Except water and the mineral substances absorbed from soil, and the carbohydrates formed in the course of photosynthesis necessary as a source energy and building blocks of protoplasm, the vegetative cage for optimum growth requires also some other chemical substances. The organic connections named hormones concern them, in particular. The requirement of a plant for hormones is usually extremely small, and in most cases hormones are synthesised in enough by a plant. However by means of corresponding experimental methods it is possible to exhaust hormonal stocks in the whole plant, body or a fabric, and then, having shown that hormones really exist and function, to make the conclusion about the nature and specificity of their action.

Any hormone represents substance, obrazuemoe in small quantities in one part of an organism and transported then in other part of a plant where it makes specific effect. distance on which the hormone is transported, can be rather big, for example from sheet to a kidney, but it can be and less - from apikalnoj meristemy to lying below cages - or even absolutely insignificant - from one organelly to another within one cage. Solving criterion is migration of a hormone from a synthesis zone to a place of its action where it represents itself as ' the chemical courier '. It has been established that in the higher plants the important classes of hormones regulating growth contain some: auksin, gibberelliny, tsitokininy, abstsizovaja acid and etilen which we now also will consider. Gibberelliny and tsitokininy meet in the form of groups related, it is similar operating molecules whereas each of three other classes in the nature is presented only by one connection. Because of difficult chemical and physiological distinctions between hormones we will consider them as if they would operate on cellular processes separately. but this differentiation artificial. During any given moment at a cage or a fabric are present a little or even all from these rostovyh substances. Hence, growth or development of this or that fabric it is caused by presence and interaction of all these connections.

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