A GYMNOSPORANGIUM WITH REPEATING SPORES

Abstract

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 characteristics 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 Libocedri. This aecidioid form, however, showed its Gymnosporangial relationship by occurring on the Malaceous genera Amelanchier and Crataegus. A further advance was made in finding gradations between the two