The Canher of the Larch. 
305 
endeavours by an increased formation of wood under the still 
living bark to provide adequate channels for the transmission of 
the sap, which is prevented wherever the mycelium is present, 
and to strengthen mechanically the weakened portion. 
I have never found the fungus beginning an attack on an 
old stem. AVhen the external bark is no longer vitally active 
it is unable to give nourishment to the young fungus in the 
early stages of growth, when it pushes out its mycelium from 
the germinating spore. The normal dead bark, covering a tree 
of several years' growth, accordingly becomes a protection to 
that stem. The nuraei'ous specimens examined all show that 
they have been attacked before they were three or at the most 
four years old. 
It must not, however, be forgotten that any part of the tree 
less than three or four years old is liable to be attacked, conse- 
quently a plantation, say of twelve years old, may have escaped 
the canker, but if spores reach it under suitable conditions, the 
upper and younger parts of the stem and 
branches will probably be attacked. 
In Fig. 2 we have an instance of a 
tree attacked twice by the canker, first 
at the beginning of its fourth year's life, 
and later on in the same year another 
attack was made at the opposite side, so 
that in the fifth year a very small pro- 
portion of healthy bark was left, and very 
little wood was laid on ; a greater activity 2.— section of stem of 
of wood forming, though over a small jarcli, from S1iavste.l, attacked 
o' ^ hy canker at tlie cml of its 
area, took place in the sixth year, which t'lifi year, ami nearly de- 
'•-i ."^ r. p stroycd in its seventh year. 
was again reduced by the vigorous liie 01 xaturai size, 
the parasite in the seventh year, and it is 
difficult to believe that, had the tree not been cut down, it 
could have survived another year. 
Fig. 3 is a section of a tree cut down in the spring of the 
tenth year of its life, which was attacked at the close of its third 
year, and the fungus surrounded half the stem, so that in the 
fourth year the wood was formed only round one half of the 
tree. During the five other years before the tree was cut down 
the canker continued to hold possession of even more than half 
the circumference, so that in the end the original centre, con- 
sisting of the first three years' growth, was outside the tree. The 
resin due to the attack of the fungus is shown in a large mass 
below to the left of the figure. 
Fig. l' is the section of a stem cut down at the begin- 
ning of the thirteenth year of its existence, which has been 
