IIEMIASCOM YCETES 



155 



tendency often attract a third of different tendency. Occasionally 

 copulation may be retarded and the tubes attain a considerable length 

 or, as the ascus is torn by them, they may grow into the open. Further- 

 more, the copulation processes may go in a meridianal direction and fuse 

 with the spores of the other pole ; or the spores may develop unsimultane- 

 ously or abort, in which case fusion with spores of another ascus may occur 

 (Fig. 97, 9). Finally, as an exception, the spores may germinate parthe- 

 nogenetically, especially in old cultures, in which case there results a 

 special strain which only germinates parthenogenetically; it does not 

 differ morphologically from the original strain, and forms a germ tube 

 which ruptures the ascus wall. 



After the copulation processes have come into open communication, 

 the nuclei migrate into the bridge and fuse (Fig. 97, 6 and 7) ; occasionally 

 the fusion may occur in one of the spores instead of in the canal or may 



Fig. 97. — Saccharomyces Ludwigii. Copulation and development of asci. (X 750; after 



Guillcrmond, 1905.) 



be retarded and take place only in the germ tube which grows out of the 

 copulation canal, breaks through the ascus wall and germinates to a 

 sprout mycelium. 



If one imagines this copulation entirely suppressed (as occurs in cer- 

 tain strains), one arrives, as in the Torulaspora-Schwanniomyces series, to 

 asexual forms of Saccharomyces cerevisiae. Only these forms, in contrast 

 to the former, would be regarded as apogamous since their thallus belongs 

 to the diplonts. The forms of the S. cerevisiae type thus may be considered 

 biphyletic, where it is not easy to distinguish which belong to the partheno- 

 genetic and which to the apogamous groups. It need hardly be said that 

 in reality the roots of these asexual forms are much more numerous and 

 that the Saccharomycetaceae form a polyphyletic family since Endo- 

 myces capsularis and its relatives could have led directly to such forms. 



In order to demonstrate more clearly the present conception formu- 

 lated by Guillermond, the different forms have been connected according 

 to the similarity which they show in the point of view given in our treat- 

 ment on page 156. 



