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, Tondaspora 

 Delbrucki, 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 Fig. 34. Germination of Ascospores 



- ,, i i j.i ' in Saccharomyces cerevisiae (Ob- 



means of the pressure which they se rvations from a Bottcher Moist 



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 physiologic des ferments 

 alcooliques, 3, 1891. 



Chamber). 



a, 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). 



