THE FUNGI : ASCOMYCETES AND BASIDIOMYCETES 301 



STOMA 



UREDOSPORES 



Fig. 293. — Puccinia gratninis. Germination of the 

 Uredospores on Wheat leaf and the entry of 

 the germ tube through a stoma. {After Allen.) 



during which meiosis occurs, producing a row of four monoploid nuclei, 

 which are then separated from each other by transverse walls. This four- 

 celled structure is termed the basidium (Fig. 299). It is comparable to the 

 basidium in the Agaricales, but differs in being transversely septate, whereas 

 in the latter case it is non-septate. 



From the side of each of the four cells a short, narrow tube or sterigma 

 grows out, on the end of which a single basidiospore develops and the 

 monoploid nucleus from each cell passes through the sterigma into the 

 developing spore. The sexual character is apparently segregated at the first 

 nuclear division in the basidium so that two of the basidiospores are of ( + ) 

 strain and two of ( - ) strain. They are carried by wind to the leaves of the 

 Barberry and begin the cycle again (Fig. 300). 



