94 TEXT-BOOK OF FUNGI 



as in the Ustilagineae ; the two nuclei fuse, and the 

 oospore passes into a resting-stage, protected by a double 

 membrane. 



Each oospore, on germination, produces a promycelium 

 in which the sexual nucleus undergoes a double karyo- 

 kinetic division. From the prophase of the first division, 

 the sexual nucleus, which contained 2 chromosomes due 

 to fusion in the gametangium, never shows more than n ; 

 it has thus returned to the normal structure. The promy- 

 celium becomes divided into four cells, 'each containing a 

 nucleus, and each cell by budding produces a single spore 

 or conidium. 



If the grouping of the gametangia into a teleutospore is 

 abstracted, it is observed that the sexual reproduction in 

 the Uredineae is entirely in agreement with that of the 

 Ustilagineae. 



The Protobasidiomycetes only differ from the Uredineae 

 in the oospore germinating at once without a resting-stage. 

 Almost immediately after fertilisation the oospore [basidium] 

 increases in length, the sexual nucleus undergoes two 

 bipartitions, and the four nuclei are separated by cross- 

 walls. The promycelium stage occurs within the oospore 

 instead of externally, as in the Uredineae ; each of the four 

 cells gives origin to a spore. In this family the septa are 

 parallel to the axis, or perpendicular, according to the 

 genera. 



The Basidiomycetes are the most elevated of the series. 

 The cells of the mycelium generally contain two nuclei ; the 

 division preceding the separation of the young basidia 

 agrees with that in the Uredineae. The young basidia 

 represent the gametangia of the preceding groups, and 

 fertilisation is also effected under similar conditions. The 



