4 KANSAS UNIVERSITY SCIENCE BULLETIN. 



having to do with modifications of micro-organisms induced 

 by altered conditions of culture, unless such modifications 

 are known or supposed to originate from single varying cells. 



Hansen, who has been the pioneer in work of this char- 

 acter conducted on yeasts, succeeded in obtaining asporoge- 

 nous races of Sacchoromyces pastorianus I, II, and III, S. 

 cerevisise I, S. ellipsoideus I and other normally spore-bearing 

 species by plating in gelatin and testing the offspring of vari- 

 ous colonies by placing them on gypsum blocks. He found 

 great variation in the spore-producing power of these colonies, 

 varying from normal to races which have remained asporog- 

 enous, though cultivated under diverse conditions for twelve 

 years. He found that some varieties, as johannesberg II, 

 could not be made to produce asporogenous forms, except by 

 previously cultivating the yeast at temperatures approaching 

 the optimum temperature of budding, and that in practically 

 all forms the per cent, of asporogenous varieties was in- 

 creased by this preliminary treatment. Here we have to do 

 with a possible transformation associated with selection ; but 

 in the case of those forms which gave asporogenous varieties 

 without this treatment, for example 5. pastorianus I, which 

 gave five to ten per cent, of asporogenous colonies at the start, 

 we deal with probably spontaneous variations. 



Associated with the loss of power of producing spores, Han- 

 sen found the loss of power to produce veils. S. anomalus, 

 however, did not lose this faculty in asporogenous varieties. 



Further, the author found types presenting growth of 

 cheesy character and branching filaments, forms which per- 

 sisted for a number of generations. Again, cells showing a 

 tendency to extend in an elongated mycelium-like form were 

 found to transmit their peculiarities. In the case of S. lud- 

 wigii the mycelium-like type returned to the normal form 

 when grown in wort. In type No. I of carlsherg, Hansen 

 obtained a strain presenting abnormally elongated cells which 

 preserved its peculiarities during two months' cultivation in 

 wort. This type finally returned to its normal form. 



A number of races physiologically different which proceed 

 from the same pure culture are mentioned by Hansen. 

 Among these are types showing an increased power of pro- 



