38 



DURATION OF THE SEVERAL MITOTIC STAGES 



Owing to the individuality of the physico-chemical complex char- 

 acterizing each mitotic stage herein set off, we do not expect orderly 

 fluctuation in the reactions of the successive stages (see chart 18) to 

 the same temperature any more than we expect serial order in the 

 reactions of different organisms selected at random and unseriated; 

 but (see also charts 16 and 17) we do expect to find, in the same 

 organism, that a characteristic and orderly curve plots the reactions 

 to orderly increments in temperature, of the same mitotic stage, of 

 any given combination of mitotic stages, of the entire cell as a unit, 

 or of the more complex organism as a whole. 



The effect of temperature increments of 10° C. upon the velocity of each of the several 

 mitotic stages in the dividing root-tip cells of the onion. Qio values. 



Note. — Each of the above values when preceded by a + or a — sign constitutes 

 the usual Qio calculation. 



The above shows, in terms of velocity rather than of duration, the 

 effects of temperature increments of 10° C. upon the increased rapidity 

 of each of the several mitotic stages in the dividing root-tip cells of 

 the onion. (Table 15 and charts 16, 17, and 18 give in detail the 

 comparative effects of temperature upon the duration of the several 

 individual mitotic stages.) In two instances it will be seen that 

 mitotic velocity is slowed down by the 10° C. temperature-increase, 

 while in all other cases it is speeded up. On the whole the increased 

 velocity exceeds the retarding influences, so that a rise in tempera- 

 ture increases the rate of mitotic activity. Stages 1 and 6 are, to a 

 greater degree than any other stages, slowed down by a rise in tem- 

 perature, while stages 2 and 8 are greatly accelerated by the same 

 change. The former pair (stages 1 and 6) apparently have little in 

 common, while in the latter pair stage 2 is constructing chromosomes 

 and stage 8 is breaking them down. 



