292 
PROFESSOR K. PEARSON AND OTHERS ON 
tion ” only Ey tlie roughest tests and by largely untrained powers of observation. I 
have examined my material to see if it gave obvious signs of heterogeneity in the 
tabidated l)ulk. I liave examined my individuals and their organs for obvious out- 
rvard signs of differentiation. But I have not studied the morphological evolution 
of the organs considered, or questioned whether the parts counted were all due to the 
saine source. Hence it is quite jJossible that the botanist may reject at once some of 
my series. Wliat I have endeavoured to do is to take as wide a range of as different 
organs as possible in different types of life and trust to the bulk of my statistics to 
give me a substantially accurate average value of p to compare with the values of B 
we liave determined on other occasions. At the same time the material here pre¬ 
sented does not by any means exhil)it all the trials made ; we often enough at the first 
attempt did not get a suitable character to measure or count, or again the individuals 
collected were occasionally insufiicient. Nothing, however, has been omitted which 
was unfirvourable to the conclusions idtimately drawn. Thus the Nigella Ilispanica 
statistics have been retained, although there is not the slightest doubt of a verv 
considerable difterentiation in the flowers growing at different parts of the plant. 
When such a differentiation takes place the i-esult will generally be a great reduc¬ 
tion in the correlation ; for “ like ” organs on the same individual, say A and a if 
difterentiated, will really be less closely related to each other than to B and h respec¬ 
tively, the corresponding organs in a second individual. On the other hand a 
heterogeneity of material, say a mixture of two ditierent local races, will tend as a 
rule to raise the correlation,^' for it generally amounts to compounding two very 
like correlation surfaces with the mean of one approximately shifted along the 
regression line of the second. If we bear these two opposing influences in mind, 
differentiation tending to reduce, heterogeneity to increase the actual degree of corre¬ 
lation of undifferentiated like organs, it will not seem incompatible with an actual 
approximate constancy of such correlation to find a fairly wide range of values in our 
statistics. We set them forth as the first rough attempt to appreciate the resem- 
])lance of like })arts within the individual. To the specialist in the future must be 
left the work of selecting, with special knowledge, truly homogeneous material and 
absolutely undifferentiated characters, and thus obtaining the required correlation to 
a much higher degree of accui'acy. 
(4.) It remains to explain the process by which the correlation was deduced. Let 
us take as an illustration heech-leaves. One hundred trees fairly of the same age and 
belonging to the same district, were selected, and twenty-six leaves specified by the 
letters of the al})habet were gathered from each of these. The leaves were gathered 
so far as possilfie all round the outside of the tree, roughly about the same height from 
the ground, and scattered over dlflerent parts (fi’ the individual boughs. Thus each 
tree was supposed to be individualised by twenty-six leaves. The veins on these leaves 
were then counted, and varied for heech-leaves in general between ten and twentv-two. 
See ‘Phil. Trans.,’ A, vol. 192, p. 277. 
