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PLANT HORMONES 



AND THE ANALYSIS 

 OF GROWTH 



KENNETH V. THIMANN,* associate professor of plant 



PHYSIOLOGY, THE BIOLOGICAL LABORATORIES, HARVARD UNIVERSITY 



/T IS probably true that, in the field of biochemistry and 

 physiology, there are at least a dozen workers studying 

 animal material for every one studying plants. It would be expected, 

 therefore, that progress toward an understanding of the chemical 

 mechanisms operative in plants would be achieved more slowly than 

 in the corresponding field of animal biochemistry. Nevertheless, 

 when we survey the plant research of the last twenty years, the results 

 appear surprisingly good. The list of the elements needed for plant 

 nutrition has been more or less completed. The whole field of the 

 relationship between light and flowering has been opened wide, and 

 though the knowledge acquired has not yet been brought to the 

 chemical level, it is of great importance, both for physiology and for 

 agriculture. Somewhat parallel studies of the influence of tempera- 

 ture on flowering are developing. The chemistry of practically all 

 the known plant pigments has been thoroughly worked out; and, 

 while it is true that little is yet known about the formation and inter- 

 conversion of these pigments, this field is ripe for physiological ex- 

 ploitation. Classical problems such as the interconversion of starch 



* At present on leave of absence for service in the Navy Department, 



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