374 History of a Sod. 
these, with the others, enclose and shelter the stamens and ovary. 
With the structure of the seed we do not think it necessary to deal. 
Suffice it to add, that in the counsels of a watchful Providence, it 
has been so ordained that that rapidity of sjrowth which is essen- 
tial to the speedy covering of the earth with her green mantle, 
has been both foreseen and beautifully provided for in its fabrica- 
tion. 
We may consider that two chemical processes meet in our sod — 
the one belonging to the chemistry of life, the other to that of decay 
and death. To take the last first. *If the roots of the sod are 
carefully examined, it will not be difficult to separate the living 
from the dead; and the latter class includes the decaying and de- 
cayed. The brown, friable, pulverulent matter which is called 
mould, and composes a considerable portion of the underground 
mass of the sod, is vegetable fibre having undergone its complete 
decay. Chemists call it humus. It is insoluble, or nearly so, in 
water; it cannot, therefore, although rich in carbon, contribute 
any of that element directly to the thick vegetation flourishing 
above. Yet it was long considered that this^ery humus was the 
real and only origin of the wood of plants. As, however, plants 
can only receive soluble particles by their roots, and those of humus 
are insoluble, it is a very simple and just conclusion to arrive at, 
that the source of carbon in vegetation lies not for the most part 
in the soil. The thin air and the viewless winds will better an- 
swer the question. Is the humus of the sod, then, altogether use- 
less? Not so. It is the reservoir of all the alkaline and mineral 
ingredients of the last generation of plants, and these are absolutely 
essential to the well being, even to the existence, of vegetation. 
In the undisturbed greensward, allowed to lie for years by the 
grazier, this stock of salts amount to a large quantity; and if the 
plow is now sent through it, the smiling sod torn up, broken, 
and crushed and sown for wheat, a crop of vast luxuriance follows. 
But this only lasts for a year or two, and the land returns to its 
former average, or possibly falls under, for reasons not to be here 
entered into. In the upper layers of the sod, vegetable fibre in 
the actual process of decay is sure to be found. It may be recog- 
nized by its crumbling character and brown color. Possibly it 
consists of the slain bodies of the grasses w4iich were felled by the 
last winter's frosts. Water and air are busy here; the work of 
destruction hastens on ; the woody fibres undergo " eremecausis," to 
use the Liebigian phrase — that is, they are slowly, or by degrees, 
consumed. In so doing, they are continually evolving small por- 
tions of carbonic acid gas; the fibres become more and more broken 
up; until at length it is not possible to distinguish them from the 
pulverulent humus above mentioned. In this process all the salts 
and mineral constituents which entered into the composition of the 
