I a 
controversy, both friendly and acrimonious; and 
even exciting causes, but especially aggravating 
causes, are probably several in number, diversi- 
fied in their mode of action, and much controlled 
by the peculiarities of climate, soil, culture, spe- 
cies, and age. Some phytologists think that 
canker is occasioned wholly by coldness and 
churlishness of climate; others regard it as a 
topical disease in the parts immediately affected, 
brought on by some bruise or other injury, and 
exasperated by an unhealthy sap, consequent 
upon unfavourableness of situation, soil, and cul- 
ture; others view it as an effect of the lodgment 
of minute, parasitic fungi, growing from spores 
either taken up from the soil through the spon- 
gioles, or received from diffusion through the 
atmosphere into cracks or wounds in the bark; 
and others think that it is a disease in the con- 
stitution or whole organic system of trees, that 
it springs from a vitiated and peccant state of 
all the juices, and that it will again and again 
break out, independently of any external injury 
or agency, so long as the juices continue to be 
unaltered. 
The notion that coldness of climate is the sole 
cause of canker, does not include the influence 
of bruises, insects, bad culture, and unfavourable 
soil, but merely regards these as ancillary or ag- 
gravating causes, unable of themselves to de- 
velop it with any considerable virulence, yet in- 
creasing the power of the one grand cause; and, 
thus modified, it was propounded, six years ago, 
by Mr. Pearson of Kinlet in the Gardener’s Ga- 
zette and the Quarterly Journal of Agriculture, 
and afterwards defended, in the former of these 
periodicals, throughout a long controversy. “For- 
merly,” says Mr. Pearson, “it appeared singular 
to me, when I read the practice of various au- 
thors on the cure of canker in fruit-trees, that 
they always blamed the subsoil; yet the subsoil 
of every situation varies as much as the superin- 
cumbent soil. One blames cold, clayey rotch, 
while another blames sandy rotch; a third does 
the same with clay, while a fourth blames the 
sand; and the prevention of the roots penetrat- 
ing these various subsoils seems to be the pana- 
cea for all the cankering evils of these various 
situations; but is it not singular enough, that 
the cankering matter should be found in every 
subsoil in the kingdom, or wherever a gardener 
chooses to stick in his spade? The mystery is 
solved at once when we come to consider the 
withering and penetrating power of the weather 
on spongy, unripened wood. Canker proceeds 
also from cuts, bruises, and the attacks of in- 
sects; but all these produce insignificant effects 
compared with those of the atmosphere. It may 
appear difficult to reconcile the above theory 
with the canker in the larch. I say nay; for as 
there are times when the atmosphere hangs be- 
tween deposition and evaporation, that is, a 
lurking atmosphere which is neither cold enough 
to freeze, nor warm enough to send off the su- 
CANKER. 
$$$ 
perabundant moisture, it may be that this is the 
time in which the glands of the tender bark of 
unthinned or improperly thinned larches be- 
come affected.” Mr. Drummond of Perth, who 
writes expressly on the canker in the larch, and 
who contends that the sole cause of it is an ex- 
cess of cold and moisture in the atmosphere, says, 
“T do not pretend to account for the physical 
action of the climate in producing the disease in 
the plant. Perhaps the injury the foliage sus- 
tains may prevent the due perspiration of the 
plant, and the fluids may be deprived of their 
proper aerial nourishment necessary for the cir- 
culation, or a moist and an excessively cold atmo- 
sphere may act upon the open texture of the 
bark, when the vessels are full of sap, in the 
same manner as it acts on and destroys certain 
bulbous roots.” “The canker,” says Mr. Drum- 
mond elsewhere, when stating the grounds of his 
opinion as to the cause of it, “is invariably to be 
found in excess in the immediate vicinity of 
water, marshy ground, on all cold retentive 
soils, and in situations where hoar-frost prevails. 
Among trees planted on the sides of mountains, 
where the soil and adjoining grounds are dry, 
little or no disease is to be found; but it is quite 
common on elevated situations if they are ex- 
posed to fogs or the vapours arising from damp 
or marshy ground. I have observed the trees 
free from disease on a limited extent of marshy 
ground, and those on the dry ground immedi- 
ately overhanging it in a diseased state; which 
would indicate that an excess of moisture at the 
root is not the cause, but that the exhalations 
from damp ground have an immediate connexion 
with it. It has appeared towards the east coast 
in all its virulence. There is less of it as you 
proceed to the west ; and in Argyleshire, where 
the climate is more temperate (being removed 
from the influence of the east winds), and where 
is superabundant atmospheric moisture, the 
woods are comparatively free from the disease, 
but which would have been either dead or dying 
in similar situations in this part of the country. 
These observations led me to conclude that a 
moist climate is not alone the cause of the dis- 
ease, but that it is produced by an excess of cold 
and moisture in the atmosphere.” 
Opinions as to fungi being the cause of canker 
are exceeding various and conflicting. Minute 
parasitic fungi unquestionably attend most in- 
stances of canker, and sometimes exist in such 
myriads as to impart a peculiar tinge to the 
whole stem of cankered trees; but very different 
fungi attack different species of trees, several kinds 
sometimes attack the same species, and possibly 
some are either causes or aggravations of canker, 
while most are merely innocuous effects. The 
stromatospheria multiceps so commonly and 
greatly abounds on cankered pear-trees, particu- 
larly on the jargonelle, the Windsor, the swan’s 
eggs, the summer bergamot, and the autumn ber- 
gamot varieties, and seeming to make their young | 
