rx. IV. 



PRUXITO AXD THINKING. 



203 



The rapidity of the heahng will be directly as the 

 rapidity of the growth in girthing of the stem. Suppose 

 the width of the new annual layer of wood to be a 

 quarter of an inch, it would take twelve years to heal 

 over the end of an amputated branch, whose diameter 

 was six inches. During those twelve years, the grain 

 of the new wood deposited over the end of the branch 

 will be curled ; after that, straight-grained wood will 

 be annually deposited. These are reasons for prevent- 

 ing the undue growth of side-branches in bulk, and for 

 finally taking them off while small. 



On cutting across the part of a branch which I had 

 rung, I found that in the course of twelve years the 

 outside wood had died, and dried in only to the thick- 

 ness of paper. From this I imagined that the case 

 would be the same with the ends of amputated branches. 

 I think it, however, probable that the reason why so 

 slight a surface of the rung branch died and dried was, 

 that the whole of the internal wood remained the con- 

 duit of the upward sap. In the case of amputated 

 branches, the internal wood would cease to be a conduit 

 of sap, and the whole probably dies and dries in as far 

 as the cross-grain. This would occasion a knot to that 

 extent ; but it would be a knot united annually growth 

 for growth with the stem- wood, and not hke the de- 

 tached knots which are formed by the inclosing in the 

 stem of branches which have died. 



The healing takes place over a dead branch which 

 is cut off in the same manner as over a hving one. 



