VIII. Internal Characteristics and Size. . . 108 



Assortative Mating 108 



The Effects of Conjugation 112 



Endomixis and Rhythms 117 



IX. Some External Factors and Size 122 



Temperature 122 



Food 128 



Age of Culture Medium 135 



Chemical Environment 146 



Radiations 157 



X. Size in Relation to Body Surface. ... 158 



Diffusion of Oxygen 158 



Diffusion of Other Substances 163 



Locomotion 164 



Forces Peculiar to Surfaces 166 



XL Size of Nucleus 171 



Some Internal Factors 171 



Some External Factors 181 



XII. Conclusion 189 



Size Regulation and Other Regulations 189 



Individuality 194 



Appendix. Spirogyra Cells 197 



Bibliography 209 



Index 231 



