HOMOTYPOSLS IX THE VEGETABLE KINGDOM. 
291 
for cross-heredity, ■“ and which appears to be approximately true for that case. We 
shall consider later statistics bearing on tliis result. 
Assuming accordingly that (iv.) holds, we find from (iii.) 
0 -- X Iv = p{t{ci/(r/) + S(/3/a-'/) + 2t{a 
■p^qO'pO'^ 
PQ 
)\ 
^ P 
X cr" by (ii.). 
Hence we conclude that 
= P.(v-)- 
Or: The correlation between brothers will be equal to the rneani correlation beticeen 
the undifferentiated like organs put forth by an individual. 
Now, if this result he true, it is very remarkable and very fundamental. We 
should hardly expect it to he absolutely true, for it is very unlikely that the coefficient 
of correlation between undifferentiated like organs is the same whatever the organs 
may he. This equality may rather he spoken of as belonging to an ideal theoretical 
vital state approaching the actual state, })erhaps, as Boyle’s Law or the perfect fluid 
approach phenomena observed in physical nature. What we should expect woidd 
he a general a])proximation between the values of R and p, and a tendency to equality 
when large series are averaged. Tins is the point which we shall investigate in the 
sixtli section of this paper, after placing before the reader in the fourth section a fairly 
wide! range of actual statistics. 
It will be seen at once that if (v.) rejiresents an approximate or average truth of 
living nature, then the problem of inlieritance is to a large extent the same as the 
proldem of variability in the individual. We have not answered, of course, even in 
part, tlie problem of why two brothers resemble each other, but we see that it is 
part of a much more general problem having nothing to do with sexual reproduction. 
It is one with the problem of the likeness in leaves of the same tree, or the likeness 
in scales on the same spot of a moth’s wing. It brings the prolflem of heredity into 
closer touch with the problem of variability. When we ascertain the sources of 
variation in the individual, then we sliall liave liglit on the problem of fraternal 
resemblance. 
III. On the Variability and Correlation of Undifferentiated like Organs 
IN THE InDIYIDLTAL. 
(3.) I must frankly admit tliat I have collected my material from the standpoint of 
the mathematical statistician and not of the trained field naturalist. I have sought 
things which were easy to count and measure, and endeavoured to avoid “ differentia- 
* “ The Law of Ancestral Ilererlity,” ‘ Roy. Soc. Proc.,’ vol. 62, p. 411. 
t Not wide when we regard the natural range of living forms, hut fi'om the standpoint of the laboui' 
that has been spent on the collection. 
2 P 2 
