Sidebilder
PDF
ePub

a

and the opinions of these great men accord; but Sir Humphry, farther says “ If any

fresh

vegetable matter which contains sugar, mucilage, starch, or other of the vegetable compounds soluble in water, be moistened and exposed to air, at a temperature of from 50 to 80, oxygene will soon be absorbed and carbonic acid formed, heat will be produced, and elastic fluids, principally carbonic acid, gaseous oxyde of carbon, and hydro-carbonate will be evolved, a dark coloured liquid of a slight sour, or bitter taste, will likewise be formed ; and

l if the process be suffered to continue for a time sufficiently long, nothing solid will remain except earthy and saline matter, coloured black by charcoal.

“ Animal matters are in general more liable to decompose than vegetable substances, oxygene

is absorbed, and carbonic acid and ammonia formed. In the process of their putrefaction they produce compound elastic fluids and likewise azote; they afford dark coloured acid and oily fluids, and leave a residuum of salts and earths mixed with a calcareous matter, the ammonia given off from animal compounds in putrefaction, may be conceived to be formed at the time of their decomposition, by the combination of hydrogene and azote; except this matter, the other products of putrefaction are analagous to those afforded by the fermentation of vegetable substances, and the soluble substances formed, abound in the elements which are the

[ocr errors][merged small][merged small][merged small][merged small][ocr errors][merged small][ocr errors]

wise says,

obe

[ocr errors][ocr errors]

constituent parts of vegetables, in carbon, hydro-
gene, and oxygene." .

Again, 66 The circumstances necessary for the
putrefaction of animal substances, are similar to
those required for the fermentation of vegetable
substances, a temperature above the freezing point,
the presence of water and the presence of oxygene,
at least in the first stage of the process. He like-

“ It is probable that as yet we are not acquainted with any of the true elements of matter."

It however appears that both animal and vegetable matters are reducible to the same principles, and so far simplified as to be clearly capable of the different combinations required to reproduce and sustain both animals and vegetables.

Kirwan observes, “ Hence we see on the last analysis the only substances common to the growing vegetables, and the soils in which they grow, are water, coal, different earths and salts : these therefore are the true Food of Vegetables ; i to them we should also add, fixed air, though by reason of its decomposition it may not be distinctly found in them, or at least not distinguishable from that newly formed during their decomposition.”

Sir Humphry adds,“ Vegetable and animal substances deposited in the soil, as shewn by universal experiences are consumed during the process of vegetation, and they can only nourish

.

* Animal' matter containing nitrogene, which vegetable matter does not.

1

the Plant by affording solid matter capable of being dissolved by the fluids in the leaves of vegetables ; but such parts of them as are rendered gaseous and that pass into the atmosphere, must possess a comparative small effect, for gases soon become diffused through the mass of the surrounding air.

The great object in the application of manures should be to make it afford as much soluble matter as possible to the Roots of the Plant, and that in a slow and gradual manner, so that it may be entirely consumed in forming its sap

and organized parts.

So far the component parts of the Food of Plants seem to be generally understood and admitted; and on the medium of its application and consumption, Kirwan observes, “ The agency of water in the process of vegetation, has not till of late been distinctly perceived : Dr. Hales has shewn, that in the summer-months a sun-flower weighing three pounds avoirdupois, and regularly watered every day, passed through it or perspired 22 oz. each day, that is, half its weight. Dr. Woodward found that a sprig of common spearmint, a Plant that thrives best in moist soils, weighing only 28.25 grs. passed through it 3004 grs. in 77 days, between July and October, that is somewhat more than its whole weight each day. He did more, for he found that in that space of time the Plant increased 17 grs. in weight, and yet had no other food but pure rain water, but he also found that it increased more in

[ocr errors][ocr errors][merged small][ocr errors][ocr errors][merged small][merged small]

weight when it lived on spring water, and still
more when its food was Thames water. Secondly,
that the water they thus pass nourishes them merely
as water, without taking any foreign substance into
account, for 3000 grs. of rain water, in Dr. Wood.
ward's experiment, afforded an increase of 17 grs.,
whereas by Margraaf's experiments, 5760 grs. of
that water contain only fd of a grain of earth :
but, Thirdly, it also follows that water con-
tributes still more to the nourishment of Plants,
besides the service it renders them in distributing
the nutritive parts throughout the whole structure,
forming itself a constituent part of all of them,
may be understood from modern experiments.
Dr. Ingenhouz and M. Senebier have shewn that
the leaves of Plants exposed to the sun produced

Now water has of late been proved to
contain about 87 per cent. of pure air, the remain-
der being inflammable air; WATER IS THEN DECOM-

its and

مر گیا

[ocr errors]

pure air.

[ocr errors][ocr errors]

POSED BY THE ASSISTANCE OF LIGHT WITHIN THE

VEGETABLE, ITS INFLAMMABLE PART IS EMPLOYED
IN THE FORMATION OF OILS, RESINS, GUMS, &c. ITS
PURE AIR IS PARTLY APPLIED TO THE PRODUCTION
OF VEGETABLE ACIDS, AND PARTLY EXPELLED AS
EXCREMENT.

This last Theory will be found to accord with
every practical observation, and must form the
groundwork of every system of Horticulture, ar-
ranged on demonstrative principles that can be
expected to be sustained with success.

[ocr errors]

Kirwan further states, “ To Mr. Hazenfraz we owe the discovery, that coal is an essential ingredient in the food of all vegetables; though hitherto

i little attended to, it appears to be one of the primeval principles, as ancient as the present constitution of our globe, for it is found in fixed air, of which it constitutes above one fourth part, and fixed air exists in lime stones and other substances which date from the first origin of things.

“ Coal not only forms the residuum of all vegetable substances that have undergone a slow and smothered combustion, that is, to which the free access of air has been prevented, but also of all putrid vegetable and animal bodies, hence it is found in vegetable and animal manures that have undergone putrefaction, and is the true basis of their ameliorating powers ; if the water that passes through a putrifying dunghill be examined, it will be found of a brown colour; and if subjected to evaporation, the principal parts of the residuum will be found to consist of coal; all soils steeped in water communicate the same colour to it, in proportion to their fertility, and this water being evaporated, leaves also a coal, as Hazenfraz and Fourcroy attest.” Sir Humphry Davy says, “ No substance is

" more necessary to Plants than carbonaceous matter, and if this cannot be introduced into the organs of Plants, except in a state of solution, there is every reason to suppose that other substances less essential will be in the same case. I found by some experi

« ForrigeFortsett »