246 



MORPHOLOGY. 



forming a confused plexus in the node, which, for the most part, merges 

 into the axillary bud (fig. 159. e). The innermost vascular bundles in the 

 nodes supply the lowest leaves, the external bundles the upper ones, as in 

 Grasses, the cane-stemmed Palms, and the Commelinacece. There are 

 many groups that have not yet been examined. The whole of the vas- 

 cular bundles in the same internode are simultaneously formed and 

 developed, and the internode itself, when perennial, does not continue to 

 increase in thickness, whether the plant becomes branched or not. The 

 primary, like the secondary, axes only grow upwards ; in fact, they are 

 devoid of a cambium-layer. 



2. Undeveloped Internodes. 



The stalks (in Pistia obovata, for instance), and the stems of Palms, 

 herbaceous Liliacea, bulbs of Allium, Lilium, &c., have a conical terminal 

 bud, sometimes longer, and 

 sometimes shorter, in accord- 160 



ance with which the vascular 

 bundles run from below and 

 the exterior, upward and 

 towards the interior, and then 

 from thence upwards and ex- 

 ternally, to pass into a leaf 

 (fig. 160. d and e). The arc, 

 which is convex towards the 

 interior, is longer or shorter 

 according to the length of the 

 terminal bud; and the vas- 

 cular bundle likewise passes 

 through a longer or shorter 

 portion of the whole axis, 

 according to the same con- 

 ditions. 



In the full-grown stems of 

 the Palms, the vascular bun- 

 dles connected with the upper 

 leaves do not reach the base 

 of the stem, notwithstanding 

 the length of the arc. In 

 the simplest case the vascu- 

 lar bundles are wholly 

 isolated ; they are, however, 

 more frequently connected 

 by intermediate branches, 

 seldom from within exter- 

 nally, but often laterally with 



180 Diagram of the course of the vascular bundles in the monocotolydenous stem, with 

 undeveloped internodes, and roundish, conical, terminal hud. a b, The lower, fully de- 

 veloped, part of the stem, c c, External firmer portion of the stem formed by the 

 closer course of the vascular bundle, d d d, Vascular bundles running as far as the 

 cicatrices of leaves that have died off. e e e e e, Leaves in the bud in the order in which 

 they are developed, with the vascular bundles belonging to them, f /, The latest- 

 formed leaves : all that is cut off by the line x y above the stem has originated at the 

 same time with the pair of leaves (,r x). 



