CANKER. 



CANKER. 



such instances, it might be strictly designated 

 */Mr, IT <i'"n^i'ti /in suiiiogii. 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 tin- 

 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- 

 i to have seen any; I have never rb- 

 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 n marks of di>. 

 yond the mere unnatural enlargement. In the 

 course of a few years, l.->s 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 inci* 

 size, and the alburnum has become extensively 

 dead: the superincumbent bark crack 

 in discoloured scales, and decays even more 

 rapidly than the wood beneath. If the caries 

 is upon a moderately si/ed branch, the decay 

 soon completely encircles it, extending through 

 the whole ai burnuin 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 j 

 products are Sir H. Davy and VauqueMn ; 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. (Elem. 



fhcnristry, 2d edit. p. 264.) 

 Vutiquelin 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 

 which the transparent sanies flows attains the 

 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. 

 varnish. It sometimes is discharged in such 

 quantities as to hang from the bark like sta- 

 lactites. The matter of which these are com- 

 posed is alkaline, soluble in water, and with 



acids effervesces. The analysis of this dark 

 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 - 342 

 Carbonate of lime - 5 



Carbonate of magnesia ... 03 



100-0 



Although young trees are liable to this dis- 

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

 ence most obnoxious to its attach.. 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, alter the lapse of that 

 period, gradually become as decrepid as th 

 parent tree. The unanimous experience ot 

 naturalists agrees in testifying that every or- 

 gani/ed creature has its limit of existence. In 

 plants it varies from the scanty period of a 

 lew month* to the long expun.se of ;is many 

 centuries: but of all. the days are numbered; 

 and though th< i '>, like the physician's 



>kill, mav retard the onward puce of death, he 

 will not be permanently delayed. In the last 

 periods of life they show everv symptom that 

 accompanies organi/ation in i:s old uge not 

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

 mer developem'-nts., a languid circulation, and 

 eJ organs. 



The canker, as already observed, attends es- 

 pecially the oil age of some fruit trees, and of 

 these, the apple is most remarkably a sufferer. 

 "I do not mean." says Mr. Knight, "to 

 that there ever was a lime 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 beyo.id 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 

 <>f Mr. Forsytes Plaster, by T. A. Knight, Esq. 

 1802.) 



Among the individuals particularly liable to 

 be infected, are those which have been marked 

 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 

 injudiciously pruned, or growing upon an un 

 genial soil, are more frequently attacked than 

 those advancing under contrary circumstances 

 The ildest trees are Always the first attacked 



255 



