194 PRACTICAL TREE REPAIR 



of the decay. The basic principle we have so far 

 been working on is that the purpose of cavity work 

 is to stop decay, and that decay can be stopped 

 only by the complete excision of the contaminated 

 wood. Is there anything, then, which can be 

 done if complete eradication is impossible? To 

 this question, I believe, an answer, provisional 

 perhaps, can be made in the affirmative. Decay 

 undoubtedly progresses at different rates under 

 different conditions. Weather, moisture, and in- 

 sects favor the destruction of wood by decay; dry- 

 ness and freedom from the attacks of insects re- 

 tard most types of decay. Many rot-producing 

 fungi work so slowly that the infested wood re- 

 tains a fair amount of tensile strength and a very 

 considerable amount of compressive strength for 

 a great many years. It is worth while to prevent, 

 as long as possible, the complete disintegration of 

 this dead wood through the activity of insects and 

 of " follow-up " fungi and bacteria. As to this 

 last point very little is definitely known, but it is 

 probable that bacteria are very important in the 

 final bi caking down of decay-infested wood. 

 Moisture, it is well known, is essential to the 

 growth of bacteria, as of other fungi. 



There are times, then, the writer believes, when 

 it may be profitable simply to treat a cavity so 

 that insects and moisture may be kept out in so far 

 as is possible, and that the conditions may be 



