AMERICAN URED1KE--E. 



379 



been a growing conviction for a decade or more, that the 

 whole order has attained such a high degree of specialized 

 parasitism that the particular species of the host plant, and 

 often the particular part of the host bearing the rust, is an 

 item of the utmost importance in identification. Thus it is no 

 longer considered sufficient to say that a certain rust occurs 

 " on various grasses." but the particular species must be named. 

 Furthermore, it is advisable to say what part of the plant is 

 affected, for instance Puccinia panic/ occurs on one side of 

 the leaf blade, while Uromyces graminicola occurs on both 

 sides and also on the sheaths and culms of the same host: Puc- 

 cinia poculifonnis and Puccinia rubigo-vera often grow on the 

 same host, but the former chiefly affects the sheaths and culms, 

 while the latter occupies the leaf blade. It has also been 

 established that in some cases hetercecismal species having 

 uredo and teleutospores with slight morphological distinctions, 

 yet bear their alternate stage upon very different species of 

 host plants. In such species the aecidial characters are a highly 

 important part of the complete diagnostic description. 



With the growing recognition of the value of a knowledge 

 of the host and of the aecidial form in circumscribing the species, 

 has come an awakening regarding the highly important nature 

 of the uredo for providing additional diagnostic characters. It 

 was not until the uredo stage was studied that the very dis- 

 tinct species. Puccinia phragmitis and P. mag'nusiaua, both 

 upon Phragmites communis, were separated. This is a case 

 in which the uredospores can be distinguished with ease and 

 certainty, but the teleutospores unassociated with uredo are 

 scarcely distinguishable. The two common, but usually con- 

 founded, species on Andropogon scoparius are even a better 

 illustration. Other cases of a similar nature could be cited. 



The development of our conception of the species to include 

 the several forms or stages and the specific nature of the para- 

 sitism, as requisite elements in establishing diagnostic charac- 

 ters in uredineous plants, has left no footing, so it seems to us> 

 for the old view which exalted the teleutosporic stage, and left 

 the other factors out of consideration. We do not, therefore, 



