RUST FUNGI 



195 



been known to germinate, and the large size of their nuclei suggests that 

 we arc dealing with male cells. 



The mature tcliospore, which may be looked upon as a spore 

 mother cell, has a single fusion nucleus. "The fusion nucleus is large, 

 round and (when unstained) perfectly clear and homogeneous, but for 

 its nucleolus, so that it looks like a vacuole; it occupies almost invari- 

 ably the middle of a cell. The dense chromatin mass is loosened out 

 into a kind of spireme which becomes shorter and thicker; the nuclear 

 membrane then disappears, and the spireme thread splits longitudi- 

 nally, though the splitting is often indistinct. It then divides trans- 

 versely into segments which become arranged, or strung out, on a 

 spindle (sometimes, but more rarely, in an equatorial plate) ; then the 

 daughter nuclei are formed at the poles, and the next division, which 

 is homotypic, follows immediately" (Harper and Holden, 1903; 

 Blackman, 1904). These nuclei are found in each of the four cells 

 which form the basidium, and ultimately, they pass into each of the 

 four basidiospores which are uninucleate and haploid. 



The alternation of generations which has thus been determined by 

 the various cytologic studies of recent years may be displayed in a 

 diagram adapted from Grove (Fig. 69). 



The same life cycle may be represented in another way. 



Basidiospore 



Gametophyte 

 (w generation) 



Sporophyte 

 (2« generation) 



Mycelium 



Pycnium 



Female cells Pycnospores 



Fusion cell 



II 

 .^ciospore mother cell 



. ^ \ 



iEciospore Intercalary eel 



Urediniospore (repeated) 



Teliospore 



Jicium 



0000 

 4 Basidiospores 



