External Factors and Size 



131 



very considerably, compared with the cultures in which 

 the algae synthesized their own materials from light. 

 Increased oxygen supply (row 2) had the marked ef- 

 fect of reducing the mean size of the cells but at the 

 same time inducing them to multiply just enough 

 faster to make the total bulk in the culture the same. 

 In the dark the body size increased markedly over the 

 size in the light. One is left in some doubt as to why 

 the total bulk was the same in the light as in the dark ; 

 perhaps there were actually materials in the medium 



Table 11. 



Body Size and Total Bulk of Scenedesmus Costulatus Growing in a Basic Inorganic Medium 



at 24.5° in Strong Light, to Which Medium were Added Various Substances in One 



Per Cent Concentration. The Values Listed are Those Found on the Ninth 



Day of Age of the Culturk. (Data of Roach, '26.) 



utilizable without photosynthesis. Roach concluded 

 that glycerine, mannite, and xylose actually inhibited 

 what growth and multiplication would otherwise have 

 occurred. 



It is surprising to find that clear-cut effects of single 

 nutrients have not been measured upon the sizes of 

 bacterial individuals. 



Judging from the results that have been obtained 

 with different kinds of living or synthetic foods, it 

 appears inevitable that sizes should be diverse at dif- 

 ferent times in cultures of organisms such as ciliates 

 which are feeding upon unknown mixtures of bacteria. 



Quantity of food. The amount or concentration of 



