A GYMNOSPORANGIUM WITH REPEATING SPORES^ 
J. C. Arthur 
The group of rusts now known under the generic designation of 
Gymnosporangium was the first to receive attention from systematic 
botanists. The earliest taxonomic record of any rust is that of a 
species on Juniperus described and figured by the pre-Linnaean 
author Micheli, to which he gave the generic name Puccinia. For a 
time this name was used for all rusts having the same general form of 
teliospore, then became shunted over to rusts of the general char- 
acteristics of Puccinia graminis, while the name Gymnosporangium 
was applied to the cedar rusts. 
It has been easy to recognize the members of this latter genus in the 
telial stage by the gelatinous matrix arising from the pedicels of the 
teliospores coupled with occurrence on Juniperaceae, and in the 
aecial stage by a distinctive roestelioid peridium enclosing spores 
with colored walls and evident germ-pores, coupled with occurrence 
on Malaceae. These generic characters have been taken to indicate 
a highly specialized development parallel to the group represented by 
Puccinia graminis. 
The genus Gymnosporangium has also been especially notable 
among the rusts by the utter absence of a repeating stage, either of 
uredinoid or aecidioid nature. 
The bridging of the gap between the two groups of rusts was 
recently begun by finding aecia lacking the roestelioid characteristics 
and possessing all the features of a true Aecidium such as belong with 
rusts of the P. graminis group, as illustrated by Aecidium Blasdaleanum 
of the Pacific coast, found by cultures to go to Gymnosporangium 
Lihocedri} This aecidioid form, however, showed its Gymnosporan- 
gial relationship by occurring on the Malaceous genera Amelanchier 
and Crataegus. 
A further advance was made in finding gradations between the two 
1 Presented before the American Phytopathological Society at the Philadelphia 
meeting, January i, 1915. 
2 Arthur, Cultures of Uredineae in 1908. Mycologia i: 252. 1909. 
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