AMERICAN 
JOURNAL OF BOTANY 
Vol. VIII November, 1921 No. 9 
THE INTERRELATIONSHIP OF THE NUMBER OF 
THE TWO TYPES OF VASCULAR BUNDLES 
IN THE TRANSITION ZONE OF THE 
AXIS OF PHASEOLUS VULGARIS 
J. Arthur Harris, Edmund W. Sinnott, John Y. Pennypacker, and G. B. Durham 
(Received for publication January 17, 1921) 
Introductory 
In papers^ on the anatomy of dimerous^ and trimerous and of hemi- 
trimerous seedlings we have shown that Phaseolus vulgaris is characterized 
by a structure of the vascular system at the base of the hypocotyl which 
is rather infrequent in seedling anatomy in general. This is the presence 
of a variable number of accessory bundles which usually lack protoxylem 
elements. These are the ''Zwischenstrange" of Dodel. We have elsewhere 
called them intercalary bundles. They may make their appearance in 
the upper part of the root or in the lower region of the hypocotyl, some 
rising blindly below and others originating by division of a primary double 
bundle. These intercalary strands may be distinguished from the other 
bundles with perfect certainty because of their position and of the absence 
within them of any protoxylem elements. 
In another place^ we have dealt with the correlations between the 
number of bundles at different levels in the seedling, that is, the relationship 
between the vascular system at the base of the hypocotyl and that in the 
central region of the Jiypocotyl and epicotyl, and between the bundle 
system in the hypocotyl and that in the epicotyl. Our present problem is 
to consider the interrelationships between the two types of bundles present 
in the hypocotyl just above the region of transition from root to stem struc- 
tures, and between each of these types and the total number of bundles 
in this zone. 
1 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 vascular anatomy of hemitrimerous seedlings of Phaseolus 
vulgaris. Amer. Jour. Bot. 8: 375-381. 192 1. 
2 Dimerous seedlings have 2 cotyledons and 2 primordial leaves; trimerous seedlings 
have 3 cotyledons and 3 primordial leaves; and hemitrimerous seedlings have 3 cotyledons 
and 2 primary leaves. 
3 Harris, J. Arthur, Sinnott, E. W., Pennypacker, J. Y., and Durham, G. B. Correla- 
tions between anatomical characters in the seedling of Phaseolus vulgaris. Amer. Jour. 
Bot. 8: 339-365. 1921. 
[The Journal for October (8: 375-424) was issued November 14, 192 1]. 
