AMERICAN 
JOURNAL OF BOTANY 
Vol. VIII October, 1921 No. 8 
THE VASCULAR ANATOMY OF HEMITRIMEROUS SEEDLINGS 
OF PHASEOLUS VULGARIS 
J. Arthur Harris, Edmund W. Sinnott, John Y. Pennypacker, and G. B, Durham 
(Received for publication January 17, 192 1) 
Introductory 
In an earlier paper^ we discussed the gross vascular anatomy of dimerous 
and trimerous seedlings of the garden bean. By dimerous seedlings we 
understand those of the normal type, characterized by two cotyledons and 
two primordial leaves, both sensibly opposite in insertion. By trimerous 
we mean those which have a whorl of three cotyledons and three primordial 
leaves. The cotyledons may be, and frequently are, more or less irregular 
in insertion. The primordial leaves are, in the seedlings considered, inserted 
in a regular whorl. 
In addition to these two types of seedlings, those which are in a sense 
intermediate in superficial structure between the two types hitherto studied 
may occur. These are seedlings with a whorl of three cotyledons but with 
a normal pair of primordial leaves instead of three as in the case of trimerous 
seedlings. These we have called hemitrimerous. They are extremely rare 
in occurrence, but during the four years during which these studies have 
been under way a number sufficiently large to justify a brief discussion of 
their gross vascular anatomy has been secured. 
Our purpose in this paper is to compare the anatomy of these hemi- 
trimerous seedlings with the trimerous seedlings (in common with which 
they have three cotyledons) on the one hand and with dimerous seedlings 
(in common with which they have two primordial leaves) on the other. 
For convenience of reference the three types will in some cases be 
designated by the number of cotyledons and primordial leaves: 2-2 = dim- 
erous, 3-3 = trimerous, and 3-2 = hemitrimerous. 
Materials 
The hemitrimerous plants and the trimerous and dimerous seedlings 
with which they are compared were largely secured in the series of germina- 
^ Harris, J. Arthur, Sinnott, E. W., Pennypacker, J. Y., and Durham, G. B. The 
vascular anatomy of dimerous and trimerous seedlings of Phaseolus vulgaris. Amer. 
Jour. Bot. 8: 63-102. 192 1. 
[The Journal for July (8: 323-374) was issued August 31, 1921] 
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