GERMINATION OF ASCOSPORES 



29 



view, the yeasts are comparable to Saprolegniaceae, in which Bary has 

 pointed out a similar process. 



If one glances over the Saccharomyces, he will be able to dis- 

 tinguish four steps in the progressive evolution of sexuality (Fig. 

 33) : firstly, those which have preserved ancestral copulation in origin 

 of the asc (Schizosaccharomyces, Zygosaccharomyces and Debaromyces 

 globosus); secondly, those which have lost this characteristic but 

 may have kept traces of it (Schwanniomyces occidentalis, Torulaspora 

 Delbriicki, and the yeast of L. Rose); thirdly, those which have lost 

 ancestral copulation and replaced it by a parthenogamy between asco- 

 spores (Johannisberg II, Willia Saturnus and S. Ludwigii); fourthly, 

 those which have lost all traces of copulation and have become par- 

 thenogenetic. 



Germination of Ascospores 



When placed under favorable conditions, ascospores germinate 

 and produce numerous vegetative 

 cells. The manner of this is dif- 

 ferent and depends upon the species. 



First Example, Saccharomyces 

 cerevisiae (Fig. 34): Let us start 

 this discussion with S. cerevisiae, 

 which has been studied by Hansen. 1 

 In the first phases of germination, 

 the ascospores undergo a swelling 

 but the wall subsists. This swelling 

 is so great that the ascospores, by 

 means of the pressure which they 

 exert on one another, give the im- 

 pression that the asc is chambered. 

 In fact, the walls of the ascospores 

 enter into intimate contact, and often 

 they fuse completely in such a way 

 that there are really walls in the asc 

 which then becomes a cell with many 

 chambers. (Fig. 34, c, d, f, and g.) 

 During this time the wall of the asc 

 becomes thinner and finally breaks. 

 It acts as a plaited veil which retains 

 the ascospores, or is completely ab- 

 sorbed by the ascospores. Each ascospore then takes the form of 



1 Hansen, E. C. Recherches sur la morphologic et physiologie des ferments 

 alcooliques, 3, 1891. 



Fig. 34. Germination of Ascospores 

 in Saccharomyces cerevisiae (Ob- 

 servations from a Bottcher Moist 

 Chamber) . 



o, three ascospores in an asc, the wall of which 

 has broken; a' and a", germination of these 

 three ascospores; b, asc with four asco- 

 spores; b', germination of these four asco- 

 spores; the wall of the asc is broken; c, asc 

 with four ascospores, three of which are 

 visible; c' and c", germination of these as- 

 cospores; in c' the wall of the asc is broken, in 

 c" budding has commenced; d, asc with three 

 ascospores; d and d', germination of these 

 ascospores; in d" the wall of the asc is broken; 

 e, e', e", e'", e"", various stages in the ger- 

 mination of two ascospores in an asc; in 

 e'"" the two ascospores have fused into a 

 single one by absorbing the separating wall; 

 /, /', /", g, g', g", germination of ascospores 

 in two ascs; h, h', and h", germination of two 

 ascospores in an asc; in h" the wall between 

 the two ascospores has disappeared; a 

 single cell is thus formed (after Hansen) . 



