THALLOPHYTA— FUNGI 



87 



out a number of short protrusions, each composed of a nimiber of 

 hyphse. These, which are called stromaia, bear each a rounded 

 head, which is covered by a number of depressions. In each of 

 these is developed a perithecium (figs. 845, 846, and 847), the 

 asci of which develop each eight filiform ascospores (fig. 848). 

 These, when they germinate on the flowers of the host-plant, 

 again produce the sphacelia form. 



Sub-Class V. — jEcidiomycetes. 



In this group are included two orders of parasitic plants, 

 which are characterised by a stUl further degradation of the 

 sexual processes. Indeed it is doubtful if any sexual organs 



Fig. 847. 



Fig. 848. 



Fiff. 847. A single perithedum of Claviceps purpurea, magnified, showing the 



contained asci. After Tulasne. Fig. 848. Asci of the same, containing 



the long slender ascospores. After Tulasne. 



exist, though a peculiar form of fructification, the (Bcidium, 

 occurs in some of the members, which is thought by some 

 botanists to be homologous with the ascogonium of the preceding 

 group. The gametophyte is consequently potential and not 

 actual, in most if not in all cases. It is very polymorphic, and 

 bears several different kinds of gonidia, all produced by abstric- 

 tion. 



The most characteristic fungus of this group is Puccinia 

 graminis, which forms the rust of wheat. It has avery peouhar 

 life history, inhabiting two host plants in different stages of its 

 existence. In the first of these it is found infesting the stems 

 and leaves of Wheat and other grasses, whose tissues are pene- 



