Arthur: Nineteen Years of Culture Work 15 



others, although a careful comparison of the three forms made 

 it seem " not improbable that the three represent more correctly 

 the biological variations of one species," as was stated at the time. 

 In the further study of these forms it was thought that the telial 

 stage might be found to be restricted to certain species of Carex, 

 or to particular sections of the genus, as was believed to be true 

 of the European Carex rusts, which assumption in the case of 

 the American forms, however, could not be established in any 

 definite way. The hosts were shown finally to be even less re- 

 stricted than supposed, as the Aster form was eventually carried 

 over to Euthamia for its aecia and to Dulichium for its telia. 



The necessity soon became acute to find criteria by which to 

 judge of the standing of species among the rusts, and all the more 

 so because the manuscript was now under preparation for the 

 North American Flora. It was soon decided that, for the pur- 

 poses of the Flora, morphological characters must be the final 

 test for species. Yet for purposes of study outside of taxonomy 

 it might be serviceable and desirable to maintain the so-called 

 biological or physiological species in any rank desired, but they 

 ought not to be recognized as species proper in taxonomic classi- 

 fication. Consequently in 1912 the three Carex forms were com- 

 bined with certain European forms under the name Puccinia 

 extensicola Plowr., a name which has been supplanted by P. 

 Asterum (Schw.) Kern, since the cultural series closed. Further- 

 more, the cultures of 191 3 disclosed that P. vulpinoidis with its 

 covered telia had its aecia on Solidago, and was a part of this 

 same species heretofore known only with naked sori, making the 

 much emphasized character of covered telia a secondary one to be 

 associated principally with the host. 



Thus the idea of species among the rusts grew into a far more 

 definite, although more complex form, than could have been pos- 

 sible without the aid of cultural studies. A liberal view was now 

 also required regarding hosts, and also the stress on certain 

 morphological characters called for modification, but the end was 

 not yet. 



In 1910 a number of cultures with the Carex rust, Uromyces 

 perigynius, revealed a remarkable parallelism between this species 



