350 
PROFESSOli K. PEARSO^' AXl) OTHERS OX 
Aljsolute Dimensions of Wild Ivy Leaves. 
Character. 
Mean. 
8.1). 
Coefficient 
of variation. 
8.1). of 
array. 
Perceirtage 
variation. 
Correlation. 
1 
i 
Length. . ■ 
Breadth . 
10-9504 + -0457 
13-2148 ± -0323 
3- 3885 ± -0612 
4- 5384 ± -0433 
30-9442 
34-3430 
2- 8033 
3- 8376 
82-73 
84-56 
-5618 [+ -0092' 
-5332 [± -0096; 
Cross-Correlations. 
Length and breadth, organic 
-8718 + -0032 
Length and breadth, homotypic 
-5157 [±-0099] 1 
These results differ very considerably from those for the mushroom gills. The 
coefficients of variation are even higher than those for the gills, and I think this is a 
result of a certain amount of heterogeneity, as well as of the leaves on individual 
runners not being all quite at the same stage of development. In the case of the 
deciduous trees the leaves were gathered in the fall of the year, and no further 
development of veins was possible ; hut in the ivy leaves, taken indeed at the same 
time, the equal development of all the leaves taken from the runner could hardly have 
been reached when they were gathered. On the other hand the correlations are much 
lower than in the case of tlie gills,—much more within the range of the results 
obtained for other characters. I am inclined to think, therefore, that there has been 
some balancing of o})posing factors here, heterogeneity due to locus of collection and to 
stages of growth being to some extent counteracted by a differentiation due to position 
of the leaf on the runner.* I have not included these results for lengths and breadths 
of ivy leaves in my homotypic series because the values, although well within the 
range of the other determinations, appear to me to be somewhat fictitiously so. The 
disturbing factors referred to above seem to me to have also given the cross homotypic 
correlation a higher value tlian it ought to have. It will be seen that the correlation 
of length and breadth of pairs of leaves from the same runner is almost as high as that 
of the breadths of pairs of leaves from the same runner. I should expect a consider- 
ably greater inequality. I regret that the great labour of these cross-correlation 
investigations has hindered their being carried further than these two cases in the 
vegetable kingdom, but in the zoological data, which we have at present in hand, I hope 
to get material less o})en to criticism than in the cases of mushroom gills and ivy leaves. 
I’hese two series were originally undertaken witli the view of ascertaining how far 
the use of indices would cancel the influence of the factor of growth. As we have 
* The reader must of course bear in mind that the leaves were taken from runners which had not 
reached the tops of their walls or trees, i.e., they were not from reproductive shoots. 
