Growth Substances and the Formation 

 of Buds in Plant Tissues 



FOLKE SKOOG AND CHENG TSUI 



THE analysis of developmental processes of plants, particularly in 

 relation to the role of growth substances, is beset by difficulties of 

 many kinds, but perhaps mainly from two sources. One is the continuous 

 change in composition and rates of synthesis of growth factors in the 

 tissues, and another is the complex influences of each part on the growth 

 of other parts and on the development of the plant as a whole. In fact, 

 from comparisons based on mere inspection of normal and patho- 

 logical plant materials, one may conclude that normal development, as 

 contrasted with simple growth, must depend more directly on correlative 

 processes, often of an inhibitory nature, than on the actual synthesis of 

 new cell materials. For experimental purposes, therefore, it seems 

 necessary to start with simple materials with limited capacities for 

 autotrophic growth and difl^erentiation. 



This report deals primarily with the chemical induction of organs, 

 especially of buds, in parenchyma tissue and excised segments of stems 

 and roots grown in vitro on media of known chemical composition. Some 

 conclusions drawn from these experiments which may have a general 

 bearing on growth and morphogenesis in plants will also be discussed. 

 The intimate connection between this topic and the general problem 

 of the correlative action of growth substances in plants will be apparent. 



Experiments with tobacco callus cultures. — During the period 1937- 

 1940 several investigators (3,8,13,12,10) obtained evidence of different 



Editor's Note: This work was supported in part by the University Research 

 Committee on funds from the Wisconsin Alumni Research Foundation, and in 

 part by a grant-in-aid from the American Cancer Society upon recommendation 

 of the Committee on Growth of the National Research Council. 



