CELLS IN DIVISION 



2 and 4, while a physical process such as diffusion or viscous flow is apt 

 to have a temperature coefficient in the neighbourhood of i-2 to 1-3' 

 (HoBER^^). It may be doubted if the study of temperature coefficients 

 has proved to be of much value in biology generally, and no definite 

 contribution of this kind to the study of mitosis has yet been made. Since 

 the rate of mitotic process rises to an optimum with increase of tempera- 

 ture and then subsequently declines, calculated Qio values vary greatly 

 according to the point on the whole temperature velocity curve to 

 which they relate. The best known paper in this field is that of 



3S 



32 



28 



% 2V 



I 



f6 

 12 



8 10 



Time 



18 



Figure 28 The duration of mitosis as a function of temperature. 

 A 1st maturation division of egg of Sabellaria. From Faure- 

 Fremiet*!*. 6. Fertilization to ist cleavage in Strongylocentrotus 

 purpuratus. From Loeb*'^. C. Mitosis in erythroblasts of TnYon. 

 From Jolly. '^ D. In Spirogyra. From de Wildeman.^' 

 £. From fusion of pronuclei to ist cleavage in Ascaris. From 

 Faure-Fremiet."'! 



Ephrussi,^° who found that both in the Echinoderm Paracentrotus and 

 in the Nematode Ascaris the Q^io values for each stage of mitosis were 

 at a minimum in metaphase. However, this result was obtained by 

 comparing his own observations for Paracentrotus at a comparatively 

 high temperature with those of Faure-Fremiet^^ for Ascaris at a 

 relatively low one. Ephrussi's work on Paracentrotus was repeated by 

 Fry^^ on Arbacia over a similar temperature range with dissimilar 



87 



