io8 



THE METABOLISM OF ALGAE 





20 



) 5 10 IS 



DAYS OF GROWTH 



FIG. 15. Growth of Chlorella vulgaris in culture. A, log. cell number 

 per mm.^ of medium; B, log. volume of cells (mm.^) in lo ml. 

 of medium; C, log. dry weight of cells as mg. per 10 ml. of 

 medium ; D, relative dry weight as mg. per 10^ cells; E, 

 mean cell diameter in ft (after ref. 225). 



course,^^'^ but growth rates may alter in response to changes 

 in conditions other than those occurring as a result of 

 growth of the algae themselves. ^^^ 



A general feature of the growth of microscopic algae 

 which requires comment is that its rate is generally less 

 than that of the growth of non-photosynthetic micro- 

 organisms. For example, even after allowing for the effects 

 of differences in optimum temperatures, the maximum 

 relative growth rate recorded for Chlorella pyrenoidosa, one 

 of the most rapidly growing algae used in experimental 

 studies, is less than one half as great as that of a yeast or a 

 bacterium of the same order of size. 200 It is evidently not 

 carbon assimilation which thus limits the growth rate of an 

 alga.2^^ The explanation may perhaps lie in the fact that the 

 photosynthetic apparatus of an alga, which, as simple 

 microscopical examination shows, represents a considerable 



