POSITION REGRESSION— TERTIARY BRANCHES. 



87 



apparently attained with the production of fewer whorls in the case 

 of tertiaries than in either of the lower-order branches. 



Table 46. — Regression of leaf-number on position in 

 tertiary-branch whorls. 



We have now to consider the question as to whether the differ- 

 entiation of successive whorls which exists here is in accord with the same 

 general type of growth curve which has been demonstrated for the other 

 branches. We can of course say a priori that it is altogether likely 

 that this is the case, but it is desirable to see just what result we get 

 from the actual data, even though they are small in point of numbers. 

 The data are too few to make it worth while to attempt to fit a special 

 curve for them, nor is it necessary to do this to bring out the point. 

 What we wish to find is whether in the case of the tertiaries the rate of 

 increase in mean leaf-number diminishes as the number of whorls formed 

 increases. It is clear that one simple test of this would be to determine 

 whether the ratio between the increments in leaf- number in successively 

 formed whorls diminishes. If it does, then clearly the rate of increase 

 is diminishing. Taking the first four whorls, we have the following 

 absolute increments in mean leaf -number: 



Between first and second whorls 1.522 



Between second and third whorls 933 



Between third and fourth whorls 200 



These yield the following ratios: 



1:522 ~ ^-^^^ 



0:933 = ^-214 



Or we conclude that, so far as we can form any judgment from the 

 present data, the rate of increase in mean leaf-number in tertiary-branch 

 whorls decreases as the number of successively formed whorls increases. 

 Or, in other words, it appears that the differentiation of the whorls on the 

 tertiary branches follows the same law which has been shown to hold for 

 the other axial divisions of the plant. 



