I30 ^yrOEPHOLOGY AND LIFE-HISTORY OF YEASTS. 



what lower, and the minimum temperature rather higher, than 

 for the phenomenon of buckling. 



To examine the individual conditions more closely. That the 

 time within which sporulation occurs should be a function of the 

 temperature, requires no further analysis ; but careful attention 

 should be bestowed on the point (in i) as to the condition of the 

 cells, this being the prime factor determining the time limit. 

 The time required for ascospores to be developed by any given 

 species of Sarcharomi/ces, kept at any given temperature, differs 

 according to the physiological condition of the cells themselves. 

 Hence, if it be desired to produce sporulation (unconditionally) 

 in any given species, all that is necessary is to take cells that 

 are in vigorous condition — a state attainable by repeated pre- 

 liminary transferences into fresh nutrient solution. The case 

 is, however, different when it is a question of determining the 

 time required for sporulation to make its appearance at one 

 or another temperature. In such event, it must be borne in 

 mind that this time limit is a function, not merely of the tempera- 

 ture, but also of the physiological condition of the species under 

 examination ; consequently this latter factor must be eliminated 

 in order to enable the influence of the former to be determined. 

 Experience has shown that sporulation occurs earliest and most 

 certainly when the cells have reached the culminating point of 

 their reproductive (budding) and fermentative activity ; and it 

 is therefore in this condition that they should be employed for 

 the experiment in question. On this account the cells to be 

 examined for the time limit of sporulation should be subjected 

 to the following preliminary treatment : the sample is sowed 

 in sterilised beer wort and left to stand for several days at room 

 temperature, Pasteur flasks being the best vessels for the purpose. 

 A portion of the resulting sedimental yeast is transferred to fresh 

 sterile beer wort and kept therein for twenty-four hours at 25° C, 

 the fresh deposit being afterwards freed as carefully as possible 

 from the supernatant liquid, and employed for stai'ting the spore 

 cultures. 



One example will suffice to show the necessity of taking the 

 condition of the cells into consideration. It is afforded by 

 Hansen's experience, and relates to SaccJi. Pastorianus I. The 

 cultiu-e was first conducted for a few days at room temperature, 

 after which the sedimental yeast was retransferred, in the above 

 manner, to two flasks, one of which was kept for twenty-four 

 hours, the other for forty-eight hours, at 26° to 27° 0. before 

 starting the spore cultures. The following figures show the 

 time required for the commencement of sporulation in the two 

 cases : — 



