188 



THE GYPSY MOTH. 



the cement, provided it was properly mixed and applied, 

 remained intact for years. Small holes surrounded by sound 

 wood were also filled to advantage in this manner. The 

 cement may be held effectively if laid on a strong iron wire 

 netting nailed across and just within the mouth of the hole. 

 Whenever cement is used on growing trees, it 'should be 

 faced up within the growth of new bark and 

 wood, so that the latter may grow over and 

 hold it tightly. (See Fig. 24.) When the 

 callus has already formed on the edge of 

 the cavity, it should be cut away. This 

 cutting will stimulate new growth, and if 

 the cement is properly faced up within 

 the mouth of the cavity, the callus will 

 eventually cover it. If the hole is so filled 

 that the cement laps over the ed^e upon 



FIG. 24. Cemented cavity. 



the bark, it is likely to prove worse than 

 useless, as the growing bark beneath the cement will throw 

 it off from the tree, leaving a space as a hiding-place for the 

 caterpillars. Hard cement must be carefully applied by an 

 experienced man, otherwise it is likely to prove worthless, 

 and by crumbling and cracking leave the cavity in a worse 

 condition than before. 



This cement cannot be used during the colder months of 

 the year, as the action of the frost may cause it to crack. 

 Neither can it be used effectively to stop cracks or cavities, 

 the sides of which may be moved independently of each 

 other by the action of the wind on the branches. Experi- 

 ments in closing such cavities with plaster of Paris, mineral 

 wool, Purcell's elastic cement, Webster's elastic 

 cement, Portland cement and Roslindale cement 

 were made in the winter of 1891-92. None of 

 these materials gave satisfactory results. Tarred 

 burlap or canvas has been used for this purpose 

 with some success. If three thicknesses of bur- 

 la"p are closely and strongly tacked over the 

 opening to a hollow in a tree trunk and after- 

 ward thoroughly soaked with coal tar (Fig. 

 25) the covering will remain intact and imper- 

 vious to the weather for several vears. Oiled cloth will also 



