Regeneration 177 



in a leaf of Bryophyllum grow out the other notches of 

 the leaf are inhibited from growing. There is enough 

 material present in the leaf for all the notches to grow 

 into shoots as is proved by the fact that all will grow 

 out if they are isolated from each other. This was 

 explained on the assumption that the notches of a 

 whole which happen to develop first, create a flow of 

 these substances from the rest of the leaf to themselves 

 and thus prevent any getting to the other notches. We 

 stated that this is supported by the fact that the few 

 notches growing out in an undivided leaf grow more 

 rapidly than the many shoots growing from each notch 

 of a divided leaf. But why should a growing shoot or a 

 growing point in general produce such a suction? I 

 think this may be possible on the assumption that the 

 consumption of these substances by the growing organs 

 causes a low osmotic pressure of these substances in the 

 growing region and this fall of osmotic potential will 

 act as a cause for the further flow. This brings about 

 the apparent "suction" effect of the growing elements 

 upon the flow of substances. 



5. We mentioned that when a piece is cut from a 

 Planaria between pharynx and head a new mouth is 

 formed in the middle. It should also be mentioned that 

 according to Child the piece after regeneration is 

 smaller than it was before. 1 This indicates that 

 material in the old cells has been digested or has under- 



1 Child, C. M., Senescence and Rejuvenescence. Chicago, 1915. 



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