30 MORPHOLOGY AND DEVELOPMENT OF YEASTS 



an ordinary vegetative cell. It commences to form a bud at some 

 point on its surface (d, e, and /). This bud generally appears after 

 the rupture or the absorption of the wall of the asc, but it may 

 appear on the interior of the asc. Its appearance is soon followed 



by the formation of new buds which 



(j/ (~^) r\ / ) are formed at various parts of the sur- 



^ p, ~ ^ ? (\ face of the ascospore. During the 

 SQ <^ (fjS CD ^ formation of these buds, the ascospores 

 ^^ remain united but separate rapidly. 

 Finally these germinate; the ascospores 

 swell up and bud quickly after the 

 manner of a vegetative cell. 



Hansen has often observed, during 

 budding, the fusion of two ascospores 

 in a cell. But this fusion, which only 

 appears in an exceptional manner, is 

 not comparable to copulation which 

 has been described in certain yeasts, 

 as S. Ludwigii. It takes place only 

 after the ascospores have commenced 

 to bud, generally between an ascospore 

 Fig. 35. Germination of Asco- which hag a l rea dy formed many buds, 

 spores in Yeast Johannisberg II. , , . , . , , 



and an ascospore which is not yet de- 



a, two ascospores germinate without fus- 

 ing; e, n, i and P , copulation between veloped. Hansen supposed that one 



ascospores not included in the same asc. . 



served to nourish the other, and that 

 a case of parasitism Was involved. 



In the majority of yeasts, notably in Saccharomyces Pastorianus 

 and in many of the industrial yeasts, germination occurs in the same 

 manner as in S. cerevisiae. However in 

 certain species, germination of ascospores 

 is preceded by a copulation (parthenog- 

 amy) ; this is the case with yeasts 

 already mentioned, as Johannisberg II, 

 S. intermedius, turbidans, and ellipsoideus. 

 It will be recalled that in this species Fig> 36> _ Germination of Asco- 

 the ascospores, after swelling up, unite spores in Saccharomyces Lud- 

 two by two by means of a copulation 



J In A, Fusion of Three Ascospores. 



canal. A zygospore is thus formed by 



the fusion of two ascospores. Budding takes place at the expense of 

 the copulation canal. (Fig. 35.) It is produced at some point on its 

 surface. Often many buds appear simultaneously at different points 

 on the canal of copulation. Eventually, it happens that the buds 

 originate at the expense of the ascospores themselves. In the mean- 



