Variation and Heredity 265 
We may also study those cases in which a particular 
organ is repeated a number of times in the same individual, 
as are the leaves of a tree. If the leaves of the same tree are 
examined in respect, for example, to the number of veins that 
each contains, we find that the number varies, and that the 
results give a variation polygon exactly like that when differ- 
ent individuals are compared with one another. Let us take 
the illustration given by Pearson. He counted the veins on 
each side of the midrib of the leaves of the beech. If a 
number of leaves be collected from one tree, and the same 
number from another, and if all those having fifteen veins are 
put in one vertical column, and all those with sixteen in an- 
other, as shown in the following table, it will be found that 
No. of Veins . .| Io} 11} 12/13] 14) 15 | 16] 17| 18} 19| 20| a1 | 22 
First Tree. . .{|—]/—/]—j}—|/—] 1] 4] 7] 9] 4} 1}/—J— 
Second Tree . .{—|—/—]| 3] 4] 9] 8} 2]/—J—|—!—|— 
each tree has a mode of its own. Thus in the first tree the 
mode is represented by nine individuals having eighteen 
veins, and in the second by nine individuals having fifteen 
veins. So far as this character is concerned we might have 
interchanged certain of the individual leaves, but we could 
not have interchanged the two series. They are zxdividual 
to the two trees. Now in what does this individuality con- 
sist? Clearly there are most leaves in one tree with eighteen 
ribs, and most in the other with fifteen ribs. 
If we contrast these results with those obtained by picking 
at random a large number of leaves from different beech trees, 
we have no longer types of individuals, but racial characters. 
Pearson has given the following table to illustrate these points: 
FREQUENCY OF DIFFERENT TYPES OF BEECH LEAVES 
No. of Veins} to} 11] 12] 13 | 14 | 15 | 16] 17 | 18 | 19 | 20] 21 | 22 
(Frequency | 1 | 7 | 34] 110) 318] 479 | 595 | 516 | 307 | 181 | 36/15 | 1 
