368 



FUNGI RELATED TO THE YEASTS 



determine the sporulation of yeast (plaster blocks, cultures in yeast 

 water and slices of carrot). The optimum temperature for sporula- 

 tion on plaster blocks is between 25 C. and 28 C., the maximum is 

 34.5-35 C. and the minimum 5-8 C. The ascs always form at the 

 expense of units in the mycelium and never of the yeast-like struc- 

 tures. Finally, they only appear in contact 

 with air on solid substrates and in scums. The 

 ends of the threads separate into cells which 

 become round and produce spherical or elon- 

 gated forms similar to oidia. These cells 

 develop either by constriction or transverse 

 partition or by a process intermediate between 

 Fig. 157. Ascospores in these two processes. The cells thus -formed 

 Endomyces capsularis (ac- swe u up an( j snow a granu l ar contents very 

 cording to Schionnmg). r x - i A u j n ^ 



refractive, later changing gradually into ascs 



(Fig. 58, 2 and 3, and Fig. 157, a). Often the ases are able to form 

 from an intercalary cell in the mycelium which enlarges and becomes 

 round (Fig. 157, b). The investigations of Guilliermond l indicate 

 that the ascs possess a single nucleus like those of the Saccharomycetes. 

 A karyogamy does not take place here as with Exoascus. The ascs 

 almost constantly possess 4 ascospores. 



The ascospores are very resistant to acids. If the mycelium which 

 has produced ascs is treated with a strong solution of sulfuric acid 

 or other mineral acids, the mycelium and the 

 ascs dissolve. On the other hand, the asco- 

 spores resist and take on a beautiful red color. 

 The ascospores of the Saccharomycetes are, 

 on the other hand, strongly attacked by these 

 acids and not colored a rose color. The as- 

 cospores are ellipsoidal or oval (3.5 to 8 JJL in 

 diameter). They possess a double membrane, 

 an exosporium and an endosporium. The Fi 

 exosporium is formed of two valves in which 

 the adjacent edges cause a sort of projecting 



ring by means of which the ascospores resemble those of Willia 

 Saturnus. This ring separates the ascospore into two unequal parts 

 (Fig. 158). 



Reaching the adult stage, the ascospores absorb their wall quite 

 rapidly, setting free the ascospores, but these more often remain united 

 in groups of four. When the ascospore germinates, the exosporium 

 cracks to form two unequal parts which remain united at the point 



1 Guilliermond, A. Recherches cytologiques et taxonomiques sur les Endomy- 

 cetees. Rev. gen. Bot. 21, 1909. 



158. Germination of 

 scospores in Endomyces 

 cavsularis. 



