METHODS FOR THE INVESTIGATION OF NATURAL 

 AUXINS AND GROWTH INHIBITORS! 



J. P. NitschJ 

 Biological Laboratories, Harvard University 



The field of knowledge of plant growth substances has developed tremend- 

 ously, but unequally. Thus, the knowledge of synthetic compounds capable 

 of modifying the growth of plants in a manner similar to native substances has 

 accumulated at a prodigious pace, as have the horticultural and agricultural 

 applications of this knowledge. One must admit, however, that the science of 

 auxins rests upon the small and shaky foundation of the meagre and in- 

 adequate knowledge we have of the identity of the native substances at work 

 in the plant. Moreover, the numerous attempts which have been made to 

 explain how 'auxins' in general regulate growth may be futile unless we 

 actually know the nature of all the auxins that occur in the normal develop- 

 ment of plant tissues. It is high time that physiologists and chemists made a 

 really comprehensive survey of the native growth-promoting and growth- 

 inhibiting substances present in plants. 



The main difficulty in such work arises from the extraordinarily low 

 concentration of these substances in plants. Fortunately, the new techniques 

 of paper chromatography and paper electrophoresis, recently applied to 

 auxin problems by many different workers, show great promise as tools in 

 this task. While trying to proceed in this direction, however, the plant 

 scientist encounters many technical problems which have to be solved before 

 any real advance can be made. Among these, one may list: a reliable 

 extraction method, a good chromatographic technique, and a suitable 

 bio-assay. Like other workers, we have been faced with these questions, and 

 have tried to study the matter systematically. The results of our effort will 

 be presented in this paper. We will consider successively the extraction of the 

 active substances from the plant material, the purification of the extract, 

 the chromatographic techniques, the bio-assay, and, finally, a technique for 

 the chemical identification of the substances on the chromatograms. 



THE EXTRACTION OF AUXINS FROM PLANT MATERIAL 



When we extract something from the plant, we want the extraction to be 

 complete; we want no more and no less than what is actually present in the 

 tissues. This means that we do not want any synthesis of auxin to take place 



i" This work was supported in part by the American Cancer Society, Inc.. as recommended 

 by the Committee on Growth of the National Research Council, and in part by the National 

 Science Foundation through grants-in-aid made to Professors R. H. Wetmore and 

 K. \'. Thimann of Harvard University. The author expresses his deep gratitude to Professor 

 Wetmore and Professor Thimann for the facilities, help, and inspiration which they so 

 generously provided, and to his wife, who performed a large number of the experiments. 



J Present address: Department of Floriculture and Ornamental Horticulture, Cornell 

 University, Ithaca, New York, U.S.A. 



