nanan cebhimened 
ROTATION 
84 
soils, which, being in their nature more suited 
to the growth of wheat, were once valued more 
highly. And it isas much by the slow and al- 
most insensible amelioration of such land, as by 
any increased breadth of cultivation, that the 
country has become in any degree capable of 
supporting the vast numbers which have been 
added to her population. A small parish might 
be pointed out in which an aged farmer remem- 
bers the time when a single rick was all that it 
could produce of wheat in one year, whereas, 
without any increase of its ploughed ground, that 
same parish now yields five or six yearly. Its 
sandy soil was then drifted like snow before the 
wind, and the scanty barley might be sometimes 
seen borne away also; whereas, the very fields, 
still called ‘the Sands,’ are now, by that glutin- 
ous quality which high condition imparts—by 
the droppings and the tread of the sheep which 
are fed on the turnips that now grow in garden- 
like order where before was a naked fallow— 
compacted into a brown and adhesive, though 
still lightish loam,” 
Six general laws of vegetation, or six sorts of 
phenomena everywhere observable in the econo- 
| my of plants, may be named and briefly illustrat- 
| ed as involving all the principles which originate 
and control an enlightened system of rotation of 
crops,—first, that all plants more or less exhaust 
| the soil, and naturally possess appliances for 
| shifting their ground upon their native habitats, 
i —second, that all plants do not exhaust the soil 
in the same degree,—third, that plants of different 
families and different habits do not exhaust the 
soil in the same manner,—fourth, that all plants 
|| do not return to the soil either the same quan- 
|| tity or the same kind of manure,—fifth, that 
| plants differ widely from one another in the en- 
| couragement they give to the growth of weeds 
|| which either smother useful vegetation or rob 
|| the soil of nourishment,—and sixth, that all cul- 
tivated plants, particularly such as are grown in 
large quantities in the fields, may be classified 
|| into exhausting and ameliorating, or into groups 
which are cultivable mainly on their own ac- 
| count, and groups which are cultivable partly or 
mainly for the sake of affording benefit to their 
successors, according to the predominant prin- 
ciples which they abstract from the soil, or ac- 
cording to the balance between the effects of 
|| their obstructing action and the effects of their 
excreting and manuring action. We shall de- 
vote a paragraph to the succinct discussion of 
each of these laws ; and shall afterwards speak of 
the causes of the exhaustion of soil by plants, 
|| the practical principles which ought to regulate 
rotations, and the chief or most noticeable of the 
many kinds of rotation which are in use, in dif- 
ferent districts and countries, on different kinds 
of land. 
All plants, we have said, more or less exhaust 
the soil, and naturally possess appliances for 
shifting thie ground upon their native habitats ; 
| 
l 
{ 
OF CROPS. 
so that when any of them are cultivated from 
year to year upon the same piece of land, they 
either degenerate more and more toward un- 
productiveness and sickliness and extinction, or 
they must, by means of rotations and manurings, 
be supplied artificially with advantages tanta- 
mount to those which they obtain by their na- 
tural migrations. All draw out of the soil some 
of the principles of their nourishment or some of 
the substances which form their organisms and 
secretions ; and all more or less yield up some 
portion of these principles or substances to other 
spots by the expansion of their branches, by the 
dispersing action of winds, by the browsing of 
quadrupeds, by the picking of birds, and by 
other agencies ; and just in the degree in which 
they do not eventually deposit any of these prin- 
ciples of their nutrition in the spot whence they 
derived them, they deprive that spot of power to 
produce or maintain a future race of plants of 
their own species, and also any other plants which 
feed on the same substances. All plants have 
naturally a power of migration proportionate, in 
the rapidity and extent of its action, to the speed - 
with which they exhaust soils and the cravings 
they make for new sources of nourishment. Mul- 
titudes of herbs, both annual and perennial, 
belonging to many families, produce winged or 
downy seeds, and send off these on the gentlest 
breezes to germinate on distant grounds ; and 
multitudes of trees and shrubs, of the most di- 
versified constitution and opposite habits, pro- 
duce their seeds within the substance of plea- 
sant esculent fruits, and present these to birds | 
and other animals to be carried away by them, 
and deposited in other places. 
less storehouses of vitality, and compendiums of 
organic energy, than vehicles of vegetable migra- 
tion. See thearticle Sxzp. But all plants, from 
the sturdiest and most stationary to the feeblest 
and most fugitive, also travel, or are locomo- 
tively reproductive, by means of some one or 
other organism which developes contemporane- 
ously with either their own main growth, or 
their progress to maturity, or their advance to- 
ward decay. Many a tree, on finding the soil so 
deteriorated as to be incapable of any longer 
affording a due supply of nourishment to its 
young shoots and twigs, endeavours to escape 
from the spot on which it grows by sending up 
side-suckers which may push their individual 
roots beyond the sphere of the deteriorated soil, 
Either a tree or a shrub, so Jong as it is young, 
healthy, vigorous, and fully fed, remains steadily 
in its original site, entirely enjoying the riches 
of the subjacent soil, and making not the re- 
motest effort to migrate otherwise than by its 
seed ; but when it becomes old or stunted or ill- 
fed, whether it be an ancient plum or pear tree, 
in the orchard, or a decaying currant or goose- 
berry bush in the garden, or a starved rose-bush 
on thé flower-border, or any other kind of lig- 
All seeds, in fact, | 
whatever be their particular economy, are not | 
