182 MASS. EXPERIMENT STATION BULLETIN 170. 



luis a tendency to displace the tacks; consequent!}^ the metal covering: 

 becomes loose and valueless in a short time. Metal is inclined to deteri- 



orate in a few years, and cannot 



accommodate itself to much 

 movement in the tree vuiless it is 

 used in sections and imbricated 

 or overlapped like shingles. 



Sometimes metal is used to 

 cover cement-filled cavities, but 

 this is of no particular value, and 

 does not im]irove the appearance 

 of the tree. The principal pur- 

 pose in using it over cement is to 

 cover the cracks, and when used 

 in connection with iron bands 

 over the surface it is supposed 

 to help hold the cement in place. 

 In some cases where metal is used 

 in this way it is lapped over on 

 the bark 4 or 5 inches, but this 

 destroys the underlying tissues 

 and arrests their future develop- 

 ment, thus defeating one of the 

 '., encouraging and directing the 



Fig. 51. — Chestnut tree cavity resulting 

 from stump growth, with cavity covering 

 of cement about 6 inches thick. (See 

 Fig. 52.) 



main objects of treating cavities, — 

 healing tissue or callus formation. 



Elastic Cement. — Elastic cement, such as is emploj^ed by slaters, has 

 been used for some years in tree repair 

 work, and was recommended for this pur- 

 pose by the Massachusetts Forestry Associ- 

 ation about 1000. Its principal value in 

 tree repair work consists in its elastic 

 properties and its adaptability to places 

 where there is considerable movement. It 

 is too expensive for use in large cavities, 

 costing from 4 to 15 cents per pound, but 

 it has been employed to some extent for 

 filling small spaces and also as a thin 

 covering for cavity openings. In the latter 

 case wire mesh is strung across the cavitj' 

 opening, the wire mesh being re-enforced 

 with iron and shaped to conform to the 

 outer contour of the tree; and the elastic 

 cement is plastered on the mesh. (See 

 Figs. 54 and 55.) 



This method of treating cavities has been especially recommended by 

 Mr. L. F. Prouty, associated with the citj^ forestry department, Spring- 



FiG. 52. — Illustrating cross-sec- 

 tion of the cemeut surface 

 covering to cavity shown in 

 Fig. 51. W, wire stapled to 

 sides of cavity; I, iron reen- 

 forcing; C, cement. 



