. Fig. 198. — Detailed view of exca- vated and bolted cavities. Above cross-section of a young tree trunk showing how the new wood and bark grow into an unfilled cavity from the margin. (The line on the wood indicates the amount of ex- cavating that would be needed be- fore filling the cavity.) 3. — Cross- section of a tree trunk showing the manner of using two single- headed bolts to brace a cavity. After Collins.

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Keywords: ., bookauthorstevensf, bookcentury1900, bookdecade1920, bookyear1921