85 
125 Cropping a Garden. As we have just copied directions, 
which we hope will be useful in enabling the cultivator of the 
kitchen garden to select from amongst the numerous sorts of 
peas those which will prove most useful for the purposes requi- 
red ; we shall now extract from the same source a few general 
directions to be observed in cropping a garden. “The object 
to be obtained by a system of cropping is that of procuring the 
greatest quantity, and the best quality, of the desired kind of 
produce, at the least possible expense of labour, time, and ma- 
nure ; and, in order that this object may be effectually obtained, 
there are certain principles which ought to be adopted as guides. 
The chief of these is to be derived from a knowledge of what spe- 
cific benefit or injury every culinary plant does to the soil, with 
reference to any other culinary plant. It ought to be known 
whether particular plants injure the soil by exhausting it of par- 
ticular principles ; or whether, as has been lately conjectured by 
De Candolle, and as some think proved, the soil is rendered un- 
fit for the growth of the same or any allied species, by excretions 
from the roots of plants; while the same excretions, acting in 
the way of manure, add to the fitness of the soil for the pro- 
duction of other species. The prevailing opinion, as every 
one knows, has long been, that plants exhaust the soil, generally, 
of vegetable food ; particularly of that kind of food which is pe- 
culiar to the species growing on it for the time being. For ex- 
ample, both potatoes and onions exhaust the soil generally ; 
while the potato deprives it of something which is necessary to 
insure the reproduction of good crops of potatoes; and the on- 
ion of something which is necessary for the reproduction of 
large crops of onions. According to the theory of De Candolle 
both crops exhaust the soil generally, and both render it unfit 
for the repetition of the particular kind of crop : but this injury, 
according to his hypothesis, is not effected by depriving the 
soil of the particular kind of nutriment requisite for the partic- 
S ular kind of species ; but by excreting into it substances pecu- 
liar to the species with which it has been cropped, which sub- 
stances render it unfit for having these crops repeated. Both 
these theories, or rather perhaps hypotheses, are attended with 
some difficulty in the case of plants which remain a great many 
years on the same soil; as, for example, perennial-rooted herba- 
ceous plants and trees. The difficulty, however, is got over in 
143 AUCTAaiCM. 125, Card. Map. Vol. IJ, 476. 
