1920] BISBY— UROMYCES 195 



These forms are more especially found in the warmer parts of the 

 continent, just as all Uromyces seem to be more numerous in warmer 

 regions. While in North America some three times as many species 

 of Puccinia as of Uromyces exist, the relation of the forms when 

 divided according to their life cycle is strikingly different; for about 

 140 short cycle species of Puccinia are known for North America, 

 in contrast to these n species of Uromyces. 



P. and H. Sydow (25), in their monograph of Uromyces, de- 

 scribed only the telial stage for 183 of the 504 species considered in 

 that work. For only a very few of these, however, were pycnia 

 described. When full information is in hand, a large number of 

 the 183 forms will of course be found not to be short cycled. It 

 appears, however, that a comparatively greater preponderance of 

 these short cycle forms of Uromyces may be found in the more 

 tropical regions. The observation of Magnus (17) and of Fischer 

 (15), that increased altitude results in shortened life cycles for the 

 rusts, is somewhat borne out by the fact that certain short cycle 

 Uromyces are limited to the Rocky Mountain region. The effect 

 of altitude and temperature can be better noted with the more 

 numerous short cycle species of Puccinia. 



Orton (21) has touched upon the relation of a group of rusts 

 with a common life cycle, opsis forms of Puccinia (the genus 

 Allodus), to other groups with different life cycles. Comparable 

 relationships and correlations with other rusts are to be noted 

 with the group of rusts considered in this paper; some attention 

 is directed to these points w r ith the discussion of the several species. 

 The rust in its development is intimately dependent upon its host. 

 Fischer (13) in 1898 emphasized the similarity between the 

 teliospores of certain short cycle rusts and of long cycle heteroecious 

 rusts whose aecia occurred upon the host of the short cycle form. 

 He considered that this similarity indicated a phylogenetic rela- 

 tionship between such rusts with different life cycles. Dietel (9) 

 considered that the Uredinales have probably developed during 

 geological times along with their hosts. Arthur (5) has pointed 

 out that the relationships of the rusts often reflect the relationships 

 of the hosts upon which they occur. The writer (6) has also dealt 

 somewhat with this point. 



