40 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Perhaps the most convenient method of dealing with the 

 subject in detail is to analyse, paragraph by paragraph, all that 

 is stated relating to canker by some recent and recognised autho- 

 rity ; that splendid work, the "Herefordshire Pomona," is possibly 

 the best for the purpose, as it may be assumed to contain a 

 summary of the most recent knowledge of all that relates to 

 orchard growth. The first paragraph of the passage in that 

 work relating to canker states that "it is always due to direct 

 injury." In a controversy a clear and definite issue is most 

 satisfactory, therefore, with all submission, I venture to assert 

 that it is never due to such cause. That canker may appear in 

 parts which have been injured is no proof that the injury caused 

 the canker, although the injury may determine the particular 

 spot where the disease makes itself visible. A well-nourished 

 and consequently healthy tree may be injured to any extent 

 without development of canker, while an ill-nourished tree, or, 

 to avoid begging the question, a tree infected with the disease, 

 will develop in all parts the external signs without the slightest 

 injury or abrasion of any kind, and very frequently on parts 

 where, from their well-protected position, such as the angles of 

 the branches with the main stem, it is almost impossible that 

 injury could take place. The coincidence of canker and an 

 injured part is no more proof of the former having been caused 

 by the injury than a hole in a building through which the flames 

 of a conflagration are first visible is the cause of the fire. 



The second paragraph states that " weakness is at the bottom 

 of the canker." This weakness cannot be want of apparent 

 vigour of growth, for I have frequently observed trees attacked 

 which for a number of years have made the strongest growth, 

 yet the disease has appeared before any external signs of weak- 

 ness were visible ; the very vigour of the growth in some cases 

 appearing to hasten the attack in a soil containing too limited 

 a supply of the necessary food, as that supply is sooner exhausted, 

 and the time arrives when the large tree can no longer find 

 within reach of its roots sufficient for its maintenance. It may 

 be that only one element of food is failing, but every element is 

 indispensable for perfect growth of the whole tree, and that 

 failure would fully account for arrest of growth in parts, weak- 

 ness, and consequent disease. 



The third paragraph is " the tree is old." This may be 

 expressed in other words — the tree has for a long time been 

 growing in the same soil. It is not difficult to realise that in the 

 course of many years a tree may exhaust the most fertile soil. 

 Many seem to overlook the necessity of restoring to the soil 

 what is taken away year after year by large crops of fruit. How- 

 ever rich the soil may have been originally, each crop takes away 

 a definite quantity of the food required by the tree, until in time 

 insufficient remains ; then the tree fails, not through age, but 



