46 DURATION OF THE SEVERAL MITOTIC STAGES 



increments might indeed be considered as a mistaken interpretation 

 due to bad statistical methods, or to experimental errors, if we did not 

 have corroborative evidence. If the temperature-response of stage 6 

 in cells growing at 20° C. is compared with those growing at 10° C. we 

 find a slowing-down, both relatively and absolutely, caused by an 

 increased temperature, and when we take the duration at 10° C. or 

 that at 20° C. as a basis, we find also that at 30° C. there is a similar 

 response, namely, a slowing-down relatively to the velocity increments 

 of the preceding and following stages. This is seen graphically in 

 Chart No. 18 and is too consistent to have been due to error. The 

 decrease in the velocity of stage 6 caused by a rise in temperature is 

 outstanding and real. This brings within range of profitable experi- 

 mentation work seeking to determine the nature of the forces moving 

 the chromosomes from the equator toward the poles. 



From whatever angle viewed, the problem of the nature of mitotic 

 forces enters the field of physical chemistry, and consequently a more 

 refined analysis of its dynamics is being sought with greatest profit in 

 the realm of this science. Analysis by differential temperature-reac- 

 tions is only one means of attacking the problem, but its possibilities 

 are promising. In a supplementary study^ there were brought together, 

 for the purpose of aiding in the analysis of the mitotic potential, (a) the 

 facts concerning the velocity-reactions to temperature-differences of 

 the several mitotic stages of the growing root-tips of the onion as 

 determined in the present investigation, and (6) data from the experi- 

 ments recorded in scientific literature on the temperature-coefficients of 

 a number of elementary and complex physical, chemical, and physio- 

 logical processes. 



SUMMARY. 



(1) This study sets forth and demonstrates the mathematical and 

 biological soundness of a statistical and cytological method of measur- 

 ing both the relative and absolute durations of the several arbitrarily 

 delimited progress-stages in cell-division. 



(2) The net results of this investigation are given in concise form in 

 the accompanying table (No. 3) ''Principles and formulas for determin- 

 ing the relative and absolute durations of the several mitotic stages," 

 and in the ''Summary Chart," which constitutes the frontispiece and 

 which gives in detail the measurements and ratios found by applying 

 the demonstrated principles to three actual cases, namely, to meas- 

 uring and comparing the duration of the ten active and one resting 

 mitotic stages in the dividing root-tip cells of the common onion 

 {Allium cepa) at 10°, 20°, and 30° C. 



'Laughlin, Harry H. The Dynamics of Cell-Division. Pro. Soc. Exp. Med. and Biol., 

 XV, 8, No. 179 (1357), pp. 117-122. May 1918. 



