THE CULTIVATOR. 
Ill 
ed for herbage or green feed, may, in compliance with common language, 
be still termed the Sown or Artificial Grasses. 
Further, distinguishing these different classes of crops according to 
their effects upon the fertility of the farm, they might be divided thus: 
1. Corn-crops,—exhausting crops, and favorers of weeds. 
2. Pulse-crops—exhausting but cleaning crops, or capable of being 
rendered so. 
3. Green or fallow-crops,—restorative and cleaning crops. 
4. Green forage-crops,—restorative and sometimes cleaning crops. 
5. The sown grasses,—restorative crops. 
Knowing these the general characters of the cultivated plants, we 
have, in devising a rotation, to cause the restorative and cleaning ciops so 
to alternate with the exhausting crops, as that the land may be preserved 
fertile and clean. Further, when we find that land cannot be sufficiently 
cleaned by means of cleaning crops, we must make use of the summer- 
fallow ; and again, when w : e find that land requires rest, we may lay it 
down to grass for a longer or shorter time, taking care when this is done 
that the land shall be in as fertile a state as circumstances will allow, and 
free of weeds. 
Science of Agricnitiis’e. 
From Chaplul’s Chemistry applied to Agriculture. 
THE CHANGES PRODUCED IN PLANTS BY NOURISHMENT. 
Plants are principally nourished through their leaves and roots; the first 
absorb from the atmosphere oxygen, carbonic acid, and water; and the 
second receive from the soil the oxygen and carbonic acid contained in it 
in a free state, or dissolved in water, and also the juices and salts which 
are mixed with the earth. 
Water appears to be the necessary vehicle of nearly all the nutritive 
portions of the soil; so that it not only serves to nourish plants, by yield¬ 
ing to them the elements of which it is itself composed, but it conveys into 
their internal organs all the substances which can serve them as food. 
The substances which chiefly afford nourishment to plants, present in 
their composition only carbon, hydrogen, and oxygen; the numerous pro¬ 
ducts formed in the course of vegetation, do not upon analysis furnish any 
other principles: the salts, the earths, and the metals are generally found 
in them in very small quantities, and under a very different iorm from that 
in which they exist in the soil. 
Strictly speaking, the three principles necessary to vegetation, are ox¬ 
ygen, carbon, and hydrogen, combined in various proportions; and it is 
this difference in the proportions which causes the immense variety in the 
vegetable kingdom; some hundredths more or less of carbon, oxygen, or 
hydrogen change the character of the body. 
The chymist in experimenting upon dead plants produces at pleasure a 
part of these effects; fermentation and spontaneous decompositions give 
rise to a great number. But the constant uniformity of the products in 
the same species of plants, and the analogy existing between those deiiv- 
ed from different species of the same genus; their variety in the different 
organs, and the peculiar compounds, apparently so complicated, of each 
one of them, form altogether so many phenomena beyond the power of 
art to explain. 
We know the substances received by plants, and those which they re¬ 
ject; we determine by analysis the nature and the composition of the pro¬ 
ducts which they form; but this is the utmost extent of our knowledge. 
All that passes within the plant is still a mystery, and belongs to the laws 
of vitality, which modify by their action those physical laws that are known 
to us. 
However, as the laws of vitality governing vegetables are in their ap¬ 
plication less independent of the physical laws, than those that reign in 
the animal kingdom, we can even now raise a portion of the veil, and fol¬ 
low at least the progress of the changes, though we can as yet neither 
produce them nor discover their mode of action. 
The germination of seeds and the swelling of buds in the spring, are al¬ 
most entirely the result of physical laws: oxygen is the only agent neces¬ 
sary to produce them; water and heat are necessary auxiliaries, but they 
do not in any way enter into the new combinations; they only facilitate 
the changes that are going on. The oxygen unites with carbon to form 
caibonic acid gas; by this means the mucilage and starch are reduced to 
the state of a milky liquor, which serves as the first aliment of the young 
plant or twig. 
As soon as the plant has unfolded its leaves, or the radicles of the seed 
have penetrated into the soil, the system of nourishment is changed: eve 
ry part of the plant in contact with the atmosphere gives out carbon dur¬ 
ing the night, or when in darkness; but the carbonic acid which this forms 
with oxygen, instead of remaining in the air, as at the period of germina¬ 
tion, is absorbed piincipally by the roots and leaves, and decomposed in 
the last by the solar rays; the carbon remaining fixed in the plant, whilst 
the oxygen is exhaled in the form of a gas. Plants are likewise nourished 
by that aqueous fluid which, constantly existing in the atmosphere in 
greater or less abundance, is, by the diminished temperature of the air 
during the night, deposited in the form of dew. The water contained in 
the soil dissolves the juices of the manures, and transmits them to the 
plants. 
But in order that plants should flourish, it is not sufficient that they have 
at their disposition all their necessary aliments; it is further requisite, that 
the elaboration of these be favored by other causes possessing equal influ¬ 
ence over vegetation. 
I have already remarked, that leaves do not transpire oxygen excepting 
when exposed to the r.iys of the sun; so that the carbonic acid remains in 
the plant during the whole time that the solar rays are hidden. The es¬ 
tablishment of this fact enables us to explain many of the most important 
phenomena of vegetation: we learn from it, why plants that grow in the 
shade never produce fruits having the same taste, perfume, or texture, as 
those borne by plants of the same kind growing in the sun; and why the 
various sorts of fodder and green herbs are of bad quality, when the sun 
has not access to them to facilitate the decomposition of carbonic acid and 
the elaboration of nutritive fluids. 
Independently of the light of the sun, without which the plants cannot 
flourish, vegetation requires a certain degree of heat; buds generally do 
not begin to unfold till the atmosphere is at the temperature of from 50 3 
to 54°; and vegetation gains strength in proportion as the heat of the at¬ 
mosphere increases, provided that at the same time the earth be sufficient¬ 
ly moist for the water to convey to the plants the nourishment it contains, 
and to furnish to them the means of transpiration. The influence of tem¬ 
perature over vegetation is so marked, that we can see the latter diminish 
as the heat lessens, and resume its energies as that is augmented. Warmth 
renders the sap fluid, and quickens its circulation; cold thickens it and 
renders it stagnant. If a right degree of atmospheric temperature, the in¬ 
fluence of the solar rays, or a suitable quantity of the aqueous fluid be 
wanting, the growth of plants is retarded. Thus we see it is not enough 
that plants are abundantly supplied with nourishment; it is necessary that 
the concoction of it should be favored by agents which concur in causing 
its digestion. 
When the soil is too abundantly provided with manures, especially of 
kinds that may be easily conveyed into plants by water, their growth may 
be prodigiously increased: but if the digestive organs and the constant in¬ 
fluence of the sun do not concur in elaborating their juices, the result will 
be, as I have before remarked, a kind of obesity; and none of the pro¬ 
ducts will have either the savor or the odor that they would have acquired 
if the nourishment had been less abundant and better digested. It is not 
uncommon for fruits and herbs to yield the odor peculiar to the manure 
with which they have been nourished, when it has been too abundantly 
supplied. 
The juices circulate in plants, not only with the same regularity of 
movement that we observe in animals more perfectly organized, but with 
a degree of torce sufficient to carry them into all the organs, that they may 
receive in each one of them a peculiar elaboration. 
The roo's absorb fluids from the earth by means of their capillary ves¬ 
sels; but the force with which they are conveyed into the internal organs 
of the plant, and even into the leaves, where their carbon combines with 
oxygen, is superior to that of capillary attraction, and the weight of the 
atmosphere. 
The celebrated Hales cut a branch of a vine four or five years old ; this 
he cemented carefully into a glass tube bent in the form of a siphon, fill¬ 
ed with mercury; by the force of the ascending sap alone, the mercury 
rose at the end oi some days to 38 inches. M. Mirbel has confirmed this 
experiment , and added many others of great importance, but which would 
carry me too far from ray subject. 
As the sap circulates in plants by the aid of numerous vessels and cells, 
which have no rectilinear communication, the force with which the sap 
ascends may be explained by a principle deduced from the experiments of 
M. de Montgolfier, who has proved, that, by means of a very small force, 
liquids may be raised loan almost indefinite height, provided the pressure 
of the column of liquid be destroyed by numerous interceptions or valves. 
The force with which the sap ascends is proportioned to the health of 
the plants, and the abundance of its transpiration; a stalk deprived of its 
leaves will raise less mercury than one retaining them; and trees having 
smooth, spongy leaves abounding in exhaling pores, such as the wild 
quince, the alder, the sycamore, the peach, the cherry, &c. raise it to a 
much greater height than those of which the leaves are varnished or dry. 
The beautiful experiments of Hales have verified these results. 
All the water imbibed by the different parts of plants, but especially by 
the roots, is first employed in mixing the juices; and facilitating their cir¬ 
culation; it is then decomposed, and a part of it furnishes hydrogen, so 
abundant in the products of vegetation, but the greatest portion is evapo¬ 
rated, principally by the leaves, and thus maintains their temperature be¬ 
low that of the atmosphere during the burning heat of summer. Hales 
observes, that a sun-flower plant transpired by the leaves, in the space of 
twelve hours, 11b. 14oz. of water. 
The cold which begins to make itself felt in autumn, retards the move¬ 
ment of the sap; the fluids become thickened, the solids contracted, the 
leaves cease to inhale, and the roots no longer absorb nourishment from- 
the soil, and at length the vital functions are suspended. The returning 
warmth of spring brings renewed life to the organs; the fluids and the sp- 
