62 



Regulation of Size in Unicellular Organisms 



lar ('24) measured the diameters of the spherical cysts 

 which are formed by the organisms when food is de- 

 nied them. In the formation of cysts reorganization 

 occurs, and although most cysts are zygotes, a few 

 are parthenogenetic cysts ; and these latter show in the 

 frequency curves for diameter (figure 27) as minor 



100 

 90 



80 



70 



60 



50 



40 



30 



20 



10 







-a 

 a» 



t- 



to 



CO 



CU 



CD 



£ 



20 22 24 26 28 30 32 34 36 



Diameter in micra 



38 40 42 



Figure 27. Distribution of diameters in a clone of Actinophrys sol which 

 had been allowed to form cysts. The skewness and minor modes are due 

 to the admixture of parthenogenetic cysts among the usual conjugation 

 cysts. The mean diameters are represented by vertical lines. (Redrawn 

 from Belar, '24). 



modes. The values at the minor modes correspond 

 approximately to half the volumes of those at the ma- 

 jor modes. Belar made four series of measurements, 

 each based on 200 to 600 cysts, upon normal organisms 

 cultivated under uniform conditions over a period of 



