52 



VARIATION AND DIFFERENTIATION IN CERATOPHYLLUM. 



in general marked agreement between the variation constants of plants 

 which have similar percentage constitutions in respect to number of 

 whorls. Thus, to take only a single example, we see from table 25 that 

 plant 2 of Series I, and plant 1 of Series II, have very nearly the same 

 percentage constitutions, although they are very different in abso- 

 lute size. Table 2 shows that their variation constants are likewise in 

 remarkably close agreement. This is of course what we should expect 

 from our result that whorls on different portions of the plant form 

 differentiated classes, and the fact that experience accords so closely 

 with expectation is strong corroborative evidence, if any be needed, 

 of the truth of our previous conclusions. 



Table 28. — Frequency distributions for size of tertiary branches. 



We may turn now to the question of variation in the size of the 

 different axial divisions of the plant. In dealing with this phase of the 

 subject, the number of whorls on any division of the plant will be taken 

 as the measure of its size. For our present purpose this is a more 

 satisfactory measure than absolute length would be. What we wish to 

 determine is the mira-plant variability in respect to size of branch. 

 In the analysis of the morphogenetic processes which will be taken up 

 in a later section of the paper, it will be necessary to have some quan- 

 titative appreciation of how the branches of different orders compare in 

 size, and what degree of variation in size they exhibit. We may turn 

 at once to the data. The data respecting size of main stem have already 

 been given in tables 5, 11, and 12. In table 26 (p. 50) is given for each 

 plant, the frequency of primary branches of different sizes (i. e,, con- 

 taining different numbers of whorls). In tables 27 (p. 51) and 28 are 

 given in the same way the frequencies of secondary and tertiary branches 

 of different sizes. 



As was to be expected, the range of variation in the number of whorls 

 to the branch is very large for the primary branches, and distinctly less 



