426 
Development of Roots of Agricultural Plants. 
partly by what is contained in the soil and partly through the 
medium of the cotyledons, whether remaining or not in contact 
•with the albumen, and then in order to produce as extensive an 
absorbing surface as possible, giving off in a multitude of instances 
numerous delicate absorbent hairs. 
The next stage is to produce from the axis, either above or 
below the plumule, secondary or adventitious roots, which either 
remain simple or ramify in every direction. The tips of these 
processes, which consist always of naked spongy tissue, not 
covered with cuticle, are certainly in many, if not in most, cases 
the only parts capable of absorbing nutriment from the soil, 
always excepting the delicate threads above mentioned, which 
are produced also from the surface of the roots at various periods 
of growth, sometimes even in the third stage, which will be con- 
sidered presently. Even supposing that in the first instance, as 
the radicle elongates, the surface has some absorbent power, the 
walls of the cells become frequently so hardened and thickened 
with corky matter, besides being clogged up with colloid or 
gummy substances, that they seem rather destined to protect the 
subjacent tissues from injury, than as absorbents; while, on the 
contrary, the tissue of the spongelet is constantly renewed, 
the old elfete cells being rejected backwards so as to invest the 
cuticle. 
In their earliest stage of growth, whether normal or adven- 
titious, roots consist of a little convex body composed of appa- 
rently homogeneous cells resting upon the elongated cells of 
which the greater part of the woody tissue is composed, and 
more or less converging at the apex. The outer cells at the apex 
soon, however, become distinct or separated from the rest of the 
mass all round, so as to form a little close-fitting or loose cap 
attached only in the centre. The whole gradually forces its way 
through the bark or outer coat, either turning aside the tissue 
or absorbing it, so as ultimately to become free, the spongy cap 
still adhering and forming the principal, or at least the most 
permanent, part by which nutritive matter is imbibed. As the 
young roots are in immediate connexion with the albumen, 
from which their central tissue is directly derived, and the 
spongy mass rests on the tip of the cone of elongated cells, it is 
evident that the matter imbibed by the roots is at once con- 
veyed to the very part of the plant where the upward current is 
most active.* 
As the tissue of the spongelet is very delicate, and easily 
assumes the form of anything against which it presses, it can 
* This paragraph is taken, with slight alteration, from Sections 46 and 50 of my 
series of papers on Vegetable Pathology in the • Gardener's Chronicle.' 
