HETBR0ECSIM4L UKEDINE^. 



25 



HETEROECISMAL, UREDINE^. 



BY WM. TKELEASE. 



Of late years, most mycologists who have paid any attention to the 

 rust-fungi have had more or less to say about the connection of secidial 

 forms on the one hand, with teleutosporic forms on the other ; and cul- 

 tures have been tried by experimenters of all grades of skill, with a view 

 to connecting isolated forms of both sorts. As a result, the botanical 

 literature of the last decade or two is filled with notices on the subject, 

 ranging from speculations based on the simultaneous occurrence of two 

 forms, to evidence accumulated in an experimental way by such men as 

 De Bary, Cornu and Magnus. 



Since Deslangchamps suggested, in 1862, that Gymnosporangium 

 fuscum might be genetically connected with Uoestelia cancellata, 

 Oersted, Cornu, and Magnus have instituted cultures the published 

 results of which show that species of these genera are in reality alter- 

 nating generations complementary one to the other ; yet it should be 

 noted that in this country, where they reach their largest numbers, cul- 

 tures by Farlow have given only negative or contradictory results, while 

 Eathay has had no better success in Europe. 



The experiments of Scholer on Aecidium berberidis, in the early 

 part of the century, and the later and better ones by De Bary, Cornu, 

 Schroeter, and many others, have apparently proved that a number of 

 species of Fuccinia and Uromyces are connected with secidia (often 

 scarcely distinguishable themselves) living on other host-plants, whose 

 only connpction with those bearing the teleutospores is cohabitation. 

 Still the number of unconnected secidial and teleutosporic forms is now 

 large— a fact especially true of America, where cultures have not been 

 resorted to; and even in Europe it is doubtful whether anything is 

 gained by attempts to classify the species with reference to their life- 

 history. 



One of the latest papers on heteroecism is by Kostrup [Bevue mycolo- 

 gique, October, 1884), and contains a number of statements which will 

 interest American students. Fuccinia suaveolens, the fragrant rust of 

 the Canada thistle, is joined to the heteroecismal species, although its 

 alternating generations occur on different plants of the same host. 

 Fuccinia phragmitis, a rust common on the reed, and morphologically 

 easy of recognition, seems far from being one of the simplest, since 

 Nielsen and Kostrup claim, as the result of cultures, that its secidium 



