YEASTS 67 



nucleolus always persists on one side of the spindle. At a subsequent 

 stage the chromatic granulations or chromosomes are divided between 

 the two poles of the spindle, the nucleoplasm is mixed with cytoplasm, 

 then the spindle elongates, while the chromatic granulations form a 

 homogeneous mass at the two poles (Fig. 49 d, e, g and h). The 

 nucleolus is quickly absorbed, then the two nuclei are formed at the 

 expense of the two chromatic masses (Fig. 49,./). To summarize, 

 therefore, this division consists in mesomitoses of a primitive kind, 

 which appear to take place in the interior of the nucleus, whose mem- 

 brane is absorbed only at the end of the phenomenon. They show 

 the characteristics of the mesomitoses which have been described in 

 the asci of the higher Ascomycetes. 



^ 6 f^' fju s ^ 



Z ^-^ 6 7 6 



Fig. SO- — Successive stages of copulation and sporulation in Schizosaccharomyces 

 pombe. 1-2, Cells just as sporulation is about to begin. 3-7, Union of the two 

 gametes and nuclear fusion. 8, Ripe ascus. Cellular fusion being incomplete, 

 the ascus retains the shape of the two cells joined by a channel of copulation. 



When these divisions are accomplished, the nuclei seem to be scat- 

 tered in the cell (Fig. 48, i) ; they are soon surrounded by a thin layer of 

 cytoplasm which is separated from the cytoplasm by a membrane; 

 these are the ascospores. At first very small, these gradually increase 

 at the expense of the cytoplasm which has not been used in their forma- 

 tion—in other words epiplasm — then reach the point where they oc- 

 cupy the whole of the ascus, after having absorbed this epiplasm (Fig. 

 48, j.) The metachromatic corpuscles scattered in the vacuoles of 

 the epiplasm disappear during these phenomena, being absorbed by 

 the ascospores. At no time during the development of the ascus can 

 glycogen be seen any more than in plant cells, but this is replaced 

 by an amyloid substance which is stained blue by iodo-iodide of potas- 

 sium. This substance impregnates the membrane of the ascospores 

 and disappears during their germination, utiHzed as a reserve product. 



In some Schizosaccharomyces or ordinary yeasts which bud (zygo- 



