﻿BOTANICAL GAZETTE 



long been recognized. The nature of the control is not specified, but it is 

 suggested that it is in the nature of nerve impulses. 



In this part, also, is considered senescence in the higher forms, in man him- 

 self, and the various changes in the tissues are pointed out. Various theories 

 are criticized and the evidence examined, showing that here, also, the accumula- 

 tion of colloidal material in some of the cells is probably the cause of senescence. 

 By fasting a limited degree of rejuvenescence is possible. Various theories 



Part IV brings the sexual or gametic reproduction of animals and plants 

 into the dicussion. A great number of cases are examined, particularly in 

 plants, where the conditions are especially illuminating. The phenomena of 

 the conjugation of the gametes is interpreted from the same point of view. 

 The gametes are highly differentiated cells; they are, therefore, old cells, and 

 are among the most senescent in the body. In this the author agrees with 

 MlNOT. By conjugation, rejuvenescence is produced and a young individual 

 formed. The fact of this rejuvenescence is demonstrated by the study of the 

 rate of metabolism of quite a number of larvae and embryos at various stages 

 of their life history; and the progressive rejuvenescence is followed not only 

 by the change in structure of the protoplasm but by the increasing rate of 



Part V is theoretical and critical, and in this the conception that senescence 



growth is an autocatalysis, is criticized adversely. Finally, the problem is 

 raised whether there is not also a progressive senescence in the protoplasm 

 as a whole, a growing old of races as well as individuals, and whether this is 



will make clear the author's standpoint and also illustrate the interesting and 

 thoughtful style of the book. 



course of evolution from the lower to the higher forms. All organisms, from the 



fledge and of experirr 



