84 BIOMETRY 
the species A and C have each a characteristic mean 
size of fruit, and the existence of this definite mean 
is not affected by the fact that the range of variation 
FIG 2. 
overlaps in all three cases. Species B, on the other 
hand, seems to show signs of division into at least two 
separate groups. 
Differences of a similar kind are sometimes to be 
found among the progeny of the same individuals. 
Races of garden peas may be selected which, amongst 
other differences, are characterized by the presence of 
large and of small seeds respectively. In each case 
there is variation of a normal kind about a mean value, 
but in each case the mean is quite distinct. There is 
evidence that if a race of large-seeded peas is crossed 
with a small-seeded variety, and the resulting cross-bred 
plants are self-fertilized, their progeny in the second 
generation will be separable into different groups, and 
some of these will show almost exactly the same size 
