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THE POPULAR SCIENCE MONTHLY 



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 com- 

 pression, 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, heavv-timbered 







Fig. 2. Showing mushroom rupturing concrete. 



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, labor- 

 ing under the impression that burglars were responsible for the dis- 

 placement 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 deli- 



