TEMPERATURE LIMITS AND OPTIMUM 169 



have shown that ascospore formation has very definite limits of tem- 

 perature, and outside of these temperatures, none are formed. Cer- 

 tain temperatures are especially favorable (optimum). For a given 

 temperature, situated between these limits, the ascospores form 

 most abundantly. Hansen has also shown that at the tempera- 

 ture limits and the optimum the duration of ascospores formation 

 varies with the variety. He regards these as very important char- 

 acteristics. It is, then, feasible to determine for each variety the fol- 

 lowing: 



1. The temperature limits, maximum and minimum. 



2. The optimum temperature. 



3. The temperatures at which ascospores form between the tem- 

 perature limits. 



To secure these characteristics with accuracy, the various yeasts 

 are placed in a carefully controlled incubator. They should be under 

 the same conditions and on plaster of Paris blocks. The number of 

 hours or days which are necessary for the first rudiments of ascospore 

 formation to appear, should be noticed. 1 



Hansen has expressed graphically by means of a curve the results 

 secured with six varieties: S. Pastorianus, cerevisiae, ellipsoideus, 

 validus, intermedius and turbidans. The temperature of ascospore 

 formation was expressed on the abscissa and the time of ascospore 

 formation on the ordinate. The curves for all of the varieties were 

 identical. The curves were convex towards the temperature axis. 

 They are limited since they do not go beyond the temperature of 

 ascospore formation. When studied relatively, it can be noted that 

 their convex parts are little different; on the other hand their extremes 

 are quite distinct from one another. These are, then, the temperatures 

 which it is important to note well. 



The time necessary for ascospore formation in six varieties under 

 the same conditions of temperature is equally interesting to consider. 

 At the maximum temperature ascospore formation is accomplished in 

 about 30 hours; at the optimum temperature, there is little difference 

 among the different varieties; at the lower temperatures, the dif- 

 ferences are more and more striking. Thus, for example, S. cerevisiae 

 does not develop ascospores at 11.5 until about 10 days, S. inter- 

 medius at the end of 77 hours, etc. 



The following tables will indicate the limits of temperature, the 

 optimum temperature and the time necessary for ascospore formation 

 of six varieties studied by Hansen. 



1 How one is to tell when ascospore formation has begun is variable. It will 

 be necessary to adopt some criterion for the beginning of the ascospores. 



