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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^^ 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 tetrarch 
(with four protoxylem poles), and gives rise in the base of the hypocotyl 
to eight bundles which continue to the cotyledonary node. From the 
vascular complex at this point two strands are given off to each cotyledon 
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 bundles 
may not all divide, however, so that the number of bundles in the central 
region of the epicotyl is variable, ranging in general from fourteen to 
eighteen. 
12 While the material employed in this study traces its origin from individual plants, 
the possibility of hybridization in the field is not excluded. Thus any comparison which 
may be made in this place must be regarded as preliminary merely. 
