26 C. M. CHILD. 



carry the organism back to the original starting point. The 

 spore, which arises from a part of the sporophyte has come to 

 possess different capacities from the zygote and these become 

 evident in the gametophyte into which it develops. There is 

 certainly no reason for believing that the spore consists of or 

 contains undifferentiated germ plasm. On the basis of such an 

 assumption its development into a gametophyte becomes in- 

 explicable. It seems to me that we can regard the spore only 

 as a differentiated part of the sporophyte which in the course of 

 regulation following its isolation from the sporophyte body does 

 not entirely lose the physiological characteristics which it has 

 acquired and therefore produces something different from that of 

 which it formed a part. Moreover, in cases where apospory 

 occurs parts of the sporophyte give rise to gametophytes without 

 the formation of spores and in some cases regeneration in the 

 sporophyte gives rise to gametophyte-like structures. Evidently 

 then other parts of the sporophyte than those which normally 

 form spores are specified in the direction of gametophytic de- 

 velopment, but only in certain cases or under certain conditions 

 do such parts become physiologically isolated. 



In many forms also the gametophyte may reproduce asexually, 

 giving rise to new gametophytes by various forms of budding. 

 Here, as in the sporophyte, with every such reproduction a 

 greater or less degree of dedifferentiation and redifferentiation 

 undoubtedly occurs. 



The existence of this type of life cycle shows very clearly that 

 there is no immediate or necessary connection between matura- 

 tion and fertilization. In these plants the maturation divisions 

 are followed by the development of a new individual in which the 

 cells all possess the reduced number of chromosomes. Since 

 we know practically nothing concerning the physiological sig- 

 nificance of the maturation process, the reason for its occurrence 

 in connection with spore-formation is not apparent. The process 

 seems, however, to be associated with a low rate of reaction and 

 with conditions which prevent nuclear synthesis. 



As the gametophyte becomes old it in turn gives rise to gametes, 

 which, as in the animal are, so far as appearance goes, highly 

 differentiated cells and if their behavior is any criterion are also 



