218 
THE COTTAGE GARDENER. 
but if the seed of an aquatic plant be germinated in 
water, under a double glass receiver, like the accom¬ 
panying drawing, one compartment of which is filled 
with hydrogen, or nitrogen, and the other compart¬ 
ment with atmospheric air, the plantlet invariably 
directs its growth into the latter. We also know j 
that germinated seed, placed in vacuo, refuse to ad- j 
vance any further in vegetation. 
The absorption of moisture, and consequent en¬ 
largement of the cotyledons of a seed, is followed by 
another change in them. Oxygen gas is absorbed, 
and carbonic acid gas is evolved, the starchy nature 
of the seed being completely changed—it usually 
becoming sugary, though sometimes it attains acidity 
—but in every case its components become soluble 
in water, more liquid, and adapted to the nutriment 
of the embryo plant. The quantity of oxygen ab¬ 
sorbed by seeds differs in every species, but they en¬ 
tirely agree in emitting it all again in the form of 
carbonic aoid; it is absorbed, therefore, for the pur¬ 
pose of diminishing the seed’s carbon. 
The seeds of beans and lettuces absorb the one- 
hundredth part of their weight of oxygen, to enable 
them to germinate; purslain, onion, and radish seed, 
the one-thousandth only; and the weight absorbed is 
always proportionate to the weight of the cotyledon. 
The fact of carbonic acid being extricated, aids to 
explain why germination proceeds more slowly in 
clay soils, and in soils rolled firm, even under other¬ 
wise favourable contingencies, tlian it does in porous, 
well-pulverised soils. Not only does the atmospheric 
air get to the seed in the former soils with more 
difficulty, but in these the carbonic acid emitted, 
during germination, is confined in immediate contact 
with the seed; and M. Saussure found that carbonic 
acid, almost in any proportion, retards the commence¬ 
ment of germination. 
That the atmospheric air is that mixture of oxygen 
and nitrogen gases which is most favourable to the 
duo progress of germination, is proved by the expe¬ 
riments of M. Saussure; for he found that seeds ger¬ 
minating in it always .absorbed a portion of the 
nitrogen, but which they did not do if the proportion 
of oxygen was increased. 
These facts hold out some beacons worthy of being ! 
attended to, as guides for the operation of sowing. 
They point out that every kind of seed has a par¬ 
ticular depth below the surface, at which it germi 
nates most vigorously, as securing to it the most 
[January 24. 
appropriate degree of moisture, of oxygen gas, and of 
warmth. From a quarter of an inch to two inches 
beneath the surface, appear to be the limits for the 
seeds of plants usually the objects of cultivation; 
these, however, must vary for the same seeds in 
different grounds and countries. The depth must 
be the least in clayey soils and dry climates. Sowing 
should in general be performrd in dry weather, espe¬ 
cially on heavy soils, not only because ot the greater 
saving of labour, but because it prevents the seed 
being enveloped with a coat of earth impermeable by 
the air, “which,” says Sir H. Davy, “is one cause of 
the unproductiveness of cold, clayey soils.” Perhaps 
the time at which any ground may be raked with the 
greatest facility, is as good a practical criterion as 
any, to judge when it is most fit for sowing. In 
general, if clay does not predominate in its constitu¬ 
tion, a soil rakes best just after it has been turned 
up with the spade. If clay does predominate, it 
usually rakes with most facility after it has been dug 
two or three days, and then immediately after a 
gentle rain. But it is certain that the sooner seed is 
sown after the soil is dug for its reception, the earlier 
it germinates. In the droughts of summer, water is 
often required to newly-sown beds. Such applica¬ 
tion must not be very limited or transitory; for, it 
the soil is only moistened at the immediate time of 
sowing, it induces the appearance of the radicle, 
which, in very parching weather, and in clayey 
caking soil, we have known wither away, and the crop 
to be consequently lost from the want of a continued 
supply of moisture. 
Pursuing our plan of inserting such answers, edi¬ 
torially, as we consider generally interesting, though 
called forth by a correspondent’s particular inquiry, 
we do so, in the present instance, relative to the 
mode of heating a small pit. 
A correspondent, signing himself “ P. T. R.,” 
writes thus:— 
“I have a four-light pit, 18 feet by 5 feet, and 
now heated by linings of dung. In this pit I am 
growing cucumbers, and succeeding pretty well; but 
several inconveniences present themselves. First, 
I have to buy the dung, which has to be fetched 
some distance. Secondly, the time, trouble, and 
expense of often stirring it are objectionable; and, 
thirdly, the appearance is bad. By what means 
can I obviate these inconveniences, without much 
expense? I have an Arnott’s stove; can that be 
made applicable ? or, what other plan can you re¬ 
commend, and what expense will be probable in 
making the alteration you advise?” 
Now, to these queries we reply that, though dung 
is dirty, troublesome, and expensive, Arnott's stove 
would not be much better. Heating by hot water 
would be cleanest, least troublesome, and the cheap¬ 
est in the end. A small boiler, supplying a tank 
