40 



VARIATION AND DIFFERENTIATION IN CERATOPHYLLUM. 



compared with main-stem whorls have on the average nearly one less 

 leaf to the whorl, and are relatively 20 to 80 per cent more variable. 



The analytical consideration of the variation in primary-branch whorls 

 will be taken up later in connection with the secondary-branch distri- 

 butions. 



It is shown in this section that ivhorls on primary branches are as a 

 class differentiated from whorls borne on the main stem. As we pass 

 from main-stem whorls to primary-branch ivhorls the mean number of 

 leaves in the whorl decreases and the variability increases. 



VARIATION IN WHORLS ON SECONDARY BRANCHES. 



The frequency distributions for the variation in leaf-number in this 

 portion of the plant are given in table 17. 



Table 17. — Frequency distributions for variation in leaf-number in whorls on 



secondary branches. 



It is apparent from the totals of this table that secondary branches 

 (in the present material at least) contribute less than half as many 



