BASIDIOMYCETES. 421 



BASIDIOMYCBTES. 



The sporophores, known as basidia, are structures with a 

 definite shape, and with lateral branches, the sterigmata, from 

 which a definite number of exospores — basidiospores — are ab- 

 jointed, the basidia then becoming functionless. Basidia and 

 basidiospores are characteristic of all Basidiomycetes, conidia 

 and chlamydospores being produced only exceptionally. 



The basidia generally arise from an extended layer — the 

 hymenium — which in the higher genera forms part of a con- 

 spicuous complex sporophore. The basidia do not therefore 

 originate from the germination of a spore, as do the promycelia 

 of the Uredineae and Ustilagineae, but from special sporophores 

 (rarely from the mycelium itself), whose surface they occupy, 

 or in which they are enclosed. 



In the course of development, two nuclei have been found 

 to copulate in the basidial cells. Thereafter they divide and 

 produce four (rarely two) new nuclei (Autobasidiomycetes), or 

 after the division of nuclei, cross-septa are formed, thus making 

 the basidia pluricellular (Protobasidiomycetes). In both cases 

 the nucleus passes through the sterigmata into the developing 

 basidiospores, and on the germination of these spores, it divides 

 into two nuclei, the starting points for further nuclear division. 



As just indicated two divisions of the group may be dis- 

 tinguished : (1) Protobasidiomycetes, (2) Autobasidiomycetes. 



Protobasidiomycetes. 

 Under this class are included the Auricularieae, JPilacreae, and 

 Treinellinae, the first two possessing basidia divided, as a rule, 

 by cross-septa into four cells, the last with basidia also divided 

 into four cells, which are formed, however, by two longitudinal 

 walls set at right angles to each other. A sterigma grows out 

 from each cell and produces a single spore, after which the 

 basidium dies away. The basidia of the Pilacreae are produced 

 inside closed sporocarps (angiocarpous), those of the other two 

 groups are exposed (gymnocarpous). Parasites are unknown 

 amongst the Protobasidiomycetes. 



Autobasidiomycetes. 

 Basidia unicellular (autobasidia), the sterigmata formed on 

 the apex of the basidium, and each giving off a single basidio- 



