258 HEREDITY IN SACCHAROMYCETES. 



furnished some colonies consisting of oval cells, whilst those in 

 others were elongated and therefore abnormal in shape. Both 

 sets of colonies when grown by themselves produced descendants 

 which retained their characteristic shape for some time, the 

 elongated cells only resuming their normal form after recultiva- 

 tion in wort for a certain period. In the brewery, also, the 

 normal elongated form was retained during several fermentations. 

 The asporogenic form of Sacch. intermedius (=>S. Past. II.) 

 obtained by cultivation at 25 C. on wort gelatin, produced cells 

 which, when grown in wort cultures, furnished vegetations some 

 of which resembled /S. ellipsoideus and others S. Pastorianus, the 

 difference persisting during a large number of cultures, both at 

 the ordinary room temperature and at 25 C. 



The clarifying power of beer yeast can be influenced to some 

 extent by the previous method of cultivation (see also pp. 157, 

 1 88, vol. ii.), as was clearly shown by the experiments of 

 HANSEN (XLII.) with Carlsberg bottom yeast Nos. i and 2. The 

 cultivation of these two species separately in aerated wort furnished 

 vegetations which clarified satisfactorily in the brewery ; but 

 when the same species were grown in unaerated wort,, the result- 

 ing yeasts did not act normally in practice until they had been 

 put through several fermentations. The No. i yeast reverted to 

 its original condition quicker than No. 2, the transitory modifica- 

 tion sustained by them both having been greater in the one case 

 than the other. The beer obtained by the fermentation of the 

 unaerated wort was highly opalescent, and, as a rule, little 

 improvement in this respect was effected by prolonged storage, 

 the beer remaining cloudy even after the yeast cells had settled 

 down and the liquid had remained exposed to ordinary room 

 temperature for several days. This was more particularly the 

 case with the beer fermented with the No. i yeast. The subject 

 of variation in clarifying power has also been reported on by 

 A. JORGENSEN (XII.), who observed that top yeast kept on gelatin 

 clarified more slowly and gave a higher attenuation than when 

 kept in wort. There is no doubt that chemical influences are 

 concerned in this case, as may be concluded from Hansen's obser- 

 vation that Sacch. Pastorianus I., when repeatedly grown for many 

 generations in a solution of saccharose in yeast water at 32 0., 

 loses for a time its property of producing the characteristic 

 disagreeable taste and smell in wort (see p. 116, vol. ii.). 

 Continued cultivation in wort, however, soon causes the vegeta- 

 tion to revert to its original state. 



These instances of temporary variation may be supplemented 

 by the following, also observed by HANSEN (XXXVIII.). The film 

 cells of certain species, and also cells derived from old vegetations 

 grown in saccharose solution, gave, in wort cultures, a loose, curdy 

 deposit, quite different from the ordinary, pasty form ; but the 

 original type was restored by repeated cultures in wort. Similar 



