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119 



CAN 



natural enlargement. In the course of| about the canker of an elm, that 500 

 a few years, less in number in propor- pounds weight of its wood must have 

 tion to the advanced age of the tree,! been destroyed. There is no doubt 

 and the unfavourable circumstances un- that such a discharge is deeply injuri- 

 der which it is vegetating, the swelling ous to the tree ; but the above learned 

 is greatly increased in size, and the i chemist appears to have largely erred, 

 alburnum has become extensively dead ; for he calculated from a knowledge of 

 the superincumbent bark cracks, rises the amount of the saline constituenta 



in discoloured scales, and decays even 

 more rapidly than the wood beneath. 

 If the caries is upon a moderately-sized 

 branch, the decay soon completely en- 

 circles it, extending through the whole 

 alburnum and bark. The circulation of 



n the healthy sap, whereas in the dis- 

 eased state these are much and unna- 

 turally increased. I once was of opi- 

 nion that the disease does not arise 

 from a general diseased state of the 

 tree, but that it is brought on by some 



the sap being thus entirely prevented, , bruise or injury, exasperated by an un- 

 all the parts above the disease of ne- healthy sap consequent to an unfavour- 

 cessity perish. In the apple and the able soil, situation, and culture; but 

 pear, the disease is accompanied by more extensive and more accurate ex- 

 scarcely any discharge ; but in the elm ] aminations convince me, that the dis- 

 this is very abundant. The only che- , ease is in the tree's system ; that its 

 mists who have examined these morbid ' juices are vitiated, and that disease will 

 products, are Sir H. Davy and Vauque- continue to break out independent of 

 lin ; the former's observations being : any external injury so long as these 

 confined to the fact, that he often found {juices continue peccant and unaltered, 

 carbonate of lime on the edges of the This conclusion will be justified, I 



canker in apple trees. 



think, by the preceding facts, as well 



Vauquelin has examined the sanies as by those distributed through the fol- 

 discharged from the canker of an elm j lowing pages. 



with much more precision. He found j The disease is not strictly confined to 

 this li(iuor nearly as transparent as ' any particular period of the tree's age. 

 water, sometimes slightly coloured, at i I have repeatedly noticed it in some of 

 other times a blackish-brown, but al- | our lately introduced varieties that have 

 ways tasting acrid and saline. From ] not been grafted more than five or six 

 this liquor a soft matter insoluble in years ; and a writer in the Gardener's 

 water is deposited upon the sides of the [ Magazine, vol. v., p. 3, states, that the 

 ulcer. The bark over which the trans- | trees in his orchard, though "only of 

 parent sanies flows, attains the appear- four years' growth, are sadly troubled 

 ance of chalk, becoming white, friable. With the canker." Although young 

 crystalline, alkaline, and effervescent trees are liable to this disease, yet their 

 with acids. A magnifier exhibits the old age is the period of existence most 

 crystals in the forms of rhomboids and • obnoxious to its attacks. It must be 

 four-sided prisms. When the liquid is remembered that that is not conse- 

 dark-coloured, the bark a[)pears black- quently a young tree which is lately 

 ish, and seems as if coated with varnish, grafted. If the tree from which the 

 It sometimes is discharged in such scion was taken be an old variety, it is 

 quantities as to hang from the bark like only the multiplication of an aged in- 

 stalactites. The matter of which these j dividual. The scion may for a few 

 are composed is alkaline soluble in years exhibit signs of increased vigour, 

 water, and with acids effervesces. The ' owing to the extra stimulus of the more 

 analysis of this dark slimy matter shows abundant supply of healthy sap supplied 

 it to be compounded of carbonate of by the stock ; but the vessels of the 

 potass and ulmin, a product peculiar to ' scion will, after the lapse of that period, 

 the elm. The white matter deposited gradually become as decrepid as the 



round the canker was composed of 

 Vegetable matter .... 605 

 Carbonate of potass . . . 342 

 Carbonate of lime .... 50 

 Carbonate of magnesia . . 3 



parent tree. The unanimous experi- 

 ence of naturalists agrees in testifying 

 that every organized creature has its 

 limit of existence. In plants it varies 

 from the scanty period of a few months 



Vauquelin calculated from the quantity to the long expanse of as many centu- 

 of this white matter that was found ries ; but of all the days are numbered ; 



