50 



Regulation of Size in Unicellular Organisms 



2. 

 Some of 

 variability 

 mentioned 

 and many 

 constancy 

 mains the 

 moreover, 



1.16 



Correlatives of Body Volume 

 the factors which have proven to influence 

 of size among individuals have already been 

 ; such as heredity, age, reproductive rate, 

 environmental factors. But granted the 

 of all the identified conditions, there re- 

 residuum of "normal" variability, which, 

 in itself leads to important consequences. 



16 



18 



6 8 10 12 14 



Diameter in micra 



Figure 21. Frequency curve of diameters (solid line), and correlation of 

 diameters with specific gravities (broken line), in the green alga Scenedes- 

 mus. (Redrawn from Allison, '24, permission of Annals of Applied Biology). 



Some of the causes and the consequences of being 

 larger than the mean or smaller than the mean, can be 

 realized from the consideration of some of the func- 

 tions and properties which are bound up with size. 



Specific gravity. Specific gravity or density was 

 demonstrated by Allison ('24) to be correlated with 

 size. He studied several species of spherical organ- 

 isms, determining their specific gravity by means of 

 the time required to fall through normal culture fluid. 

 From the diameters and Stokes's law the relative den- 

 sities were then calculated. It turned out (figures 21 



