External Factors and Size 



141 



concentration were shown not to be responsible for 

 the size difference. 



Algae. In Scenedesmus the progression of body size 

 was studied by Roach ('26). Under the conditions 

 studied, adult individuals were small in young cultures, 







4 8 12 16 20 



Age of culture in hours 



2A 



Figure 45. Progression of body length in three species of bacteria after 

 implantation from a 24-hour old culture into new broth. Each point is an 

 average of ten measurements of fixed individuals. (Redrawn from Clark 

 and Ruehl, '19). 



that is, during the period of logarithmic multiplication. 

 When reproduction slowed up, the mean size in- 

 creased. Whereas in the young cultures most adults 

 reproduced four progeny at one time, in the old cul- 

 tures 8 to 16 progeny resulted from about half of the 

 reproductive divisions. 



