IO-S 



S. O. MAST AND YASUSHI IBARA. 



TABLE I. 



THE EFFECT OF TEMPERATURE AND FOOD ON ENCYSTMENT IN DIDINIUM. 



Note that the percentage of encystment is greater in the cultures with food 

 than in those without and that it is greatest at 25-30, the optimum tempera- 

 ture for reproduction. 



cystment occurred in a much greater proportion of the cultures 

 than at any other temperature, both in those with and in those 

 without food, that at all of the temperatures excepting the lowest 

 it occurred in a much greater proportion of the cultures which 

 contained food than in those which did not, and that the difference 

 in the extent of encystment in the cultures with and without food 

 was least at 25-3O. They show that at 39, which is only a few 

 degrees below the maximum, there was but little encystment, and 

 that at 4-i6 there was none at all. 



In the preceding experiments the didinia died out in relatively 

 more cultures at the higher and the lower temperatures than at the 

 others. At 4-i6 and at 39 they died out in over half of the 

 cultures in two days, while at 27 they died out in less than one 

 tenth of the cultures in the same time. Moreover, the death rate 

 was greater at all of the- temperatures in the cultures without food 

 than in those with food. In two days at 39 two thirds of the 

 cultures without food died out and only one half of those with 

 food, at 30-35 a little over one half of those without food and 

 less than one eighth of those with food, at 27 nearly one sixth of 

 those without food and less than one twenty-fifth of those with 

 food, etc. Furthermore, reproduction took place more rapidly at 

 2 5-3 tnan at the ot her temperatures. At 25-3O the fission 

 rate ran up in some instances to 8 a day. At 39 it never exceeded 

 one or two a day, and at the lower temperatures of 4-i6 there 

 was no reproduction at all. 



