214 



GEORGE ALFRED BAITSELL 



III. HISTORY OF THE CULTURES 



1 . Oxytricha fallax 



The culture work with this hypotrichous infusorian was begun 

 on October 19, 1911, by the isolation of a single specimen from 

 a laboratory hay infusion. The individual was placed on a de- 

 pression slide and some of the regular beef extract medium added. 

 The progeny from this individual furnished the material for all 

 the cultures of Oxytricha fallax mentioned in this paper. Four 

 different cultures were under observation and each of these is 

 described in detail in the following sections. 



Oct 1911 



Nov 



Dec 



Jan -1912 



Diagram 1 Graph giving the life history of Oxytricha fallax, Culture Ob, 

 showing the average daily rate of division of the four lines of the culture, again 

 averaged for five-day periods. Beef extract culture medium. 



a. Culture Ob. This daily isolation culture, bred on the bee 

 medium, was started October 19, 1911, and continued until Feb- 

 ruary 10, 1912, a period of 115 days, during which time it passed 

 through 131 generations. Diagram 1 shows graphically the life 

 history of this culture. With the exception of two five-day 

 periods, the division rate was at all times below two divisions 

 per day, and during the last two months the rate was never as 



