111. } EFFECTS OF SOIL, &¢., 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 
