Oct., 1921] 
HARRIS AND OTHERS PHASEOLUS VULGARIS 
381 
the six lines the average number of bundles in the epicotyl is significantly 
lower in the hemitrimerous than in the trimerous seedlings, and (probably) 
significantly higher in the hemitrimerous than in the dimerous seedlings. 
In epicotyledonary structure the hemitrimerous seedlings occupy as a 
matter of fact almost exactly an intermediate position between the dimerous 
and the trimerous types. 
Summary 
The purpose of this paper is a comparison of the gross vascular anatomy 
of hemitrimerous seedlings of Phaseohts vulgaris with those which are 
trimerous and those which are dimerous. By dimerous seedlings we under- 
stand those with two cotyledons and two primordial leaves, by trimerous 
seedlings those with three cotyledons and three primordial leaves, and by 
hemitrimerous seedlings those with three cotyledons and two primordial 
leaves. The hemitrimerous is, therefore, intermediate in external form 
between the dimerous and the trimerous seedling. In the internal structure 
of the axis at the transition zone, which here occurs at the base of the 
hypocotyl, the hemitrimerous seedling is clearly differentiated from the 
trimerous type by a slightly smaller average number of primary double 
bundles, and possibly by a slightly larger number of intercalary bundles. 
The total number of bundles in the basal region of the axis of hemitrimerous 
seedlings is not sensibl}^ different in hemitrimerous and trimerous plantlets. 
The hemitrimerous are conspicuously differentiated from the dimerous 
seedlings by a larger number of primary double bundles and a larger total 
number of bundles. On the basis of the data available they cannot be 
asserted to differ significantly from the dimerous plants in the number of 
intercalary bundles. 
In the central region of the hypocotyl, the vascular anatomy of the 
hemitrimerous seedling conspicuously exceeds that of the dimerous in 
bundle number but agrees very closely indeed with that of the trimerous 
plantlet, although it may have a slightly lower average number of bundles. 
In the central region of the epicotyl the mean number of bundles in the 
hemitrimerous seedling is, roughly speaking, intermediate between that 
of the trimerous and that of the dimerous types. 
Recapitulating, it appears that in internal structure the hypocotyl of 
the hemitrimerous seedling is practically identical with that of the trimerous 
seedling with which it has in common a whorl of three cotyledons. The 
epicotyledonary internode in the hemitrimerous seedling, limited by a 
trimerous cotyledonary and a dimerous primordial node, is intermediate in 
anatomy between the trimerous type with three cotyledons and three 
primordial leaves and the dimerous type with two cotyledons and two 
primordial leaves. 
