Leaves
It is easier to identify trees and shrubs by leaves than by other organs. The flowers and fruits of many tree species are inconspicuous, located high. Their flowering time often coincides with school holidays, which makes it difficult to display and collect natural material. The leaves of the trees are usually large with clear morphological features. The shape of the leaves is more or less characteristic of each plant species.
Classes can be held partly in the classroom when studying the external structure and shape of leaves, during extracurricular activities, before and after excursions to the forest, parks, squares, as well as on excursions, in summer pioneer camps.
Purpose of the lesson
Observe, describe and compare the morphological characteristics of leaves in various trees and shrubs.
To instill in schoolchildren some skills in using determinants (acquaintance with signs, terms). Develop observation.
Equipment
For every student: sets of dry leaves under the numbers in the folders; description plan; lists of plants; tasks; simple pencils with an elastic band; tweezers, magnifiers.
For the whole class: instructive visual aids - drawings of the forms of simple and complex leaves, bases, tops, edges, venation, dismemberment of the leaf blade; herbaria and collections of leaves and shoots.
hardwood
In autumn, without damaging the plants, you can easily collect fallen leaves, dry them in presses, under an iron. This will be a good material that can be used throughout the school year, especially in winter when going through the topic "Leaf". It is better to distribute the leaves to the students not sewn in order to see the underside of the sheet. Sets of leaves are well placed in folders with pockets.
You need to get acquainted with the basic concepts of leaf morphology in the previous lesson. When describing leaves, it is necessary to analyze as many morphological features as possible for the development of observation, taking into account that often leaves in shape and other features even on the same annual shoot, but in different places can differ significantly from each other. The variability of the form of aspen leaves is shown in fig. 2.
Plan for describing trees and shrubs by leaves
1 - sheet simple or complex; 2- sheet petiolate or sessile; 3- leaf blade shape: a) simple leaves - round, oval, oblong, lanceolate, linear, ovate, obovate; b) compound leaves - pinnately compound (paired and unpaired), palmately compound; 4 - leaf base shape: wedge-shaped, rounded, heart-shaped; 5 - leaf tip shape: dull, acute; 6- venation: pinnate, palmate; 7- dissection of the leaf blade: whole, lobed, separate, dissected; eight - blade edge shape: entire, serrated, serrate, crenate, notched; nine - color, shine, pubescence and other features (Tables VI, VII).
To describe the leaves, it is necessary to have special notebooks in which to write down only the answers to the questions of the plan, putting down their numbers. In this case, it is necessary to give drawings of leaves from nature. Answers can be arranged in the form of a table; then the same characters in different plants fall into the same column and can be easily compared with each other. Assignments for independent work are best given in writing.
Let us give examples of the description of leaves in the order of the questions of the plan (see tables III, IV, V).
Linden small-leaved. 1 - simple; 2 - petiolate; 3 - ovoid; 4 - heart-shaped; 5 - pointed with an oblique top; 6 - palmate; 7 - whole; 8 - crenate-toothed, entire in the lower half; 9 - dark green above, glabrous, soft-haired below.
Oak summer, ordinary, or pedunculate. 1 - simple; 2 - petiole 3 - 7 mm; 3 - oblong-obovate; 4 - narrowed into petiole; 5 - blunt or notched; 6 - pinnate; 7 - bladed, 4 - 7 blunt blades; 8 - whole; 9 - dark green above, shiny, bluish-green below, glabrous on both sides.
Birch warty, or drooping. 1 - simple; 2 - petiole half as long as leaf blade, 15 - 30 mm; 3 - triangular-ovate or rhomboid, leaf blade length 30 - 70 mm, width 25 - 50 mm; 4 - straight cut or at an angle of 120 °, sometimes slightly heart-shaped; 5 - acute; 6 - pinnate; 7 - whole; 8 - solid-extreme at the bottom, double-serrated at the top; 9 - naked on both sides.
Mountain ash. 1 - complex, pinnate, leaflets 11 - 21; 2 - petiole 80 - 170 mm, naked or hairy; 3 - oblong; 4 - unequal at the base; 5 - acute; 6 - pinnate; 7 - whole; 8 - solid in the lower part, serrated above; 9 - dark green above, bare, gray below.
Acacia yellow, or caragana. 1 - complex, paired, 4 - 8 pairs of leaflets; 2 - petiolate, common petiole 50 - 80 mm, there are stipules leathery, prickly; 3 - oval; 4 - wedge-shaped; 5 - sharp with a bristle; 6 - pinnate; 7 - whole; 8 - whole; 9 - naked, hairy in youth.
Comparison tasks
1. Let's compare the leaves of viburnum ordinary and Siberian hawthorn. What are the similarities and differences? (Table VIII).
similarity Leaves are simple, petiolate. Leaf blades are ovoid (hawthorn is obovate); with pinnate venation, lobed. difference: the base of the leaf blade in hawthorn is wedge-shaped, in viburnum it is rounded. The hawthorn has more blades, the viburnum often has three. In hawthorn, the leaf is covered on both sides with short hairs; in viburnum, it is naked, wrinkled from above, and fluffy from below. In hawthorn, stipules are larger, in viburnum - filiform.
2. Let us compare the compound leaves of common ash, ash-leaved or American maple, and red elderberry (see Table VIII).
similarity Leaves are compound, pinnate, with pinnate venation. difference: ash has the largest leaf, 7-15 leaves; leaf length is up to 40 cm, common petiole up to 15 - 25 cm. Lateral leaves almost sessile. Ash-leaved maple has 3-5, less often 7 leaves. Common petiole 10 - 22 cm and lateral leaflets have petioles. The red elderberry has 5 - 7 leaves, the common petiole is 5 - 11 cm with two stipules. The leaves are almost sessile. Leaves with a slight odor.
Common ash has an obovate upper leaflet. Lateral leaflets lanceolate, cuneate at base. In the ash-leaved maple, the upper leaflet is ovate-lanceolate, unequal; wedge-shaped base. In the first pair, the leaves are lanceolate, cuneate at the base, they are especially similar to ash leaves. In the second pair, leaflets are broadly ovate-lanceolate. The red elderberry leaves are almost sessile, oblong-oval with an oblique pointed apex, unevenly rounded at the base.
Let us compare the dissection and shape of the edge of the leaf blades: in the common ash and the red elderberry, the leaf blade is intact, while in the ash-leaved maple the middle leaflet and the lower lateral ones are often lobed. The shape of the edge of the leaf blades: in ash, serrated or crenate-serrated; in elderberry - serrated; in the ash-leaved maple, the lateral leaves are whole or with sparse teeth; upper - large-toothed.
3. Compare the leaves of the common elm, hazel, gray alder, hornbeam (see Table VIII).
What do these leaves have in common and what is the difference?
similarity: leaves are simple, petiolate, with pinnate venation, with a whole leaf blade (sometimes almost lobed in hazel), with a sharp apex, not entire. difference: Elm has the shortest hairy petiole 4 - 5 mm; at hazel 10 mm with glandular bristles; at the hornbeam 10 - 15 mm, long-haired, often glandular; in gray alder 10 - 25 mm, naked. Leaf blade of gray alder 40 - 90 mm(oblong-ovoid), in smooth elm oval or obovate. Lack of equilateralness at the base of the leaf blade is most often and stronger in the elm, and also occurs in the hornbeam. In gray alder, the leaf base is rounded or wedge-shaped. The edge of the leaf in the smooth elm is serrated, in hazel, gray alder and hornbeam - serrated (in alder with large prominent teeth). The upper side of all leaves is dark green, but in gray alder and hornbeam it is naked, in hazel it is finely hairy, rough with depressed nerves, in elm it is rough. The underside of the leaves of gray alder is covered with gray felt over the entire surface; at the hornbeam - naked; in hazel it is hairy, sometimes with glandular bristles, in elm it is soft hairy.
Exercise: draw from memory the leaves of birch, maple, elm, hawthorn, viburnum. Who will draw faster and more correctly. Write the name of the plants under the drawings of the leaves.
Review questions
1. What tree and shrub species have simple leaves?
Answer: poplar, linden, aspen, hazel, Tatar maple, hawthorn, viburnum, etc.
2. What tree and shrub species have compound leaves?
Answer: pinnate: ash-leaved maple, common ash, common mountain ash, common rosehip, red elder, white acacia, etc.; parenpinnate: yellow acacia, honey locust.
3. Name simple leaves with palmate venation.
Answer: balsam poplar, small-leaved linden, maple, holly, etc.
4. Name simple leaves with pinnate venation.
Answer: oak, birch, Tatar maple, hornbeam, alder, hazel (hazel), etc.
5. Name the leaves simple with a whole leaf blade.
Answer: balsam poplar, small-leaved linden, elm, warty birch, Tatar honeysuckle, hornbeam, aspen, alder (hazel), etc.
6. Name the leaves simple lobed.
Answer: summer oak, Norway maple, ginnala maple, Siberian hawthorn, common viburnum, etc.
7. Name the leaves simple, entire.
Answer: oak, Tatar honeysuckle, brittle buckthorn, etc.
8. Name the leaves with a serrated edge of the leaf blade.
Answer: balsam poplar, small-leaved linden (entire-edged in the lower half, crenate-toothed above), aspen, etc.
9. Name the leaves with a notched-toothed shape of the edge of the leaf blade.
Answer: Norway maple, etc.
10. Name the leaves with a serrated edge of the leaf blade.
Answer: warty birch, mountain ash, red elderberry, ginnal maple, Tatar maple, etc.
11. What are the forms of leaf blades of summer oak, warty birch, Norway maple, small-leaved linden?
Answer: obovate, triangular-ovate, rounded, ovoid.
12. In which leaves does the base of the leaf blade have a heart-shaped shape?
Answer: in small-leaved linden, Norway maple, etc.
13. Which leaves are unequal at the base?
Answer: smooth elm leaves, etc.
14. What are the similarities and differences between the leaves of warty birch and downy birch?
Answer: similarity - leaves are simple, petiolate, with pinnate venation, the length is the same; the difference is that the shape of the leaf blade in the warty birch is often triangular-ovate or rhombic, the base is wedge-shaped or truncated, less often rounded, and in the fluffy birch the shape of the leaf blade is ovoid or oval, the base is round, heart-shaped, less often narrowed. The shape of the top of the leaf of the warty birch is long-pointed, and that of the downy birch is short-pointed. The shape of the edge of the warty birch is sharply serrated, and that of the downy birch is coarsely serrated. The warty birch has bare leaves, while the fluffy birch has young leaves densely pubescent and the pubescence on the petiole remains for a long time.
conifers
The leaves of conifers are most often in the form of needles, less often in the form of scales (cypress, thuja). They can be on the run spirally(singly, in pairs, in bunches, in two rows), for example: spruce, pine, Siberian cedar, fir; opposite(crosswise), for example: cypress, western thuja; whorled(three-four-membered whorls), for example: juniper. In some conifers, the shoots on which the leaves are located are divided into elongated and shortened ones, for example, pine, Siberian cedar, larch); other species (spruce, fir) have only elongated shoots. Shortened shoots grow insignificantly during one summer, and elongated shoots grow by 35 cm and even more. Sometimes shortened shoots develop into elongated ones.
The needles are annual, soft, dying off in the autumn of the first year (for example, in larch) and hard, long-term, it dies off no earlier than the autumn of the second year.
The plan for the description of conifers by needles
1 - arrangement of needles: spiral (singly, in pairs, bundles, two-row), opposite (crosswise), whorled (three-four-membered whorls); 2- shape, size and etc.; 3- color, shine and other features (see Table II).
We give examples of the description of the leaves of conifers in the order of the questions of the plan.
Scotch pine. 1 - spiral, steam needles, coming out of the brown-gray leathery sheath; 2 - semi-cylindrical or semi-circular, sharp at the end, finely serrated along the edges, rigid, strongly twisted; 3 - dark green on the upper convex side, and on the lower grooved side - bluish or whitish; stomata are located on the lower side.
Siberian cedar. 1 - spiral, 5 pieces in bundles, which are surrounded by a yellow-brown early falling sheath; bundles are close to each other; the needles are densely located on the shoot; 2 - trihedral, serrated along the edges, size 11 cm; 3 - bright or dark green, hard.
Siberian larch. 1 - spiral, on shortened shoots and old trees - in bunches from 25 to 50 pcs. in a bunch, and on elongated and young trees singly along the entire shoot; the size of the needles increases from the top to the base of the shoot, which is often surrounded by a crown of the longest needles; needle size 30 - 35 mm; 2 - narrowly linear, flat, slightly widened towards the apex, with blunt ends; 3 - bright green with a bluish bloom, the needles are soft, tender; stomata are arranged in rows on both sides.
Norway spruce. 1 - spiral, singly around the shoot and directed in all directions; 2 - tetrahedral, short, hard, thin, prickly, length - 15 - 25 mm; 3 - dark green, shiny, sits densely, raised up.
Siberian fir. 1 - spiral, singly, directed to two opposite sides in a comb-like manner; 2 - flat, with a rib in the middle and two white stripes of stomatal rows; length up to 30 mm; 3 - the upper side is dark green, shiny, the lower side is paler; young fir shoots have a light, yellowish-green color; the needles are soft, narrow, sitting densely; the end is blunt with a notch, so the needles are not prickly.
Review questions
What is the difference between the needles of Siberian cedar and Scotch pine?
Answer: cedar needles are much longer, softer than those of pine, and are arranged in bunches of five needles (in pine - of two needles).
2. With what coniferous species does Siberian larch have some similarity in the form of needles?
Answer: with spruce, but larch needles are much narrower and longer, and besides, they are soft and have a lighter tone.
3. What is the difference between fir and spruce needles?
Answer: fir needles have pronounced upper and lower sides of different colors, it is flat, wide, while spruce needles are tetrahedral and the sides are difficult to distinguish; if fir needles are rubbed between the fingers, it gives off a balsamic smell reminiscent of the smell of lemon peel. The needles are located on the shoot of the fir scallop-shaped on two opposite sides, and of the spruce in all directions.
4. From the needles of which tree is a valuable essential oil for the perfume industry produced?
Answer: from fir needles.
