INTRODUCTION 



the species, and are well seen in Elder, Beech, and Birch, in the latter being 

 conspicuous as narrow slits measuring from a half to four inches in length. 



The bark of many deciduous trees and shrubs is brightly coloured, and 

 advantage is often taken of this in planting for winter effect. 



Several of the Dogwoods have red stems, and browns are common among 

 the Spiraeas and Syringas {Philadelphus). White is familiar in Silver Birch 

 and the White-stemmed Bramble, greens in the Kerrias, Genistas, and Brooms, 

 while in the Willows we have all shades of orange, yellow, and purple. 



The bark of many trees is subject to the attacks of Scale insects, Aphides, 

 and various species of Bark Beetles, some of which are mentioned in the 

 detailed descriptions, while the leaves of trees and shrubs are also largely 

 eaten by various kinds of larvae. Man utilises the bark of the Cork Oak in 

 many ways, and that of Oak and Birch is much used in tanning, though 

 fast being superseded in this country by chemicals. 



The valuable alkaloid quinine is obtained from the bark of several species 

 of Cinchona, and the popular Cascara Sagrada or Sacred Bark comes from 

 the Rhamnus PursMana, a small tree closely allied to the English Buck- 

 thorn, and found in abundance in the United States of America. 



USES OF TIMBER AND TREES GENERALLY 



Before leaving the main stem of the tree we may refer to the innumerable 



uses to which the timber is applied. The mere mention of only the principal 



would occupy several pages, and the ever-increasing demand being made on 



the world's forests by the advance of civilisation is becoming a serious problem. 



It has been said that forests have a remarkable influence on climate, especially 



as regards the rainfall, that forests check evaporation, and, by cooling the 



air above them, act as condensers of the aqueous vapour, causing the minute 



particles to unite and form drops which fall through the action of gravity. 



But recent research tends to prove this to be somewhat exaggerated, though 



over forests the rainfall may be slightly greater than in the open. In 



many districts, where the land has been cleared of trees, a diminution in 



the rainfall has occurred. The presence of trees tends directly to keep up and 



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