262 HEREDITY IN SACCHAROMYCETES. 



material for these modification experiments is taken from a young 

 and vigorous vegetation, grown in wort under ordinary conditions 

 and at a suitable temperature. A new culture is started with 

 this material in wort, at a temperature between the maxima for 

 sporulation and budding, this temperature varying for different 

 species. After this method of culture has been in progress for a 

 short time, an average portion of the vegetation grown at the 

 high temperature being transferred every day to a new flask of 

 wort at the same temperature, the cultures being shaken up 

 several times a day, asporogenic vegetations are obtained. The 

 number of cultures necessary for producing this result varies 

 according to the species. In this manner Hansen obtained con- 

 stant asporogenic varieties of all the species that have been proved 

 to belong to the genus Saccharomyces ; but no modification could 

 be produced by this treatment in the case of the genera Pichia, 

 Willia and Saccharomy codes. 



In order to elucidate the progress of this modification, HANSEN 

 (XLIY.) afterwards carried out special investigations, the chief 

 result of which may be summed up as follows : The material con- 

 sisted always of a single cell of the species in question ; in some 

 cases a vegetative cell, in others a spore, the material throughout 

 being thoroughly capable of sporulation, and in which the strictest 

 examination failed to reveal a single asporogenic cell. To facilitate 

 the examination of the conditions of sporulation throughout the 

 treatment, plate cultures were prepared by transferring the cells 

 to the surface of wort gelatin by means of a platinum stylus. 

 The mature colonies, when of sufficient size, were transferred 

 direct on to moist gypsum blocks for sporulation, those too small 

 for this treatment being first placed in wort and the sedimental 

 yeast therefrom transferred to the gypsum. The principal ex- 

 periments were made partly with Sacch. Past. I. at 32 C., and 

 partly with Johannisberg 2 wine yeast at 36 0. The following 

 table gives an example of the results obtained from the former 

 yeast during the various stages of the treatment. 



In stage 2 i per cent, of constantly asporogenic cells was found. 

 4 60 

 7 ioo 



Each stage represents twenty-four hours. 



To settle the fundamental question whether this formation of 

 asporogenic varieties is due to selection on transformation, Hansen 

 instituted further investigations with Johannisberg 2 yeast. In 

 the normal vegetation it was absolutely impossible to find a single 

 cell which did not produce sporogenic vegetations when grown 

 under normal conditions. The vegetation employed for starting the 

 experiment was analysed by isolating at least 1000 cells and testing 

 the resulting vegetation for sporulation, an abundance of spores 

 being found in every case. The experiments also showed that the 



