SUGGESTIONS. 227 



ly trenched and lightened up as it necessarily must be to allow 

 of a paving to be made under it. The paving does not probably 

 much retard the natural descent of water from the surface, nor 

 does it interfere with its capillary ascent ; the trenching makes 

 the descent of superabundant water from the surface more rapid, 

 while the increased porosity of the trenched soil gives it increased 

 power of absorption, both from the subsoil and the atmosphere, 

 as well as of retention of a healthy supply of moisture. The 

 paving also prevents the roots from descending below where this 

 most favorable condition of the soil has been made to exist. The 

 effect would doubtless be greatly better if thorough-draining were 

 given in addition ; but so far as it goes, the under-paving and 

 trenching is calculated to effect the same purpose as deep drain- 

 age : to secure a healthy supply of heat, light and moisture to all 

 the roots. 



It is evident that the precautions and remedies which have 

 been found of service against canker, whether operations upon 

 the roots or the foliage, are all such as are calculated to establish 

 or replace the tree in circumstances favorable to its general 

 thriving, healthy condition. 



This suggests the idea that canker may be the result of a gen- 

 eral constitutional debility of the tree, not occasioned by any one 

 cause or set of causes, but resultant from all and any circum- 

 stances unfavorable to the healthy growth of a tree ; and it is a 

 question whether the same may not be thought of the peculiar 

 diseases of other trees, the peach, the pear, the plum, the syca- 

 more, and perhaps even of the rot of the potato. 



