Orton: Correlation between Puccinia and Uromyces 203 



same distribution. It seems very probable, therefore, that this 

 one-celled form has aecia of the, same character as those con- 

 nected with Puccinia Pammellii and on an upright form of Eu- 

 phorbia. 



Several other examples have been observed which have for their 

 telial hosts identical or closely related species of the same genus, 

 only a mention of which is made here. Among the heteroecious 

 forms the following have been noted : 



1. Puccinia Eleocharidis Arth. with Uromyces Eleocharidis 

 Arth., both on Eleocharis spp., the Puccinia having aecia on 

 Eupatorium perfoUatum, 



2. Puccinia angustatoides Stone with Uromyces Rhynchosporae 

 Ell., both on Rhynchospora spp. 



The following autoecious species present the same striking 

 correlation in all their spore forms as do the heteroecious species : 



1. Puccinia heterantha Ell. & Ev. with Uromyces plumharius 

 Peck, both on several representatives of the Onagraceae. 



2. Puccinia Gentianae (Str.) Link with Uromyces speciosus 

 Holw. on Gentiana spp. 



3. Puccinia Ruelliae-Bourgaei Diet. & Holw. with Uromyces 

 Ruelliae Holw. on Ruellia spp. 



4. Puccinia opaca Diet. & Holw. with Uromyces cucullatus 

 Sydow both on Zexmenia spp. 



There are a few slight comparative dififerences worthy to be 

 noted in a careful study of these correlated species. From a com- 

 parison of accurate measurements of a large number of uredinio- 

 spores it is found that those of the Puccinia species are usually 

 slightly larger and have thicker walls than those of the correlated 

 Uromyces form. There is also sometimes noticed a marked dif- 

 ference in the vigor of the two forms, the Puccinia being the more 

 vigorous in its attack upon the host plant. These differences, 

 however, only mean that the genus Puccinia has a greater adapta- 

 bility to environmental conditions and seems better fitted to sur- 

 vive than the less vigorous form. This is also brought out in the 

 preponderance in numbers of species in the genus Puccinia as 

 compared to the number in the genus Uromyces. 



There are many correlated species among the long-cycle forms 

 of Puccinia and Uromyces which are not mentioned in this paper. 



