76 
THE SOUTHERN CULTIVATOR. 
ON THE alternation OF CROPS. 
It has long since been found by experience, 
that the growth of annual plants is rendered im- 
perfect, and their crops of fruit or herbs less 
abundant, by cultivating them in successive 
years on the same soil, and that, in spite of the 
loss of time, a greater quantity of grain is ob- 
tained when a field is allowed to lie uncultiva- 
ted for a year. Durihg this interval of resf, the 
soil in a great measure, regains its original ler- 
tility. 
It has been further observed, that certain 
plants, such as peas, clover, flax, thrive on the 
same soil only after a lapse of years; while oth^ 
ers, such as hemp, tobacco, helianthus tuberosus^ 
rye and oats, may be cultivated in close succes- 
sion when proper manure is used. It has also 
been found, that several of these plants improve 
the soil, while others, and these are the most nu- 
merous, impoverish or exhaust it. Fallow tur- 
neps, cabbage, beets, spelt, summer and winter 
barley, rye and oats, are considered to belong to 
the class which impoverish a soil; while by 
wheat, hops, madder, late turpeps, hemp, popies, 
teasel, flax, weld, and licorice, it is supposed to 
be entirely exhausted, 
The excrements of man and, apiinals have 
been employed Ironi the earlist tirnes foi the 
purpose of increasing the fertility of soils; and 
it is completely established by all experience, 
that they restore certain cpnstituents to the soil, 
which are removed with th,e roots, fruit or grain 
or entire plants grown upon it. 
But it has been observed that the crops are 
not always abundant in proportion to the quan- 
tity of manure employed, even although it may 
have been of the most powerful kind; that the 
produce of niany plants for example, diminishes 
in spite of the apparent replacement by manure 
of the substances removed from the soil, when 
they are cultivufed on the same field for several 
years in succession. 
On the other hand it has been remarked, that 
a field which has become unfitted for a certain 
kind of plant, was not on that account unsuited 
for another; and upen this observation, a sys- 
tem of agriculture has been gradually founded, 
the principal object of which is to obtain the 
greatest possible produce with the least expense 
of manure. 
Now it was deduced from all the foregoing 
facts, that plants require for their growth differ- 
ent constituent of soil, and it was very soon 
perceived, that an alteration of the plants culti- 
vated maintained the fertility of a soil quite as 
well as leaving it at rest or fallow. It was evi- 
dent that all plants must give back to the soil in 
vrhichthey grow difierent proportion? of certain 
substances, which are capable of being, used as 
food by a succeeding generation. 
But agriculture has hitherto never sought aid 
from chemical principles, based on the know- 
ledge of those substances which plants extract 
from the soils on which they grow, and of those 
restored to the soil by means of manure. The 
discovery of such principles will be the task of 
a future generation, for what can be expected 
from the present, which recoils with seeming 
distrust and aversion from all the means of as- 
sistance ofiered it by chemistry, and which does 
not understand the art of making a rational ap- 
plication of chemical discoveries! A future 
generation, however, will derive incaleuiable 
advantage from these means of help. 
Of all the views which have been adopted re- 
garding the cause of the favorable efiects ol the 
alternations of crops, that proposed by M. De- 
candolle alone deserves to be mentioned as rest- 
ing on a firm basis, 
Decandolle supposes that the roots of plants 
imbibe soluble matter of every kind from the 
.soil, and thus necessarily absorb a number of 
substances -which are not adapted to the purpo- 
ses of nutrition, and must suhsequently be ex- 
pelled by the roots, and returned to the soil. — 
Now, as excrements cannot be assimulated by 
the plan which ejected them, the more of these 
matter? which the soil contains, the more un- 
fertile must it be for the plants of the same spe- 
cies. The excremeatitious matters may, how- 
ever, still be capable of assimilation by another 
kind of plant, w'hich would thus remove them 
from the soil, and render it again iertfle for the 
first. And if the plants last grown also expel 
substances from their roots, which can be ap- 
propriated as food by the former, they will im- 
prove the soil in two ways. 
Nqw a great number of facts appear at first 
sight to give a high degree of probability to this 
view. Every gardner knows that a Iruit tree 
cannot be made to grow on the same spot where 
another of the same species has stood; at least 
not until alter a lapse of several years. Before 
new vine stocks are planted in a vineyard from 
which the old have been rooted out, other plants 
are cultivated on the soil for several years. In 
connexion with this it has been observed, that 
several plants thrive best w'hen growing beside 
one another; and on the contrarj', that others 
mutually prevent each other’s development. — 
Whence it was concluded, that the beneficial in- 
fluence ip the former ease depended on a mutu- 
al interchange of nutriment between the plants, 
and the injurious one in the latter on a poison- 
ous action of the excrements of each on the 
other respectively. 
A series of expet iments by Macaire Princep 
gave great weight to this theory. He proved 
beyond all doubt, that many plants are capable 
of emitting extractive matter from their roots. — 
He found that the excretions were greater du- 
ring the night than by day (?), and that the wa- 
ter in which plants of the family of the Le^umi- 
nma grew acquired a brown color. Plants of 
the sariic species placed in water impregnated 
with these excrement-, rvere impeded in their 
growUh, and laded prematurely, while, on the 
contrary, corn plants grew vigorously in it; and 
the color ol the water diminished sensibly; .so it 
appeared that a certan quantity of the excre- 
ments of the LeguviiTwsee had already been ab- 
sorbed by the corn plants. These experiments 
afibrded, as their main result^ that the charac- 
ters and properties of the excrements of difler- 
ent species of plants are different from one an- 
other, and that some plants expel excrementi- 
tious matter of an acrid and resinous character; 
others mild substances resembling gum.. The 
former of these, according to Macaire Princep, 
may be regarded as poisonous, the latter as nu- 
tritious. 
The experiments of Macaire Princep afford 
positive proof that the roots, probably of all 
plants, expel matters, which cannot be convert- 
ed in their organism either into woody fibre, 
starch, vegetable albumen, or gluten, since their 
expulsion indicates that they are quite unfitted 
for this purpose. But they cannot be consider- 
ed as a confirmation of the theory of Decan- 
dolle, for they leave it quite undecided whether 
the substances were extracted from the soil, or 
formed by the plant itself from food received 
from another source. It is certain that the gum- 
my and resinous excrements observed by Ma- 
caire Princep, could not have been contained in 
the soil; and as we know that the carbon of a 
soil is not diminished by culture, but on the con- 
trary increased, we must conclude that all ele- 
ments which contain carbon must be formed 
from the food obtained by the plants from the 
atmosphere. Now, these excrements are com- 
pounds, produced in consequence of the trans- 
formations of the food, and of the new' forms 
which it assumes by entering into the composi- 
tion of the various organs. 
M. Decandolle’s theory is properly a modifi- 
cation of an earlier hypothesis, which supposed 
that the roots of difierent plants extracted differ- 
ent nutritive substances from the soil, each plant 
selecting that which w'as exactly suited for its 
assimilation. According to this hypothesis, the 
matters incapable of assimilation are not ex- 
tracted from the soil, -while M. Decandolle con- 
siders that tkev are returtied to it in the form of 
excrements. Both views explain how it hap- 
pens, that after com, corn cannot be raised to 
advantage, nor after peas, peas; but they do not 
explain how a field is improved by lying fallow, 
and this is in proportion to the care with -which 
it is tilled and kept tree from weeds; nor do they 
show' how a soil gains carbonaceous matter by 
the cultivation of certain plants, such as lu- 
cerne and sainfoin. 
Theoretical considerations on the process of 
nutrition, as w'ell as the experience of all agri- 
culturists, so beautifully illustrated by the ex- 
periments of Macaire Princep, leave no doubt 
that substances are excreted from the roots of 
plants, and that these matters form the means 
by Avhich the carbon received from humus in 
the early period of their growuh, is restored to 
the .soil. But -we may now inquire whether 
these excrements, in the state in which they are 
expelled, are capable of being employed as food 
by other plants. 
The excrements of a earaivorous animal 
contain no constituent fitted for the nourishment 
of another of the same species; but it is possD 
ble that an herbivorous animal, a fish or a fow'l 
might find in them undigested matters capable 
of being digested in their organism, from the 
very circumstance of their organs of digestion 
having a difierent structure. This is the only 
sense in which we can conceive that the excre- 
ments of one animal could yield matter adapted 
for the nutrition of another. 
A number of substances contained in tJie food 
of aniinals, pass through their alimentary or- 
gans without change, and are expelled from the 
system; these gre excrements, but not excre- 
tions. Now, a part of such exerementitious 
matter might be assimilated in passing through 
the digestive apparatus of another animal.— 
The organs of secretion form combinations, of 
which only the elements -sv'ere contained in the 
food. The production of these new compounds 
is a consequence of the changes which the food 
undergoes in becoming chile and chyme, and of 
the further transformations to which these are 
subjected by entering into the composition of 
the organism. These matters, likewise, are eli- 
minated in the excrements, which must there- 
fore consist of two difierent kinds of substances, 
namely, of the indigestible constituents of the 
food, and of the new compounds formed by the 
vital process. The latter substances have been 
produced in consequence of the formation of 
fat, museular fibre, cerebral and nervous sub- 
stance, and are quite incapable of being con- 
verted into the same substances in any other 
animal organism. 
Exactly similar conditions must subsist in 
the vital processes of plants. When substan- 
ces, which are incapable of being employed in 
the nutrition of a plant, exist in the matter ab- 
sorbed by its roots, they must be again returned 
to the soil. Such excrements might be service- 
able, and even indispensable, to the existence of 
several other plants. But substances that are 
firmed in a vegetable organism during the pro- 
cess of nutrition, which are produced, there- 
fore, in consequence of the formation of woody 
fibre, starch, albumen, gum, acids, &c., cannot 
again serve in any other plants to form the same 
constituents of vegetables. 
The consideration of these facts, enables us 
to distinguish the difference between the views 
of Decandolle and those of Macaire Princep, 
The substances which the former physiologist 
viewed as excrements, belonged to the soil; they 
W'ere undigested matters, which although not 
adapted for the nutrition of one plant, might 
yet be indispensable to another. Those matters 
on the contrary', designated as excrements by 
Macaire Princep, could only in one form serve 
for ^e nutrition of vegetables. It is scarcely 
nei^sary to remark, that this exerementitious 
matter must undergo a change before another 
season. During autumn and -winter, it begins 
to suffer a change from the influence of air and 
water; its putrefaction, and at length, by contin- 
ued contact -with the air, -which tillage is the 
means of procuring, its decay are effected; and 
at the commencement of spring it has become 
conv’erted, either in whole or in part, into a 
substance which supplies the place of humus, 
by being'a constant source of carbonic acid. 
The quickness with which this decay ol the 
