No. 463-] STUDIES ON PLANT CELL. VI. 475 



expressed it ('94a, p. 288), a return on the part of the plant 

 organism in each life history to the condition of an ancestral sex- 

 ual generation (garnet ophyte). Reduction phenomena in them- 

 selves are not the result of a gradual evolution, whatever may 

 be the complicated history of the sporophyte generation, for 

 they consist always in the sudden reappearance of the primitive 

 number of chromosomes, characteristic of the generation in 

 which sex arose (gametophyte). The cause of reduction phe- 

 nomena is phylogenetic. The interval that may separate this 

 phenomenon from the responsible sexual act varies immensely in 

 the plant kingdom according to the evolution of the groups con- 

 cerned. But the suddenness of the appearance of sporogenesis 

 tells in every case the same story of an immediate and total 

 change in the potentialities of the protoplasm in the spore 

 mother-cell, a change which can only be understood as a phylo- 

 genetic process deeply seated in the race. 



When the events of sporogenesis in plants are considered as 

 processes of spermatogenesis or oogenesis we disregard the most 

 remarkable historic outlines that plant phylogeny can present, 

 to the confusion of clear thought. Botanical science may well 

 be proud of its achievement in outlining with such exactness the 

 relations that the critical periods of gametogenesis, fertilization, 

 and sporogenesis bear to reduction phenomena and too great 

 stress can hardly be laid upon the importance of the results. 



4. REDUCTION OF THE CHROMOSOMES. 



There are perhaps no activities of the cell which have been 

 the subject of more investigation and discussion than those of 

 chromosome reduction in animals and plants. The reasons are 

 clear. The events of gametogenesis in animals and of sporogen- 

 esis in plants have the deepest significance for an understanding 

 of the organization of protoplasm because these are periods when 

 great changes are made evident in the structure of the cells con- 

 cerned and at the same time in their potentialities. We are 

 forced to conclude that some of the structural changes at least 

 are the cause of the new potentialities and the attempt to estab- 

 lish the cause and effect has been one of the most fruitful and 



