20 North American Forests and Forestry 



of its own kind or a different species. Again, the 

 main objects of the struggle are light and moisture. 

 To gain these necessaries, each tree adapts its 

 manner of growth, the shape of its trunk, branches, 

 roots, and leaves in a most marvellous manner. 

 Everybody must have noticed that no tree is the 

 exact counterpart of another of the same species. 

 Aside from differences in age and size, each tree 

 has a different way of disposing its branches, 

 twigs, and leaves. This difference is invariably 

 exactly of the kind which is most favorable to the 

 growth of the tree under the particular local cir- 

 cumstances among which it must develop. As a 

 tree cannot run away, it has to make the best it 

 can out of the situation in which it finds itself as 

 a seedling. Sometimes the devices the tree hits 

 upon in difficulties are absolutely startling. Here 

 is an illustration : At Devil's Lake, Wisconsin, a 

 pine tree is standing on the side of the almost 

 vertical quartzite rocks of the locality. It had 

 originally sprouted in a cleft where there is hardly 

 a shovelful of soil. The tree is now about six 

 inches in diameter. From its little cleft, it sends 

 out a single root, as thick as the trunk, along a 

 narrow ledge, on which there is practically no soil 

 at all. On the surface of this ledge, lying on the 

 exceedingly hard rock, this root runs along, almost 

 horizontally, for twenty-six feet, where it finds an 

 accumulation of soil and enters the ground. 



While there are infinite variations of form grow- 

 ing out of this struggle for moisture and light, 



