METHODS OF EXPERIMENTATION WITH COCKLEBUR 91 



small and should not concern us much at this point in the development 

 of the science. 



The numerical values assigned to the 8 stages happen to be such 

 that when one expresses Floral Stage as a function of time after the 

 dark period, the points approximate nearly straight lines, as shown 

 in Fig. 5-9. Development usually begins about 2^ days after the 



8-0 

 7-0 

 6-0 

 5-0 

 4-0 

 30 

 2-0 

 1-0 



16 hour 

 dark period 



I 2 3 4 5 6 7 8 



DAYS AFTER THE INDUCTIVE DARK PERIOD 



Figure 5-9 

 Floral development curves; Floral Stage as a function of time after in- 

 duction by a 10, 11, or a 16-hr dark period. Some of the points lie un- 

 usually far from the lines for this kind of experiment, but as might be 

 expected (Fig. 3-7) this is most true for the shorter dark periods. 

 Inductive dark periods were initiated on June 12, 1962. Data previously 



unpublished. 



inductive dark period, and the line continues fairly straight up to 

 9 to 12 days, when controls have usually reached the maximum stage. 

 Since the lines are nearly straight (or at least curve in about the same 

 way for various treatments), it is not necessary to measure flowering 

 by following development rate in this way. Stages reached by some 

 arbitrary time after the inductive dark period will be proportional to 

 rate of development of the buds during this time. In our standard 



