B) Forms of leaf blades.

Topic 3 “Vegetative organs. Sheet”

General characteristics.

The leaf is a vegetative organ of the 2nd order, the lateral (lateral) part of the shoot. Leaf growth is limited and short-lived (it grows not at the top, but at the base and edges of the leaf blade). The typical leaf is flat and double-sided. The upper (ventral) and lower (dorsal) sides of the leaf differ in anatomical structure, pubescence and color.

The sheet has 1 plane of symmetry – it divides it into 2 halves. Radial leaves (coniferous) are also known. In some species, adventitious roots and buds may form on the leaves.


1) photosynthesis (the more photosynthesis develops, the more organic substances accumulate in seeds, fruits, tubers).

2) transpiration (evaporation of water in the form of steam) (1 sunflower plant evaporates about 200 liters of water during the summer and cooling p).

3) Gas exchange (plant respiration) absorption of O 2 and release of CO 2 and water vapor with air.

4) Modified leaves can perform the functions of protection, attachment and storage of substances.

Leaf size: average 3-10 cm, but can be from a few mm, up to 15 m long and d 5 m (leaves of some palms).

leaf morphology.

A) building. A developed leaf consists of a blade and petiole.

Lamina (1) is a flat, expanded part of a sheet that performs the functions of a sheet.

Petiole (2) – an elongated, cylindrical, stem-like part of the leaf passing into the base (functions: support, conductive, motor – leaf towards the light, down, up).

A leaf that has a petiole is petiolate; if it is not, it is sessile. Base (3) – the place of attachment of the leaf to the stem. The base may be inconspicuous, or expanded in width and length and covers the stem, forming a sheath (cereals).

In some plant species, flat outgrowths are formed at the base of the leaf – stipules (4). They can be paired, of various shapes and sizes, free or fused with the petiole (bicotyledonous – legumes, pink fused clover, free vetch).

When the stipules grow together, a funnel-shaped or tubular structure is formed – a bell (buckwheat). The leaves with a bell have petioles.

b) The leaves are simple and compound.

simple : has 1 leaf blade and falls off entirely. In herbs, the leaves do not fall off, but die off along with the shoot. There are simple leaves, but with a strong dissection – carrots: they have a leaf-like flat border that connects all parts of the leaf blade together.

Complex : on 1 petiole (rachis) there are several leaflets (plates). Leaves fall off individually. Leaves may be sessile or petiolate.

Compound leaves are called: * if the leaves are located in two rows on the sides of the rachis, then it is pinnate; if there is no leaflet at the top, then it is paired-pinnate (4) – peas; if there is a leaflet, then unpaired pinnate (3) is a wild rose. There are twice, thrice pinnate leaves. * if the leaflets are attached to the top of the rachis and diverge radially, like fingers, this is a palmate complex (2) (lupine, chestnut). * if there are 3 leaves, it is ternary (1) (clover, strawberry).

B) Forms of leaf blades.

Simple leaves come with

– whole and

– dissected leaf blade.

Sheets with a solid leaf blade have a different shape (shape).

The main forms of the leaf blade 1. Broadly ovate leaf 2. Rounded (aspen, budra) 3. Reversely broadly ovate 4. Ovate 5. Elliptical (bird cherry) 6. Obovate 7. Narrow ovate 8. Lanceolate 9. Oblong 10. Reverse narrow ovate 11. Linear

Also found: – spatulate – rhombic 10 – heart-shaped 12 – thyroid – swept 14 – spear-shaped 15 – needle-shaped 1 – sword-shaped, – saber-shaped, – sickle-shaped, – subulate. – unequal.

D) Dismemberment of simple leaves.

The leaf blade is not complete. Dissection is the degree and shape of the indentation of the leaf blade.

They take into account how the protruding parts of the plate are located in relation to the petiole: – symmetrically from 2 sides – pinnate .. – as if from the 1st point palmate .. – 3 lobes – ternary …. According to the depth of the cuts: lobed (dissected to less than the middle of ½ of the leaf, – separate (deeper than half of the half-plate, parts are called lobes, – dissected – if the incision is up to the midrib, the protruding parts are segments. Name: pinnatiform, palmately dissected, etc. There are also: doubly dissected, multi-dissected, plow-shaped; comb-shaped interrupted.

D) the edge of the sheet.

The shape of the edge indentation is said to be when the depth of these cuts does not reach ¼ of the half-plate. The edge of the sheet is varied.

1. Whole-edge (no teeth) lilac; 2. Notched (deepening of the teeth are rounded);

3. Wavy; 4. Prickly; 5. Toothed (straight teeth); 6. Double-toothed;

7. Serrated (oblique inclined to one side); 8. Gorodchaty (teeth are rounded)

– ciliated

f) Forms of the base and top of the sheet.

Top shapes are varied .

1. Spinous; 2. Pointed; 3. Pointed, or sharp; 4. Dull; 5. Rounded; 6. Truncated; 7. Notched

Obtuse truncated acute pointed pointed notched


plate base

1. Heart-shaped; 2. Reniform; 3. Arrow-shaped; 4. Spear-shaped; 5. Notched; 6. Round; 7. Round-wedge-shaped; 8. Wedge-shaped; 9. Drawn; 10. Truncated

truncated descending

G) venation of leaves.

The system of vascular bundles (veins) on a leaf is called venation.

1. Parallel – the veins of others are parallel, run along the plate, in linear leaves (cereals) .; 2. Arcuate veins diverge from the base in an arcuate bundle and reunite at the apex (monocots: lily of the valley, plantain.) Pinnate – 1 central vein and second-order veins go from it from 2 sides Palmate – several veins depart from one point – petiole. 3. Pinnatiform (veins of the 2nd and 3rd branching orders do not reach the edges of the leaves, not far from the edge they wrap and connect with each other, forming a loop-like network along the edge); 4. Palmate-looped; 5. Pinnate marginal (small veins reach the edge); 6. Palmate marginal; 7. Pinnatiform (small veins round off and form a loop-like network); 8. Palmate mesh; 9. Dichotomous (ancient in algae, paparatnikov) 10. Simple – a sheet of pl-ku penetrates only 1 vein from the base to the top (mosses, club mosses, conifers, elodea).

leaf formations.

The size and shape of the leaves, the distance between them change along the length of the annual shoot. At the base of the shoot, lower leaves develop on closely spaced shoots (these are cotyledons = embryo leaves, kidney scales in herbs. They have a simple outline, a whole edge, small sizes).

Median – in the middle part of the shoot, these are typical leaves of the plant.

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