IN THE DIVIDING ROOT-TIP CELLS OF THE ONION. 31 



least 1,000 cell-counts from each sample. This would be a long 

 and arduous task, possibly to be carried out best on a cooperative 

 plan, but it would supply valuable and accurate standards for the further 

 quantitative analysis of mitotic processes. 



(b) To make studies on the duration of the several mitotic stages at 

 the awakening and end of mitotic activity as affected by temperature 

 changes; also on the effects of light, electricity, moisture, pressure, 

 gra\'ity, foods, and poisons upon stage-durations. Much qualitative 

 work, but none of a quantitative nature, has been done in this direc- 

 tion; for instance, V. Sabline,^ in subjecting the roots of Vicia Jaba to 

 different temperatures, lack of oxygen, quinin sulphate, sulphuric ether, 

 and other substances and conditions, noted their effects upon mitosis 

 up to the instant of killing. The analysis of vital phenomena by 

 timing mitotic stages thus modified is most promising. 



(c) To follow the clue presented by the effect of temperature on stage 

 6, in constructing working models simulating this stage of mitotic 

 activity, seeking by a temperature rise to weaken the tension of strands 

 appearing to pull the chromosomes toward the different poles. Indeed, 

 if such strands could be made to appear in a gelatine cell, by a current of 

 electricity, the simulation would be all the more promising as a possible 

 real parallel to mitotic force. (See p. 45). 



{d) To time in detail the mitotic process, not only in cell-division 

 characteristic of growth in undifferentiated tissue, as in this study, but 

 also in cell-division in tissues undergoing differentiation. 



(e) To make studies in cell-size, cell-number, mitotic activity, and 

 bulk-increase in the same tissues as affected by temperature-differences. 

 Tissue growth consists in an alternation of cellular bulk-increase and 

 mitosis. The experimentation herein proposed would determine the 

 proportion of the limitation set upon growth by lowering temperatures 

 due to (a) slowing-down the mitotic process, and to (6) reducing the 

 absorption of food materials and delaying the metabolism necessary to 

 creating the chemical potential which must precede mitosis. 



RESULTS AND DISCUSSION. 



The accompanying tables and charts give in detail the cell-countings, 

 the mitotic stage-classification, and the determinations derived from 

 them; they give also the formulas used, and finally they set forth 

 graphically and comparatively the results of the experimentation and 

 calculations for each temperature series. Nevertheless, a short dis- 

 cussion is perhaps permissible. 



1 Sabline, V. "L'influence des agents externes sur la division des noyaux dans les racines 

 de Vicia faba." Rev. Gen. Bot. 15:481-497, 1903. 



