n The key situation into which the 

 situation b, that actually found in mitosis 

 in onion root-tip cells, tends to be corrected 

 by means of the P. I. The condition-com- 

 plex of Type IV is the one analyzed in the 

 method chart (Chart No. 1) because of this 

 direct appUcabiiity to the case in hand. 



For meaning of formulas see table No, 3, 

 "Principles and Formulas." 



stage-d urations) 



Notes: 



1. Only when M. I. is constant (but regardless of variation i 

 S. I. of a given stage in a given observation ocA. R. D. in a single sample. 



2. £ S. I. for the same stages is always cc A. R. D., regardless of variation i 

 stage duration or constancy in M. I. 



3. Jamming is the confusion of the orderly processions of S. I. which results when one fluc- 

 tuation in M. I. follows another so closely that a considerable percentage of cells beginning 

 mitosis in the first fluctuation have finished so small a portion of the cycle that the same 

 stage in both the first and second waves is recorded in the same time interval. The shortening 

 of observation -intervals tends to diminish, but can not totally correct, this difficulty. 



4. The amount of fluctuations in M. I. is not essential (however, the greater and more sudden 

 the fluctuation the easier the determination) to determining absolute duration by the P. I . method, 

 but the time intervening between pulsations (i. e., changes in M. I.) is very important — relatively 

 long intervals simplifying, relatively short intervals complicating, the determination. 



