microspores (pollen) megasporophyll, micropyle, ovule, megaspore, and bract.
Conifers are seed-bearing plants with ovules on the edge of an open sporophyll. The sporophylls are arranged in cone-like structures. Conifers are pyramidal or conical trees with long straight stems that taper to an apical growing point, the leader. The almost horizontal branches bear narrow needle-shaped leaves. The original tap root dies leaving shallow roots that let the tree be blown over by storms. Smaller roots have no root hairs but have a sheath of fungus that penetrates into the root epidermis. Small microspore cones at the ends of branches produce microspores, pollen grains. Large megaspore cones are made up of leaf-like sporophylls that contain the ova. The fertilized ova develop to form seeds released when the woody cone opens. Most conifers produce woody cones by lignification of the seed-bearing sporophylls, but Juniperus, Podocarpus and Taxus have soft fruit.
Examine the male and female cones of Pinus. Dig up some shallow roots and examine the mycorrhiza under the microscope.

9.51 The parts of a flowering plant, (angiosperms, enclosed seed plants), Phylum Magnoliophyta
1. Angiosperms have the following characteristics:
1.1 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.
1.2 Double fertilization produces a zygote that becomes the embryo plant and endosperm nutritive tissue in the seed for the developing plant embryo.
1.3 Stamens with pollen sacs produce pollen.
1.4 Phloem tissue consisting of sieve tubes and companion cells for the transport of nutrients and hormones.
2. 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.

9.52 Monocotyledons, grass
See diagram 9.52: Monocotyledon, grass
Look for a grass plant and flowers (inflorescence) ligule, leaf blade, parallel veins, leaf sheath, node, internode, and fibrous roots,
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.
Cut stems transversely, e.g. bamboo, sugar cane and corn. Note the similarities in the cross-sections. Note the tubes of vascular bundles scattered through the pith.

9.53 Dicotyledons
See diagram 9.53: Dicotyledon, diagrammatic
Look for a 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.
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, eucalypts, passionfruit, sesame, pepper, coffee, citrus, tomato, potato, cocoa, tea, jute, and many trees and shrubs.
Cut stems transversely, e.g. willow, geranium, tomato. 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. 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.

9.54 The plant cell, cork cells, Robert Hooke
See diagram 9.54: Plant cell
Look for cytoplasm, nucleus, chloroplasts, cell wall, and cell membrane.
Robert Hooke (1635-1733) examined very thin slices of cork. He noted compartments that reminded him of cells, the small rooms used by monks in monasteries. He was looking at the dead cell walls. The cavities of the compartment previously contained the living cells. Cut a wedge-shaped thin slice of cork and pith from the centre of a stem, e.g. potato, watermelon, tomato. Observe the cells as seen by Robert Hooke.

9.55 Human cheek cells
See diagram 9.55: Human cheek cells
Look for a nucleus, cytoplasm, plasma membrane or plasmalemma, and granules.
You may have to seek approval to do this experiment because saliva can carry disease. Instead of taking cheek cells you can use prepared slides of cheek cells from a school laboratory supplier
Observe human epithelial cells from inside the cheek. Use a clean toothpick to gently scrape the inside surface of the cheek. Put the whitish scraping into a drop of water or 0.65% saline solution on a microscope slide. Add a drop of stain, e.g. methylene blue or iodine solution, and apply a coverslip. View under low power and high power. Note the protoplasm containing a central nucleus and granular cytoplasm. The outer boundary of the protoplasm is the plasma membrane. Adjacent cells look like paving stones. The nucleus and cytoplasm have a different refractive index, so note the interfaces between them. In later experiments, compare the animal cell with the plant cell. The animal cell has no cell wall.

9.56 Leaf scale cells of onion
See diagram 9.56: Plant cell (diagrammatic) | See diagram 2.30: Detach epidermis from leaf
A cell wall, B middle lamella, C nucleus, D cytoplasm, E plasma membrane, F tonoplast (plasma membrane) G vacuole containing cell sap
1. An onion bulb is a condensed shoot with a very short stem enclosed by fleshy leaf-bases, leaf scales. Cut an onion bulb in half, longitudinally (downwards). Use forceps to peel off the thin epidermis from the concave (inner) side of an onion leaf scale. Put a small flat piece of it in a water drop on a microscope slide. Apply a coverslip and examine the structure of the cells under low power. Stain the cell contents by putting one drop of iodine solution at the edge of the coverslip, then draw the solution under the coverslip by putting absorbent paper on the opposite edge. Note the cytoplasm enclosing several large vacuoles and the normally colourless nucleus now pale yellow because of the iodine solution. Note the thin cellulose cell wall surrounding the whole cell.
2. Methyl green acetic acid solution and carmine acetic acid solution simultaneously fix and stain. Transfer a drop of methyl green acetic acid to a slide with a glass rod. Detach a small piece of epidermis from the inner side of a scale of an onion. Put it immediately into the drop of methyl green acetic acid. Apply a coverslip and examine the preparation at a magnification of 250 X. The cell nuclei will be stained a strong blue-green colour, while the cell walls will only be weakly tinted. The rest of the cell contents remain unstained. The image in the microscope will be even more contrasting if, after the desired intensity of staining has been reached, the dye solution is replaced by 2% acetic acid. Apply a drop of 2% acetic acid to one edge of the cover glass with a glass rod, and suck it under the cover glass by applying a piece of filter paper to the opposite side. If carmine acetic acid is used, the cell nuclei are stained a deep red. Use methyl green acetic for more fragile plant specimens and for showing the nuclei of protozoa.

9.57 Cells and tissue sections, T.S., L.S., R.L.S., T.L.S
See diagram 9.57: Tissue sections 1 | See diagram 9.57.1: Tissue sections 2 | See diagram 9.57.2: Wood section
1. A slice across a stem, at right angles to the axis of the stem, is a transverse section, T.S. Any slice parallel to the axis of a stem is a longitudinal section, L.S. A slice parallel to the axis of the stem, along the radius, is a radial longitudinal section, R.L.S. A slice parallel to the axis of the stem, along a tangent to the cross-section, is a tangential longitudinal section, T.L.S.
2. Cut a wedge-shaped transverse section across a soft stem, e.g. tomato, potato, sunflower. Note the groups of similar cells, tissues. The epidermis is the one cell thick outer layer. It may have a waxy cuticle on the outside to protect against desiccation. The bundles of cells, vascular bundles, contain food-conducting phloem cells on the outside and water-conducting xylem cells on the inside. The walls of the xylem cells, vessels, are strengthened. Old xylem forms wood. Groups of cells with very thick walls, sclerenchyma, strengthen the stem. Parenchyma tissue is the loose packing cells. Between the xylem and the phloem are closely packed cells with large nuclei and thin walls, the cambium. Cambium cells produce new cells by mitosis to make the stem thicker. Draw a map diagram to show the different tissues.
3. Observe the remaining stump of a cut down tree or the sawn end of a thick branch. Note the sap wood, heart wood, annual rings, phloem and bark. The appearance of the rays shows the type of section. In transverse section, T.S., the rays are radial lines often only one cell in width. In radial longitudinal section, R.L.S., the rays appear as partial brick walls. Any broken appearance is caused by the section not being exactly radial. In tangential longitudinal section, T.L.S., the rays appear as lens-shaped areas and from this type of section the actual vertical extent and width of the rays may be accurately determined. L.S., longitudinal section, refers to any section at right angles to the axis.
Examine the T.S., R.L.S. and T.L.S. sections of the wood of the linden tree (Tilea europea). Find the rays and identify the type of section.

9.58 Parenchyma cells of tomato
See diagram 9.58: Parenchyma cells of tomato
Look for the thin cell wall, plasma membrane, vacuole, cytoplasm, chromoplasts, and nucleus.
Remove a very small portion of the pulpy tissue immediately beneath the skin of a tomato fruit. Mount this on a slide in water and then tease it out with dissecting needles. Apply a coverslip and examine under high power. Note the parenchyma cells containing orange-red chromoplasts and cytoplasm, nucleus and vacuoles. Stain with iodine solution and examine the structure in detail.

9.59 Phloem cells of pumpkin, Cucurbita
See diagram 9.59.1: T.S. Pumpkin stem | See diagram 9.59.2: T.S. Vascular bundle | See diagram 9.59.3: L.S. and T.S. phloem cells, high power
Look for collenchyma, cortex, endodermis, pericycle, pith (often broken) parenchyma (packing tissuse) phloem, xylem, cambium, bicollateral vascular bundle (phloem both outside and inside xylem), characteristic of pumpkins and melons.
Examine a transverse section and a longitudinal section. Note the general arrangement of the bicollateral bundles, with the phloem both internal and external to the xylem in the vascular bundles. Sieve tubes form vertical files of cells placed end to end. Where each cross wall is perforated is called a sieve plate. Each sieve tube element has a companion cell next to it. Companion cells are small with dense cytoplasm.

9.60 Section-cutting by hand
See diagram 2.28: Cut sections by hand
1. Use a razor blade, preferably one-sided, to cut a very thin slice from a cork or a stick of pith. Be careful! Cut away from the body! Examine the slice with a magnifying glass or low power microscope. Cut an incomplete shaving, like a thin slice of cheese, and examine its thinnest edge. Note the arrangement of the dead cell walls.
2. Cut a transverse section, T. S., at right angles to the long axis of the organ or plant. Cut a longitudinal section, L. S., parallel to the axis of the organ or plant. Cut a radial longitudinal section, R. L. S., as with a longitudinal section but cut along the radius of the organ or plant.
3. Make a transverse section by cutting a carrot or piece of pith in half longitudinally. Then hold the tissue to be sectioned between the two halves of the carrot or pith and cut across, away from you, with a one-sided razor blade, e.g. "Gem".

9.61 Microscope staining techniques
See diagram 2.26: Drawing stain across specimen under coverslip
Use safety glasses and nitrile chemical-resistant gloves when working with stains.
1. Irrigation
Mount a section of plant tissue in a drop of water on a microscope slide. Put a coverslip on the drop of water so that no air bubbles remain under the coverslip. Put a drop of stain near the edge of the coverslip so that it is in contact with the edge of the drop of water. Touch the other side of the drop of water under the coverslip with absorbent paper to draw the stain across the plant tissue.
2. Immersion in iodine solution
Put sections of plant tissue in iodine solution for one minute. Remove the sections, rinse in tap water and mount them on a microscope slide in dilute glycerine.
3. Immersion in acid phloroglucin solution
Put sections of plant stem in phloroglucin solution for 30 seconds. Use a mounted needle to transfer the section to a drop of concentrated hydrochloric acid for two seconds. Mount the section in glycerine and apply a coverslip. Observe the lignin in xylem or woody tissue stained bright red.
4. Immersion in safranin and haematoxylin solutions
Put sections of plant tissue in 50% by volume alcohol / water solution. Use a mounted needle to transfer sections to safranin solution. Wash sections with tap water. Transfer sections to Delafield's haematoxylin solution. Observe the section under a microscope to monitor the staining. If the section is overstained, destain in acidified alcohol solution. Wash sections, mount in glycerine and apply a coverslip.

9.62 Stamen hair cells of Tradescantia
Tradescantia, is an important plant for study because the purple hairs on the stamens are "self staining". So it is possible to observe the movements of the contents of a live plant cell with the contents already stained. Use forceps to remove a stamen from a Tradescantia young flower. Pull off one purple hair from the stamen, mount it in a drop of water, apply a coverslip and examine it under low power. Note the following: 1. the cuticle that sheaths the cell and whole filaments of cells 2. the cellulose cell wall around each cell 3. the middle lamella layer between neighbouring cells only 4. the peripheral cytoplasm containing organelles that give it a granular appearance 5. the nucleus in the peripheral cytoplasm or suspended by cytoplasmic strands in the centre of the vacuole 6. the vacuole containing dissolved substances, e.g. purple anthocyanin pigments 7. the movement of granules in the cytoplasm, cytoplasmic streaming 8. the movement of the nucleus. Check the position of the nucleus in the same cell every five minutes.

9.63 Cells of a waterweed, Elodea
See diagram 9.63: Elodea cells
1. Examine the small leaves near the end of the stem of the waterweed Elodea. Put a single small leaf in a drop of water on a glass microscope slide, apply a coverslip and examine with a microscope. In strong light the cellular contents may have a flowing motion, cytosis or protoplasmic streaming.
2. Put a drop of a salt solution at one edge of the coverslip. While still looking down the microscope, draw the salt solution under the coverslip by placing a piece if absorbent paper at the opposite side of the coverslip so that liquid on the slide rises up the absorbent paper. Water diffuses out of the cells into the salt solution. As diffusion proceeds, the cellular contents shrink, but the rigid cell walls retain their original structure, a process called plasmolysis.

9.64 Wood cells, Eucalyptus, poplar
See diagram 9.57.2: Section of cut wood
Be careful! Do not allow students to use concentrated nitric acid. Use safety glasses and nitrile chemical-resistant gloves when working with concentrated acids.
Prepare woody elements for microscopic examination by maceration of a small woody twig. In a fume cupboard, fume hood, cover the pieces with concentrated nitric acid, add crystals of potassium nitrate, and heat the beaker in a fume cupboard. When the reaction has finished, remove all the acid by repeated rinsing with water. Mount twig tissue in 50% alcohol / water mixture and tease it apart with mounted needles. Observe vessels with characteristic thickening on the walls, wide lumens (internal spaces) and perforated end walls. Observe xylem parenchyma fibres and tracheids, long narrow cells with lignified walls and narrow lumen.

9.65 Leaf of a bushy plant
See diagram 9.65.1: Parts of a leaf | See diagram 9.65.2: Mung bean leaves | 9.65.3.1: Vertical section of leaf showing water movement
1. Examine the leaves of a bushy plant. Most leaves are flat and thin to catch plenty of sunlight. The bushy plant leaf has three parts: 1. leaf 2. petiole and 3. leaf blade. The leaf-base attaches the leaf to the stem. The petiole turns and holds up the leaf blade like a handle. The leaf blade takes in sunlight to make food. Leaf veins are arranged in a network. A leaf is attached to the stem. In the angle between the leaf and stem is the axillary bud. A leaflet is part of a leaf. There is no axillary bud between the leaflet and the stem.
Choose a simple form of leaf and examine its external appearance in detail. Note the leaf, showing the swollen leaf-base, the petiole and the lamina. Examine the type of venation, and note how the veins gradually diminish in size, until the ultimate branches are scarcely visible.
Cut a vertical section of a leaf or examine the tissues in a prepared slide.

9.66 Leaves of agricultural plants
See diagram 9.66: Papaya leaf
Examine leaves of agricultural plants, e.g. banana, breadfruit, chilli, cassava, cocoa, coconut, pineapple, swamp taro, sweet potato, yam. Draw each leaf and label the parts and describe the leaf in your own words. For example, the lamina of the leaf of the Papaya plant has tooth-shaped lobes and the petiole is long and hollow.

9.67 Grass leaf
See diagram 9.67: Grass leaf
The grass leaf has three parts: 1. leaf blade 2. leaf sheath and 3. ligule, an outgrowth where the leaf blade and sheath join. The leaf veins are arranged in parallel.
Cut a vertical section of a grass leaf or study a prepared slide and observe the following: 1. upper and lower epidermis, chlorenchyma 2. lack of differentiation into palisade and spongy mesophyll 3. small lateral veins cut at right angles because of parallel venation 4. sclerenchyma forming L-shaped girders around lateral veins and midrib 5. border parenchyma surrounding the veins.

9.68 Eucalyptus leaf, isobilateral leaf
See diagram 9.65.8: Eucalyptus leaf, T.S.
When Eucalyptus leaves are isobilateral, twisting of the petiole allows the leaf to hang vertically and show many xeromorphic characters, e.g. thick cuticle and sunken stomata. Observe the mesophyll with palisade cells, like fence palings, next to both surfaces and the oil glands seen as large circular cavities.

9.69 Stomates in a leaf
See diagram 9.69: Stomate, T.S. and V.S. (vertical section)
1. Use a one-sided razor blade to make an incision on the lower surface of a soft leaf and use forceps to strip off a small section of epidermis. Be careful! Cut away from the body! Mount the strip in water on a microscope slide with the outer surface uppermost. Most soft leaves have no stomates in the upper epidermis. A stomate is a small pore surrounded by two kidney-shaped guard cells. The guard cells usually contain s but epidermal cells do not usually contain chloroplasts. Put salt solution on the stomate and see if the guard cells become plasmolysed and so close the pore of the stomate. Plasmolysis is the contraction of the protoplasm away from the cell wall due to loss of water through osmosis. The stomate should be open if the weather is bright and sunny.
2. Cut a transverse section of the leaf and look for a stomate cut in section. Notice the shape of the guard cells and the pore. Note also the large air space in the mesophyll immediately adjoining the stomate pore.
3. Pour collodion on the lower surface of a leaf. Wave the leaf in the air until the collodion dries, then pull it off as a strip. See and feel the shape of the stomates in the leaf.

9.70 Leaf with aerenchyma, water lily
See diagram 9.70: T.S. Water lily leaf
Leaves of water lilies float on the surface of the water so xylem and mechanical tissues are reduced and aerenchyma is typically present. Stain a section in acid phloroglucin solution and mount it in glycerine. Observe the following parts: 1. Upper epidermis with cuticle and stomata, 2. lower epidermis without cuticle, 3. palisade mesophyll interspersed with elongated sclereids, 4. aerenchyma containing large intercellular cavities and interspersed with stellate sclereids, 5. veins showing small amounts of xylem.

9.71 Dicotyledon root and monocotyledon root
See diagram 9.71.1: T.S. Young root with root hairs | See diagram 9.71.2: T.S. Older root, high power (not the same plant)
The xylem vessels carry water and dissolved substances from the root up towards the shoot. The sieve tubes in the phloem carry water and dissolved foods towards the root. The xylem is arranged in a star-shaped pattern with 5 or 4 points. Small protoxylem vessels are at the points of the star outside the larger metaxylem vessels. Between the points of the xylem star are groups of sieve tubes and companion cells of the phloem. The xylem and phloem are surrounded by parenchyma tissue. Within the parenchyma are meristematic cells of the root cambium that later produce secondary thickening of the root. The xylem, phloem and parenchyma and the layers of parenchyma cells surrounding the pericycle, together are called the stele or vascular cylinder. The outer layer of the vascular cylinder is the pericycle that later forms fibres. The cortex is the outer cylinder of parenchyma and intercellular spaces. The innermost layer of the cortex forms the endodermis, a layer of cells that controls movement of solutions into and out of the stele. Later, the endodermis has suberized thickening but cells opposite the protoxylem groups, remain thin-walled and are called passage cells. The outermost layer of the root is the piliferous layer that produces root hairs. Lateral roots originate in the pericycle. Monocotyledon roots have much pith and many scattered xylem and phloem bundles.

2. Cut a transverse section of a broad bean root. Use the thumb and forefinger to hold the root between two pieces of pith or carrot tissue. Dip the material in water to moisten it. Never cut dry material. To cut microscope sections use a one-sided razor blade dipped in water. Hold the material vertically and draw the razor blade quickly across it away from the body. Cut the thinnest possible sections as wedge shapes. Wash the sections into a small dish of water. Use a camel hair paint brush to select the thinnest section, mount it in water on a microscope slide and apply a coverslip. Irrigate the section with aniline sulfate to colour the xylem elements yellow.
Observe the following:
2.1 the piliferous layer, with its root hairs,
2.2 the cortex, composed of the cortex proper and the endodermis,
2.3 the stele, composed of xylem (protoxylem and metaxylem) phloem and pericycle. These tissues are all embedded in parenchyma.
2.4 Note the relative positions of the various tissues. Examine the tissues under high power and note the cellular structures.

9.72 Legume roots, broad bean, clover, Rhizobium
See diagram 9.72: Legume root and root nodules | See diagram 9.209: T.S. Root nodule | See diagram 9.72.1: Legume plants
Look for root nodules on legumes, clover. Prepare a transverse section of such a root to pass through a nodule. Note the red colour usually shown by the central part of the nodule and study the large infected cells present in this region.

9.73 Apogeotropic roots of mangrove
See diagram 9.73: Mangrove roots
Mangroves live in tidal swamps and have apogeotropic roots containing aerenchyma. The roots grow upwards. Aerenchyma gas spaces provide an internal passage for oxygen gas in plants growing in flooded and anaerobic habitats.

9.74 Excretion of acids by roots
See diagram 9.74: Excretion of acid by roots
Plants excrete acids through the roots. These acids dissolve the otherwise insoluble chalky constituents of the soil. Put a marble plate or bathroom tile with the polished side upwards in a sloping position in a flowerpot. Fill the flowerpot with soil. Plant a bean seedling with roots about 2 cm long in such a position that the roots are forced to grow along the polished surface. After three weeks, remove the marble plate and rinse it with water. The polished surface of the marble plate has become etched where it was in contact with the roots. To make the etched lines clear, apply black shoe polish with a pad of cotton wool. The acids excreted by the roots of the bean plant have dissolved the marble, calcium carbonate, at the points of contact.

9.75 Root hairs of a germinating bean
See diagram 9.75: Root hairs of germinating bean seed
Put bean seeds or mustard seed on damp absorbent paper. Cover the seeds to keep the paper damp. After germination, use a magnifying glass to examine the cylindrical radicle, the root cap and the tiny root hairs growing from the side of the root just behind the root tip. They are very thin walled outgrowths of the epidermal cells. Most plants take water and plant nutrients into their roots through the root hairs. Root hairs may be damaged by careless transplanting, salty soil and lack of oxygen in waterlogged soil.

9.76 Root structure of mung bean
See diagram 9.72.1: Mung bean plant
Wash the soil from the roots of a small bushy plant, e.g. mung bean, and a grass, e.g. para grass. Bushy plants have a main root, the tap root or primary root, and smaller lateral roots or secondary roots. These roots can grow very deep. Grasses and palms have no main root, only many fibrous roots. These are thin roots and do not grow deep.

9.77 Root function, Tradescantia
Put a rooted and an unrooted shoot of Tradescantia each in a test-tube. Select the shoots so that they have the same leaf area. Fill two test-tubes with tap water to 2 cm below the rim. Pour a thin layer of paraffin oil on the water in each test-tube. Mark the height of the surface of the liquid on the test-tube with a felt pen. Put the test-tubes in a test-tube rack. Record the level of water in the two test-tubes each day. The surface of the liquid drops slightly in the test-tube containing the unrooted Tradescantia shoot, but drops more in the other test-tube containing the well-rooted shoot.

9.78 Celery stalk
See diagram 9.78: T.S. Celery stalk
Celery stalks are enlarged petioles. The stem of the celery plant is reduced to a disc. 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. Wear safety glasses and nitrile chemical-resistant gloves.
Observe the following tissues:
A The epidermis is a single layer of cells with a thick cuticle covering the outermost surface.
B The collenchyma has cellulose thickenings in the corners of the cells.
C The parenchyma has large cells with thin cell walls.
D The vascular tissue is arranged as discrete collateral bundles. Each vascular bundle has phloem to the outside, xylem to the inside and cambium between. E. The sclerenchyma caps the vascular bundle.

9.79 Dicotyledon stem, sunflower, Helianthus
See diagram 9.79: T.S. Young sunflower stem | See diagram 9.78.1: Sunflower Stem LS
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.

9.80 Monocotyledon stem, maize, (corn), Zea
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.

9.80.1 Other monocotyledon stems
See diagram 9.78.4: Dracaena | See diagram 53.4: Coconut