2 6o HEREDITY IN SACCHAROMYCETES. 



nor has this tendency been found in any case of spontaneous 

 variation. 



With regard to the influence of chemical and physical factors 

 on the production of more or less temporary variations, the reader 

 is also referred to chapter xlvi. of the present volume. 



274. Hansen's Researches on Asporog-enation. The 

 Production of Constant Varieties by Transforma- 

 tion. 



HANSEN'S (XL.) discovery, in 1889, of asporogenation, i.e., the 

 loss of the capacity for producing spores, in Saccharomycetes, 

 opened up a new stage in the investigation of variation among 

 these micro-organisms. He observed in the case of Saccharomy- 

 codes Ludwigii that a number of cells lost the power of forming 

 spores when grown for some time on one and the same nutrient 

 medium, whilst another portion of the cells was considerably 

 weakened in this respect; the remainder, however, remaining 

 unaffected. This variation proved hereditary for some time in 

 wort cultures. The same peculiarity was also observed in other 

 species, e.g., Sacch. cerevisice, Sacch. Pastorianus, Sacch. intermedius 

 (= Sacch. Pastorianus //.), Sacch. validus (== /Sacch. Pastorianus 

 ///.), Sacch. ellipsoideus I., and several bottom-fermentation beer 

 yeasts, when kept on wort gelatin or in wort, a larger or smaller 

 proportion of the cells losing the faculty of producing spores. 

 BEIJERINOK (XXII. and XXIY.) subsequently found the same 

 behaviour in the case of Schizosaccharomyces octosporus. This 

 worker also noted several points of difference between the asporo- 

 genic cells and the others, the former producing less trypsin and 

 larger quantities of acid. Another species, which he named Sacch. 

 orientalis, also revealed the existence of a relation between sporo- 

 genation and proteolysis, inasmuch as the asporogenic colonies in 

 a surface-plate culture did not liquefy the gelatin, whilst the 

 sporogenic cultures did. Moreover, the former cells were quite 

 destitute of glycogen, though the sporogenic cells contained that 

 substance. The loss of sporogenic capacity in Saccharomycetes 

 stored in the laboratory is also mentioned by LINDNER (XXIX.). 



In these cases the variation is partly transitory and partly 

 constant. In certain instances Hansen succeeded in restoring 

 the faculty of sporogenation to asporogenic cells of Sacch. Lud- 

 wigii, by cultivation in a nutrient medium containing dextrose. 

 In other cases, however, both this and other culture methods 

 proved unavailing, the cells remaining asporogenic. In this con- 

 nection mention may also be made of KLOCKER'S observation (III.), 

 that a vegetation of Sacch. Marxianus, which produced only a few 

 spores, was considerably strengthened in this respect by cultivation 

 in a medium containing dextrin. 



