IN THE DIVIDING ROOT-TIP CELLS OF THE ONION. 45 



Further, if we take each of the 10 active stages singly, we find that the 

 same rule appHcable to the 10 stages as a whole holds good, with the 

 single exception of stage 3, the spireme stage, in which an increase of 

 temperature from 10° to 20° C. causes an increase in velocity of 2.9599 

 times, while from 20° to 30° C. velocity is increased only 2.6404. This 

 decrease is sUght, but it operates in the direction of general physio- 

 logical rather than simple chemical expectation. (See pp. 38 and 42.) 

 Nevertheless the values are so close that, considering stage 3 only, the 

 fitting to van't Hoff's rule is most striking. Thus, judged by the 

 van't Hoff rule alone, from its reactions to heat, stage 3 seems to be 

 a comparatively simple chemical reaction; but, as seen through the 

 microscope, it is characterized by molar changes also. So it is prob- 

 able that the close approximation of its Qio value to +3.0 at both the 

 upper and lower temperature ranges is due to its being the resultant 

 of a number of conflicting higher and lower values, else all processes 

 involved were alike in having the same Qio characteristics, which latter 

 is possible, but not probable. 



The movement of chromosomes. — Stages 4 to 7, as designated in this 

 study, involve the movement of chromosome-bodies within the cell. 

 Although the chromosomes may be attached by strands, it may be 

 profitable to make comparison with the action of heat upon the rate of 

 movement of other bodies in protoplasm. In Davenport's ''Experi- 

 mental Morphology" a diagram^ shows the relation between tempera- 

 ture and the rate of movement of the chlorophyll-grains floating in the 

 protoplasm of the cells of three species of green plants. These curves 

 show a rapid rise in rate of movement from slightly above 0° C. to from 

 33° to 39° C, and then a rapid falling off. Before their breaking points 

 they are essentially the shape of the curves plotted for velocity-reactions 

 of most of the mitotic stages to temperature-changes. The curve is 

 specific for each particular species. So, with the specific mitotic stages, 

 there is a specificity of reactions due, doubtless, as among the different 

 species and processes above referred to, to a distinctive complex of 

 physiological {i. e., physico-chemical) properties. 



The peculiar reaction of mitotic stage No. 6. — From the present 

 experimentation one of the most interesting results is in reference to 

 mitotic stage No. 6, in which the chromosomes are moving from the 

 equatorial plate toward the poles. One would naturally suspect that a 

 rise in temperature would increase the speed of these moving bodies, 

 as a rise in temperature increased the rate of movement of the 

 chlorophyll-granules above referred to, but such is not the case. 

 "WTiereas it is true that a rise in temperature increased the speed of the 

 whole mitotic process, it actually decreased the speed of this particular 

 stage. The unexpected response of this stage to temperature- 



^ Davenport, Charles B. Experimental Morpholog>-, p. 226, 1899. Data from Velten, W. 

 Die Einwirkung der Temperatur auf die Protoplasma-bewegung. Flora 59: 177-217, 1876. 



