IN THE DIVIDING ROOT-TIP CELLS OF THE ONION. 37 



their different chemical composition and makes possible the micro- 

 chemical analysis of cell structures, but the same evidence of com- 

 plexity demands the greatest refinements in measuring unhampered and 

 elementary vital processes. The mathematical formulas for physio- 

 logical constants are, as a rule, not nearly so dependable as are such 

 velocity-reaction formulas for substances in the world of non-living 

 protoplasm. Doubtless the reason is that in living protoplasm there is 

 a more complex interplay of forces and the consequent manufacture of 

 new products which, in turn, by their presence affect their differential 

 influences upon the whole subsequent course of vital activity. Such 

 can not, without great difficulty, be resolved into its elements and given 

 mathematical interpretation. 



D. PHYSICO-CHEMICAL ASPECT. 



(a). INDIVIDUALITY IN VELOCITY REACTIONS OF THE SEVERAL MITOTIC 

 STAGES TO THE SAME TEMPERATURE CHANGES. 



It should be noted that there is a differential response characteristic 

 of each of the several mitotic stages here listed. This is not surpris- 

 ing, for each mitotic stage possesses its own individuality so far as its 

 physico-chemical complex is concerned. This is most strikingly shown in 

 chart No. 18, in the parallelism between the graphs plotting the velocity 

 reactions of the successive stages at 20° C. compared with the velocities 

 at 10° C, and those for 30° C. compared with the velocities at 20° C. as a 

 standard. If the specimens had been grown at temperature-intervals 

 of 2° C, one would expect, from the response shown in table on page 38, 

 through the temperature series a characteristic and orderly increment or 

 decrease in the velocity-response of each arbitrarily marked-off section 

 (mitotic step or stage) of the mitotic cycle, the same as from the cell- 

 organization as a whole, only in slightly less complex manner. 



With the microscope it can be seen readily that the mitotic process 

 involves gross molar movements and, as the cycle progresses, differ- 

 ential staining proves the change of minute cellular structures, "the 

 production of structure from metabohsm," involving chemical change. 

 In a homogeneous chemical system it is possible to measure the quan- 

 tity of the homogeneous reaction-product produced in a given amount 

 of time; but in mitotic activity it is the progress of the complex-train 

 with all of its many products that is measured by dividing it into 

 arbitrary but recognizable progress-stages. It is not the mass of its 

 reaction-products that is measured. Thus the end speed of the whole 

 mitotic process is the resultant of many cooperating and conflicting 

 forces; but, regardless of the number of complications, a thing that is 

 measurable and is varied by the change in complicating factors shows 

 orderly change and rhythm. Such measuring is a step in advance 

 because it admits of analysis further than has been made and points 

 the way toward still greater refinements. 



