12 BRITISH PLANTS 



picked up in their journey over a wide stretch of sea. 

 This oceanic type of chmate prevails over western Europe 

 and the British Isles. Owing to the humidity of the 

 atmosphere, the winters in these regions are mild and 

 the summers cool. Regions remote from the sea have 

 a continental type of climate, in which the dryness of the 

 atmosphere leads to extremes of temperature, the summers 

 being very hot and the winters very cold : such is the 

 chmate of Russia and the interior of Canada. 



3. Proximity to Highlands and Mountain Ranges. — 

 Highland masses cool the air-currents, and much of 

 their contained moisture is consequently condensed to 

 liquid water, and falls as rain. There is a " wet " and 

 a " dry " side to mountain chains ; the side facing the 

 direction of the prevaihng Avinds is wet, for the air- 

 currents, following the rising gradients of the ground, 

 become cooled and gradually damper, the excess of 

 moisture falling as rain ; as the currents descend on the 

 other side, they become warmer and drier. Places 

 situated on the " lee " or dry side are said to he in the 

 rain-shadow of the mountains. A good example of this 

 is Bray, a watering-place near Dublin, which hes in the 

 rain-shadow of the Wicklow Hills. Though on the sea- 

 coast, it is one of the driest spots in Ireland. In the 

 same way, the desert of Atacama is a rainless region 

 lying along the coast of ChUi in the rain-shadow of the 

 Andes. 



Elevated plains, especially when they are very ex- 

 tensive, as in Spain and India, are usually very dry, and 

 subject to wide extremes of temperature. The winds 

 that blow over them lose most of their moisture whUe 

 they are ascending the flanks. The latter, being exposed 

 to the falling rain, are richly clothed with vegetation, 

 whilst the plateaux themselves are grassy plains or 

 semi-deserts. 



4. Direction of the Prevailing Winds. — If these have 

 passed over a broad expanse of water, they will be moist ; 

 if, on the other hand, they have travelled over a great 

 land-surface, they will be dry. Again, winds blowing 

 from the north are cold and dry, whUe those which come 

 from the south are warm and moist. North winds blowing 

 southwards must gradually become warmer, and, if at 

 the same time they are travelling over a wide "land- 



