Development of a mature plant from a seed - surprising process. This process includes cellular division, growth of cages by a stretching, differentiation of separate bodies (roots, stalks, leaves, tsvetkov) and, at last, variety difficult and is rather strict koordinirovannyh chemical transformations. The final form of a plant is defined also by the genetic program put in impregnated jajtsekletke, and action of the external factors, capable to influence realisation of this program. The genotype sets limits of variability of a plant, from Wednesday depends, what will be finally - in these, limits - realised type of development.

The Seed (fig. 3.2) contains a germ of a plant and a stock of necessary nutrients. Surrounds and protects seed contents a seed cover. The plant germ has a bipolar axial structure: on its one pole there is a point of growth of a stalk, and on other - a point of growth of a root. Besides, the germ contains lateralno settling down cotyledons (or - at odnodolnyh-one cotyledon). There are kinds of plants at which cotyledons narrow and remind leaves; such cotyledons serve a plant in the beginning for use! Stocks: endosperma, but later they turn to usual green photosynthesizing bodies. in other cases of a cotyledon are the fleshy reserving bodies developed at germination of a seed over or underground and absorbed stocks endosperma still before maturing of a seed; cotyledons of this kind seldom become similar to the present leaves and usually do not participate in photosynthesis. Fleshy cotyledons, as a rule, fall down, after stocks of nutrients containing in them will remove to growing zones of a sprout.

At early stages of the germination the seed absorbs multiwaters that leads to the certain chemical changes stimulating in points of growth mitoticheskuju activity. On not clear while to the reasons the root almost always starts to develop the first. In a point of growth of a stalk rostovaja activity clears up later; sometimes this backlog is measured by hours, but it can make also some days and even some weeks. On both poles of an axis of a germ growth is carried out as a result of formation of new cages meristematicheskoj (actively sharing, or educational) by a fabric of points of growth with the subsequent stretching and differentiation of these cages.

In a root processes of cellular division, a stretching and differentiation proceed in the accurately enough outlined zones which, however, are strongly enough blocked. As the growing root on the way is compelled to overcome resistance of such firm environment as soil, its gentle tip should be somehow protected from istiranija. This problem carries out root chehlik - multicellular formation (from several thousand cages), covering root meristemu. It is formed chehlik by division adjoining to it chehlikovoj meristemy; its cages continuously slushchivajutsja and so not preryvno are replaced with the new.

At corn, for example, chehlikovaja meristema it is capable to form a day before 10 000 cages that provides almost every day a regeneration chehlika. Breaking up cages chehlika osliznjajutsja, and this slime serves for a root some kind of ' as greasing ', facilitating to it advancement through soil.

One of obvious distinctions between plants and animals consists that at the first growth is dated for the certain limited zones adjoining to meristemam, and at the second growth zones are distributed on all organism. To make sure of such strict localisation of growth at plants it is possible by means of simple reception; For this purpose on a surface of a growing root or a stalk put (any nontoxical substance, for example the charcoal mixed with lanolinovoj by paste) a number of parallel lines equally spaced one from another (fig. 3.3). In some days it is possible to be convinced that labels have dispersed non-uniformly; further all it will defend now from each other on a piece directly adjoining a tip of a root or a top of a stalk so it is clear what exactly here and occurs the fastest growth. it is a zone of a stretching of cages. Certainly, the increase in the sizes of a plant cannot be caused one only cellular division however this process delivers new capable units to a stretching which increase in sizes later when the body top already will a little be removed from them as a result of repeated divisions top meristemy.

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