234 TEXT-BOOK OF FUNGI 



part in the scheme of evolution, all succeeding groups 

 being derived from the Zygomycetes. 



Choenophoreae, a family of the Zygomycetes possessing 

 both sporangia and conidia, gives origin to the Hemiasci. 

 The latter are divided into two groups : Exohemiasci, 

 without any trace of a perithecium, and the Carpohemiasci, 

 having the first rudiment of a perithecium or protective 

 covering enclosing the hemiascus. This last feature is 

 inherited from the Carposporangia group of the Zygomy- 

 cetes. The important character of the Hemiasci consists 

 in the variable number of spores contained in the ascus- 

 like sporangium. The Ascomycetes are derived from the 

 Hemiasci, and are characterised by the ascus containing a 

 definite number of spores. The Exoasci are derived from 

 the Exohemiasci, and the Carpoasci from the Carpohemi- 

 asci. Chaetocladieae is a family considered by Brefeld to 

 possess conidia only as its asexual form of fruit. Most 

 other mycologists consider Brefeld's conidia as sporangia. 

 These structures differ from ordinary sporangia in contain- 

 ing only one spore instead of a large number. From this 

 family alone Brefeld derives the Hemibasidii. This group 

 consists of two main sections, the Ustilagineae, having a 

 promycelium divided into three or four cells by cross- 

 walls; each cell gives origin to several sporidia or secondary 

 spores. The second group, Tilletiae, has an aseptate 

 promycelium which bears a variable number of secondary 

 spores at its apex. The Basidiomycetes are derived 

 directly from the Hemibasidii, and again are divided into 

 two principal groups. Protobasidiomycetes come from the 

 Ustilagineae, and differ from the latter in each cell of the 

 promycelium bearing one sporidium only. This difference 

 raises a promycelium to the rank of a basidium, and the 



