2 

 [Reprinted from the AMERICAN JOURNAL OF BOTANY, 8: 425-44^. November, 1921.] 



THE INTERRELATIONSHIP OF THE NUMBER OF 



THE TWO TYPES OF VASCULAR BUNDLES 



IN THE TRANSITION ZONE OF THE 



AXIS OF PHASEOLUS VULGARIS 



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

 (Received for publication January 17, 1921) 



INTRODUCTORY 



In papers 1 on the anatomy of dimerous 2 and trimerous and of hemi- 

 imerous seedlings we have shown that Phaseolus vulgaris is characterized 

 y a structure of the vascular system at the base of the hypocotyl which 

 , rather infrequent in seedling anatomy in general. This is the presence 

 f a variable number of accessory bundles which usually lack protoxylem 

 tements. These are the &quot;Zwischenstrange&quot; of Dodel. We have elsewhere 

 ailed them intercalary bundles. They may make their appearance in 

 ie upper part of the root or in the lower region of the hypocotyl, some 

 :sing blindly below and others originating by division of a primary double 

 undle. These intercalary strands may be distinguished from the other 

 undies with perfect certainty because of their position and of the absence 

 dthin them of any protoxylem elements. 



In another place 3 we have dealt with the correlations between the 

 umber of bundles at different levels in the seedling, that is, the relationship 

 etween the vascular system at the base of the hypocotyl and that in the 

 entral region of the hypocotyl and epicotyl, and between the bundle 

 ystem in the hypocotyl and that in the epicotyl. Our present problem is 

 o consider the interrelationships between the two types of bundles present 

 n the hypocotyl just above the region of transition from root to stem struc- 

 ures, and between each of these types and the total number of bundles 

 a this zone. 



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. Jour. 

 Jot. 8: 63-102. 1921. The vascular anatomy of hemitrimerous seedlings of Phaseolus 

 ulgaris. Amer. Jour. Bot. 8: 375-381. 1921. 



2 Dimerous seedlings have 2 cotyledons and 2 primordial leaves; trimerous seedlings 

 lave 3 cotyledons and 3 primordial leaves; and hemitrimerous seedlings have 3 cotyledons 

 .nd 2 primary leaves. 



3 Harris, J. Arthur, Sinnott, E. W., Pennypacker, J. Y., and Durham, G. B. Correla- 

 ions between anatomical characters in the seedling of Phaseolus vulgaris. Amer. Jour. 

 3ot.8: 339-365- 1921. 



[The Journal for Octobsr (8: 375-424) was issued Novembar 14, 1921]. 



425 



