18 BRITISH PLANTS 



factor is the water-supply, the next is the temperature. 

 The amount of water available to a plant affects its 

 nutrition, the temperature affects its vital activities. 

 The two things together constitute the climatic surround- 

 ings of the plant. 



At this stage, and especially as we are chiefly con- 

 cerned with our own country, it is advisable to draw 

 attention to the influence of man upon the vegetation of 

 the land upon which he has settled. Experience has 

 taught him from the earhest times the importance of 

 water upon the fertility of the soil, and by regulating and 

 controlling the water-supply — that is to say, by drainage 

 and irrigation — he has, modified the face of the land to 

 meet his requirements. Bogs have been drained, moor 

 and heath reclaimed ; forests have fallen beneath his 

 axe, and vast tracts of country, previously incapable 

 of yielding crops, have been brought into profitable 

 cultivation. Man, however, modifies the vegetation only 

 through the soil-factors. By removing or planting 

 forests, he may modify the humidity of the atmosphere 

 (p. 13), but otherwise he has no control over the climate. 



The Cultivation of Food-Products in the British Isles. 



This is an interesting and instructive subject, and we 

 touch upon it briefly because it is an excellent illustration 

 of the work of man in regulating and modifying the 

 vegetation. 



The land of Great Britain may for the present purpose 

 be divided into three main regions : 



1. Uncultivated Land, including alpine regions, moors, 

 heaths, lowland-swamps, and natural pastures. 



2. Woodland. 



3. Cultivated Land : 



{a) Arable Land — (i.) In which t^Aeosi can be grown, 

 (ii.) In which wheat cannot be 

 grown. 

 (6) Pastures — (i.) Permanent pastures. 



(ii.) Pastures under clover and 

 grasses in rotation. 



Most of the cultivated land was at one time covered 

 by forest. Porest-sofl, if properly drained, is naturally 



