UKRMrNATION OF THE SkEu 
105 
Fig. 115 
Pig. 115 represents a young monocotyle* 
donous plant ; at a, is the cotyledon ; at b, is 
the second leaf, which, in the example just 
given of the rye, appeared on the sixth day; 
at c, is the primordial leaf,* which, at first, en- 
velops and conceals the other leaves ; at d, 
are the several branches of the root, bearing 
their radicles, and at their base enveloped by 
a pecuUar covering, e,t through which the ex- 
tremities have forced their way. 
Earth, though not absolutely essential to 
germmation, is useful, as affording to the 
vegetable egg a favourable situation, where it 
may receive the influence of the various 
agents, which are to perform their offices in 
the development of its parts. It seems, too, 
not improbable that some of the constituent 
elements of earth may be absorbed by the 
germinating plant and converted into nour- 
ishment. It is, however, sufficiently apparent 
that plants may vegetate without earth. The 
parasite grows upon the bark of other plants ; 
many seeds vegetate in water, and some will 
grow if moistened and placed on cotton, or 
any other supporting substance. 
Air, is essential to vegetation ; under an ex- 
hausted receiver a seed will not germinate, 
although possessing every other requisite. 
Seeds that become imbedded deeply in the 
ground, do not vegetate, unless accidentally 
ploughed up, or exposed to the contact of the 
atmosphere. Acorns supposed to have lain 
for centuries, have germinated as soon as 
raised sufficiently near the surface of the 
earth to receive the influence of air. 
You will recollect that in the process of ger- 
mination, oxygen gas unites with the carbon 
of the seed, and carries it oflT in the form of 
carbonic acid. Air furnishes that important 
agent, oxygen, which is the first moving prin- 
ciple of vitality. 
Carbon constitutes the greater part of the 
substance of seeds ; and this principle, being 
in its nature opposed to putrefaction, prevents 
seeds from rotting, previous to their being 
sown. Some seeds having an abundance of 
carbon, are capable of being preserved for 
ages ; while others, in which this element exists 
out in a small proportion, require to be sown almost as soon as ripe ; 
and such as are still more deficient in carbon lose their vital prin 
ciple before separating from the pericarp. 
You can now understand that oxygen is important to germination 
on account of its agency in removing the carbon which holds the 
living principle of the seed in bondage. 
Called by Mirbel, the p^'leole. 
t The coleorhize. 
Explanation of Fig. 115 — Earth imponant tu vegetation' — A.ir essential to ves,dla« 
tion— -Oxygen an important agent— Carbon. 
