f Reprinted from the AMERICAN JOURNAL OF BOTANY, 8: 375-381 October, 1921.] 



HE VASCULAR ANATOMY OF HEMITRIMEROUS SEEDLINGS 

 OF PHASEOLUS VULGARIS 



ij. ARTHUR HARRIS, EDMUND W. SINNOTT, JOHN Y. PENNYPACKER, AND G. B. DURHAM 

 (Received for publication January 17, 1921) 



INTRODUCTORY 



In an earlier paper 1 we discussed the gross vascular anatomy of dimerous 

 nd trimerous seedlings of the garden bean. By dimerous seedlings we 

 nderstand those of the normal type, characterized by two cotyledons and 

 NO primordial leaves, both sensibly opposite in insertion. By trimerous 

 te mean those which have a whorl of three cotyledons and three primordial 

 iaves. The cotyledons may be, and frequently are, more or less, irregular 

 i insertion. The primordial leaves are, in the seedlings considered, inserted 

 i a regular whorl. 



In addition to these two types of seedlings, those which are in a sense 

 itermediate in superficial structure between the two types hitherto studied 

 lay occur. These are seedlings with a whorl of three cotyledons but with 

 normal pair of primordial leaves instead of three as in the case of trimerous 

 2edlings. These we have called hemitrimerous. They are extremely rare 

 i occurrence, but during the four years during which these studies have 

 een under way a number sufficiently large to justify a brief discussion of 

 heir gross vascular anatomy has been secured. 



Our purpose in this paper is to compare the anatomy of these hemi- 

 rimerous seedlings with the trimerous seedlings (in common with which 

 hey 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 

 lesignated by the number of cotyledons and primordial leaves: 2-2 = dim- 

 rous, 3-3 = trimerous, and 3-2 = hemitrimerous. 



MATERIALS 



The hemitrimerous plants and the trimerous and dimerous seedlings 



rith which they are compared were largely secured in the series of germina- 



1 Harris, J. Arthur, Sinnott, E. W., Pennypacker, J. Y., and Durham, G. B. The 



ascular anatomy of dimerous and trimerous seedlings of Phaseolus vulgaris. Amer. 



our. Bot. 8: 63-102. 1921. 



[The Journal for July (8: 323-374) was issued August 31, 1921] 



375 



