362 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1940 



rather than to subculture the root tips indefinitely. Partial success 

 has been attained with the root of the white moonflower ( Colony ction 

 aculeatum). This species seems to have much simpler nutrient re- 

 quirements than any of those mentioned above. A root system, de- 

 veloped from an excised root tip, which exhibits more or less normal 

 secondary thickening is shown in figure 3. This root was grown in 

 a nutrient solution containing only inorganic salts and sugar with- 

 out any other organic material. It has been proved by analysis that in 

 such a medium the moonflower root is able to elaborate its organic 

 nitrogenous constituents, such as amino acids and proteins, from 

 supplied inorganic nitrogen. 



FiauEB 2. — Excised pea roots after continued subculturin?. This species branches very 

 sparingly in culture. Courtesy of Dr. F. T. Addlcott (Anier. Journ. Bot., October 1939). 



We may now examine briefly some of the problems of plant physi- 

 ology toward the solution of which the study of excised root cul- 

 tures has been directed. 



In the first place the nutrient studies themselves are beginning 

 to throw some light on the chemical transformations that occui' 

 in the plant. The three growth factors, vitamin Bi, nicotinic acid, 

 and vitamin Be, which have been claimed as essential, all belong to 

 the large vitamin B complex. So far as is known at present those 



