[Reprinted front the AMERICAN JOURNAL OF BOTANY, 2: 63-102. February, 



VASCULAR ANATOMY OF DIMEROUS AND TRIMEROUS 

 SEEDLINGS OF PHASEOLUS VULGARIS 



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 

 lants have been purely descriptive in character. As a result of observation, 

 he typical or average condition of plant structures has been recorded in 

 erms which are general and often indefinite. Comparatively few morpho- 

 ogical papers deal with the problem of the variation of the structures under 

 -.onsideration, treat of their correlations with one another, or even present 

 ;he 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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