oe e+ 
|, catalogues of the middle of the seventeenth cen- 
tury, are unproductive of fruit, and in a state of 
| debility and decay.” 
_ The sap of a cankered tree acquires an excess 
| of alkaline or saline matter, in consequence ap- 
| parently of the power of its roots to select suit- 
| able food becoming enfeebled. M. Saussure 
| found, in the course of his experiments, that, on 
_ account of their losing their sensitiveness and 
|. energy necessary for selecting or rejecting, the 
_ roots of plants growing in saline solutions ab- 
_ sorbed the largest proportions of such salts as 
were injurious to their health. Thus, when 
| polygonum persicaria and bidens cannabina were 
grown in a solution of acetate of lime, sulphate 
_ of soda, and chloride of sodium, they wholly re- 
_ jected the acetate of lime; but when grown in a 
solution of acetate of lime and sulphate of cop- 
per, they abundantly imbibed both of these 
salts ; yet the sulphate of copper was found to 
be more deleterious to them than any other salt 
employed in the experiments. The proportions 
of the salts absorbed in the former of the two 
solutions were six per cent. of sulphate of soda, 
and ten of the chloride of sodium; and the pro- 
portions in the latter were thirty-four of the sul- 
phate of copper and thirty-one of the acetate of 
lime. Now roots, though in a less degree, will 
be debilitated by an ungenial soil as certainly as 
by a solution of powerfully deleterious salts, and 
will in consequence absorb soluble alkaline mat- 
ters in the soil with increasing facility of imbibi- 
tion and diminishing ability of discrimination ; 
and while the roots will either thus, or by the 
weakening effects of canker inflicted by other 
causes, cease to make a healthy performance in 
taking up liquid nourishment from the soil, the 
leaves of the debilitated branches will become 
diminished in at once energy, size, and number, 
and will fail to effect a sufficient elaboration of 
the sap for its conversion into healthy cambium. 
The sap which ought to feed all existing organs 
and to afford matter for the formation of new 
ones, is thus at once deficient in quantity, dete- 
riorated in quality, and ill-digested in phylline 
elaboration ; and it therefore corrodes in the vas- 
cular system of the tree, and throws out the pe- 
culiar crystalline deposits which constitute so 
singular a symptom of some of the worst kinds 
of canker. 
The prevention and cure of canker are neces- 
sarily various, and must, in any one instance, be 
directed against the special forms which the 
disease assumes, or the particular cause by which 
it is excited. If coldness of climate be the only 
cause which can fairly be assigned for it in any par- 
| ticular orchard, covering with glass is the chief 
| preventive, and this, of course, can be applied to 
only a few select wall-trees. If fungi can, in any 
instance, be regarded as a chief exciting cause, a 
proper remedy might probably be the free use of 
the knife, and a subsequent copious washing 
with caustic lime water. If plethoric or dropsi- 
CANKER. 
cal habit seem to be forming, or have already 
formed, one of the main roots of the tree may be 
removed, and an admixture of poor loam, sandy 
mould, or even of drift sand or any other diluting 
matter, may be worked into the soil. A cultivator 
of Devonshire, whose opinions are recorded by 
Mr. Marshall, believed canker to be caused by 
excessive fertility in the soil, or a too abundant 
“dressing”? about the roots, and regarded the 
application of common river sand to the roots as 
an infallible remedy. If mere weakness of con- 
stitution or defect of functional energy appear to 
be the cause, while no one kind of exciting in- 
fluence can be detected or inferred, a very effi- 
cient remedy, known by experiment to induce a 
complete cure, is to cut away all the infected 
parts, and make a judicious pruning among the 
remaining branches; and even if such exciting 
circumstances as unfavourable climate, ungenial 
soil, or previous bad culture can be detected, an 
excellent effect may be produced by the gradual 
sawing and cutting away of exuberant or super- 
numerary shoots and boughs. “If canker in a 
fruit-tree is a consequence of old age,” says Mr. 
Johnson, “it is probably a premature senility, 
induced by injudicious management, for very 
few of our varieties are of an age that insures to 
them decrepitude. I have never yet known a 
tree, unless it was in the last stage of decay, that 
could not be recovered by giving it more air and 
light, by careful heading in, pruning, improve- 
ment of the soil, and cleansing the bark. Ifthe 
soil, by its ungenial character, induces the 
disease, the obvious and only remedy is its ame- 
lioration; and if the subsoil is the cause of the 
mischief, the roots must be prevented striking 
into it. In all cases, it is the best practice to re- 
move the tap-root. Many orchardists pave be- 
neath each tree with tiles and broken bricks. 
If the trees are planted shallow, as they ought to 
be, and the surface kept duly fertile, there is not 
much danger of the roots striking into the worse 
pasturage of the subsoil.” A method of plaster- 
ing cankered trees with a preparation of cow- 
dung, lime-rubbish, wood-ashes, and sand, made 
a vast sensation about half-a-century ago, and 
was rewarded by a parliamentary grant of money ; 
but it was afterwards shown by Mr. Knight, and 
is now generally believed, to have been a piece 
of sheer quackery. Other persons recommend, 
and many successfully practise, the removal of 
all decayed or exuviated bark, and the applica- 
tion of various liquid washes, such as a solution 
of common salt, or a diluted lquid compound 
of cow-dung, soap-suds, and urine. When any 
bruise or other injury is inflicted, of a kind likely 
to induce or develop canker, a piece of living 
bark from another tree might be exactly fitted 
into the excision in the same manner as in the 
operation of budding. The grand preventive of 
canker in larch is to select, for plantations, such 
situations and soils as shall not subject the trees 
to combined coldness and moisture.— Papers | 
