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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
ance in the upper part of the root or in the lower region of the hypocotyl, 
some ending bhndly below and others arising by division of the primary 
bundles. These intercalary bundles, which are not a very common feature 
of seedling anatomy in general, perhaps serve to increase the conductive 
capacity of the hypocotyl and may be associated with the large size of the 
seedling. They usually lack protoxylem elements. 
At the cotyledonary node there is a rather complex anastomosis of the 
bundle system. The details of this vary somewhat, but its fundamental 
features are as follows : The two members of each of the two original pairs 
of bundles in the cotyledonary plane (that is, opposite the two points where 
the cotyledons will later arise) become widely separated, and each member 
fuses with the adjacent member of the intercotyledonary pair (fig. 4). 
Four large bundles or bundle aggregates are thus produced. Each breaks 
up immediately, usually into three parts. The lateral member of each group 
of three which is in the cotyledonary plane approaches the corresponding 
bundle of the next group of three, and these two strands become the coty- 
ledonary traces and enter the base of the cotyledon. The lateral member 
of each group of three which is in the intercotyledonary plane approaches 
the corresponding bundle of the next group and fuses with it. The changes 
which are made and the resultant condition at this stage are shown in 
figure 5. Two strands (solid black) are here departing to each cotyledon, 
and six bundles are left as the basis for the vascular system of the epicotyl. 
The details of this nodal complex vary somewhat owing to the different 
levels at which fusion and separation of bundles take place, and to the 
presence of intercalary bundles. These intercalary bundles, as they ap- 
proach the cotyledonary node, fuse with the others and are completely lost, 
exactly six epicotyledonary strands almost invariably emerging from the 
complex, quite regardless of the number of intercalary bundles which may 
have entered it from the hypocotyl. This fact we shall find to be of im- 
portance when we consider the statistical relationships of bundle number 
in hypocotyl and epicotyl. 
Above the cotyledons, the six remaining bundles approach one another, 
closing the cotyledonary gaps and forming a ring, the members of which 
almost immediately divide. The twelve bundles thus produced (fig. 6) 
persist throughout the first internode of the epicotyl. 
At the first node of the epicotyl are inserted the two primordial leaves. 
Phaseolus, like other Leguminosae which have been investigated, possesses 
a trilacunar node, the leaf being supplied by three traces, each of which 
causes a separate gap in the vascular ring.^ The two primary leaves there- 
fore remove six of the twelve bundles of the epicotyl (solid black in fig. 6). 
The six new bundles which appear just above the cotyledonary node are, 
therefore, evidently downwardly extending leaf traces. These facts make 
^ Sinnott, E. W. The anatomy of the node as an aid in the classification of Angio- 
sperms. Amer. Jour. Bot. i: 303-322. 1914. 
