CYTOLOGY OF SACCHAROMYCES CERVICI.K. 443 



After being distributed to the two daughter cells the chromo- 

 somes become collected at one point and apparently fuse forming 

 a uniformly basophilic mass in which the individual chromo- 

 somes cannot always be identified. The imbibition of achro- 

 matic material results in the alveolization of the outer part of 

 this mass. The limiting membrane (nuclear membrane) is 

 frequently bulged between the linin strands (Fig. 25). A con- 

 tinuation of alveolization results in a spherical nucleus with a 

 nucleolus of moderate size, the resting condition. 



The division of the cytoplasm in the isthmus occurs shortly 

 after the separation of the chromosomes and the disappearance 

 of the spindle (Fig. 24). Although the cytoplasm has separated, 

 the cell wall frequently does not divide for a considerable length 

 of time and holds the two cells together. In this way a number 

 of cells are sometimes connected, somewhat resembling a my- 

 celium (Fig. 8). 



No attempt has been made to study the formation of asco- 

 spores, but according to previous accounts the nucleus divides 

 by mitosis. 



DISCUSSION. 



The above account leaves two points without adequate solu- 

 tion, namely the transformation of the nucleus into chromosomes 

 and the migration of chromosomes through the isthmus. Fortu- 

 nately these are matters of detail and the remainder of the 

 account shows conclusively that the nucleus of yeast, in the 

 formation of buds, does not divide by constriction, but that 

 chromosomes are formed, divide (Fig. 18), separate, and give 

 rise to daughter nuclei in the same way as in higher organisms, 

 and yeast can be placed in the same category with higher animals 

 and plants, and protozoa as enunciated by Conklin and Kofoid 

 respectively. 



To accept Guilliermond's descriptions of the indirect division 

 of the nucleus in the formation of ascospores and direct division 

 in budding would be to admit the reproductive nature of amitosis 

 and, secondly, that a nucleus produced by this method may 

 later divide, in the ascus, by perfectly normal mitosis. This 

 would make untenable many of the generalized conceptions of 

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