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of the species. 
ROTATION 
neous plant in any situation whatever, it strives 
to send up as many or as distant suckers as will 
correspond to the degree in which the immediate 
soil has become exhausted; and, in general, 
whatever be its species, it makes this kind of 
effort, at an earlier or later period of its existence 
and in a lesser or greater amount of strength, 
proportionately to its voracity for some of the 
rarer principles of the soil, and to the presence 
or absence, the abundance or the paucity, of its 
making migrations by means of seeding. Similar 
remarks might be made, with far more force, re- 
specting the rhizomas, the bulbs, the tubers, the 
offsets, the runners, and the stolons of herbaceous 
plants; but are, in many instances, so obvious 
and striking, that they will spontaneously occur 
to any ordinarily attentive observer. Straw- 
berries and potatoes may be quoted as familiar 
examples. “ And these,” remarks Sir Humphrey 
Davy, “at first produce luxuriantly in virgin 
mould recently turned up from pasture; but in 
a few years they degenerate, and require a fresh 
soil, and their organization is such, as to be con- 
stantly producing the migration of their layers. 
Thus the strawberry by its long shoots is con- 
stantly endeavouring to occupy a new soil; and 
the fibrous radicles of the potato produce bulbs 
at a considerable distance from the parent plant. 
Lands in a course of years,” he continues, “ often 
cease to afford good cultivated grasses; they 
become, as it is popularly said, tired of them. 
The most remarkable instance of the powers of 
vegetables to exhaust the soil of certain princi- 
ples necessary to their growth is found in certain 
funguses. Mushrooms are said never to rise in 
two successive seasons on the same spot, and the 
production of the phenomena called fairy rings 
has been ascribed by Dr. Wollaston to the power 
of the peculiar fungus which forms it, to exhaust 
the soil of the nutriment necessary for the growth 
The consequence is, that the 
ring annually extends, for no seeds will grow 
where their parents grew before them, and the 
interior part of the circle has been exhausted by 
preceding crops; but where the fungus has died, 
nourishment is supplied for grass, which usually 
rises within the circle, coarse, and of a dark 
green colour.” 
All plants do not exhaust the soil in the same 
degree. Though all are nourished by air, water, 
and the juices of the soil; yet they differ widely 
from one another in the quantity of the last of 
these which they abstract. Some require to 
have their roots constantly immersed in water, 
some require a sandy and arid situation, and 
some thrive only in rich, loamy, high-manured 
soils; and no two of these and other great 
classes, or even of many subordinate ones, agree 
in the amount of their dependence on the soil 
for supplies of air and moisture, and especially 
in the proportion of saline ingredients which 
they withdraw from land. “The cereal plants 
and most of the grasses,” remarks Chaptal, 
OF CROPS. 
“throw up long stems, consisting chiefly of 
fibrous matter ; and these are furnished at their 
foot with a few leaves, which, on account of the 
compactness of their texture, and the small sur- 
face which they present, can absorb, compara- 
tively, but little either of air or water. These 
plants therefore derive their nourishment prin- 
cipally from the soil, and their stalks are em- 
ployed either for litter or food for animals; so 
that while they greatly exhaust the soil, they re- 
turn scarcely anything to it,—their stalks being 
cut and taken away from the ground for the 
purposes just mentioned, and their roots, which 
alone remain, being dried up and drained of all 
their juices, in the process of forming and of 
maturing the seed, Plants, on the contrary, 
abundantly furnished with large, thick, porous 
leaves, that are constantly green, imbibe from 
the atmosphere carbonic acid and oxygen, and 
draw from the earth such other substances as 
they require for their nourishment. When plants 
of this kind are cut in a green state, the loss of 
nutritive juices sustained by the soil is less sen- 
sibly felt, inasmuch as these are in part given 
back to it by the roots. Such plants as are usually 
cultivated for fodder are nearly all of this descrip- 
tion. There is another class of plants, which, 
though cultivated principally for their seed, are 
less exhausting to the soil than the cereal plants ; 
we refer to the numerous family of legumes, 
which holds an intermediate place between the 
two classes of which we have just spoken. The 
long perpendicular roots of the leguminous plants 
divide the soil, and their large leaves, and thick, 
soft, spongy stems, readily absorb both air and 
water. The different parts retain for a long 
time the juices with which they are so abun- 
dantly impregnated, and give them back to the 
soil, when the plants are ploughed in at a period 
before they become mature; and by this means 
alone, the soil may be put in a condition to pro- 
duce a good crop of grain. Beans are particu- 
larly valuable in this respect ; while vetches and 
pease, and more especially the latter, are less fer- 
tilizing in their effects. Generally speaking, if 
plants be cut in a green state, and at the time 
they are in flower, whatever may be their parti- 
cular nature, they do not exhaust the soil; since 
up to this period they have drawn their nourish- 
ment almost exclusively from the earth, air, and 
water. Both their stalks and roots abound in 
juices, and the parts remaining after the former 
are cut, return to the soil all that has been taken 
from it for the support of the plants. But as 
soon as the seed once begins to form, the process 
of nutrition undergoes a change. The plant, as 
before, still abstracts nutritive principles from 
the earth and atmosphere; but in addition to 
this, it now resorts to the juices contained in its 
stalks and roots, and these likewise are made to 
contribute to the formation of the seed ; so that, 
from this time, the stalks and roots are both 
gradually dried up and exhausted.:..and when at 
