180 VARIATION OF SPECIES 



constant variation in the characteristics of yeasts. Guilliermond has 

 observed in a young culture of Schizosaccharomyces Pombe in beer 

 wort a certain number of abnormal mycelial forms which suggest 

 the appearance of little specks scattered in the growth among or- 

 dinary cells. (Fig. 73.) These have been isolated and obtained in 

 pure culture and maintained constantly in the same mycelial struc- 

 ture. Lepeschkin has also isolated a similar mycelial 

 structure which appeared in the growth of a young 

 culture of Sch. mellacei developing in glucose yeast water. 

 (Fig. 74.) These mycelial forms in Sch. mellacei are 

 either with or without spores. They make up, then, 

 a constant species incapable of transforming them- 

 selves into ordinary cells and seem to result from an 



73- ~ M y- hereditary modification of the cells. This transforma- 

 cehal Forma- ,. . 



tion in Sch. tion, caused without apparent cause, seems to fall into 



Pombe ( after the category of de Vries' mutations. In the sporulation 



of yeasts we often find variations. Yeasts seem to lose 



very easily the power of forming ascospores and often do not recover 



it. Definite asporogenic races of yeasts are thus formed. Hansen 



made the first observations on this subject. 



In isolating a large number of cells of 

 S. Ludwigii, this author obtained three dif- 

 ferent races; one is marked by its ability to 

 form ascospores; another group is made up 

 of yeasts in which this power is almost 

 extinct; the last contains yeasts in which it 

 has entirely disappeared. There are, then, 

 three races, an asporogenic, a feebly sporogenic Fig. 74. Mycelial Forma- 

 and a sporogenic. The asporogenic race can 

 be maintained for a long time. 



On the other hand, Lindner 1 has shown that when S. Bailii, P. 

 hyalospora and P. farinosa are cultivated for a long time on must 

 gelatin they lose completely their ability to form spores. Holm has 

 reported the same thing with cultures of Saccharomyces multisporus, 

 cultured for a long time on beer wort with sucrose. Beijerinck 2 has 

 secured similar results to those of Hansen with Sch. octosporus. In 

 cultivating this yeast on nutrient gelatin, this investigator noticed 

 three types of colonies; first, white colonies made up of cells which 

 do not produce ascospores; secondly, light brown colonies made up 



1 Lindner, P. Mikroskopische Betriebskontrolle in den Garungswerben, 

 Paul Parey, edit. Berlin, 6th edition 1909. 



2 Beijerinck, M. W. Weitere ' Beobachtungen iiber die Octosporushefe. 

 Cent. Bakt. 3, 1897. 



