leaf arrangement (location of leaves on the stem)

The leaves of rye, birch, sunflower, rosehip grow one at a time in a node and are arranged alternately in a spiral on the stem. This arrangement of leaves is called next (1).

In lilac, jasmine, maple, nettle leaves grow two in a node - one leaf against another. This arrangement of leaves is called opposite (2).

In some plants, the leaves develop three or more at the nodes, as, for example, in the elodea or the crow's eye. This arrangement of leaves is called whorled (3).

SHEET

A leaf is a part of a shoot that occupies a lateral position on it.

Outwardly, the leaves of different plants vary greatly, but there is much in common between them. Leaves

most plants are green in color and consist of leaf blade and petiole by which they are connected to the stem.

If we carefully examine the leaf blade, we will see clearly defined veins on it. They contain conducting vessels, through which water with minerals rises from the root, and solutions of organic substances move from the leaf to other organs. The arrangement of veins on a leaf is called venation.

In the leaves of some plants, the veins are parallel to one another.

This type of leaf venation is called parallel. It is typical for many monocots plants (wheat, rye, barley, corn, onion).

Lily of the valley leaves have arc venation, which is also characteristic of monocots plants.

At the leaves dicots plants, the veins branch many times and form a continuous network. it

mesh venation.

But there are exceptions. For example, in a monocotyledonous plant, the crow's eye, the leaves have a reticulate

venation, and in a dicotyledonous plant plantain, leaf venation is arcuate.

Leaf venation: 1 - mesh, 2 parallel, 3 - arcuate.

If there is one leaf blade on the petiole, the leaf is called simple. Simple leaves develop from

birch, maple, poplar, oak.

A leaf consisting of several leaf blades connected to a common stalk by small

petioles are called difficult. In such leaves, each plate falls off independently of the others. Complex leaves develop in ash, mountain ash, raspberry, strawberry, acacia.

1, 2, 3 - simple leaves, 4, 5, 6, 7 - compound leaves.

The leaf consists of cells, cells are not the same and perform different functions. The integumentary tissue covers the outside of the leaf.

The cells of the skin are alive, they are different in size and shape. Some of them are larger, colorless, transparent and fit tightly to each other, which increases the protective properties of the skin. The transparency of the cells allows sunlight to penetrate inside the leaf, where photosynthesis proceeds with its help. Number 4 in the figure.

Other cells of the skin of the leaf - stomatal (1): they consist of two guard cells and, unlike other cells of the integumentary tissue, are green in color, because contain chloroplasts (3). The gap between guard cells is called stomatal (2).

Stomatal function: transpiration - the evaporation of water by the leaves, as well as to absorb oxygen for respiration and carbon dioxide for photosynthesis (gas exchange). There are more stomata on the underside of the leaf.

Under the skin is the pulp of the leaf, or the main tissue. Each cell of this tissue has a thin shell, cytoplasm, nucleus, chloroplasts, vacuole. The presence of chloroplasts gives the green color to the tissue and the entire leaf. The cells that are adjacent to the upper skin of the leaf are elongated and arranged vertically. For the external similarity of each individual cell with a column, the fabric is called columnar.

The main tissue lying under the columnar (closer to the lower skin) is called spongy since its cells are located loosely and large intercellular spaces filled with air are formed between them. In the intercellular spaces of the main tissue, water vapor accumulates, coming here from the cells.

The main tissue of the leaf is permeated with veins. Veins– these are conductive bundles. The veins are formed by mechanical and conductive tissues. Through the sieve tubes of the veins, a solution of sugar, formed during photosynthesis, moves to all organs.

In addition to sieve tubes, the veins also include vessels through which water with minerals moves from the root to the leaf cells.

Conductive bundles, in addition, perform a supporting function - they give the sheet strength. Numerous veins include fibers. These are long cells with pointed ends and thickened lignified shells.

The picture shows longitudinal section of the sheet: top and bottom of the sheet skin -

integumentary tissue, under the skin - the main tissue (cells with chloroplasts), in the center is a vascular fibrous bundle. It consists of sieve tubes and vessels - conductive tissue and fibers of mechanical tissue.

FLOWER

Flowers are generative organs, i.e. involved in the sexual reproduction of plants. Only as a result of flowering fruits and seeds are formed.

The most visible part of the flower whisk. In some plants, for example, in cherries, apples, the corolla consists of separate petals, in others, they fuse together - a long, like fragrant tobacco, or short, like a forget-me-not, tube with teeth or lobes at the top is formed.

The rim is usually surrounded cup, consisting of sepals. Like the corolla, the sepals can grow together, or they can remain unfused. If the brightly colored corolla serves to attract insects, then the role of the calyx is to protect parts of the flower, especially in buds.

In the center of the flower are its main parts - stamens and pestle. The stamen is made up of anther on the filament. Pollen develops inside the anther. The number of stamens in flowers is different: wheat has three thousand, cherries up to thirty, and rose hips have a hundred.

In the very center of the flower is one or, less often, several pestle. The pestle consists of three parts: the lower extended - ovary, medium narrow - column and top - stigmas. The most important part of the pistil is the ovary, where ovules. From them, after pollination and fertilization, seeds are formed, and from the ovary, the fruit.

1 - pistil, 2 - stamen, 3 - petal, 4 - sepal, 5 - calyx, 6 - pedicel.

The parts of the flower around the stamens and pistil are called perianth. The perianth may consist of a calyx and a corolla, as, for example, in an apple tree, cherry, poppy. In this case, the perianth is called double. In a tulip, lily, iris, the perianth is not divided into a calyx and a corolla, and all the leaves are homogeneous. Such a perianth is called simple.

All named parts of the flower - perianth, stamens and pistil - are located on receptacle - axial part of the flower.

Most flowers develop on pedicels, which are part of the stem. But there are plants in which flowers do not have pedicels and they are called sedentary(for example, plantain).

If flowers have both stamens and pistils, they are called bisexual. Most plants have bisexual flowers.

But in some plants, for example, birch, alder, corn, cucumber, some flowers have only pistils, while others have only stamens. These are unisexual flowers. If a flower has only stamens, it is called male or staminate, and if only pistils - it is called feminine or pistillate.

Unisexual flowers, staminate and pistillate, can be located on one plant, for example, birch, alder, corn, cucumber. Such plants are called monoecious. And poplar, hemp, willow have staminate flowers on some plants, and pistillate flowers on others. Such plants are called dioecious.

Small flowers are usually collected in inflorescences, which makes them highly visible to pollinating insects. This is the biological significance of inflorescences.

Inflorescences are groups of flowers located close to each other in a certain order.

Inflorescences are simple and complex. In a simple inflorescence, all flowers are located along the main axis on pedicels or without (sessile).

A complex inflorescence, in addition to the main axis, has lateral ones, the flowers are located only on the lateral axes.

Types of inflorescences: a - brush, b - ear, c - cob, d - umbrella,
d - basket, e - head, w - shield, h - panicle,
and - a complex shield, k - gyrus, l - curl

FRUIT

A fruit is a plant organ that develops from the ovary of a flower after fertilization.

What is the fruit made of? The fruit consists of seeds and pericarp. Seed is formed from the ovule, therefore, how many ovules are in the ovary, so many seeds are formed after fertilization. Pericarp - it is the outer part of the fruit. It is formed from the walls of the ovary. But often other parts of the flower are also involved in the formation of the pericarp: the receptacle, perianth, stamens, for example, in a wild rose, the pericarp is formed from the receptacle.

Why does a fetus form a pericarp? The pericarp protects the seeds from drying out, mechanical damage, and adverse environmental influences. The pericarp also plays an important role in the distribution of seeds, as some plants have thorns, prickles, produce a sticky substance, and edible fruits attract animals.

The fruits are very diverse, so they are divided into different groups. First, by the number of seeds per single-seeded(wheat, sunflower) and multi-seeded(pumpkin, peas, tomato).

The fruits are also distinguished by the structure of the pericarp. If the pericarp is juicy, then the fruits are called juicy, if dry, then the fruit - dry. Juicy fruits include cucumber, gooseberry, cherry; to dry - the fruits of corn, sunflower, peas, poppy.