26 Regulation of Size in Unicellular Organisms 



which can be obtained much more easily. In a mass 

 culture of a clone in which growth and reproduction 

 are proceeding at a steady rate, the frequency with 

 which each size occurs in the culture, at some one time, 



§ 180 



80 100 



Time after fission in percent 

 of one generation 



Figure 12. Growth in length and in volume in Paramecium caudatutn, as 

 calculated from the frequency of occurrence of each length and each volume 

 in an actively multiplying culture. One hundred and ninety-five individuals 

 were fixed and measured in length and breadth. Volumes were calculated 

 as / X b 2 In the lengths the one longest individual was discarded; in the 

 volumes the 44 smallest and 31 largest individuals were discarded in order 

 to leave a range in size of only 100 per cent. (Data utilized are from Jen- 

 nings, '08, p. 412). 



will be, roughly, inversely proportional to the length 

 of time required to grow through that size. To make 

 use of this method properly, not only is an old popula- 



