48 CYTOLOGY OF YEASTS 



this moment only, the nucleus, without changing its location, elongates 

 and takes the shape of a dumb-bell. One of the heads of this enters 

 the bud. (Figs. 46 and 47.) A separation then takes place which 

 frees the two heads from one another. One part remains in the 

 mother cell while the other is in the bud. Both nuclei thus formed 

 retain for some time the shape of a club before assuming their normal 

 appearance. The nuclear division does not offer the characteristics of 

 karyokinesis contrary to the opinion of other authors (Swellengrebel 1 

 and Fuhrmann). It seems to consist simply of a direct division. 



B. Transverse Division: Division is not observed as we have seen 

 in the Schizosaccharomyces. It consists simply in the formation in 

 the middle of the cell of a transverse partition which separates the 

 two daughter cells. During this phenomenon, one may observe at 

 both extremities of the cell, the formation of a little vacuole, since 

 the nucleus situated in the center elongates into a dumb-bell, both 

 heads of which are placed at ends of the cell. The middle connecting 

 link is severed and the two heads form the nuclei of the two daughter 

 cells which are to be separated by a transverse wall. 



Cytological Phenomena of Sporulation 



We have seen in the preceding chapter that a certain number 

 of the yeasts possess sexual processes which function either at the 

 moment of sporulation or germination of the ascospores. In the first 

 case (Schizosaccharomyces, Zygosaccharomyces, Debaromyces) the asc 

 results from the isogamic copulation of two cells. In the second 

 (Saccharomy codes, Willia saturnus) copulation is effected between 

 two ascospores at the time of their germination. We have been 

 able, in order to present clearly, to describe by anticipation the 

 phenomena (nuclear and cytoplasmic fusion) which take place during 

 this copulation. We shall not repeat here. 



With the exception of these species, none of the yeasts present 

 any trace of sexuality; with them the asc forms at the expense of each 

 cell without preliminary copulation. 



It has been stated that the sporangium of yeasts is similar to 

 the asc of the Ascomycetes, especially that of Exoascees. However, 

 a difference exists between the asc of yeasts and the organ of the 

 same name in the Ascomycetes. In all of the Ascomycetes which 

 do not copulate at the moment when the asc forms, especially the 

 Exoascees, this organ includes by its origin two nuclei, and it is only 

 after the fusion of these two nuclei that it assumes its definite volume 



1 Swellengrebel, H. La Division nucleaire dans les levures pressees. Ann. 

 Institut Pasteur, 19, 1905. 



