Influence of Climate on Cultivation. 
163 
cereal crops in moist and in wet climates is exhibited b}^ the , 
place which wheat occupies in the rotation. In moist climates it 
thrives best after a bare fallow or green crops, in dry climates 
after seeds. Throughout Scotland, Ireland, and the West of 
England, wheat is a somewhat precarious crop after seeds, and 
accordingly oats are in general substituted for it. It is somewhat 
difficult to account for this well-known fact, but there are pro- 
bably two causes which are the principal in operation. In the 
moister climates the straw of wheat, unless in particular soils, 
seldom assumes a fine healthy colour when sown after seeds. 
The fresh decaying vegetable matter has the effect of producing a 
certain grossness in the plant which is not thrown off by the 
greater amount of direct sunshine that prevails in the drier 
climates. It is weaker in winter as well as in spring, and a thin 
plant is a frequent result, arising from depredations of insects or 
otherwise. 
When the climatic conditions are tlius less favourable, the 
health of the wheat plant is greatly promoted in its early stages 
by the soil being better prepared. Land that has had a summer 
fallow, or the benefits of cultivation which a root-crop insures, is 
in a much better state for allowing the young plants to run 
through the soil and gather food than after seeds. Wheat sown 
after green crops, such as potatoes or turnips, produces a more 
healthy plant and finer quality of grain than when sown after 
seeds. 
Another still more palpable reason for wheat not succeeding so 
well after seeds in moist climates is the greater vigour of the 
grasses. These are worse to extirpate, and any that remain 
in the soil are not kept in check by the wheat plant in spring 
and early summer : the grass consequently grows up among 
the wheat, and the land is left in a foul and unthrifty state. 
When oats follow grass, the result is very different ; they 
are sown broadcast over the ground, and a liberal allowance of 
seed insures a thickly-planted crop, which having the start of 
the grasses smothers them, or, at all events, ])revents their growling 
with much vigour. To such a degree is this the case, that Mr. 
Acland, in his Report ontlie Farming of Somersetshire, mentions 
that, after grass, oats are taken " to clean the land," as the farmers 
say, and permit its being sown with wheat the succeeding year. 
No plant seems so dependent on the physical properties 
of the soil as wheat ; more especially in dry climates. One 
of the causes, therefore, of wheat succeeding better after seeds 
in these, is owing to the remains of the stems and roots of 
the seeds making up to a certain extent for the physical de- 
fects of the soil. It might be thought that this manuring in the 
vegetable form would chiefly act by retaining ammonia within 
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