Kern: Studies in the genus Gymnosporangium 50! 



senting nearly all possible ecological conditions. This method of 

 treatment has revealed some undescribed species and the existence 

 of some foreign species not before recognized. In Dr. Dieters 

 account of the genus Gymnosporangium in Engler and Prantl's 

 Naturlichen Pflanzenfamilien in 1897 * he ascribed eight species to 

 North America. This account omitted one which was known at 

 that time and should have been included. Two more were described 

 shortly after this work appeared. In a recent paper the writer has 

 described three new forms of Gymnosporangium and three of 

 Roestclia, all from the Rocky Mountains or the west coast. f The 

 present paper characterizes three more forms and includes one for- 

 agn species recently reported from this country,^ making in all 

 a total of eighteen species under consideration. 



The study Jof the relationship between the rust species and the 

 host species is now rendered more complicated than it was formerly, 

 owing to the much larger number of rusts recognized on the same 

 number of hosts. In the telial stage, the species of rust, so far as 

 is now known, infest the family Juniperaceae, represented by- 

 four genera, Sabina, Juniperus, Chamaccyparis, and Libocedrus. 



On the genus Sabina are found twelve species of rust, of which 

 e 'ght inhabit the one host species, Sabina virginiana, four of the 

 e 'ght not occurring on any other species of Sabina. Four species 

 °ccur on Juniperus, two on Chamaccyparis, and one on Libocedrus. 

 1* is a remarkable fact that each of the Gymnosporangium species 

 ls confined in the telial stage to a single genus of host plants, with 

 l ta exception of one, which is reported on both Sabina and Juni- 



P er «s, and there is a suspicion that here two species may really 

 exist. 



ft is a notable fact that in the genus Gymnosporangium belong 

 the onI y rusts which are heteroecious and yet do not possess all 

 s Pore-forms, the uredinial stage being lacking in all the species. 

 Tlle re is known a uredo-form on Juniperaceae from Alaska, § how- 



*E. & p Nat i>fl anzenfam x i** . 50 . ^97. 



t New western species of Gymnosporangium and Roestelia. Bull. Torrey Club 34 I 

 4S H6 3 . IQ07 . y 



v 



- -»-> 1907. 



. ^ T »e existence of Koestelia penidllata and its telial phase in North America. 

 le nce IT „„ . 



***Hn*93i. 1908. 



« Harriman Alaska Expedition 5 : 36. 1 904. Uredo NootkaUnsis Trel. 

 a **"yfiaris NootkaUnsis. 



on 



