﻿31-4 Row lee and Dohertv : The Histologv 



off to the scutellum. When they emerge from this node into the 

 first internode, they show very little change either in structure or 

 relative position. The vessels of the xylem have moved slightly 

 outward and the large inner elements have become smaller (fig. 3). 

 The phloem has spread slightly laterally. This latter change be- 

 comes more apparent as we approach the second node and is the 

 first step in the transition from radial to collateral arrangement. 

 In the second node the elements composing the bundles decrease. 



This decrease is accompanied by a bending of the bundle outward. 

 The phoem of the primary bundles then disappears and only a very 

 few of the xylem elements are distinguishable. Before the disap- 

 pearance of the phloem of the root, the xylem of the leaf-trace 

 bundles makes its appearance. These leaf-trace bundles arise, 

 either internally or externally or laterally in close proximity to the 

 root bundles. They pass toward the center of the stem, the xylem 

 and phloem elements of the bundle at once assuming the collateral 

 position. The bundles of the sheath and the first leaf originate in 

 the same manner. 



Four collateral bundles segregate into two pairs at almost op- 

 posite points in the node, then pass out with a sharp curve into the 

 sheath. This curve of the leaf-traces of the sheath is so sharp 

 that in cross-section many of the xylem elements are cut length- 

 wise. The leaf-trace bundles of the first leaf pass inward to near 

 the center of the stem and upward through the second internode. 

 After traversing about one-half the length of the second internode 



they commence to curve outward and at the third node pass out 

 into their leaf. In the cross-section of this node a new set of 

 bundles much smaller than those just considered, and about equal 

 in number to them, make their appearance. They are the bund! 

 which pass into the leaves above. The course of the bundles m 

 the succeeding nodes and internodes corresponds to the type o f 

 bundle distribution found in palms and other monocotyledons. 



In conclusion : i. The bundles of the primary root of India* 1 

 corn are of the true radial type. 2. The innermost elements of 

 the xylem are anomalous and doubtfully to be considered as trw 

 ducts. These anomalous elements occur in many species 

 grasses but have not been met with in other orders. 3. The lea'' 

 trace bundles of the scutellum do not in any way affect the ar- 



