THE VASCULAR ANATOMY OF DIMEROUS AND TRIMEROUS 
SEEDLINGS OF PHASEOLUS VULGARIS 
J. Arthur Harris, Edmund W. Sinnott, John Y. Pennypacker, and G. B. Durham 
(Received for publication August 21, 1920) 
Introductory 
The great majority of investigations dealing with the anatomy of 
plants have been purely descriptive in character. As a result of observation, 
the typical or average condition of plant structures has been recorded in 
terms which are general and often indefinite. Comparatively few morpho- 
logical papers deal with the problem of the variation of the structures under 
consideration, treat of their correlations with one another, or even present 
the detailed measurements which might serve for the solution of such funda- 
mental morphological problems. 
The older comparative morphology is indispensable. It provides a 
general knowledge of plant structures and serves as a basis for the classi- 
fication of the vegetable kingdom. The recognition that description must 
be supplemented by the results of experimentation has, however, led to the 
establishment of the newer special science of experimental morphology. 
The time has come to extend still further our study of plant form by calling 
to the service of vegetable morphology the methods of measurement and 
mathematical analysis. These methods are particularly useful in an attack 
upon the fundamental problems of morphogenesis. It is by measuring 
exactly the various plant structures during their successive stages of develop- 
ment, in terms of size or number; by determining their relative variability 
in different organs or regions of the plant, or under varying external con- 
ditions, and by discovering such correlations as exist, both among the 
structures themselves and between them and their progenitors and their 
environment, that we shall be able to build up a body of fact on which 
morphogenetic theory may rest. 
The present paper gives a portion of the results of a biometric analysis 
of a comparatively simple morphological problem, that of the gross vascular 
anatomy of certain normal and abnormal bean seedlings. Our purpose 
has been: 
1. A study of the vascular anatomy of normal and of abnormal seedlings 
from the point of view of descriptive morphology — a preliminary which we 
believe to be essential to a sound interpretation of any statistical results. 
2. A statistical study of the number and variation of the vascular 
elements in different regions of the seedling. 
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