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.' This indicates that 



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



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

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