302 PRINCIPLES OF GARDENING. [CH. VIII. 



not an unnatural contraction of the sap vessels — be- 

 cause, in such case, the treatment might be injurious 

 rather than beneficial. I have ahvays found it aris- 

 ing from an excessive production of sap, if the tree, 

 when afflicted by extravasation, produces at the same 

 time superluxuriant shoots. 



3. Local contraction of the sap vessels. If the ex- 

 travasation arises from this cause, there is usually a 

 swelling of the bark immediately above the place of 

 dischari^e. 



I had a cherry tree in my garden, in Essex, of 

 which the stock grew very much less freely than the 

 graft. Consequently, just above the place of union, 

 a swelling, resembing a wen, extended round the 

 whole gii'th of the tree, from which swelling, gum 

 was continually exuding. In the stem below it 

 I never observ^ed a single extravasation. In a case 

 such as this, the cultivators only resource is to 

 reduce cautiously the amount of branches, if the 

 bleeding threatens to be mjuriously extensive, other- 

 wise it is of but little consequence, acting like tem- 

 porary dischaiges of blood from the human frame, 

 as a relief to the system. 



4. The extravasation of the sap from a wound is 

 usually the most abundant, and therefore the most 

 exhausting ; and as the wound, whether contused 

 or cut, is liable to be a lodgement for water and 

 other foreign bodies, opposed to the healing of the 



