CHAPTER IV 

 PHYSIOLOGY OF YEASTS (CONTINUED) 



Living Conditions of Yeasts. Their Relations to Their Environ- 

 ment. Parasitism and Symbiosis 



IN this chapter we shall consider the living conditions of yeast, 

 i.e., their habitat, their duration of life, the physico-chemical 

 conditions which are necessary for their development, the in- 

 fluences which determine budding, the production of spores, and 

 finally, the pathogenic yeasts and the question of symbiosis. 



Habitat of Yeasts 



Devoid of chlorophyll, the yeasts, like all other fungi, are unable 

 to assimilate atmospheric carbon. They are, then, necessarily para- 

 sites or saprophytes. A certain number among them, such as the beer- 

 yeasts and industrial yeasts, the cultivated yeasts, have been prop- 

 agated from time immemorial by man. The greater part of them live 

 saprophytically, especially when sugar is available. These are able to 

 be regarded to a certain extent as domestic yeasts. In certain regions 

 fruits make a good environment on account of their sugar content. 

 However, a nectar may also be found in certain flowers (Berlese), 1 in 

 the mucous secretions of trees (Ludwig, Hansen, 2 Lindner, Rose 3 ) 

 and rarely in the detritus from vegetable decomposition. It will be 

 pointed out later on, that at the end of autumn, the yeasts are intro- 

 duced into the soil by the fall of the fruits and the rains and there 

 pass the winter. 



The investigations of De Kruyff have shown that, contrary to the 

 conditions in Europe, the yeasts in Java are very much more distrib- 

 uted on the leaves, both living and dead. The exceptional climato- 

 logical conditions of this country, humidity and heat, favor this mode 

 of life. Many Torula, Mycoderma and a few true yeasts have been 



1 Berlese, A. Verhalten der Sacch. an den Weinstocken. Rivista di pat. 

 vegetal!, 5, 1897. 



2 Hansen, E. C. Ueber die im Schleimflusse lebenden Baume beobachten 

 Mikroorganismen. Cent. Bakt. 5, 1889. 



3 Rose, L. Beitrage zur Kenntniss der Organismen im Eichenschleimfluss. 

 Inaugural Dissert. Universitat Berlin. 25 June, 1910. 



106 



