CYTOLOGICAL PHENOMENA OF SPORULATION 51 



disintegrate and are finally ingested by the ascospores. Little by 

 little they disappear entirely, being absorbed by the ascospores during 

 their development. (Fig. 47, 10.) The glycogen and the fats undergo 

 the same fate and are absorbed by the ascospores. A part of these 

 different products is consumed by the ascospores, the other is kept 

 in reserve in the ascospores to serve during germination. The asco- 

 spores increase little by little in size and eventually occupy the entire 

 volume of the asc, after having absorbed the entire epiplasm with 

 its metachromatic corpuscles, fats, and glycogen. 



The ascospores reach the adult state presenting a thick membrane 

 and a central nucleus from which the cytoplasmic rays containing 

 fats start, and which delimit small vacuoles. These include a little 

 glycogen and a few corpuscles, products which will be consumed at 

 the moment of germination. 



In all of the yeasts, the cytological phenomena are the same 

 differing only in details. In Saccharomyces cerevisiae, ellipsoideus, and 

 Pastorianus, instead of forming at two poles, the ascospores originate 

 generally in the middle of the cell in a zone of sporoplasm. They 

 undergo one or two divisions depending on the number of ascospores, 

 and the nuclei which result remain very close to each other in the 

 same zone of sporoplasm which soon concentrates about each of them 

 to make up the ascospores. 



In the Schizosaccharomyces and especially in Sch. octosporus, the 

 asc contains many less metachromatic corpuscles and basophile 

 grains than in other yeasts; also the cytological phenomenon of the 

 formation of the ascospores is much easier to observe. After the 

 nuclear fusion, the nucleus grows and soon undergoes a first division. 

 Guilliermond 1 has shown that this is a karyokinesis similar to that 

 described among the Ascomycetes. It is almost always accomplished 

 in the direction of the long axis and is manifested by the presence 

 of an achromatic spindle made up of small granular particles more 

 or less distinct which represent the chromosomes of the equatorial 

 plate. The chromosomes then distribute themselves along the spindle. 

 At this moment, the nuclear membrane seems to be absorbed while 

 the spindle elongates in such a manner as to form granular masses 

 at each end of the cell. The nucleolus persists at the side of the 

 spindle, but finally disappears. Two nuclei are thus formed which 

 go to. different parts of the cell. The two daughter nuclei which 

 result emigrate to both extremities of the cell to undergo another 

 -division and sometimes a third, from which result 4 or 8 ascospores. 

 The nuclei thus formed are disseminated in the cytoplasm, which has 



1 Guilliermond, A. Sur la division nucleaire des levures. Annales de Tlnsti- 

 tut Pasteur, 31 (1917). 



