January 12, 1893. ] 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
27 
the Eevs. H. A. Berners, F. R. Burnside, and J. A. Williams, with 
Messrs. John Harkness, Edward Mawley, George Paul, and W. H. 
Williams form a symposium and chat on “ Tea Roses” pithily, usefully, 
and agreeably. The Editor discourses on “ French Rosarians ” and the 
“ National Rose Society,” Mr. Charles Grahame on the “ Deterioration of 
Roses,” while Mr. Alexander Hill Gray continues his cheery “Jottings.” 
Mr. Mawley has the closing chapter, as usual, on “ The Weather of the 
Rose Year,” in which so much careful observation is displayed. A 
casual glance through the pages shows that there is plenty of variety in 
them—plenty of valuable matter and good reading for a shilling. So 
now let all who love Roses buy the book and be happy, for they can 
scarcely be completely so without it. It is published hj Bemro^e and 
Sons, London and Derby. _ 
[A very interesting letter from Mr. Henry V. Machin, Gateford Hill, 
Worksop, will be published next week.] 
CANKER ON FRUIT TREES. 
Mr. Walter Kruse, in his communication (page 564, December 
29th, 1892), loses sight of the fact that those scientists who have investi¬ 
gated this subject consider canker a disease of fungoid origin, conse¬ 
quently only produced indirectly by the composition of the soil in which 
affected trees happen to be growing. Indeed, it is a question whether 
the presence of one infected tree in a garden or orchard is not more 
conducive to the spread of this malignant disease than any quantity of 
iron oxide or other chemical usually found in mother earth, for from 
every cankerous growth spores are thrown off in quantity, germinating 
wherever they effect a lodgment, owing to defects in the bark, and 
quickly producing those excrescences we unfortunately know too well. 
Directly remedial measures have therefore been recommended in 
preference to indirect ones, scraping and paring the parts attacked, to 
be followed by liberal applications of paraffin oil or other powerful 
antiseptic during the months of May and June, when the fungoid 
growth is most active, being the proposed cure. Those who have 
advised this method of combatting the pest believe that if energetically 
pursued year after year it would in time result in the diminution, if not 
complete extermination of the disease. Has Mr. Kruse tried this 
remedy?—B. D. K. _ 
Mr. Kruse does well in directing attention to this tantalising and 
hackneyed subject {Journal of Horticulture, December 29th, 1892, 
page 564). His case is very clearly and plainly stated, except that part 
where he says, “ Apples and Pears are liable in a certain soil (of 
which an analysis is given) to canker, and Cherries to gum ; Plums, 
Gooseberries, and Black and Red Currants do well.” This refers to 
matters of fact, and may not be (nor are they) questioned ; but the 
statement appears, to me at least, ambiguous, or to imply that because 
Apple and Pear trees canker and Cherry trees gum in “ a certain soil,” 
some analogous disease ought to be expected to infect the Plums, Goose¬ 
berries, and Currants, if canker and gum are due to external cause, that 
is, caused by the attacks of parasitic fungi. This is the other side of 
the question—What is the cause of canker and gum ? Mr. Kruse does 
not allude to the possibility of these diseases being due to the direct 
cause and action of parasites, but is strictly empiric, and attributes 
canker and gum to predisposing cause—excess or deficiency of soil con¬ 
stituents. Predisposing causes—heredity and environment—are no doubt 
the “ root ” from whence parasitic infestions spring. Animal or vegetable 
parasites, however, will attack and thrive if let alone on any and every 
plant that supplies them with their essential food. That is the point; 
attack on the one hand, resistance on the other hand, is Nature’s un- 
deviating law, and the “ weakest go to the wall ”—the plethoric and the 
starved. In this we have the “ survival of the fittest ; ” that plant 
which becomes located where the soil and environment is best suited to 
its requirements will thrive the best and longest. So far I cordially 
agree with Mr. Kruse and the empirics. Cultivators, however, ought 
not to act on empirical lines, but, like the “ boards of health,” should 
take care to remove the predisposing causes of disease, and so safeguard 
■their cultures against attacks or lessen the malignity of parasitic infec¬ 
tion. This can only be done by a thorough knowledge of the disease 
and its origin. 
Now, canker on Apple and Pear trees does not infect Cherry, Plum, 
Gooseberry, and Currant trees, nor any species of Cerasus, Prunus, or 
Ribes, but is found on Ash, Elm, Oak, and many other trees. That is 
one reason why “ Plums, Gooseberries, and Black and Red Currants do 
well ” where “ Apples and Pears are liable to canker ”—namely, different 
plants are subject to different diseases, and have no connecrion whatever 
with soil constituents beyond that required in the host for the growth 
of the disease. Nevertheless a fungus of the same genus as the canker 
fungus is often found on the dead twigs or branches of Currant and 
Gooseberry bushes, and is very interesting and beautiful. Almost any 
small branch or twig which has been lying on the ground in a damp 
situation a year affords specimen in November, when “ the whole 
surface of the twig is covered from end to end with bright pink pro¬ 
minences bursting through the bark at regular distances, scarcely a 
quarter of an inch apart. Towards one end of the twig probably the 
prominences will be of a deeper, richer colour, like powdered cinnabar. 
The naked eye is sufficient to detect some difference between the two 
kinds of pustules, and where the two merge into each other specks of 
cinnabar will be visible on the pink projection. By removing the bark 
it will be seen that the pink bodies have a sort of paler stem, which 
spreads above into a somewhat globose head, covered with a delicate 
mealy bloom. At the base it penetrates the inner bark, and from it the 
threads of mycelium branch in all directions, confined, however, to the 
bark, and not entering the woody tissues beneath. The head, placed 
under examination, will be found to consist of delicate parallel threads, 
compacted together to form the stem and head. Some of these threads 
are simple, others are branched, bearing here and there upon them 
delicate little bodies, which are readily detected, and form the mealy 
bloom which covers the surface. These are the conidia, little slender 
cylindrical bodies rounded at the ends. 
“ Passing to the other bodies, which are of a deeper colour, it will soon 
be discovered that, instead of being simple rounded heads, each tubercle 
is composed of numerous smaller, nearly globose bodies, closely packed 
together, often compressed, all united to a base closely resembling the 
base of the other tubercles. If for a moment we look at one of the 
tubercles near the spot where the crimson tubercles seem to merge into 
the pink we shall not only find them particoloured, but that the red 
points are the identical globose little heads just observed in clusters. 
This will lead to the suspicion, which can afterwards be verified, that 
the red heads are really produced on the stem or stroma of the pink 
tubercles. 
“ A section of one of the red tubercles will show us how much the 
internal structure differs. The little subglobose bodies which spring 
from a common stroma or stem are hollow shells or capsules, externally 
granular, internally filled with a gelatinous nucleus. They are, indeed, 
the perithecia of a sphoeriaceous funsus of the genus Nectria, and the 
gelatinous nucleus contains the fructification. Still further examina¬ 
tion will show that this fructification consists of cylindrical asci, each 
enclosing eight elliptical sporidia, closely packed together, and mixed 
with slender threads called paraphyses. 
“ Here, then, we have undoubted evidence of Nectria cinnabarina, 
with its fruit, produced in asci growing from the stroma or stem, and 
in intimate relationship with what was formerly named Tubercularia 
vulgaris. A fungus with two forms of fruit, one proper to the pink or 
Tubercularia form, with naked slender conidia, the other proper to the 
mature fungus, enclosed in asci and generated within the walls of a 
perithecium. Instances of this kind are now known to be far from 
uncommon.”—(Fungi, Cooke and Berkeley, page 193). 
The foregoing comprehensive extract depicts the fungus, Nectria 
cinnabarina, found on Gooseberry and Currant twigs or branches 
detached and laid on damp ground, also on dead twigs or branches on 
the bushes. The fungus is also common on stakes of Ash, Maple, 
Sycamore, and other trees used in mending gaps in hedges. Anyone, 
therefore, can readily see how a fungus may and does cause the bark 
to peel off a dead twig or branch, and hang in rags. This the fungus 
effects by living on and abstracting the substance of the inner bark, so 
that the bark is separated from the wood, which remains, so far as this 
fungus is concerned, intact, but exposed to tbe destructive effect of 
the weather, and to the inroads of other fungi. Nectria cinnabarina 
will not live on living twigs, for if we put in a stake of a Currant, and 
the upper or any part of it die, the dead part only affords a fitting soil 
and a peculiar food for its growth, health, and reproduction. 
Now, the fungus Nectria ditissima causing canker in Apple and Pear 
trees, acts similarly to N. cinnabarina, with a material difference— 
namely, it lives and feeds on the living inner bark of Apple and Pear 
trees, also Ash, Beech, Elm, Mountain Ash, Oak, and other trees. It is 
not of internal, but of traumatic or wound origin, for its germs cannot 
pierce sound healthy bark, clean, dense, and elastic ; but when the bark 
is injured by hailstones, sun and frost cracks, punctures of insects and 
burrowing of larvte, pecks of birds, bites and scratches of animals, 
breaking of t\\ igs and erosion of bark by wind, bruises, abrasions, and 
manipulations, then the spores of the fungus gain access to the inner 
bark by the wounds, one or all, and set up canker by living on the 
alburnous tissues, its peculiar food. That is all that is wanted to pro¬ 
duce canker on Apple or Pear trees—the wound and the spore of the 
fungus. When the spores gain access to and become “seated” in the 
wound they germinate, push their mycelial threads through the live 
portions of the bark, cambium, and alburnous tissues, living on and 
abstracting their substances, which causes the bark to die, become 
fissured and scaly, accompanied by a considerable swelling of the sur¬ 
rounding tissues, forming an unsightly excrescence. Thus established 
the fungus strives to enlarge the wound, which the tree resists by 
throwing out an excessive callus around the circumference of the wound, 
thereby striving to expel the fungus, cover the wood with new bark, 
and so secure itself against further attacks. But the battle is never in 
doubt, the fungus always proving the victor. Young shoots and small 
twigs are encircled in the year of attack, young plethoric trees feed it 
best and succumb the soonest, sturdy trees and large limbs resist it best 
and longest, whilst aged trees continue the battle many years, during 
which they are pitiful unprofitable objects. The mycelium of the 
fungus extends only in spring and summer, when its food, the sap, is 
active and cambium abundant, its “fruits” being produced in late 
autumn, and during the winter it is quiescent. 
The attacks of the fungus are not confined to poverty-stricken or 
aged trees, though it is most malignant on crowded trees in neglected 
gardens and orchards, yet it has a penchant for young trees and new 
varieties. Heredity is beside the question, and constitutional suscepti¬ 
bility not well defined ; yet some sorts of Apples and Pears have such 
dense or elastic bark and vigorous healthy constitutions as to resist or 
throw off cankerous affections. Notwithstanding all cultural effort and. 
selection there are no varieties qf Apple or Pear that in all cpqditjqq^ 
