CONTENTS. 



Summary chart Frontispiece 



Index to charts, diagrams, and tables 4 



roof of principle : Hypothetical case 6 



Applicability of plan 7 



Stage index 9 



Mitotic stage duration and time-complex found in dividing root-tip cells of the onion. 9 



Formula for determining the average relative duration of a given mitotic stage 9 



Procession index 11 



Mitotic synchronization in homologous tissue-samples 13 



Cautions in method 13 



Adequacy of the procession index 14 



Formula for the average absolute duration of a given mitotic stage 15 



Measure of accuracy 16 



PreUminary experiments 18 



Average relative durations of the several mitotic stages; PreUminary experiments .... 18 



Probable errors 19 



Other sources of possible error 21 



Average absolute durations of the several mitotic stages: PreUminary experiments. ... 22 

 Experiments to determine the effects of temperature increments upon the several 



mitotic stages 24 



The velocity of chemical reactions: Response to temperature differences 24 



Material for the experiments 25 



Apparatus : Thermostat 26 



Sampling and counting 27 



Further development of the statistical method 29 



a. Probable errors 29 



6. Procession index 30 



c. Coefficient of mitotic homogeneity 30 



Further analysis of the dynamics of mitosis by the stage-timing method 30 



a. Quantitative increase in data 30 



b. Effects of agents other than temperatiu:e 31 



c. Possible mitotic models 31 



d. Cell-division in development 31 



e. Relation of mitosis to other activities 31 



Results and discussion 31 



A. Rhythm in mitosis 32 



(a) General 32 



(6) Ward's work 33 



(c) Additional evidence ■ 33 



(d) Summary of evidence of mitotic periodicity 34 



B. Heat factor in growth 35 



(o) General 35 



(6) Phenology 35 



C. Nature of the complex in growth and mitosis 36 



D. Physico-chemical aspect 37 



(a) IndividuaUty in velocity reactions of the several mitotic stages to the 



same temperature changes 37 



(6) van't Hoff's law 39 



(c) Isolation of factors 40 



Elimination by comparative experimental evidence 40 



A single index for two factors 41 



8 



