Chemical structure and biological activity 



Table 1 



Effect of 1 : 3-diphenyl urea [DPU) on growth of plant tissue cultures 

 (a) Carrot tissue — grown 1 7 days at 24°C 



Table 2 



Effect of 1 : 3-diphenyl urea (DPU) on growth of potato explants in liquid media containing 



2 : 4-Z) and casein hydrolysate 



Explants from potato tuber — 33 days growth at 24°C 

 2:4-D applied at 1-0 p.p.m. Casein hydrolysate applied at 0-05%. 



DPU applied at 2-0 p.p.m. Coco-nut milk (CM) applied at 10% by vol. 



( Table 3) that the predominant effect of this substance is to stimulate cell 

 division with the formation of a very large number of very small cells. By 

 comparison, the effect of the naturally occurring substance diphenylurea is 

 not conspicuously large {Table 1) though it is of a similar kind. 



The most dramatic development in the current work, however, was the 

 recording of the very first experiment in which an extract from a dicoty- 

 ledonous fruit proved effective in the carrot assay system. The fluid used was 



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