114 HARRIS AND AVERY: MORPHOLOGICAL VARIATIONS 



In each of the types of abnormality dealt with the abnoi a] 

 series show a higher proportion of the individuals with two or t ee 

 leaves at the third node than do their normal controls. 



Furthermore, seedlings showing different types of abnormity 

 at the first nodes also differ among themselves in the exter of 

 abnormality at the third node. Thus plants which are noi al 

 except for slight separation of the cotyledons have two or t ee 

 leaves at the second node instead of the single leaf normally fcid 

 in 5.63 percent, of the individuals. Plants with the cotylems 

 more widely separated have 7.63 per cent, of their numberwith w 

 or three instead of a single leaf. 



When one turns to the groups of plants which have threi n- 

 stead of two cotyledons, a conspicuous difference is at once appa: it. 

 Plants which have three cotyledons and a normal pair of primo ial 

 leaves produce two or three instead of a single leaf at the 1 rd 

 node in 27.31 per cent, of the cases. Seedlings with three c y- 

 ledons and a whorl of three primordial leaves instead of the no ial 

 pair at the third node have 32.29 per cent, of the individuals th 

 two or three leaves at the third node. 



Heretofore the number of leaves inserted at the third node as 

 furnished the only measure of variation at this region of the is. 

 We now propose to consider variation in the organization ol he 

 leaves themselves. It will not be possible to do this in the d ail 

 *n which we hope to treat the problem ultimately. The ran$ of 

 variation in the division of the bean leaf is rather great, anc he 

 laws governing it are doubtless very complicated. Some propss 

 has already been made on the problem, but for the present we all 

 limit our discussion to the number of leaflets, leaving the prol :m 

 of their arrangement for treatment when even larger series of .ta 

 are at our disposal. 



The actual frequencies of number of leaflets per leaf prod ed 

 at the third node are shown in TABLE VI. 



The most conspicuous feature of this table is the biralal 

 nature of the distribution. The modes are on three and six, is 

 to be expected from the fact that the distribution of the \ule 

 number of leaflets depends upon plants with from one to t ee 

 leaves at the third node. 



Because of the wide range of variation in leaflet number i 





