Page:Popular Science Monthly Volume 83.djvu/235

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T has been a matter of more or less common observation from time immemorial that plants possess the power to overcome obstacles. Some species of trees are not particular where they grow if there is enough soil and moisture, their roots often seeking places where apparently insurmountable obstacles must be overcome. In spite of the doubt often expressed, there are on record many cases of trees lifting large weights; and in mountainous regions large boulders are often found displaced by roots growing among them. Some trees even lift themselves slightly from their original positions into the air, as is evident from the location of the root buttresses, which are often found exposed above the surface, sometimes for a considerable distance. An instance is known of a tree growing in the center of a millstone, which later completely filled the hole and actually raised the stone from the ground.

Brick and concrete sidewalks are often ruptured and curbings displaced by roots, due to their growth in diameter, and perhaps in some cases to the actual uplift of the tree trunk and roots. The writer has had under observation for many years a black birch (Betula lenta L.), one root of which has entered a fissure in a large boulder and is slowly but constantly lifting this enormous weight. The fissure is at an