118 PHYSIOLOGY OF YEASTS (Continued) 



In determining these three temperatures for 6 varieties of yeasts 

 (S. cerevisiae, Pastorianus, intermedius, validus, ellipsoideus and twr- 

 bidans) Hansen has noticed that sporulation is dependent upon three 

 laws which are able to be announced as follows : 



First. Sporulation is accomplished slowly at low temperature 

 but increases with the rise in temperature up to a certain optimum; 

 above this temperature ascospore formation becomes slower and slower 

 until it finally ceases completely. 1 



Second. The most favorable temperature for six varieties of 

 yeasts was about 25. 



The temperature limits of these yeasts with regard to sporulation 

 are situated between 0.5 and 37.5 C. It is interesting to note that, 

 as for the formation of the scum, the temperature limits for sporu- 

 lation are included in the limits of budding. The minimum tempera- 

 ture for sporulation is not as low as that for budding and the maxi- 

 mum is not so high. Sporulation in order to be accomplished requires 

 a temperature more pronounced than budding. It seems that the 

 higher the temperature for budding, the higher is the maximum tem- 

 perature for sporulation. The experiments of Hansen indicate, how- 

 ever, that there is no parallelism between the two temperature curves 

 for budding and sporulation. 



The observations of Hansen mentioned above, as well as those of 

 many other investigators as Nielsen, Klocker, and many others, on 

 maximum and minimum temperature limits, have confirmed this. 

 Nevertheless, some species are able to attain maximum temperatures 

 of 40-41. Sometimes they are situated around 15 C. as in certain 

 Pichia studied by Klocker. With regard to optimum temperatures, 

 they range around 25. These temperatures and the times required 

 for ascospore formation vary with the yeast. Hansen has been able 

 to establish very important characteristics for the differentiation of 

 species. 



The action of temperature has been mentioned by Saito in relation 

 to formation of the asc in. certain yeasts. Saito isolated a Zygosac- 

 charomyces which, depending on the temperature, formed ascs derived 

 from a copulation, or parthenogenetically. On slices of carrot on which 

 the yeast germinates very actively, the ascs were formed by a copu- 

 lation at 25 to 27 C. At 33-39 C., on the contrary, the ascs were 

 produced by a parthenogenesis. 



1 Herzog has shown that the curves which show this phenomenon resemble 

 those of Tamman on the influence of temperature on diastatic action; these 

 reach a maximum and decrease progressively. According to the same author, 

 they also agree with van't Hoff's law that the speed of a chemical reaction is a 

 function of the temperature. 



