224 



PRUNING AND THINNING. 



PT. IV. 



another. They cannot attam to first-rate growth with- 

 out ages of contention and kilhng all their neighbours. 

 In doing so, the growth of the survivors is not only 

 delayed for centuries, but in general permanently 

 marred. The axe should gradually and successively 

 relieve them from their neighbours. 



Of course, all side-growth is, from the position of 

 its weight, more liable to break than upright or verti- 

 cal growth. When a tree takes two leaders, from 

 want of light and from want of room on the inside, the 

 leaders grow from one another to the outside ; and 

 from their weight inclining to the outside, without 

 anything to balance it on the inside, they are liable to 

 split from one another. As each leader enlarges 

 annually in girthing, the junction at their two bases 

 progresses upwards, inclosing the bark of each between 

 the two. This double stratum of thick bark is killed 

 by mechanical pressure, perhaps for a foot or two in 

 height, and rots to that extent. This prevents the 

 deposit of any new wood on those parts of the inside 

 of either leader, and consequently also prevents the 

 perfect junction, or anastomosing, of the wood of the 

 two leaders. Water lodges in the hollow at the fork ; 

 and a frost which is severe enough to freeze this water 

 will rend apart the trunk of the sturdiest oak to a 

 certainty. Besides this, the hollow at the fork becomes 

 a leaf-trap, catches any dust which may be driven by 

 wind, receives the moss and detritus of the bark which 

 are washed down by rain, and forms a cupful of fine 



