100 AMERICAN JOURNAL OF BOTANY [Vol. 8 



of the epicotyl as compared with the mid-region of the hypocotyl, in the 

 trimerous plants. 



This condition furnishes an excellent example of the importance of a 

 knowledge of descriptive morphology as an aid in interpreting biometric 

 constants. 



COMPARISON OF BUNDLE NUMBER IN THE FIVE LINES STUDIED 



From the genetic standpoint it seems a matter of considerable interest 

 to determine whether the three nominally pure lines 12 are differentiated 

 with respect to their vascular anatomy. 



A comparison of the percentage frequency distributions and the figures 

 of the foregoing discussion will convince the reader that certain of the lines 

 may be differentiated either in mean number of bundles, or in variability 

 of number of bundles, or in both average number and variability of bundle 

 number. 



Since we hope to return to this problem later with even more extensive 

 data, it seems unnecessary to consider the differences in the distributions 

 and constants in detail at this time. 



The results of this brief and superficial comparison seem to indicate 

 that while different lines may not differ greatly in respect to certain of their 

 vascular characters they may be differentiated with respect to others. 



SUMMARY 



This paper presents the results of a comparative and biometric study 

 of the gross vascular anatomy of the seedling of Phaseolus vulgaris. 



Two morphological types are considered: the normal, or dimerous 

 seedling with two cotyledons and two primordial leaves, and the trimerous 

 seedling with three cotyledons and three primordial leaves. 



In normal seedlings, the vascular system of the root is typically tetrarcl 

 (with four protoxylem poles), and gives rise in the base of the hypocoty 

 to eight bundles which continue to the cotyledonary node. From the 

 vascular complex at this point two strands are given off to each cotyledoi 

 and six are left, each of which divides into two to produce the typical twelve 

 bundled condition of the epicotyl. 



The trimerous seedlings typically possess six root poles instead of four 

 twelve bundles in the hypocotyl instead of eight, and nine primary epicoty 

 ledonary bundles instead of six. The nine primary epicotyledonary bundle 

 may not all divide, however, so that the number of bundles in the centre 

 region of the epicotyl is variable, ranging in general from fourteen t 

 eighteen. 



12 While the material employed in this study traces its origin from individual plant 

 the possibility of hybridization in the field is not excluded. Thus any comparison whic 

 may be made in this place must be regarded as preliminary merely. 



