VOLUME LVITI 



NUMBER I 



THE 



Botanical Gazette 



JULY 1 9 14 



THE MORPHOLOGY AND CYTOLOGY OF THE 



AECIDIUM CUP 



F. D. From me 



(WITH PLATES I AND II AND EIGHT FIGURES) 



Recent cytological investigations of the Uredineae have mate- 

 rially aided in clearing up the obscure points connected with their 

 complex life history and development. The nature of the sexual 

 processes involved in the transition from the gametophytic to the 

 sporophytic (haploid to diploid) stages has received much atten- 

 tion, and, although the results achieved are somewhat conflicting 

 on minor points, the general nature of the phenomena described by 

 the different authors is quite uniform. Although examples of both 

 the caeoma and cup types of aecidia have been studied from this 

 standpoint, the most clear and acceptable accounts have been given 

 for the less complicated, superficial caeomas. No comprehensive 

 cytological account of the stages in cup-formation or of the general 

 morphology of the aecidium has been given. Certain authors also 

 disagree as to whether the nuclear divisions are all mitotic or in 

 part amitotic. 



So far sexuality has been reported in 13 species of rusts; n of 

 these cases may be regarded as well established for the present, but 

 the remaining 2, Uromyces Poae and Puccinia Poarum, as reported 

 by Blackman (6), must be considered as doubtful or at best not 

 entirely understood, since only a few inconclusive fertilization 

 stages were seen. Of the remaining T t rases n atp 



Of the remaining 1 1 cases, 9 are forms that 

 primary uredosori in their life cycles, and 2 are forms 



