TYPES OF VEGETATION 19 
fertile, because of the relatively large amount of humus— 
2.€., rotting plant and animal remains—present in it. 
Some cultivated land has, however, been reclaimed from 
moorland and fen, and some even from the sea. 
Arable land is, as the name implies, land under the 
plough, and is utilized for the raising of crops. The nature 
of the crops raised depends, in the first place, upon the 
climate ; secondly, upon the soil; and, lastly, upon the 
conventional needs of the resident community .or the 
demands of neighbouring or distant profitable markets. 
By cultivation, man so modifies the soil-factors that 
the soil itself plays a part vastly inferior to that of climate 
in deciding the most suitable crop for a locality. Indeed, 
under the methods of modern agriculture, the nature of 
the soil is quite a minor matter, granted, of course, a 
certain minimum of fertility. For this reason the great 
cereal crops like wheat, maize, and oats grow on all kinds 
of soil within limits which are climatically determined. 
The water-supply dominates all other factors in cultivated 
soils, 
Agriculture and Farming in the British Isles. 
1. Wheat.—In this country wheat can only be grown 
with profit—at least, under present agricultural methods 
—where the mean summer temperature during the 
ripening of the ear is greater than 56° F. (13° C.), and 
the rainfall is less than 30 inches annually. These 
limiting factors readily determine the range of wheat- 
cultivation in the British Isles. They exclude most of 
the upland slopes over 500 feet, large parts of the West 
of England, all Wales, and most of Scotland and Ireland. 
In countries like ours, where the winter is not severe 
enough to destroy the seedlings, wheat is usually sown 
in the autumn. In Canada, on the other hand, where 
the ground is frozen hard for several months, it is sown 
in the spring, as soon as the snow has disappeared and 
the ground is sufficiently thawed to be broken by the 
plough. 
Wheat flourishes best in a dry, sunny region, and the 
winter conditions determine whether the sowing should 
be before or after the frost. The great wheat-districts 
of the world are thus the grasslands—e.g., the steppes of 
