446 



BOARD OF AGRICULTURE. [Pub. Doc. 



where, even if covered by the Avood of the trunk, they 

 extend from near the heart of the tree ahiiost to its surface, 

 forming the imperfections known as black knots (Fig. H). 

 If such branches can be removed when the tree is young, 

 the timber formed in the succeeding years will be perfectly 

 clear, so far as knots are concerned. 



The breakino- down of a limb, as shown in Fii>-. 7, leaves 

 a seamed and ragged wound, atlbrding a lodgement for 

 water and dust, which soon form a fruitful soil for propa- 

 gating the organisms of decay. These find ready entrance 

 to the trunk through the cracks and channels of the broken 

 wood. Left to itself, as the years go by, the entu'e stub 



FIG. 7. — Trunk injured by break- 

 ing down of hirge limb. 



Fig. S. — Fruitless attempt of a 

 healthy ti-ee to heal over a decaying 

 stub. 



rots away, and the disease sinks steadil}' down into the 

 trunk, until a hollow is formed large enough for the nest of 

 the squirrel or screech owl. Let such a branch as the one 

 shown in Fig. 7 be broken two or three feet from the trunk, 

 and the result may be, in time, the same. AVe have seen 

 that the elaborated sap which forms ncAv wood and bark, and 

 which alone can heal wounds, comes downward from the 

 leaves. The bare stump, bearing no leaves and having no 

 circulation, has no power of healing its wounds ; it must 

 "bleed" and die.* It dies back to the living trunk from 

 whence it sprung. Its bark, being dead, separates from the 

 wood and falls off, leaving a bare stump projecting to the 



* Such stumps sometimes send out shoots from latent buds, hut in such cases 

 are only imperfectly healed. 



