86 



VARIATION AND DIFFERENTIATION IN CERATOPHYLLUM. 



of formation of tertiary-branch whorls. We further note that the 

 correlation between these two characters is distinctly higher in tertiary- 

 branch whorls than in main-stem or primary-branch whorls. The cor- 

 relation coefficient is of about the same order of magnitude for tertiaries 

 as for secondaries, but the correlation ratio (which is the better measure 

 in these cases of skew correlation) is markedly higher for the tertiaries 

 than for secondaries (cf . table 38, supra) . 



Table 44. Comparison of increments in mean leaf-number occurring between every 



ten whorls on (a) the main stem, and (6) primary branches. Series I, II, and III 

 combined. 



The change in mean leaf -number with advance in position is shown 

 in table 46, giving the means of the arrays of table 45. From this table 

 the following points are to be especially noted: 



(a) The tertiary branches start at the first whorl with a lower mean 

 number of leaves than do either primaries or secondaries. 



Table 45. — Correlation between leaf-number and position in whorls 

 on tertiary branches. Series I, II, and III combined. 



(6) The rate of increase in mean leaf -number with successive whorl 

 formation, so far as we can judge from our present material, is much 

 more rapid in the case of the tertiaries than in the other branches. That 

 is, if we regard the production of a high mean leaf-number as the 

 "end" towards which the growth processes are tending, this "end" is 



