24 DURATION OF THE SEVERAL MITOTIC STAGES 



EXPERIMENTS TO DETERMINE EFFECTS OF TEMPERATURE INCRE- 

 MENTS UPON THE SEVERAL MITOTIC STAGES. 



The results of the preliminary study with the 13 successively taken 

 samples of 1,000 cells each accord with common-sense expectations in 

 reference to the durations of the several stages. Also the ends sought 

 by this investigation lend themselves so completely to a simple cyto- 

 logical and demonstrable mathematical method that it appeared invit- 

 ing to continue the study with a view to making practical use of the 

 method developed in measuring accurately the effects, in an actively 

 growing tissue, of some selected and controlled environmental factor 

 upon the relative and absolute durations of the several successive 

 mitotic stages and upon the mitotic cycle as a whole. 



THE VELOCITY OF CHEMICAL REACTIONS: RESPONSE TO TEMPERA- 



TURE DIFFERENCES. 



The mitotic process is, no one doubts, a complex of physical and 

 chemical activities. It is known that, in homogeneous chemical sys- 

 tems, within Umits generally from 10° to 40° C, the velocity of a chem- 

 ical reaction is about doubled or trebled for each rise in temperature 

 of 10° C. This is van't Hoff's law, which experimental physiologists 

 have tested out in reference to so many vital phenomena. It was, 

 therefore, decided to select the temperatures 10°, 20°, and 30° C. for the 

 purpose, not only of determining the effect of these different tempera- 

 ature-increments upon mitosis, but also in order to make comparison in 

 reactions to temperature-increments between mitosis and homogeneous 

 chemical reactions. Furthermore, the temperatures selected present 

 two periods of 10° C. each, both still within the growing temperature- 

 range for plants, 30° C. approximating, but still a little lower than the 

 optimum, and 10° C. well above the minimum for growth in the species 

 selected for study. In general the botanists claim that the range for 

 protoplasmic activity in plants varies from zero to about 50° C. As a 

 rule, at a temperature below zero the protoplasm is killed by freezing, 

 and above 50° C. is killed by ''heat rigor." Of course, it would have 

 been possible to have tested out van't Hoff's law by making studies 

 with smaller temperature-differences and applying the formula,^ 



_( h \^' 



Q 



but in the same quantity of sampling and counting it seemed ad- 

 visable to increase the cell-count per sample rather than, at the expense 

 of cell-count, to lessen the te mperature-intervals. In the absence of a 



» Snyder, Charles D., "A comparative study of the temperature-coefficients of the velocities of 

 various physiological actions." Am. Jour. Physiol. 22: 311, 1908. 



