Chemical induction of growth 



made, however, is this: The tissue cuhure method described is a precise 

 system in which, under controlled conditions, growth may be regulated and 

 subjected to quantitative study. It represents a useful assay tool to be applied 

 in almost all cases where the chemical induction of growth in relation to 

 molecular structure is in question. One of the challenges in this field is that 

 different biological materials respond in different ways. There are few 

 systems that cannot be reduced to a tissue culture type of growth with 

 sufficient perseverance. When supplemented by the analysis of growth in 

 terms of cell number and cell size, the system described is capable of yielding 

 much information of a kind that would otherwise be difficult to obtain. 



THE CHEMICAL NATURE OF SOME SUBSTANCES THAT INDUCE GROWTH 



BY CELL DIVISION 



The final question to be asked and answered, so far as possible, is the chemical 

 nature of the stimulus to growth which the coco-nut milk and similar extracts 

 furnish. 



It will be recalled that growth in the otherwise mature cells of carrot 

 phloem, artichoke tissue, potato tuber tissue, etc., has been induced by the 

 Hquid endosperm that nourishes the immature embryo of the coco-nut; 

 by the endosperm from immature (milk stage) fruits of corn {^ea) ; from 

 such a nutrient material as the female gametophyte of Ginkgo ; by extracts 

 of the proliferating tissue of tumours induced by the crown gall organism; 

 and by extracts of the loculus of the banana fruit in which, for genetic 

 reasons, the cells do not remain quiescent but grow into a fleshy tissue. 

 Doubtless these various extracts contain variants on the same essential theme. 

 While the type of response induced may be the same, there is no reason to 

 expect a priori that identical molecules are the causal agents. In only two 

 types of material has enough investigation proceeded as yet to tell whether 

 the same or different substances may be involved. These materials are the 

 liquid endosperm of the coco-nut (Cocos) and the liquid contents of the 

 immature fruit of the horse-chestnut (Aesculus). A brief summary will now be 

 given of the present status of these investigations. 



SUMMARY OF PREVIOUS WORK 



Previous work had shown that the most useful way of isolating the growth- 

 promoting activity of the coco-nut milk from the large number of other 

 unessential constituents was a method based on precipitation by mercuric 

 acetate from alcoholic solution. By this procedure a bulk isolation was 

 carried out from a very large volume of original coco-nut milk. From this 

 concentrate 3 crystalline active substances were obtained which could 

 induce growth, almost as actively as whole coco-nut milk, at concentrations 

 of the order of a few parts per million, though they required the simultaneous 

 presence of casein hydrolysate. Thus the growth-promoting effects of the 

 coco-nut milk consists of at least two essential parts: 



(i) A non-specific part replaceable by casein hydrolysate. 



(ii) A specific part which is replaceable, wholly or in part, by the isolated 

 materials referred to. 

 These materials were designated in 1952 as Compounds A, B, and C (Shantz 

 and Steward, 1952). Since then a further compound has been isolated in 



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