114 Harris AND AVERY: MORPHOLOGICAL VARIATIONS 
In each of the types of abnormality dealt with the abnormal 
series show a higher proportion of the individuals with two or three 
leaves at the third node than do their normal controls. 
Furthermore, seedlings showing different types of abnormality 
~ at the first nodes also differ among themselves in the extent of 
abnormality at the third node. Thus plants which are normal 
except for slight separation of the cotyledons have two or three 
leaves at the second node instead of the single leaf normally found 
in 5.63 per cent. of the individuals. Plants with the cotyledons 
more widely separated have 7.63 per cent. of their number with two 
or three instead of a single leaf. 
When one turns to the groups of plants which have three in- 
stead of twocotyledons, a conspicuous difference is at once apparent. 
Plants which have three cotyledons and a normal pair of primordial 
leaves produce two or three instead of a single leaf at the third 
node in 27.31 per cent. of the cases. Seedlings with three coty- 
ledons and a whorl of three primordial leaves instead of the normal 
pair at the third node have 32.29 per cent. of the individuals with 
two or three leaves at the third node. 
Heretofore the number of leaves inserted at the third node has 
furnished the only measure of variation at this region of the axis. 
We now propose to consider variation in the organization of the 
leaves themselves. It will not be possible to do this in the detail 
in which we hope to treat the problem ultimately. The range of 
variation in the division of the bean leaf is rather great, and the 
laws governing it are doubtless very complicated. Some progress 
has already been made on the problem, but for the present we shall 
limit our discussion to the number of leaflets, leaving the problem 
of their arrangement for treatment when even larger series of data 
are at our disposal. 
The actual frequencies of number of leaflets per leaf produced 
at the third node are shown in TABLE VI. 
The most conspicuous feature of this table is the bimodal 
nature of the distribution. The modes are on three and Six, as is 
to be expected from the fact that the distribution of the whole 
number of leaflets depends upon plants with from one to three 
leaves at the third node. 
Because of the wide range of variation in leaflet number it is 
