REGENERATION 



133 



cormophytes or plant-stocks. If a piece is cut out of a 

 leaf of a tree or of any otiier Phanerogam, the leaf does not 

 become regenerated. If, again, an anther or a stigma is cut off 

 from a flower, the corresponding filament or style will not give 

 rise to a new anther or stigma. The cells of these organs are 

 therefore not adapted for regeneration, and do not contain 

 ' supplementary determinants.' 



Botanists might be inclined to explain this fact by supposing 

 it to be due to the cells having already reached their full size, 

 and having therefore lost their power of multiplication. This is 

 certainly the case, but it does not explain matters in the sense 

 I mean : the question still remains as to why these cells have 

 not been provided with supplementary determinants. The large 

 number of cases in which adult cells of leaves or other parts, 

 W'hich have reached their full size, may under certain circum- 

 stances begin to multiply, and form buds from which entire 

 plants arise {e.g., Begonia), proves that such a provision is 

 possible. 



The solution of the above problem is to be sought for in the 

 fact that it would have been of far too slight importance to the 

 plant to be able to restore such defects in its leaves, as it pos- 

 sesses the power of producing new leaves. Buds can be 

 formed and undergo further development in many parts, and 

 thus the plant gains much more than it could possibly do by 

 mere regeneration. Regeneration can be dispe)ised wit/i, as 

 the far 7nore i)nporta7it power of budding is possessed by the 

 plant. 



The fact that the higher plants are unable to restore such 

 parts as portions of leaves, furnishes an additional important 

 proof that regeneration is dependent on external circumstances, 

 and that it is a phenomenon of adaptation. True regeneration, 

 however, occurs in those cases in which the losses or injuries 

 would be harmful to the plant, and cannot be made good by the 

 development of buds. Thus a loss of substance in the bark of a 

 tree becomes replaced by the formation of callus, which arises 

 from the edges of the wound, and grows over it, and thus the 

 underlying wood is protected from injury. The cut or broken 

 surface of a branch, even in the case of many herbaceous 

 stems, becomes covered over in a similar manner by a mass of 

 proliferating callus, which may even give rise to new growing 

 points of shoots and roots, and thus become the place of origin of 



