Page:Popular Science Monthly Volume 83.djvu/236

232 angle of about 15 degrees. The vertical diameter of the root where it enters is only 4 or 5 inches, while its lateral diameter, owing to compression, is 18 or 20 inches, or more.

Careful measurements and specific gravity determinations would indicate that the weight of the boulder is about 18 tons, and this is 'annually being lifted higher and higher by the root growing in the crack.

The roots of trees often penetrate, and, as they grow, displace the foundation walls of buildings. We recall an old, heavy-timbered

colonial house which had one corner thrown considerably out of the vertical by the growth of tree roots under the foundation. In this case the roots must have lifted many tons in weight. In another instance a gentleman noticed that the stone in a walk leading to his residence had been displaced. He became alarmed and sent for the police, laboring under the impression that burglars were responsible for the displacement and were planning some deep plot against him. But on moving the stone, which weighed 80 pounds, three large mushrooms were discovered and the mischief was explained. Instances are known of mushrooms pushing up through hard tar walks two or three inches thick without the slightest difficulty or evidence of injury to their