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HOYAL HORTICULTU11AL SOCIETY. 



than another. This, however, is merely what we observe in 

 many forms of disease, both in the animal and vegetable king- 

 dom — and, indeed, in various cases where it is clear that the 

 whole system is affected, but where it breaks out only in iso- 

 lated spots. Doubtless there is some special organic weakness 

 or predisposition to change in those parts, which makes them 

 more liable to attack, where there are no especial organisms at 

 various distances which are alone affected — as, for example, in 

 cancerous changes in the glands, which, in aggravated cases, are 

 sometimes attacked almost indiscriminately. We see something 

 of the kind occasionally where there is no question of vitality. 

 A piece of paper, for example, as the page of a printed book, 

 which has been kept in a damp room, undergoes a slow process of 

 decomposition somewhat similar in character to that which is 

 called by chemists eremocausis ; in general, however, the dis- 

 coloration is not general, but appears in the form of brown spots 

 scattered over the surface. Again, in that very curious form of 

 decay to w r hich wood is subject, in w r hich the medullary rays disap- 

 pear, and the wood-cells are here and there bleached and contracted 

 so as to form little cavities in the wood, the intermediate tissue 

 remains sound and unaltered. In that form of canker, for ex- 

 ample, to return to living organisms, which is so common in the 

 fruit of certain varieties of Apples, the whole fruit is not cankered, 

 but the soft tissue is decomposed here and there, so as to present 

 a speckled appearance ; and the same may be said of other va- 

 rieties of Canker to which the fleshy parts of plants are subject. 



In other cases, however, the evil is confined to especial spots, 

 as in the affection called gumming, which is really a form of Can- 

 ker, the cause of the local disease being sometimes distinctly trace- 

 able without any general constitutional tendency to disease, — 

 though undoubtedly this is sometimes the case ; and, indeed, forms 

 of the same affection occur where almo st every fruit-bearing twig is 

 simultaneously diseased, and where it is very difficult to assign a 

 cause. The disease in these cases is modified by the exudation 

 large quantities of gum, as in Conifers it is by the presence of 

 of resin. 



In a single rare case which has fallen within my notice, the 

 Canker appeared under the form of a deep broad annular pit sur- 

 rounding the whole trunk near the base, and penetrating deeply 

 into the w ood, and of course inducing death. 



In a few cases Canker may be induced by insects ; but where 



