88 Regulation of Size in Unicellular Organisms 



therefore, growth in size may be regarded as a pre- 

 requisite for reproduction. 



Hartmann ('21), in a species of green flagellate, 

 Eudorina, found cultural conditions under which 

 growth decreased in rate but multiplication increased 

 in rate, as compared with the normal conditions for in- 

 definite survival in cultures. The conditions consis- 

 ted in the continuous exposure of the organisms to 

 light, so that food could presumably be synthesized 

 faster than while the usual day-and-night rhythm pre- 

 vailed. This would in some respects represent the op- 

 posite effect from that produced in Paramecium by 

 starvation. But probably in neither case was the food 

 supply the essential factor. 



Hertwig ('89) noted certain cultural conditions 

 which brought about what he termed "depression" in 

 Paramecium and other protozoan species. In certain 

 phases of depression, growth of individuals was ap- 

 parently retarded, but rate of multiplication increased. 

 Similar changes were observed by Kasanzeff ('01), 

 Wallengren ('02), Chainsky ('06), and Lipska ('10) 

 in Paramecium. 



Excision of cytoplasm. Increase of body size may 

 be prevented not only by starvation and by unfavor- 

 able cultural conditions, but also by repeatedly cutting 

 away protoplasm which has been accumulated. Hart- 

 mann ('22) periodically cut away portions of the body 

 of Stentor, and found that reproduction was inhibited 

 for as long as the attainment of the normal adult vol- 

 ume was prevented. But in Stentor both nucleus and 

 cytoplasm were removed together; Hartmann ('24b, 

 '26, '28) therefore did similar experiments with Ameba, 

 in which only cytoplasm was removed. In Ameba he 

 was able to culture single, continually growing individ- 

 uals, without reproduction, for several months; while 

 sister individuals which were not cut went through 



