194 INDIVIDUALITY IN ORGANISMS 



growth or active life; that is, under conditions which 

 undoubtedly decrease metabolic rate and so decrease 

 the range of dominance. Under such conditions unicel- 

 lular forms often fragment into a number of small 

 individuals, and some of the simple plants break up 

 into their constituent cells, which then grow and divide 

 to form small individuals, even under the same conditions 

 which made impossible the persistence of the original 

 larger individual. Other plants give rise to adventi- 

 tious buds, sometimes in great numbers, under such 

 conditions, while still others break up into quiescent 

 forms, and so on. In my study of senescence and 

 rejuvenescence I have pointed out that the decrease in 

 metabolic rate with advancing senescence in the lower 

 animals and plants often leads automatically by decreas- 

 ing dominance to physiological isolation of parts and 

 so to rejuvenescence and reproduction of new individuals. 

 ' Reproduction under depressing conditions has often 

 been interpreted in a teleological way as an attempt of 

 the organism to avoid extinction by producing new 

 individuals, some of which might succeed in finding 

 favorable conditions for continued existence. As a 

 matter of fact, however, such reproduction is merely 

 the expression of physiological weakness; the individual 

 can no longer maintain itself as a unity in its original 

 size, and as the original unity disappears, new unities 

 arise as local metabolic conditions determine. 



Regarding the part played by changes in the con- 

 ductivity of the path of transmission in bringing about 

 physiological isolation and reproduction in nature, we 

 know little. It is undoubtedly a fact that the increase 

 in conductivity during development of the individual 



