IO BOTANICAL GAZETTE [july 



the side of one of the leaf traces of the first pair of leaves. This 

 single protophloem element passes inward toward the center of 

 the ring. It never reaches it, however, but turns upward, and 

 disappears in the middle of the node. The other two protophloem 

 elements arise, one from the side of the other leaf trace, and the 

 second from the adjacent face of one of the side bundles. These 

 pass toward the center, become applied to each other, and pass 

 vertically upward for a short distance; one disappears, the other 

 soon turns, and passes back to that side of the stem on which it 

 arose, becoming inserted, at the top of the node, on one of the 

 "forks" on the side nearest one of the descending traces of the 

 second pair of leaves. 



In a very similar case found in a fifth-stage seedling, a single 

 protophloem passes off toward the center from each side of each 

 leaf trace. These four protophloem elements pass toward the 

 center and turn upward, then turning back to the ring, each fuses 

 with one of the descending forks, just as these enter the ring at the 

 top of the node. In these two cases, the medullary vascular tissue 

 is all entirely intranodal, there being no trace anywhere except 

 just within the one node. 



In the fifth stage, however, there is usually developed the central 

 bundle of both xylem and phloem, passing from one node to the 

 next. There is considerable irregularity in its formation, some of 

 the fifth-stage seedlings being entirely without any medullary 

 vascular elements. Taking a seedling where the central bundle 

 has developed, we find, at the third node back from the apex, an 

 elliptical vascular ring surrounded by a well marked sheath which 

 usually, at this stage, does not possess any special endodermal 

 characters. There is no sign of any internal endodermis in this 



node. 



this node 



breaks up into four bundles, from one edge of one of the side bundles, 

 a small group of phloem and xylem elements passes inward, free 

 from the outer ring, to the center of the pith, meeting there another 

 group of vascular tissue, which has broken off from the other end 

 of the same side bundle. At a more mature stage, the medullary 

 bundle may be derived from four sources, one at each end of each 

 of the side bundles. 



