74 Regulation of Size in Unicellular Organisms 



instance in Scenedesmus, and found that logarithmic 

 increase of total bulk prevailed even though the in- 

 crease of number of individuals occurred in steps. 



It was the general rule with older techniques that a 

 considerable "lag" occurred in the rate of reproduction 

 just after transplanting to new medium. 2 It has been 

 shown that this temporary inhibition of reproduction 

 is due to differences between the old and the new med- 

 ium; though it is not always agreed as to what fac- 

 tors of the medium and of the organisms are responsi- 

 ble for every instance of lag. It seems worth pointing 

 out that a lag in rate of reproduction may be due in 

 part to an increase in the size of each individual, and 

 therefore not to any failure to accumulate protoplasm. 

 This is certainly the case for Bacillus coli, relying 

 on the data of Henrici ('23), which are given in table 

 3 and later on in figure 46. 



Influential factors. A great many factors have been 

 demonstrated to influence significantly the rate of re- 

 production of particular unicellular species. Internal 

 factors such as conjugation 3 , various forms of par- 

 thenogenetic reorganization 4 , encystment, "life cycle", 

 life history, reduplication, and regeneration, all play 

 important parts. The more directly influential exter- 

 nal factors of oxygen supply 5 , temperature 6 , age of 

 culture fluid 7 , quality and concentration of food 8 , con- 



8 In bacteria: Miiller ('95), Hehewerth ('01), Rahn ('06), Lane-Claypon 

 ('09), Coplans ('10), Penfold ('14). In yeasts: Wildiers ('01), Carlson 

 ('13),Slator ('13). In ciliates : Robertson ('21), Yocom ('27), Petersen ('29). 



"Maupas ('88), Hertwig ('89), Calkins ('02), Jennings and Lashley 

 ('13a). 



* Woodruff and Erdmann ('14), Hertwig ('14), Fermor ('13), Calkins 

 ('21). 



6 Gutmanowna ('IS), Medrkiewiczowna ('21). 



"Dallinger ('87), Maupas ('88), Ward ('95), Miiller ('95), Woodruff 

 and Baitsell ('11), Mitchell ('29). 



7 Lane-Claypon ('09), Woodruff ('11a), Penfold ('14). 



"Beers ('28a, '28b), Penfold and Norris ('12), Vieweger ('23), Cutler 

 and Crump ('24, '27), Ludwig ('28b), Adolph ('29), Butterfield ('29). 



