September 20, 1888 j 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
257 
H UMMING differs from canker in being attended by a discharge, 
\X the sap of treei where gumming is present abounding in 
astringent constituents In canker the parts affected are rarely 
ulcered or accompanied by a discharge, the sap containing a 
quantity of free acid. Canker, however, is a form of extravasated 
sap, mainly confined as regards plants cultivated for their fruit to 
varieties of the Apple and Pear. If there be no discharge in 
canker there is an enlargement of the vessels of the bark at the 
commencement of the malady. The attack is almost invariably 
accompanied by a swelling, largest in the Apple, and to a lesser 
extent, yet always present in an attack of the disease on the Pear. 
When Elms and Oaks are affected sometimes no swelling occurs, and 
in true canker of the Peach it is not preceded or accompanied by 
swelling of the affected parts. Extravasation, therefore, in canker 
is internal, and there not being any discharge it is proposed to ex¬ 
clude it from this investigation. 
Gumming is confined for the most part to the Peach, Nectarine, 
Plum, and Cherry. Almonds and Apricots are also affected by 
gumming, and so also- are many other trees whose exudations are 
gummy or resinous. Whatever may be the predisposing cause of 
the rupture of the sap vessels and the resulting discharge, the sub¬ 
stance formed is gum quite as much so as gum arabic or gum 
tragacanth, only differing in character with the producing sub¬ 
ject, though many of the resins and gum resins are not produced 
by disease. The disease known as gumming is, according to 
scientists, highly contagious, and is caused by a fungus named by 
Professor Oudemans Coryneum Beijerincki. The fungus by its 
mycelium developes a ferment, penetrating the cells and transforms 
the contents, particularly the starch granules, into gum. One 
peculiarity of the ferment is its penetration of living cells—viz.) 
those of cambium, and changing or modifying their protoplasm, 
forming tissues with new properties. The tissue so formed sooner 
or later secretes the ferment and changes the cell contents into 
gum. A singularity of the disease is that the fungus causing it 
cannot penetrate the bark. Laceration, at least abrasion, of the 
bark must take place before the germs can enter. That or those 
are common injuries arising in Nature and culture. ‘“But,” asks 
Plowright, “ how do the spores which are undeveloped in the viscid 
gum gain access to them ? They cannot be blown there by wind is 
■obvious. If the gumming occurs upon the upper branches (which 
is rarely the case) of course they may be washed down by rain or 
syringing ; but how do they spread from tree to tree ? Obviously, 
they must be carried—most probably by insects.” Unquestionably. 
Why not ants ? They usually swarm about trees liable to gum, 
•and they quickly find out any abrasion or lacerations of the bark 
■caused by trimming the trees, nailing or tying the growths, 
evidently relishing the juices of the trees so unsealed ; indeed, they 
revel on plant and insect secretions. 
Happily the disease never attacks healthy tree3. Ants or 
insects of any kind may visit abrasions and lacerations without 
gumming resulting. The virus may be abundant in one tree with¬ 
out danger of its spreading next if it is healthy. The fungus 
seems impotent until the host plant presents a fittiug nidus. It is 
not enough to introduce gum virus, abrasion and laceration are 
equally ineffective ; disorganised tissue must exist before the 
fungus can spread. Plethora, or that state of a plant's excessive 
No. 430.—Vol. XVII., Third Series. 
vigour in which the sap is formed more rapidly than the circulatory 
vessels can convey it away, must have been induced, and when that 
occurs rupture is inevitable. Fungus may be brought by insects, 
and so gain free ingress by reason of the rupture. If so, is it a 
cause or effect ? Scientists insist (and rightly) that if there were 
no fungus there would be no gumming, and it is the cause of the 
disease. Keep the fungus away, and what V The tree will make a 
clean and healthy growth, perfect fruit buds, storing food in well 
i ipened wood for the insuring of good set, a satisfactory stoning, 
and perfecting of a profitable crop of fruit. The fact is the other 
way, for the fungus can no more be kept from attacking a tree in a 
condition favourable to its existence than a healthy tree can be 
kept from effort at reproduction. The fungus, therefore, is not to 
the cultivator a first, but an after consideration, consequently it 
need not cause anxiety when the curriculum of treatment is not 
such as to create disorganisation of the host plant’s tissues—a neces¬ 
sity of the fungus which scientists, if I understand their meaning 
rightly, do not question. Fungoid disease can only subsist on food 
essential to its perfecting, which depends on destruction or change 
of the elements appropriated to its use. If the scientist pins 
his faith to the fungus as the sole cause of the disease it is allowed 
that the disease is more likely to attack trees under certain con¬ 
ditions, and its virulence corresponds in degree with the elements 
or material available for transforming into gum. On attack, a tree 
in ill health will suffer more from the effects of the disease than one 
more healthy. In combating the disease the steps taken are pre¬ 
ventive and remedial. The first are directed to sanitation and 
other precautionary measures essential to the health of the tree 
liable to attack, or avoidance of the agent by which the disease is 
fostered. 
A knowledge of the disease is of primary importance in as¬ 
signing predisposition and inherent tendency a place. Predis¬ 
position may arise from various causes, but the chief is over- 
luxuriance, whether induced in trees favoured by Nature through 
soil and climate, or culturally by soil too richly manured. Soil 
exerts considerable influence in the predisposition of trees to 
gumming ; the least disposition to the disease is on the oolitic 
formations, and greatest on alluvial. Siliceous soils favour the 
disease more than clays. Inherent tendency is obviously resolvent 
into the agency by which perpetuation or reproduction is effected. 
The disease is common enough on natives of the genus Cerasus 
and Prunus, induced perhaps by a period of moist warm we ither 
followed by cold, the sap being then in excess of the evaporation? 
and the circulatory organs become disorganised, the sap stagnates 
and contracts, and rupture follows on a return of milder, m aster 
weather. Culturally, plethora is induced by location and condition 
of soil, and by cultivation itself, of which instances may easily be 
observed in most gardens ; but we must look a little closer if we 
are to make any real effort in eradicating the disease, and begin at 
the beginning. 
The disease, as before stated, is common to wild as well as 
cultivated trees. The predisposition is natural, and the inherent 
tendency coherent. It prevails largely on Sloes and wild Cherries ; 
indeed is common to all the species and their varieties, cultivated 
or otherwise, of the genus Cerasus and Prunus ; therefore it is a 
necessity to remove these from the neighbourhood of an orchard or 
fruit garden, since the disease-producing insects and f ungoids are 
fostered by them, consequently certain to spread to ill cultivated 
trees of kindred affinity. Perhaps no tree is more subject to lose 
large branches from disease than the common Laurel, which is very 
common in the immediate vicinity of fruit trees in private gardens, 
and many other species and varieties of the Plum and Cherry 
family are planted to form ornamental and sheltering belts or 
shrubberies about gardens, and not infrequently adjoining the fruit 
tree quarters. They are unquestionably useful as shelter, but it 
does not alter the fact that a whole fruit garden of flourishing 
trees may be ruined in a few years by the injudicious introduction 
No. 2086. — V< l. LXXIX., Old Series. 
