336 CLASS ASCOMYCETEAE 



the Higher Fungi. This is closed before the cells separate from one another. 

 Fabian and McCullough (1934) reported that by growing some yeasts 

 under certain cultural conditions or by the addition of lithium salts to the 

 culture media the vegetative cells may be induced to break up into 

 minute cells which differ, not only in size and shape but in their ability to 

 cause fermentation, withstand changed environment, etc. On inoculation 

 upon the customary culture media they resume the normal size and char- 

 acteristics of the original cells. This is of interest as it shows a parallelism 

 in behavior to that demonstrated by Hadley (1927) for some of the true 

 bacteria. 



Sexual reproduction consists of the union of two equal or unequal cells 

 and the almost immediate fusion of the two gamete nuclei. This diploid 

 cell or some of its products by division enlarges to become a single ascus 

 within which are produced usually eight or four or sometimes fewer asco- 

 spores (even as low as one in the genus Monospora). In Ascoidea and 

 Dipodascus many ascospores are formed. Unlike the case in many of the 

 Ascomyceteae the ascospores in this order are mostly not expelled vio- 

 lently by the bursting of the asci. 



In the older classifications of the families within this order the forms 

 normally with mycelium are placed in two or three families and the yeast 

 forms in about as many. The fact that the same type of ascospores may 

 occur in genera assigned to several of these families throws doubt on the 

 validity of these classifications (Zender, 1926). Thus the hat-shaped asco- 

 spores occur in the unicellular genus Hansenula (Willia), in some species 

 of the filamentous genus Endomyces, and in the filamentous Ascoidea 

 ruhescens Bref. These three genera are usually placed in three separate 

 families. This spore type is apparently closely related to that found in 

 those species of the genus Aspergillus in which there are two parallel 

 ridges with a furrow between them. 



It seems to the author that the yeast forms are to be considered as 

 derived more or less independently from the Endomycetaceae and perhaps 

 other families. In that case the customary yeast family ox families are not 

 true phylogenetic units but must eventually be merged with the families 

 from which they are derived. Pending further research by students of 

 these groups the more customary family distinctions are followed here. 

 The most recent extensive work on these organisms with the modern sys- 

 tem of classification is that by Miss Stelling-Dekker (1931), Miss Lodder 

 (1934), and Diddens and Lodder (1942). 



AspoROGENOus Yeasts. Closely resembling the yeasts and the fila- 

 mentous genera of this order are many forms sometimes called the Asporo- 

 genous Yeasts. These do not produce asci nor are there any evidences of 

 sexual reproduction. Possibly some of them may be true yeasts that have 

 permanently lost the power of producing asci. Others, however, may rep- 



