1920] BISBY— UROMYCES 197 



A greater specialization and fixity may exist with short cycle forms 

 than with forms with long life cycles; of course fewer spore forms 

 upon which variability may be manifested are present. 



Pycnia may be produced, under certain conditions, in some 

 of these short cycle species of Uromyces not yet known to produce 

 pycnia. It is to be noted, however, that species in which the telio- 

 spores germinate at maturity, that is, lepto-forms, seldom produce 

 pycnia. Teliospores cannot function directly as repeating spores, 

 but in lepto-forms a comparatively rapid repetition is secured 

 through the intervention of the basidiospores, which are produced 

 immediately upon maturity of the teliospores. 



Cytological work upon the short cycle rusts indicates that similar 

 conditions obtain with the short cycle species, both of Uromyces 

 and Puccinia. The work of Sappin-Trouffy (23) upon the his- 

 tology of the rusts included a study of the short cycle forms Uro- 

 myces Ficariae (Schum.) Lev. and Puccinia malvacearum Mont. 

 His observations were corroborated and extended with the two rusts, 

 among others, by Blackman and Fraser (7). They found that 

 the general vegetative mycelium of Uromyces Ficariae consists 

 of uninucleate cells, some of the later vegetative, together with 

 the sori-forming, mycelium being binucleate. They found similar 

 conditions for Puccinia malvacearum, the binucleate condition 

 evidently arising at several different points for each sorus, shortly 

 before the sorus is formed. Blackmax and Fraser also observed 

 that the short cycle forms Puccinia Adoxae Hedw.f . and Uromyces 

 Scillarum (Grev.) Wint. had a binucleate rather than a uninucleate 

 general vegetative mycelium, and suggested that it is " probable 

 that in these two forms the conjugate condition is produced soon 

 after infection by nuclear migration, or by cell fusion, between 

 vegetative cells." Olive (20) discussed and figured sexual fusions 

 near the base of the telium in a short cycle form, Puccinia trans- 

 formans Ellis and Ev. Dealing with North American rusts, 

 Olive (19) also reported that differing conditions as to the sporo- 

 phytic and gametophytic generations occurred with certain short 

 cycle Puccinia forms; while Uromyces Rudbeckiae Arth. and Holw. 

 showed the anomalous extreme of possessing uninucleate cells 

 through all the mycelium and sorus, even including the teliospores. 



