CANKER. 



CANKER. 



such instances, it might be strictly designated j acids effervesces. The analysis of this dark 

 ulcer, or Gangrana saniosa. This disease has a 

 considerable resemblance to the tendency to 

 ossification, which appears in aged animals, 

 arising from their marked appetency to secrete 

 the calcareous saline compounds that chiefly 

 constitute their skeletons. The consequence 

 is an enlargement of the joints, and ossifica- 

 tion of the circulating vessels, and other parts ; 

 phenomena very analogous 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 

 mortifications 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 invariably attends the 

 disease when it attacks the apple tree. In the 

 pear, the enlargement is less, yet is always 

 present. In the elm and oak sometimes no 

 swelling occurs, and in the peach I do not re- 

 member vo have seen any; I have never ob- 

 served the disease in the cherry tree, nor any 

 of the pine tribe. The swelling is soon com- 

 municated to the wood ; which, if laid open to 

 view, on its first appearance, by the removal 

 of the bark, exhibits no marks of disease be- 

 yond 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 

 unfavourable circumstances under which it is 

 vegetating, the swelling is greatly increased in 

 size, and the alburnum has become extensively 

 dead : the superincumbent bark cracks, rises 

 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 encircles it, extending through 

 the whole arburnum and bark. The circula- 

 tion of the sap being thus entirely prevented, 

 all the parts above the disease of necessity 

 perish. In the apple and pear, the disease is 

 accompanied by scarcely any discharge ; but 

 in the elm this is very abundant. The only 

 chemists who have examined these morbid 

 products are Sir H. Davy and Vauquelin ; the 

 former's observations being confined to the 

 fact, that he often found carbonate of lime on 

 the edges of the canker in apple trees. (Eletn. 

 ofjgr. Chemistry, 2d edit. p. 264.) 



Vauquelin has examined the sanies dis- 

 charged from the canker of an elm with much 

 more precision. He found this liquor nearly 

 as transparent as water, sometimes slightly 

 coloured, at other times a blackish-brown, but 

 always tasting acrid and saline. From it a 

 soft matter, insoluble in water, is deposited 

 upon the sides of the ulcer. The bark ever 



slimy matter shows it to be compounded of 

 carbonate of potassa and ulmin, a product pe- 

 culiar to the elm. The white matter deposited 

 round the canker was composed of 



Parts. 



Vegetable matter - .... 60 5 



Carbonate of potassa - . . 34 2 



Carbonate of lime .... 5 



Carbonate of magnesia ... o-3 



1000 



Although young trees are liable to this dis- 

 ease, yet their old age is the period of exist- 

 ence most obnoxious to its attacks. It must 

 be remembered, that that is not consequently 

 a young tree which is lately grafted. If the 

 tree from which the scion was taken is an old 

 variety, it is only a multiplication of an aged 

 individual. The scion may for a few years 

 exhibit signs of increased vigour, owing to the 

 extra stimulus of the more abundant supply of 

 healthy sap supplied by the stock; but the 

 vessels of the scion will, after the lapse of that 

 period, gradually become as decrepid as the 

 parent tree. The unanimous experience of 

 naturalists agrees in testifying that every or- 

 ganized 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 though 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 they show every symptom that 

 accompanies organization in its old age not 

 only a cessation of growth, but a decay of for- 

 mer developements, a languid circulation, and 

 diseased organs. 



The canker, as already observed, attends es- 

 pecially 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 

 highly cultivated varieties were not more ge- 

 nerally subject to the disease than others, where 

 the soil did not suit them; but I assert, from 

 my own experience and observation within the 

 last twenty years, that this disease becomes 

 progressively more fatal to each variety, as the 

 age of that variety beyond a certain period 

 increases; that all the varieties of the apple 

 which I have found in the catalogues of the 

 middle of the seventeenth century, are unpro- 

 ductive of fruit, and in a state of debility and 

 decay." (Some Doubts relative to the Efficacy 

 r,f Mr. Forsytes Plaster, by T. A. Knight, Esq. 

 1802.) 



Among the individuals particularly liable to 

 be infected, are those which have been marked 



which the transparent sanies flows attains the by an excessively vigorous growth in their 



early years. I have in my garden a maiden 

 standard peach, which is now about sixteen 

 years old. The size and abundance of its 

 annual shoots, until within the last quarter of 

 its existence, were unnaturally large. It is 

 now grievously affected by canker. Trees 

 varnish. It sometimes is discharged in such injudiciously pruned, or growing upon an un- 

 quantities as to hang from the bark like sta- 1 genial soil, are more frequently attacked than 

 lactites. The matter of which these are com- j those advancing under contrary circumstances, 

 posed is alkaline, soluble in water, and with The oldest trees are always the first attacked 



255 



appearance of chalk, becoming white, friable, 

 crystalline, alkaline, and effervescent with 

 acids. A magnifier exhibits the crystals in 

 the forms of rhomboids and four-sided prisms : 

 when the liquid is dark-coloured, the bark ap- 

 pears blackish, and seems as if coated with a 



