IIL] EFFECTS OF SOIL, &c., ON. 23 



Trees grown in a copse might be expected to unite 

 the leading characteristics of the two forms of growth 

 just mentioned, inasmuch as, while the underwood 

 remained, the upward tendency of the stem would be 

 almost as strong as in a forest-grown tree, while each 

 time the copse was cut, the branches would have perfect 

 freedom of growth. It is, however, found that, although 

 forming curved branches and a greater length of stem 

 than can be met with in isolated trees, instead of the 

 wood being uniformly harder, the changes of temperature 

 to which the trees are subjected by the periodical loss 

 of the protecting underwood renders the quality of such 

 timber extremely variable. 



Variety of soil also exercises a direct influence upon 

 the quality of timber ; trees grown in a dry, rocky soil 

 having generally hard, compact wood ; while the wood 

 of those grown in swampy and moist situations will be 

 found comparatively soft and spongy in texture. Varia- 

 tions of temperature, violent storms, or proximity to the 

 sea or large rivers, will also affect the quality and rate 

 of growth of trees. 



It has long been supposed that the presence of trees 

 tends directly to keep up the water supply, and that 

 the clearing of large forests results, in time, in the drying 

 up of all the springs and watercourses in the neigh- 

 bourhood. That such an effect is produced is certain, 

 as attention was lately drawn to it by the condition of 

 large tracts of land in the South of France and other 

 districts, which, though long celebrated for their fertility, 

 were rapidly becoming valueless. The change in the 

 nature of the soil, consequent upon the partial drying 

 up of all the sources of water supply, was proved to 

 have commenced when the trees had been removed. 

 At the same time, it is said that in places where there 



