Size of Nucleus 187 



Depression. Comparable with the effects of hunger 

 and of age of the culture medium, are the effects of 

 conditions of cultural "depression." The full defini- 

 tion of these conditions must be left to the investiga- 

 tors themselves. In Stylonychia, Popoff ('07) stated 

 that nuclei increased in size while the bodies grew 

 smaller and reproduced less frequently. But in Ac- 

 tinosphaerium Borowsky ('10) believed that the nu- 

 clei became relatively smaller. In Tillina and Oxytri- 

 cha, (Gregory, '09; Woodruff, '13), there were no sig- 

 nificant differences in the ratio of nucleus to body at 

 periods of slow reproduction as compared with periods 

 of rapid reproduction. 



Significance of nuclear size. Something definite is 

 known, therefore, about the size of the nucleus and the 

 relative sizes of nucleus and cytoplasm under several 

 sets of conditions. It appears from the data that the 

 ratio between the sizes varies only within a limited 

 range under any one set of conditions. The ratio 

 changes with those conditions which have been tested. 

 In experiments where nearly equal proportions of nu- 

 cleus and of cytoplasm have been removed by cut- 

 ting, as in Stentor, Spirostomum, and Dileptus, it was 

 not noticed that reproduction occurred without the 

 restoration in size of both nucleus and body; rather 

 the contrary (Hartmann, '22, '28; Sokoloff, '24). It 

 seems fair to conclude that, although nuclear growth 

 does not occur independently of body growth in pro- 

 tista, it is not any progressively changing function of 

 it. Hertwig regarded the nucleus as the conservative 

 structure which controlled the cytoplasm. This is per- 

 fectly possible, and has received new significance from 

 the inter-relations known to govern the expression of 

 heritable characters. But no evidence has been found, 

 particularly in the protozoa, for an actual causal rela- 

 tionship of the size of the cytoplasm to the size of the 



