MENDEL'S LAWS OF ALTEENATIYE 
INHERITANCE IN PEAS. 
By W. F. R. WELDON. 
[Received December 9, 1901.] 
If two plants, or two animals, of different characters be allowed to breed 
together, the parental characters may affect the offspring in any one of three ways. 
In the most usual case, the characters by which the parents differ may appear so 
intimately blended in the offspring that each young animal or plant appears 
intermediate in character between its parents, but it is not generally possible for 
us at present to resolve its body into separate elements, some of which resemble 
one parent, and some the other. In other cases, however, the body of the young 
is easily divisible into regions, in some of which the character of one parent is 
presented in a recognisable and often apparently unaltered state, while the rest of 
the body presents a similar resemblance to the other parent. In the cases of the 
third class the body of the offspring may entirely I'esemble that of one parent, the 
characters of the other being apparently unrepresented. While it is perfectly 
possible and indeed probable that the difference between these three forms of 
inheritance is only one of degree, it is still convenient to discuss them separately. 
The work of Galton (No. 13) and Pearson (No. 24) has given us an expression 
for the effects of blended inheritance which seems likely to prove generally 
applicable, although the constants of the equations which express the relation 
between divergence from the mean in one generation and that in another may 
requii-e modification in special cases. Our knowledge of particulate or mosaic 
inheritance, and of alternative inheritance, is however still rudimentary, and 
there is so much contradiction between the results obtained by different observers, 
that the evidence available is difficult to appreciate. It is the purpose of this 
essay to describe .some cases of alternative inheritance, which have lately excited 
attention, and to discuss the contradictory evidence concerning them. 
