280 PRINCIPLES OF GARDENING. [CH. VIII. 



strictly be designated ulcer, or Gangrana saniosa. 

 This disease has a considerable resemblance to the 

 tendency to ossification which appears in most aged 

 animals, arising from their marked appetency to se- 

 crete the calcareous saline compounds that chiefly 

 constitute their skeletons. The consequence is an 

 enlargement of the joints, and ossification of the cir- 

 culatory vessels and other parts, phenomena very ana- 

 logous to those attending the cankering of trees. As 

 in animals, this tendency is general throughout their 

 system; but, as is observed by Mr. Knight, " like 

 the mortification in the limbs of elderly people,'" it 

 may be determined as to its point of attack, by the 

 irritability of that part of the system. This disease 

 commences with an enlargement of the vessels of the 

 bark of a branch, or of the stem. This swelling in- 

 variably attends the disease, when it attacks the 

 apple tree. In the pear the enlargement is less, yet 

 is always present. In the elm and the oak some- 

 times no swelling occurs ; and in the peach I do not 

 recollect to have seen any. I have never observed 

 the disease in the cherry tree, nor in any of the pine 

 tribe. The swelling is soon commmiicated to the 

 wood, which, if laid open to view on its first appear- 

 ance, by the removal of the bark, exhibits no marks 

 of disease beyond the mere unnatural enlargement. 

 In the course of a few years, less in number in pro- 

 portion to the advanced age of the tree, and the un- 



