The North American Forest 27 



afforded opportunity for reproduction of trees in a 

 wood otherwise unfavorable to young growth. Of 

 course the variety of circumstances making such 

 opportunities is infinite. Often it happens in the 

 primeval wilderness that whole bodies of trees are 

 overthrown by violent winds, and then the condi- 

 tions brought about by the fall of a single tree are 

 repeated on a larger scale. This matter of wind- 

 falls is perhaps not quite understood by the aver- 

 age layman. Generally speaking, trees adapt their 

 manner of growth so as to withstand the violence 

 of all winds to which they are likely to be exposed. 

 The means by which they increase their power of 

 resistance to storms are various. One of these is 

 the elasticity of their fibres, even of the trunk, by 

 virtue of which they bend before the wind, but im- 

 mediately resume the upright position when the 

 blast ceases. Another means of protection is a 

 root system going very deeply into the ground, 

 combined with great strength of the trunk. Un- 

 less the latter quality were added, a strong wind 

 might not be able to uproot the tree as it would a 

 shallow-rooted one, but the very strength and un- 

 yielding quality of the root would increase the 

 danger of the trunk being broken off. Still another 

 useful device is the very common thickening of the 

 lower part of the bole just at the place where the 

 greatest strain is suffered when the tree is bent. 

 Now, within the limits set by the characteristics of 

 each species, each individual tree develops these 

 means of defence to a greater or less degree accord- 



