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 (PL 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 j in the latter, roots are also formed irregularly on 
the internodial parts of the stem * (PI. IX. fig. I shows the scars 
left by their fall). 
* The endorhhal 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 
affinity with monocotylcdonous structure. 
