287 



Arthur: Nineteen Years of Culture Work 1 \ 



corollary, and this indication became more pronounced during 

 the year following. 



In 1902 three species of Euphorbia of unlike appearance and 

 growth habits were found to bear non-interchangeable rusts, 

 which were tentatively considered to present races of Uromyces 

 Euphorbia* C. & P., and with the more confidence because no 

 well-defined morphological distinctions could be detected. Sub- 

 sequent studies strengthened this view of races, and the idea of 

 races from this time on was constantly kept prominently in mind. 

 The attempt to evade or simplify taxonomic and cultural difficul- 

 ties by treating such races or biological strains as species, as 

 Tranzschel 2 subsequently did with these same Euphobia forms . 

 was not favored. 



It was also in 1902 that the Helianthus rust was grown with 

 indication of races, developed further in the following year, and 

 brought to a climax in 1904, with the conclusion that a number 

 of more or less well established races occur in Puccinia Hclianthi 

 Schw., having Helianthus an units as a bridging species, follow- 

 ing the lead of Marshall Ward 3 in his study of the brome rusts. 

 No further considerable effort was made to study races in autoeci- 

 ous species, or to pick out bridging hosts, as it was held that to 

 ascertain the identity of species was as great a task as could be 

 undertaken in this series of cultures, and that studies leading 

 to the separation of a species into varieties, races, forms, or other 

 subclasses, although of much biological and often of great eco- 

 nomical interest, must be left for other time and hands. 



The problems of the Carex rusts came early into view. In 

 1901 and 1902 the three remarkable co-species, having telia on 

 various species of Carex and aecia on species of Aster, Solidago 

 and Erigeron respectively were repeatedly grown from telial 

 material, and were called Puccinia Caricis-Asteris, P. Caricis- 

 Solidaginis, and P. Caricis-Evigcrontis. As no single collection 

 of teliospores was found that would infect more than one of the 

 genera named, the forms were tentatively considered to be species 

 and given distinctive names, followng the brilliant cultural 

 methods of Klebahn in Germany, Plowright in England, and 



2 Ann. Myc. 8: 1-35. 1910. 



3 Ann. Myc. i: 150. 1903. 



