SEXUALITY 23 



with others by means of small projecting tubes, some cells possessing 

 many of them, but this is hardly ever successful. It is then possible 

 that we are concerned with yeast which is in the process of losing its 

 sexuality and sporogenic function. 



Cesari 1 has recently isolated a series of yeasts from sausage and 

 salted meats which seems to act on albuminous matter and play a 

 role in the ripening process. All of these yeasts possess a heterogamic 

 copulation resulting in the formation of an asc with a single ascospore. 



(B) Copulation of Ascospores or Parthenogamy 



The copulation which has just been described, is not the only 

 form of sexuality observed among the yeasts. In certain species 

 occurs a sexually different process which is brought about by a sub- 

 sequent stage in the germination of ascospores. It 

 is thus that in S. Ludwigii and Willia Saturnus 

 and the yeast Johannisberg II, an isogamic copula- 

 tion between ascospores originating from an asc 

 formed without fusion, has been established. This 

 phenomenon will be discussed at this time without 

 entering into a detailed discussion of the germination 

 of ascospores. 



In S. Ludwigii the asc contains almost always /~aO*~ 

 four ascospores; at the moment of copulation, these vxSP 3 

 ascospores copulate two by two by means of a copu- 

 lation canal formed by the fusion of two little pro- 

 jections from each cell. (Fig. 25.) It was Hansen 2 



who showed for the first time the existence of this Fig. 25. Vari- 



! T , i i , , i ,i e ous Stages in the 



phenomenon. It is shown later that this fusion Germination of 



presents the characteristics of true copulation and Ascospores in S. 

 that it is accompanied by a nuclear fusion. servedm ^Moist 



The nucleus and cytoplasm are introduced into Chamber (ac- 

 the copulation canal and it is there that the mix- sen)" 18 

 ture of nucleus and cytoplasm takes place. The 

 fusion remains incomplete and the zygospore is formed from two asco- 

 spores united by a copulation canal. In this canal, the egg is formed 

 which brings about the germination of the zygospore. It elongates 

 into a germination tube from which originate numerous vegetative cells. 



Copulation is accomplished normally between two ascospores of 

 the same asc before the partition is absorbed. Buds result from the 



1 Cesari, E.-P. La maturation du saucisson. Comp. Rend. Soc. Biol., 1919. 



2 Hansen, E. C. Recherches sur la morphologic et la physiologic des ferments 

 alcooliques, 3, 1891. 



