92 BOTANICAL GAZETTE [august 



MORPHOLOGICAL DISCUSSION 



It cannot be decided, perhaps, on the data at present available 

 whether the fusion at the end of the uninucleated generation is of 

 a primary or secondary nature and origin. There can be no question, 

 however, that it is physiologically the fertilization stage in the develop- 

 ment of the rust, and that it is the beginning of a sporophyte generation 

 which ends with the reduction divisions in the germinating teleuto- 

 spore, as described by Maire (i6, 17) and later by Blackman (2). 

 Harper (13) has also argued, on the data given by Blackman and 

 myself, that an essentially similar alternation of generations is found 

 in the rusts to that in the ascomycetes and red algae. The existence 

 of well-defined gametophyte and sporophyte stages in these forms 

 can no longer be questioned. 



If we take up the cases of the aecidio-, uredo-, and teleuto- 

 spores in the light of the facts above described, it is plain that we have 

 in the successive production of these forms a series of asexual repro- 

 ductive cycles within the sporophyte generation. In thus showing a 

 scries of subgenerations, each ending wath a particular spore form, 

 which taken together compose the sporophyte, the rusts are unlike 

 any other group of plants in which true alternation of generations is 

 known. 



The essential characteristics of these subgenerations is that in each 

 case they begin and close with the peculiar structure first described 



basidium 



mo 



better called the basal cell. This is the 

 correct interpretation gives the key to the explanation of the puzzling 

 and hitherto unexplained reduplication of forms which is at once 

 the most conspicuous and least understood feature of the entire group- 

 \Yith the establishment of the identity of the basal cells of the 



basidium 



aecidium 



sporophyt 



mor 



aecidio-, uredo-, and teleutospores and stalk and intercalary 



becomes 



point of view, we find the game 



mm 



