220 
lieved plants can take up, amounts, as above, to 
6,700 lbs. Or this silica will alone supply the 
wants of 900 crops of corn. The soil in the fifth 
instance contains four times as much, or it 
would provide silica for 3,600 crops !—Further, 
if the insoluble portion of the soil be washed with 
water, to free it from siliceous sand, and the finer 
or clayey part be collected and fused with car- 
bonate of soda, and then treated with muriatic 
acid, a large portion of silica, in light white 
flocks, will remain behind; while the solution 
will contain alumina, lime, magnesia, and per- 
haps potash and soda, with which the silica had 
been combined in the soil. This portion of the 
silica of the soil is very large, and sometimes 
forms nearly one-half of its whole weight. In 
the form of silicates insoluble in muriatic acid, 
therefore, the soil contains an enormous quan- 
tity of silica. There can be no doubt that the 
roots of our corn crops are capable of taking up 
and appropriating that portion of the silica of 
the soil which is soluble in water, but it may be 
doubted by some if that which is taken up by 
acids, and especially if that which acids leave 
undissolved, is capable of supplying the wants of 
our growing crops. I will not offer here any of 
those theoretical considerations which induce 
chemists and physiologists to believe that both 
the silicates which are soluble and those which 
are insoluble in acids, are really a source of mi- 
neral nourishment to the plant. An appeal to 
experiment will be much more satisfactory to 
the practical man. Wiegman and Polstorf took 
fine white quartz sand, burned it to destroy any 
organic matter it might contain, digested it for 
16 hours in strong nitro-muriatic acid, and then 
washed it with distilled water. Everything so- 
luble being thus removed, seeds of different 
kinds, barley, oats, buckwheat, vetch, clover, 
and tobacco were sown in it, and watered with 
distilled water. They all grew and came to a 
greater or less height. The ash left by separate 
portions of the seeds and plants, when full grown, 
was determined and analysed. In the following 
table I have put together their comparative re- 
sults, in so far as the silica is concerned, as well 
as the height to which the plants had arrived 
when they were gathered :— 
SILICA 
—A h d e d. 
Of the Seed.jOfthe Plant.) 
op h q 
HEIGHT. BtRICS IN TRE ASH 
Barley, 5 0.034 0.355 10 
Oats, . 18 0.064 0.354 53 
Buckwheat, 18 0.004 0 075 18 
Vetch, 10 0.013 0.135 10, 
Clover, 33 0.009 0.091 10 
Tobacco, 5 0,001 0.549 500 
Thus it appears that, from quartz sand, after it 
has been digested in strong acids, plants are 
able to extract silica as well as other kinds of 
inorganic nourishment, to which, in the above 
table, I have not alluded. The sand in which 
| the plants had grown, was found, upon analysis, 
SILICA. 
to contain 97°9 per cent. of pure silica, the re- 
mainder consisting of potash, lime, magnesia, alu- 
mina, and oxide of iron. From this experiment, 
therefore, we are justified in concluding that 
plants are capable of decomposing and extract- 
ing silica even from those silicates in the soil | 
which are not attacked by acids. How much 
more easily may they decompose and appropriate 
the constituents of those silicates which are ca- 
pable of being decomposed and dissolved by 
acids! Nor is it in virtue of any mysterious 
power that this decomposition is effected. The 
prolonged action of water containing carbonic 
acid, slowly decomposes even the most refractory 
silicates. ‘The water in the soil is more or less 
charged with this carbonic acid—the decaying 
vegetable matter of the soil produces it, and the 
roots of living plants give it off—so that a simple 
chemical action is sufficient to explain how the 
plant can obtain food from such unpromising 
materials. It is an important conclusion, there- 
fore, for practical agriculture, that the silica, 
which is so necessary to the growth of our corn 
and hay crops, abounds so much in nearly all our 
soils, and in a state in which the roots of plants 
can more or less readily take up. It satisfies us 
in regard to three points,—as to where and how 
the plants obtain their silica,—that, in general, it 
cannot be necessary to add silica in any form as 
a manure to the soil,—and, therefore, that the 
broad assertions of those who say that guano or 
bones should always be mixed with silicate of 
potash or soda, and who ascribe certain alleged 
failures of these manures to the absence of such 
silicates—that these assertions are hastily made 
and are not to be depended upon. I believe 
there are very few soils indeed, which, if properly 
treated otherwise, will refuse to yield good crops 
merely because a soluble silicate has not been 
added to them. 
“There is only one legitimate purpose for 
which a silicate should be added to the soil—it 
is to supply silica to the plant. We ought not 
to add silicates for the purpose of supplying al- 
kaline or earthy matter, unless some question of 
economy interferes. We use wood-ashes which 
contain silicates, because it is cheaper to add 
potash in this than in any other form. There 
is only one evidence, therefore, that the addition 
of a silicate has done good to our corn crop—it 
must have given more silica, and consequently, 
as it is believed, more strength to the straw. 
That the crop has been generally improved, that 
it is more luxuriant and thriving, or even that 
it yields a larger return of corn, will not be a 
proof of the virtue of the silicate. The effect 
may result from the action of the potash or the 
soda it contains, and the use of these alone might 
have produced the same effect. Oats grown 
upon a mossy soil are soft and dull in the straw, 
and 1 have found such straw to be deficient in 
silica. Wheat growing rankly upon a moist soil, 
and in a moist season, or a heavy thickly grow- 
