PT. lY. 



PRUNING AND THINNING. 



197 



more or less acute with the grain of the stem. But 

 tliis cross-grain is united grain for grain ; that is, growth 

 for growth with the grain and growth of the stem. 

 And if the tree is cut while the branch is alive, the 

 branch forms no knot, but only a cross-grain. If the 

 branch dies while the tree is alive, the cross-grain dries, 

 and becomes an united knot. Afterwards the stem 

 incloses, each year, a piece of disunited dead wood 

 instead of living wood, which is united to it. This 

 forms a disunited knot, instead of an united knot, in the 

 timber ; and as the dead wood is dry when it is 

 inclosed, the living wood, when sawed up, dries from it. 

 This forms a movable knot. The bark ceases to run 

 when dead, and is frequently inclosed with the dead 

 branch. This, and afterwards rottenness of the outside 

 of branches, increase the disunion of knots from the 

 timber. But, besides the flaw in the timber, the dead 

 wood which is inclosed forms an impediment to the 

 course of the sap, and a consequent distortion of the 

 grain, as much as if a bolt of iron were passed into the 

 tree. 



Now, the great objection to a cross-grain or to an 

 united knot is, that it prevents the timber from cleaving 

 and working well, as the carpenters say : but it does 

 not weaken the timber, or render it more liable to 

 break ; but at every disunited knot the timber is 

 already broken^ besides the cross-grain. 



De Candolle remarks that, as the girthing of the 

 branch is at first extremely small, but increases 



