170 MASS. EXPERIMENT STATION BULLETIN 170. 



thick paint or coal tar, and either elastic or Portland cement used to 



cover them, allowing the cement to come flush with the exterior surface 



of the wood. By this method 

 the ends of the bolt, washer and 

 nut are covered, and the scar 

 produced by this operation will 

 heal over in a short time, leav- 

 ing no trace. 1 



The poles of public service 

 corporations are often attached 

 to trees by guy wires, and care 

 should be taken to prevent in- 

 jury to the tree from girdling, 

 etc. A large wire loop placed 

 round a tree and properly in- 

 sulated from the trunk by special 

 hard wood blocks is usually 

 harmless, and is more desirable 

 on streets than other often un- 

 sightly methods of anchoring 

 poles. These blocks may be 

 made from oak, and should be 

 2 inches wide, 1^ inches thick 

 and 8 or 10 inches long for 

 heavy wires. They should be 

 provided with a shallow groove 

 to take the wire, the groove 



being made a trifle narrower than the wire to insure a tight fit. (See 



Fig. 42.) 



Treating Decayed Cavities, Fillings, etc. 

 Decayed cavities in trees are very undesirable 

 since any fungi and insects which may be present 

 will extend their range of activity, causing decay and 

 shortening the life of the tree. Cavities result from 

 poor pruning of limbs, the breaking off of branches, 



1 The weight of a limb may be roughly obtained by multiplying 

 the average diameter by the length. This calculation should include 

 the numerous small branches, limbs, etc. 



According to Prof. C. S. Sargent (Woods of the United States, 1885), 

 the weight of a cubic foot of elm wood is 40.55 pounds when dried at 

 100 C., and according to W. S. Clark (32d Kept. Mass. State Board of 

 Agriculture for 1874) the amount of water in elm wood varies from 

 40 to 60 per cent.; thus a cubic foot of green elm wood would equal 

 about 60 pounds. A limb 40 feet long with an average diameter of 8 

 inches would weigh about 840 pounds, and a section about 34 inches 

 long would equal 1 cubic foot. Of course the leverage which must be 

 overcome is determined by angles of the limb and point of attachment 

 of the chain or wire. (See Fig. 36.) 



FIG. 33. Chain and bolt method of support- 

 ing limbs. 



FIG. 34. Tree prop- 

 erly bolted; washer 

 countersunk and im- 

 bedded in cement. 



