HOMOTYPOSIS IN THE VEGETABLE KINGDO^M. 
287 
according to their position on the wing ; tliere may be two or more classes of IjL^od- 
corpuscles. But if we take organs which are like, and so far as we can judge 
undilierentiated, there is still a ditfereiice between them. The individual in putting 
forth what I may perhaps term “ unclilferentiated like organs,”'^" does so with a certain 
measure of variability. I am not concerned at present with the source of tliis 
variability. It may be due to the individual environment, to tlie physique of the 
individual, or to some iidiereiit or bathmic tendency in the Individual due to its 
ancestral history. All I am concerned with at present is, that the undilferentiated 
like organs of an individual possess a certain variability, and that this varial)ility is 
somewhat less than that of all like organs in the race. If, however, the variability 
were entirely due to external circumstances attending growth, we shoidd hardly 
expect to find leaves gathered from different branches and on different sides of a tree 
more alike to each other than to leaves of other trees of the same race. But this is 
indeed the case ; there is a considerable correlation among the undifferentiated like 
organs of an individual notwithstanding the small reduction on racial variability. 
Among the trees and plants considered in this paper we liave data enough to enable 
us to determine whether, say, a hundred leaves placed before us were gatliered from 
a single tree, or collected at random from a number of trees. Here, of course, I mean 
by to “ determine” to state the odds for or against these two assumptions. 
Just as we can find by the methods already discussed in earlier memoirs of this 
series, the degree of correlation between brothei's and the varialjility of an array of 
brothers due to the same parentage, so we can determine tlie correlation, ie., the 
degree of resemblance between the undifferentiated like organs of the individual and 
the degree of variability within the individual. This determination is the answer to 
our first fundamental problem, that of the ratio of individual to racial variability. 
But turning to the })rocess of reproduction, the oTspring depend upon the parental 
jerms, and it would thus seem that the degree of resemblance between offspring 
* [I am fully conscious of cerhal difficulty in the phrase “ undifferentiated like organs,” Init I believe 
that the distinction between the differentiated and the undifferentiated is fpiite clear either from the 
standpoint of observation or from that of the frecpiency distribution itself. Differentiation, whether due 
to function, position on the individual, season of production, Ac., is usually connected with one or two 
well-marked dominating factors ; it is statistically discoverable by testing the frequency distiibution for 
heterogeneity. On the other hand, variability in “ undifferentiated like oi'gans ” is not to be associated 
with any one or two dominating factors which can be isolated; it is due to that combination of many 
small causes, inherent and environmental, which leads to what is familiar in both theory and observation 
as a homogeneous chance distribution. A diversity due to differentiation and a variability due to chance 
are quite distinct things. The one is the result of dominating factors which can be isolated and 
described; the other of a great number of small factors, varying from organ to organ, and incapable of 
being defined or specified. Indeed, upon each dominating factor of differentiation is superposed such a 
chance variability. Of course all things which differ even by chance variation are in a certain sense 
differentiated. But the term differentiation is throughout this paper reserved for the differences which 
arise, not from a multiplicity of small causes, but from dominating and usually easily recognisable single 
influences.—Tab/, 1901.] 
