"] 



ASCOMYCETES 



43 



continuation of the ascogenous hypha, and gives rise to fresh asci (fig. lo). 

 This process was first recorded in 1908 for Humaria rtttilans and has since 

 been observed by McCubbin in Helvella elastica, by Carruthers in Helvetia 

 crispa, and by Claussen in Pyronema confliiens. It suggests either that some 

 advantage is to be derived from an absence of relationship between the 

 nuclei which fuse in the ascus, or that a scheme of rigid nuclear economy 

 is in force. The former hypothesis is somewhat weakened by the fact that 

 no means of avoiding close relationship appear to exist in the Plectomycetes. 

 Meiosis. Very soon after the ascus is cut off, preparations are made 

 for the first nuclear division, which was shown in 1905 by Guilliermond, 

 Harper and Maire, working independently on various fungi, to be heterotype, 

 and to be followed by a second which is homotype in character; their 



U'fl 



Fig. 10. Humaria rutilans (Fr.) 

 Sacc. ; an ascus (a) the terminal cell 

 connected with which has continued 

 its growth and given rise to another 

 ascus (b) from the terminal cell of which 

 a third ascus (c) has arisen, x 1250. 



Fig. II. Humaria rutilans (Fr.) Sacc; u. asco- 

 genous hypha showing sixteen chromosomes in 

 each nucleus, x 1950 ; b. fusion nucleus of ascus 

 passing out of synapsis, x 1 300 ; <r. fusion nucleus 

 of ascus showing sixteen gemini, x 1950. 



observations have since been widely confirmed by a number of investi- 

 gators, and synapsis, the second contraction and the formation of typical 

 gemini have been seen, as well as the reduction of the chromosome number. 

 Thus in Humaria rutilans, which the exceptionally large nuclei render 

 a convenient subject of study, each of the fusing nuclei possesses sixteen 

 chromosomes (fig. 1 1 a), so that the definitive nucleus has thirty-two ; after 

 meiosis is complete sixteen can be counted in each daughter nucleus. This 

 fungus is somewhat exceptional in that synapsis begins separately in each 

 of the two nuclei of the young ascus before they fuse (fig. 8 b) indicating 



