Phytohormones: Structure and Physiological Activity. I

In plants, growth in length by cell elongation is conditioned by substances elaborated in the plant and effective in minute, thus having the nature of hormones. A number of tests have been worked out which allow of a qualitative quantitative determination of the growth-promoting properties various substances. With the aid of these biological tests the growth substances or auxins have been isolated and a of other substances have been shown to possess growth. At first sight the large number of substances which are do not appear to fall within any general classification. further investigation, however, it becomes clear that there certain common structural characteristics, and an analysis these provides a first step in attacking the fundamental problem the relations between chemical structure and physiological. This relation has in recent years been attacked in a of other fields, usually involving physiological processes animals. On the other hand, it would appear that plants offer exceptionally favorable field for study in that their structures--- possibly their physiological processes-are somewhat less. Thus, it has been found possible to differentiate some of the steps in the chain of reactions which lead to elongation, so that now it becomes possible to determine the structure required in a substance for the regulation of each these steps.