Oct., 1921] HARRIS AND OTHERS PHASEOLUS VULGARIS 381 



\ the six lines the average number of bundles in the epicotyl is significantly 

 Bower 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 



iiul the trimerous types. 



SUMMARY 



The purpose of this paper is a comparison of the gross vascular anatomy 

 of hemitrimerous seedlings of Phaseolus 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 sensibly 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. 



