164 BOTANICAL GAZETTE [September 



to surround the phloem, thus recalling the condition found by the 

 writer in grasses (6)^ where^ however, the appearance is more pro- 

 nounced. With the three foliar traces groups of mechanical fibers 

 enter the central cylinder. After anastomosing with other bundles 

 present at the node, the three lose their xylem and proceed downward 

 at the periphery of the stele, occupying the middle region of three 

 contiguous sides of the roughly oblong section of the stele (fig. 14). 

 At the next node they enlarge, move toward the center of the stele, 

 and the xylem again appears, first at the inner side of each bundle, 

 filling the cavity, thence spreading around the phloem, so far as to 

 render the bundle almost or quite amphivasal {fig. ij); the tw^o 

 lateral ones anastomose wnth other bundles, then the three approach, 

 including between them an island of parenchyma which is surrounded 

 by the xylem of the bundles. The xylem again disappears, as does 

 also the island of parenchyma, which is replaced by a cavity w^hich 

 persists through the succeeding internode. Thus the " trio " is formed 

 and descends to the next node, where tracheids appear once more, 

 first around the cavity, and thence spreading around the bundles 

 until the two lateral ones become amphivasal. At the same time the 

 three bundles enlarge, the two lateral ones fuse, then separate, and all 

 three join other bundles of the nodal complex, such as those of the 

 axillary branch which enters at this level. Both the petiole and the 

 fused stipules contain many small bundles consisting of fibers or of 

 thin-walled cells or of both. These bundles descend into the cortex 

 of the stem, some of them fusing wdth similar bundles of that region 

 derived from petioles and stipules of higher leaves. In this way 

 apparently arise the very numerous cortical strands characteristic of 

 this species, and it may be stated in general that those species which 

 possess a cortical system derive it from the petioles and stipules. : 



ih 



Two points in the foregoing account seem w^orthy of emphasis, 



namely, the presence of amphivasal bundles wherever the leaf trace 



bundles are about to fuse with other bundles, and the very different 



course pursued by the leaf traces from that which is seen in most i 



monocotyledons. < 1 



Concerning the insertion of branches it should be noted that the 

 phloem of the bundles shows a remarkable enlargement just before 

 joiningjthe stele of the main stem, as is shown in fig, 12. The elements | 



