16 MORPHOLOGY AND DEVELOPMENT OF YEASTS 



In 1895, Schionning 1 showed in a short note that the ascs of 

 Sch. octosporus resulted from the fusion of two sister cells, but not 

 having observed the cytological phenomena which accompanied 

 this fusion, he was not able to realize its significance. Hoffmeister 2 

 thought that he observed in this phenomenon a nuclear fusion, but 

 at that time the nutrition of yeasts was insufficiently known to 

 permit accurate observations. Bearing in mind the investigations 

 of these two investigators, Guilliermond 3 has succeeded in demon- 

 strating that this fusion is 

 a true copulation. It is 

 easy to observe this phe- 

 nomenon in a Bottcher 

 moist chamber in a drop of 

 beer wort gelatin. The 

 ascospores deposited in it 

 are not slow to germinate 

 and produce vegetative 

 cells which multiply very 

 actively during the first 

 two days ; toward the third 



Fig. 14. Different Stages in the Development day the multiplication de- 

 of Schizosaccharomyces octosporus. 



a, and h, germination of ascospores; c, multiplication of 



li . j _ I_A _ _ i f _ * __ e ii^ _ . _ j i/. 



colls; d, copulation and formation of the asc; e, f, g, and k, 

 copulation in a species tending to become asporogenic. 



creases. The cells are 

 then adherent in little 

 colonies of 15 or 20, per- 

 haps a few less. Some continue to divide, but most cease to multiply. 

 At this moment copulation commences and is accomplished in 

 the following manner: Two cells identical in characteristics and 

 lying adjacent to each other in the same colony are joined by means 

 of a copulation canal, formed by the fusion of two little projections 

 put out by each cell. (Fig. 15.) The middle wall which separates 

 the two cells is rather quickly dissolved, and the nucleus of each 

 cell, transformed thus into gametes, passes through the copulation 

 canal. By this operation, a single cell, which is an egg or zygospore, 

 is formed. Formed in this manner by isogamic copulation, the egg 

 soon germinates. It increases in volume, while its nucleus under- 

 goes two successive divisions, sometimes three, which give 4 or 

 8 nuclei. Then these become distributed about the zygospore and, 



1 Schionning, H. 1895. Nouvelle et singuliere formation d'ascus dans une 

 levure. C. R. lab. de Carlsberg, 4. 



2 Hoffmeister, C. Zum Nachweiss des Zellkerns bei Saccharomyces. Sitzungs- 

 ber. deutsch. naturw. mediz. Vereins f. Bohmen, 25, 1900. 



3 Guilliermond, A. Recherches histologiques sur la sporulation des Schizo- 

 saccharomycetes. Comp. Rend. Acad. Sci. 133, July 22, 1901. Recherches cyto- 

 logiques sur les levures, Storck, ed. Lyon, 1902. 



