210 



PRUNING AND THINI^ING. 



PT. lY. 



below the branch, measured at the lower edge of the 

 board, is only three inches five-sixteenths. I imagine 

 that the dead branch acted like a ligature, and that, by 

 checking the descent of the sap, it caused the swelling 

 above it. Below the branch, the growths gradually 

 and annually diminish after the sixth, which is the 

 time of the death of the branch. I have no doubt 

 that the reason of this is, that the branch was killed 

 by the proximity of neighbouring trees, and that they 

 at the same time killed, and afterwards continued to 

 kill, an undue number of side-branches, which caused 

 an unduly diminished return of descending sap, and, 

 consequently, a diminished annual ring or growth of 

 timber. So that, notwithstanding the gradual dimin- 

 ishing after the sixth growth, the first fifteen growths 

 of this board are nearly three times the size of the 

 next fifteen growths; and from after the fifteenth 

 growth of this board, the tree was doubtless one of 

 those denuded poles of which the growth of our un- 

 thinned plantations in general consists. But if room 

 is given for these poles to increase the size of their 

 heads, they will in the same proportion increase the 

 size of their annual rings of timber. 



The centre of the lower part of the tree was, 

 doubtless, much older than any part of this board. 

 I imagine that the sort of wavy cross-grain, which 

 may be observed along the upper edge of aU branches 

 which are cut like this specimen, to be the result of 

 the mechanical difficulty which the new growth has to 



