THE CULTIVATOR. 
71 
II. Certain substances of alkaline character, found principally in 
medicinal piants, to which they give their peculiar virtues. 
III. Gum, resin, oils, sugar, starch, and two substances approach¬ 
ing to animal matter in their characters, namely, albumen and glu¬ 
ten ; the former of these has a resemblance to the white of eggs, 
the latter to animal jelly or glue. 
Many other principles are separated by the same method in dif¬ 
ferent plants, but need not be enumerated by us. 
The basis of this method consits in acting upon vegetables by 
water, ether, or lectified spirits (alcohol), and the principles above 
enumerated are either simply, or in the state of combination in 
which they exist in plants, soluble in at least one of the liquids we 
have named. 
In all cases some insoluble matter is left, and this is known by 
the name of the woody fibre. 
When these principles are treated by the second method, oxygen* 
hydrogen, and carbon, are the uniform results, but in different pro¬ 
portions in the different cases; nitrogen is also detected in some of 
them, as, for instance, in the alkaline principles and in gluten.— 
This method does not appear to be adequate to determine whether 
earths and alkalis are, or are not, parts of these vegetable princi¬ 
ples. From the very remarkable fact, that some of those substan¬ 
ces, which are very dissimilar to each other, yield exactly the same 
proportions of oxygen, hydrogen, and carbon, we may fairly con¬ 
clude by chemical analogy, that one or the other, or perhaps both, 
contain some substances which have escaped the analysis. As an 
instance we may cite starch and sugar, whose characters are so dis¬ 
similar that no danger can exist of mistaking the one for the other; 
and yet their analysis by the second method gives identical results. 
The third method may be understood by comparing it with the 
process used in making charcoal. If this be so far altered that the 
heat employed shall not arise from the combustion of a part of the 
substance to be examined, but from one merely used as fuel, and if 
th ' matters which escape in smoke are condensed and collected, we 
shall have that employed occasionally on a large scale by operative 
chem’sts. In this way charcoal will be, as usual, obtained in the 
solid form. The condensible products will be water, tar, turpen¬ 
tine, or resin; and the acid which gives that character to vinegar, 
but which in the present case, is union with the tar and water, is 
called pyrolignous acid. 
If the charcoal be burnt in a current of air, all its carbon is con¬ 
verted, by union with the oxygen of the atmosphere, into carbonic 
acid, leaving a residue familiarly known as ashes. The ashes are 
made up partly of soluble, and partly of insoluble matter. The 
soluble matter is separated by the familiar process of making ley, 
and the ley, if evaporated, leaves the solid substance so well known 
as potash. 
Potash is principally composed of a carbonate of potassa, but 
contains, besides silica, rendered soluble by the alkali, sulphate and 
muriate of potassa, and a peculiar acid known by the name of ul- 
mic, which is a compound of carbon, hydrogen, and oxygen. The 
insoluble part is made up of carbonate of lime, sulphate and some¬ 
times phosphate of lime, silica. The carbonate of lime has proba¬ 
bly in no case existed in the living plant, but arises from the de¬ 
struction by heat of the peculiar acid of the plant: as, for instance, 
the citric, the oxalic, or the tartaric; all of which are by fire con¬ 
verted into carbonic acid. 
The quantity of ashes is extremely various, as is their propor' 
tion of the several soluble and insoluble substances, we have men 
tioned. Thus the ashes of the stalk of Indian corn yields 12i per 
cent of alkali, while the soft woods do not furnish more than two 
parts in a thousand. The proportion of the sulphate and phosphate 
of lime in even more various. Thus, in some cases the presence 
of the su'phate is hardly perceptible, while of the ashes of clover it 
forms a large proportion of the whole weight. Phosphate of lime 
is found in the proportion of fifteen per cent, in the grain of wheat. 
Water is not only one of the principal component parts of all plants, 
but is also the sole vehicle of their nutriment. At each extremity 
of the small fibres into which the roots of plants are divided, is an 
opening through which that fluid enters; and it appears that, ex¬ 
cept in the case of a plant having lost its vigor by continued 
drought, it is only through this channel that water can enter. By 
a powerful action inherent in living vegetables, water, which with 
all the matters it is capable of holding in solution, becomes the sap,* 
is raised to the highest parts of the plants, and forced to their most 
distant extremities. It has been ascertained that plants do not pos¬ 
sess the power of rejecting even those substances which are most 
noxious to them; it is, therefore, probable that toe character of the 
fluid admitted is the same in all the plants which grow upon the 
same soil. Whether it undergoes any change in the root does not 
appear certain, but it has recently been maintained that every de¬ 
scription of plant throws off by the surface of its roots such matter 
as, if retained, would be injurious; but this opinion does not appear 
to be well established. 
The sap, when carried up to the leaves, undergoes an important 
change, principally owing to the action of solar light. When ex¬ 
posed to light, the leaves of plants give out oxygen in considerable 
quantities. This proceeds from a decomposition of the water and 
carbonic acid, the remaining elements of which two substances and 
a portion of their oxygen enter into new combinations. These com¬ 
binations have different characters in different vegetables, but are 
most, familiarly known in the shape of gum and resin. These still 
contain the earthy and saline matter carried up by the sap, end alter 
they are formed return downwards towards the roots. In their de¬ 
scent they deposite the several parts which minister to the gi owth of 
the plant—the leaves, the bark, and the woody fibre. They also 
appear to be forced with powerful energy into the flower and the 
growing fruit, and in these a still more important action is carried 
forward, by which the reproduction of the species is ensured. 
The matters wffiich the water that enters by the roots may hold 
in solution, are either derived from the atmosphere or from the 
soil. In its passage through the air it will carry with it a conside¬ 
rable proportion of carbonic acid, and all the sulphuretted hydrogen 
it meets with. It will also take up a small quantity of oxygen, and 
of carburetted hydrogen, and a still less quantity of nitrogen.— 
From the soil it will take all the more soluble salts, small quanti¬ 
ties of sulphate, phosphate, and carbonate of lime, provided they be 
present, and silica. So also if the soil contain animal matter, or 
vegetables of which nitrogen forms a part, the ammonia generated 
by their decomposition will likewise be dissolved by the water. In 
like manner the carbonic acid, which has arisen from the decompo¬ 
sition of vegetable or animal matter, and has not yet escaped, and 
the soluble compounds of carbon, oxygen, and hydrogen, which are 
generated by the same process, will have been taken up, and carri¬ 
ed by the water into the root of the plant. It will thus appear that, 
contrary to the opinion of Mr. Puvis, the atmosphere furnishes but 
little of the fixed elements of plants, with the exception of sulphur 
and carbon: and that even if the growth of plants were to depend 
wholly upon the carbon obtained in the form of carbonic acid from 
the atmosphere, their growth must be slow and feeble. It will also 
appear, that if lime do not exist in the soil, but few plants can find 
nourishment; and that for the ripening of the seeds of grain phos¬ 
phorus must be furnished also. The latter substance may be ab¬ 
sorbed in small quantities from the phosphuretted hydrogen, which 
is occasionally present in the atmosphere; but a more certain sup¬ 
ply ought to be sought in putrescent manure, and particularly in 
that of animal origin. 
The uses of lime in agriculture, as will appear from the forego¬ 
ing remarks and the reasoning of the essay, arc as follows: 
1. When a soil contains inert animal or vegetable matter, their 
decomposition may be promoted, and it may be rendered fit for the 
food of plants, by the addition of caustic lime. 
2. If the soil contain acid, that may be neutralized either by 
caustic or carbonated dme, and besides, the organic matter whose 
decomposition may have been prevented by the acid, will be per¬ 
mitted to putrify. 
8. Soils containing too much silica, or in other words those which 
are sandy, are made more retentive of moisture by the addition of 
lime or its carbonate. 
4. Clays, may be rendered less retentive of moisture, and more 
friable by the same means. 
5. The gases which escape when vegetable or animal matter pu¬ 
trify, are retained in the soil by means of lime or its carbonate; and 
thus a given quantity of manure, or the original vegetable matter 
of the soil, will retain its efficacy longer. By a recent discovery, 
it has also been ascertained that the decomposition of plants yields 
* See Roget’s Bridgewater Treatise. 
