Chemical induction of growth 



was exposed to coco-nut milk alone after growing for varying lengths of time 

 in the synergistic mixture of coco-nut milk and 2:4-D. The data clearly 

 show that maintained rapid growth requires the continuous presence of both 

 the 2:4-D and the coco-nut milk complex. An even greater stimulus to 

 growth can be obtained by further interaction with casein hydrolysate. 



As a natural outcome of the development of this technique and its use to 

 assay the naturally occurring growth-promoting substances and growth- 

 inhibiting substances in plant extracts, the following general view has been 

 developed. 



Plant cells, fully furnished with nutrients, salts, organic substrates, water, 

 etc., may still fail to grow for different reasons. In some cases there is an 



Figure 2. Growth of potato tuber tissue explants started in basal medium with coco-nut milk and 

 2 :4-Z) , followed by transfers at varying time intervals to medium without 2 :4-Z). 



evident lack of the factors that will permit the cells actively to divide. This 

 lack may often be met by the use of coco-nut milk or its equivalent. Even so, 

 this may not alone suffice with many plant tissues from which extracts may be 

 shown to contain substances that are inhibitory even when added to the 

 carrot-coco-nut milk system. The potato tissue, shown above to require 

 2:4-D or its equivalent, is a case in point because it contains a sufficiently 

 strong inhibitory substance, or mechanism, so that small amounts of potato 

 tissue extract will antagonize the normal effect of coco-nut milk on carrot 

 tissue. Various other storage organs, dormant resting buds, and endosperms 

 like those of castor bean, have all been shown to contain such inhibitory 



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