Arthur: Uredinales of Costa Rica 149 



115. Uredo americana (Mass.) comb. nov. (on Orchidaceae) 



Cattleya Dowiana Bat. 



This rust occurred on plants brought to the Kew conserva- 

 tories from Costa Rica. The record was made in the Kew Bul- 

 letin for 1906, page 40, where it says that " only a small patch of 

 rust was present on one leaf when the plant was received from 

 Costa Rica, but this has continued to increase in size, and the 

 falling spores have also inoculated other leaves." Upon applica- 

 tion to the Kew Herbarium, a generous portion of the specimen 

 preserved there was sent me on Oct. 1 1, 191 5. The specimen 

 bears the date " 1899." I was unable, however, to find any rust 

 upon the part submitted. 



The writer has already recorded (Science 40:935. 1914) his 

 belief that the assignment of this and similar Orchidaceous rusts 

 to the genus Hemileia is not well founded. The opinion is shared 

 with other uredinologists (Sydow, Monog. Ured. 3:221. 1914) 

 that the description of teliospores made by Massee applies rather 

 to over-mature urediniospores. The distinctive characters of 

 the genus Hemileia of agglutinated pedicels and one-sided, dorsi- 

 ventral urediniospores, the ventral side being smooth, are lacking 

 among these orchid rusts. Moreover, it is difficult to believe 

 that families of hosts so widely separated as the monocotyledo- 

 nous Orchidaceae and the dicotyledonous Rubiaceae would bear 

 closely related species of rusts of a restricted generic form. For 

 these reasons this rust, which has heretofore been called Hemileia 

 americana Mass. (Gard. Chron. III. 38:153. 1905) is trans- 

 ferred to the genus Uredo. 



There are reasons for believing that Orchidaceous rusts of this 

 character are to be associated with certain rusts of the Polypodia- 

 ceae, represented by Uredo super ficialis (Speg.) DeT., and U. 

 Gymnogrammes P. Henn. They have the same peculiar forma- 

 tion of uredinia, the sori being tufted hyphae protruding through 

 the stomata, and are likely to divulge the same general charac- 

 teristics of the teliospore. Teliospores of the fern rusts have 

 been found which are of the general Puccinia-iovm. Massee's 

 view that the teliospores of the orchid rusts are of the Uromyces- 

 forrmcan safely be ignored. If these characters can be fully 



