284 PRINCIPLES OF GARDENING. [CH. VIII. 



quantity of healthy sap supplied by the stock ; but 

 the vessels of the scion vdW, after the lapse of that 

 period, gradually become as decrepid as the parent 

 tree. The unanimous experience of naturalists 

 agrees in testifying that eveiy organized creature 

 has its limit of existence. In plants it varies from 

 the scanty period of a few months, to the long 

 expanse of as many centuries ; but of all, the days 

 are numbered ; and although the gardener's,' like the 

 physician's skill, may retard the onward pace of 

 death, he will not be permanently delayed. In the 

 last periods of life, plants shew every symptom that 

 accompanies organization in old age, — not only a 

 cessation of growth, but a decay of former develope- 

 ment, a languid circulation, and diseased organs. 



The canker, as already observed, attends especially 

 the old age of some fruit trees, and of these the 

 apple is most remarkably a sufferer. " I do not 

 mean" says Mr. Knight, "to assert that there ever 

 was a time when an apple tree did not canker on 

 unfavourable soils, or that higlily cultivated varieties 

 were not more subject to the disease than others, 

 where the soil did not suit them. But I assert, 

 from my omti expeiience and obsen^ation within the 

 last twenty years, that this disease becomes progres- 

 sively more fatal to each variety, as the age of that 

 variety, beyond a certain period, increases : that if 

 an old worn-out orchard be replanted with fruit trees, 



