BASIDIOMYCETES 425 



or has only appeared after spore formation had become exogenous and 

 the ascus had been transformed into a holobasidium. That the families 

 with phragmobasidia possess many more imperfect forms and conse- 

 quently much more highly developed haplonts than the families with 

 autobasidia, suggests direct derivation from the Ascomycetes; one must 

 seek the point of departure, however, with the four-spored asci as the 

 spore number of the phragmobasidium attains a maximum of four, gener- 

 ally (in spite of four nucleation) only to two. One cannot determine 

 when this divergence occurred. 



The lack of fossils, the small variety and the small extent of develop- 

 ment of the fructifications of the orders with phragmobasidia suggests a 

 comparatively recent date. On the other hand, this may be attributed 

 to the fact that when the pragmobasidium loses its character of sporo- 

 phore it suggests great age. The pragmobasidium may, in some Uredi- 

 nales, be separated into daughter cells which develop to mycelia without 

 further development, particularly without the formation of basidio- 

 spores. In many Ustilaginales its typical structure and its ability to 

 form basidiospores is altogether lost and it develops directly after the 

 germination of the smut spores to a sprout mycelium. It may indeed 

 be that parasitism has produced these modifications, but there are also 

 parasitic, much modified holobasidiomycetes, e.g., Exobasidium and 

 Brachybasidiam in which such a decadence of the basidium has not 

 appeared. In the Uredinales and Ustilaginales, such phenomena occur 

 much more frequently than in the high Oomycetes and Zygomycetes, 

 particularly in the Pythium-Pei'onospora series of the Peronosporaceae 

 and the Thamnidum-Chaetocladium series of the Mucoraceae, in which 

 the spore formation gradually disappeared and the sporangium assumed 

 the functions of spores. 



All these considerations, however, as long as they do not rest upon 

 intermediate forms which are accessible to study, and upon geological 

 evidence, have only a speculative character. Considering the vagueness 

 of all these relationships, it has seemed desirable to use the neutral expres- 

 sions phragmobasidia and holobasidia instead of protobasidia and auto- 

 basidia with which definite phylogenetic conceptions are connected. 



In this connection there arises the question whether the cruciate 

 basidium has developed independently within the Heterobasidiae or 

 whether, connected by a preliminary foreshortening with a new orienta- 

 tion of the septa, it has arisen from the Auricularia basidia. That they 

 are connected with each other by transitional forms, particularly in the 

 Tremellaceae; and that they have in part the same imperfect forms and 

 that in both the zeugites show a tendency to develop into probasidia, 

 suggests a close relationship. 



In the same way, it is still unsettled whether the phragmobasidium 

 has developed to the Tulostoma type and the cruciate type to the Tulas- 



