48 SHADE TUBES. 



A word of warning must be given against the too free use 

 of cement or concrete in treating trees. The material un- 

 doubtedly has value in spite of a lack of elasticity that almost 

 inevitably prevents a filling from being water 

 cement too tisjht, or causes it to crack and fall out of place. 



freely. T , , 



It may always be used where a tree needs me- 

 chanical support, often where a cavity is unsightly, and some- 

 times to keep out rain. Under other circumstances it usually 

 is best to clean arid treat antiseptically a cavity, certainly a 

 superficial or shallow wound, and leave the rest to Nature. 

 In many cases a filling secretes rather than excludes mois- 

 ture, thereby inducing decay, and unless it is very carefully 

 made may interfere w T ith the normal processes of repair. 

 (See Plate III.) 



Where a cement filling must be made a few rules will 

 serve to guide: 



1. Prepare the cavity as above and in addition remove 

 the bark around its edge for about half an inch. This is 

 to expose active cells in the cambium from which the healing 

 callus may develop. 



2. Fill the cavity flush with the wood at the edge of the 

 opening but do not lap over. If desirable the cement may be 

 sculptured to resemble bark. 



3. A small cavity may be filled with pure cement. For 

 large ones use a concrete consisting of one part cement to 

 cement * wo P ai "ts of sand and reinforced with stone, 

 or concrete, brick or iron. Cover the exposed face with 

 an inch of pure cement. Spikes driven into the wood inside 

 the cavity will help to hold the filling in place. 



Another method is to cover the cavity with sheet zinc, 

 carefully fitted and securely nailed to the exposed wood at 

 Zinc its edge, and fill in concrete behind it. The 



facing. concrete should be liquid enough readily to 



adapt itself to the interior of the cavity. This is a simple 

 and very satisfactory way to get the filling in place and to 

 keep it there. Of course the zinc must be first fastened at 



