310 
The Gaiikcr of the Larch. 
can penetrate only the j'oung bark. Bark four or five j-ears old 
appears to be impervious to the attack of the fungus. 
It should be carefully observed that this disease is limited to 
the cankered portions of the stem, being purely a local injury, 
and that the trunk below is healthy, there being no connection 
between the disease and the roots of the tree. It cannot be 
communicated to other parts of the tree by the juices or through 
the wood. Each fresh canker is caused by a new and in- 
dependent attack and is entirely due to the germination of the 
spores of the fungus on the bark, and is not in any way the result 
of the physical causes which have been credited with it, such as 
confinement, excess of moisture, cold or wet seasons, spring 
frosts, &c., except so far as these have favoured the giwvth of the 
spore by providing the moisture necessary for its germination. 
From this account of the canker it must appear that no method 
can be suggested which will effectually prevent the attack of 
larclies by this disease. AVere it cle.ar that the spores could 
gain entrance into the tree only through a wound or injury, 
arboriculturists, by keeping the bark of their larches uninjured, 
would ward off" the disease. It is, however, plain that the spore 
secures a hold without the presence of a wound, and consequently 
any treatment with a view to preserving the young bark from 
injury is of no avail. 
The time to take steps to prevent or cure the canker is when 
the trees are very young. When planting, each one should be 
carefully examined, to discover if it has already been attacked, 
and every specimen found to be diseased should be rejected and 
destroyed by fire. Careful inspection should frequently be made 
of the young plantations, so as to detect the first appearance of 
the disease. This can be determined externally even before the 
small white cup makes its appearance, by the darker and 
depressed appearance of the bark where the fungus is growing, 
and should there be any doubt as to the presence of the fungus, 
the slightest cut with the knife will show tlie very dark colour 
of the injured bark. If this dark bark is carefully cut away the 
disease would be arrested. No portion of the diseased bark 
must be left, elsp the mycelium of the fungus will continue to 
live and spread from that portion through the healthy bark. 
It must be remembered that the fungus does not penetrate the 
wood, so that when the bark is removed the seat of the disease 
is got rid of. 
The same operation may be performed on older trees, but 
when the canker is largo there is little hope of the wood growing 
over the injury, whereas in the young tree one has good reason 
to expect that the injury may speedily be repaired by new wood 
