PHYSIOLOGICAL CONDITIONS OF SPORULATION 115 



cells on the margin as well as in the cells inside of the colonies. The 

 lack of food, then, has little bearing in this case because the well-nour- 

 ished cells also form ascospores. 



According to Hansen, two factors seem to determine sporulation: 

 the lack of food and the accumulation in the medium of toxic excre- 

 tion of the yeast cell. With the yeasts which are placed on gypsum 

 blocks or in distilled water, it is the lack of food which is probably 

 the reason for sporulation. With yeasts cultivated on solid media 

 (slices of carrots, or nutrient gelatin) it is the action of toxic excre- 

 tions which arrests budding and causes sporulation. It is the same 

 reason which causes some yeasts to form ascospores in a fermenting 

 solution. The alcohol may hinder budding and provoke sporulation. 

 Hansen has shown, however, that certain chemical substances, such as 

 saturated calcium sulfate, are capable of stopping budding and pro- 

 ducing sporulation. 



In recent investigations by Saito, the role of toxic substances of 

 the yeast in relation to sporulation has been studied. According to 

 this author, only the cells on the periphery of a colony sporulate. 

 It seems to be a question of the amount of food. Saito thinks that the 

 deprivation of food is the main factor inducing sporulation but that 

 Schizosaccharomyces octosporus is an exception to this rule. 



But these two factors, the lack of food and the accumulation of 

 toxic products, are not sufficient in themselves to determine the for- 

 mation of spores. The investigations of Hansen and Barker 1 have 

 shown that there are a number of secondary conditions which are 

 necessary: free access of air, temperature, humidity and condition of 

 the cells. More recent researches by Purvis and Warwick have shown 

 that light exercises an influence on sporulation. We shall now take 

 up successively these various conditions. 



A. Condition of the Cells. In order for a cell to sporulate it 

 is necessary that the .cells be young and vigorous and that they have 

 accumulated, either from former culture media or from the medium 

 in which they are taken, a reserve of products necessary for the for- 

 mation of ascospores. We have seen, indeed, that cells destined to 

 form ascospores, have accumulated metachromatic corpuscles, fats 

 and glycogen which are finally absorbed by the ascospores during their 

 formation. The media in which yeasts are placed are of much impor- 

 tance in relation to sporulation. Hansen reported that dextrose had 

 a favorable influence on sporulation in Saccharomyces Ludwigii, and 

 Klocker has reported the same observation for certain Pichia; these 

 yeasts only formed ascospores after a preliminary cultivation in beer 



1 Barker, P. On the spore formation among the Saccharomycetes. Jour, 

 of the Federated Institutes of Brewing, 8, 1902. 



