and Growth of Monocotyledons, 185 



fibrous layer ; they gradually approach one another as they pass 

 out, thus forming a kind of funnel-shaped body. The central 

 parenchyma is gradually converted into ligneous cells as the tube 

 of vessels extends outwards (PI. X. figs. 2 and 3), and the root 

 at a short distance from its point of origin presents in a cross 

 section a central cylinder of wood having a ring of vessels near 

 its periphery, the whole being inclosed in a parenchyma con- 

 tinuous, near the fibrous layer, with the cortical layer of the stem. 

 When the roots produce branches the latter are given off at right 

 angles (PI. X. fig. 2), and arise on the central fibro-vascular 

 cylinder, bursting their way through the cortical parenchyma of 

 the root as the main roots do through the outer part of the cor- 

 tical layer of the stem. When the roots fall off, they leave ori- 

 fices in the stem where they have thus burst through. Roots 

 appear very early in the buds, in fact contemporaneously with 

 the leaves. In the section of the apex of a bud of Sparganium 

 (PI. IX. fig. 3) they are seen in the nascent condition. It is dis- 

 puted whether the fibro-vascular bundles are first perfected where 

 they are in contact with the fibrous layer, or whether their bun- 

 dles are formed independently and afterwards effect a junction. 

 With regard to the roots of Sparganium, just noticed, I believe 

 their central bundle is organized contemporaneously and in con- 

 tinuity with the fibrous layer. 



The fibrous layer is not so distinctly marked in bulbs like the 

 Tulip and Hyacinth, or in tuberous-rooted Monocotyledons like 

 Asparagus and the terrestrial Orchidacese. The ends of the 

 fibro-vascular bundles of the stem are found branching and ana- 

 stomosing at the line of junction of the cortical and central re- 

 gions, and the bundles of the roots are in connexion with these 

 plexuses. The tubers of Orchis mascula are merely enlarged 

 roots ; the difference between them and the other roots arises 

 from the development of the central (otherwise ligneous) portion 

 into a parenchymatous mass, which breaks up the ring of vessels, 

 and carries them to the outer region of the tuber. 



The development of successive roots taking place from below 

 upwards, the younger roots arise from parts of the fibrous layer 

 in relation with the younger fibro-vascular bundles. In cases 

 where the internodes are developed, roots and buds are com- 

 monly produced at the nodes, as in Tradescantia, Grasses, and 

 Sparganium ; in the latter, roots are also formed irregularly on 

 the internodial parts of the stem * (PI. IX. fig. 1 shows the scars 

 left by their fall). 



* The endorhizal mode of producing roots seems to be a constant cha- 

 racter of Monocotyledons as well in the full-grown condition as in the 

 embryo. It is also found in Nymphaeaceae, which present many points of 

 alKnity with moiiocotyledonous structure. 



