68 AMERICAN JOURNAL OF BOTANY [Vol. If 



ance in the upper part of the root or in the lower region of the hypocotyl, 

 some ending blindly 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 numbei 

 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 leav&amp;lt; 

 Phaseolus, like other Leguminosae which have been investigated, possesse- 

 a trilacunar node, the leaf being supplied by three traces, each of whicl 

 causes a separate gap in the vascular ring. 5 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 mak 



6 Sinnott, E. W. The anatomy of the node as an aid in the classification of Angio 

 sperms. Amer. Jour. Bot. i: 303-322. 1914. 



