VARIATIONS IN THE SACCHAROMYCETES. 281 



it is only by a special treatment that the culture can be deprived 

 of its newly-acquired properties. In certain cases, it is found 

 impossible, even after years of methodical treatment, to cause 

 a growth to revert to its original state. 



1. The times given for the appearance of the first 

 indication of spores are based upon the understanding that 

 the growth has been cultivated at 25 C. for twenty-four hours 

 in wort. In 1883 when Hansen published temperature 

 curves for his six species, he found that growths which had 

 been developed for two days instead of one, at the same 

 temperature, developed spores more slowly and less freely 

 than usual. If, however, they are subsequently treated in wort 

 in the way described, the normal conditions are re-established. 

 This forms an example of a very feebly-rooted variation. 



2. In a gelatine culture, Carlsberg bottom yeast No. 1 is 

 often found in both oval and elongated sausage-shaped cells. 

 If a colony derived from each of the cell forms is transferred 

 to flasks containing wort, a growth is again obtained consisting 

 partly of oval and partly of elongated cells. Hansen's experi- 

 ments proved that the latter when cultivated in new flasks 

 retained to some extent the sausage-like form, and when 

 transferred to the pure culture apparatus the growth con- 

 tinued to show a mixture of such cells, but when the yeast 

 was conveyed to an ordinary fermenting tun they disappeared. 

 The variation in this case is, therefore, a more deeply seated 

 tme. It only ceases when the yeast has been transferred 

 through a series of fermentations. Another example is shown 

 by a bottom yeast which, after a long period of stunted growth, 

 had been propagated in wort at about 27 C., and formed cells 

 with a normal appearance, whilst the growth cultivated at 

 7| C. gave entangled colonies with mycelial branchings. 

 This forms a striking example of the effect that temperature 

 has upon the form of cells. 



3. Hansen's observations of S. Ludwigii supply an illus- 

 tration of a far-reaching change in the character of the cells. 

 If single individuals are grown as pure cultures, growths are 

 obtained which show a marked difference in their power of 

 .spore - formation. By systematic selection of single cells, 

 Hansen succeeded in producing growths which gave no spores 



