592 COMPARATIVE MORPHOLOGY OF FUNGI 



with the exception of Melampsora (to be considered later), they live in the 

 haplophase exclusively on conifers, in the diplophase in different ferns 

 and angiosperms. 



The zeugites gradually lost their significance and hence were no longer 

 retained in the families branching off the main line. The primary cause 

 may be that, as today in Hyalopsora and Uredinopsis, the urediniospores 

 are able to winter over; thus meiosis was in the course of time fixed at 

 their germination in the spring, i.e., the formation of the basidia was 

 shifted forward to the overwintering urediniospores which thus assumed 

 the role of zeugites and thereby attained new morphological develop- 

 mental impulses. 



At first there developed the Cronartiaceae whose urediniospores and 

 teliospores are similar and whose teliospores contribute toward propaga- 

 tion. They retained the conifers as their gametophyte hosts. 



Thus there proceeded a special permanent development from forms 

 with the single-spore type of urediniospores, all the more so as their 

 branching off went hand in hand with a period of mutation in respect to 

 physiological requirements. That such physiological mutations can 

 occur is supported by the example of Cronartium asclepiadeum whose 

 sporophytes can infect both Vincetoxicum, Paeonia and Pedicularis 

 (which appear in the north temperate zone, the home of the gametophyte 

 host, the pine, and hence may be regarded as the true hosts) and various 

 exotic angiosperms, Verbenaceae, Balsaminaceae, Loasaceae, Tropaeola- 

 ceae and Solanaceae, which it met for the first time in the course of 

 experiments (Klebahn, 1914, 1916). A relaxation of extreme speciali- 

 zation must already have been encountered in Melampsora, the only 

 genus of these three families which changed its gametophyte host by 

 migrating either to the sporophyte host, i.e., becoming autoecious, or to 

 other angiosperms, Amentiferae, Saxifragaceae, Monocotyledoneae, etc. 

 Besides the consideration set forth here, basidial formation is deferred to 

 specially formed urediniospores from which arise the stipitate teliospores 

 of the Pucciniaceae, no longer joined into crusts. 



Thus the Pucciniaceae are apparently of recent date. Since the 

 Amentiferae are not parasitized, they must have been formed later than 

 these. The oldest forms were plurivorous (omnivorous) and attained a 

 full development at the time when the earth was being covered with a 

 mass of new angiosperm families. The purely autoecious forms attained 

 a prolific development in the tropics and the south temperate zones 

 especially on Leguminosae, and in the north temperate zone chiefly on 

 Rosaceae. There they have divided into a whole series of morpholog- 

 ically distinct genera of which, on Leguminosae, we have mentioned 

 Uromycladium and Ravenelia and on Rosaceae Phragmidium, Ochropsora, 

 Triphragmium, Kuehneola and Gymnoconia. Also the partially heteroeci- 

 ous Gymnosporangium has possibly arisen from this group by a second 



