78 Regulation of Size in Unicellular Organisms 



tened. For the first reproduction, sixty hours of light 

 are again utilized for growth in one generation; but 

 thereafter reproduction proceeds much more hastily, 

 allowing less time for growth. Actually the individ- 

 uals and the colonies became more and more dwarfed 

 in each generation until they died out. In this species 

 of organism, growth inhibited reproduction over short 

 periods of time; and in fact it is well known that in 

 the Volvocales reproduction usually occurs in the first 

 few hours of darkness. When under the experimental 

 conditions photosynthesis and accretion proceeded 

 without intermission, then the balance between growth 

 and multiplication became upset, and multiplication 

 went too fast. 



Premature fissioning. The instances in which re- 

 production goes faster than growth throughout more 

 than a few generations are not known to be numerous. 

 Something of the sort occurs in those instances of "de- 

 pression" where reproduction keeps on. Starvation 

 alone is said to allow the continued reproduction of 

 smaller individuals in some species. Similar results 

 may occur in response to low tensions of oxygen. 

 Where there are diverse types of reproduction, as in 

 the formation of spores, or of cysts, or of gametes, 

 there may be multiplication without growth. And, 

 of course, the performance of two or more fissions at 

 one period of reproduction, which is common to many 

 species, particularly of Volvocales, is a variety of re- 

 production without growth which is usual and "normal." 



Various experimental methods have been employed 

 in attempts to induce early fissioning. Specific organic 

 food compounds have been reported to hasten repro- 

 duction (Ugata, '26), though simultaneous modifica- 

 tions of adult size were not looked for. Changes of 

 osmotic pressure, acidity, and salt content have been 

 found to modify multiplication in particular instances. 



