90 HEART-ROT 
of broad-leaved trees, especially in the heart-wood, wood 
gum is not infrequent ; this, however, is insoluble in water. 
A general account of the presence of gum in heart-wood, 
and as a result of wounding in Dicotyledons, is given by 
Temme (1885), and the reader is referred to this and to 
a short account in Beilstein (1893). 
A few solubility tests were carried out on the larch gum, 
and it was found to be soluble in water and nitric acid, but 
insoluble in alcohol, ether, chloroform, sulphuric acid, and 
caustic potash, and is doubtfully soluble in hydrochloric 
acid. It has a high power of attraction for water, even 
absorbing it from the air. When heated to 120°C. in an 
oven it becomes somewhat changed, and does not dissolve 
so freely in water, though its adhesive power is much 
increased. In this respect, as also in its solubility,it resembles 
gum arabic. 
In pure cultures of Fomes annosus in sterilized blocks of 
larch wood, the gum is formed in a few days after infection, 
and may be found at a distance of an inch from the nearest 
fungal hyphae, though none is present in similar blocks 
which have not been infected. We must suppose that 
enzymes, presumably including a lignase, are secreted by 
the fungus, and that these, or the products of their digestion 
or both, become diffused through the tissues of the wood 
blocks. It is curious that gum should appear at a time 
when the only delignification that is apparent is in the 
bore-holes, to be described hereafter, through which the 
hyphae grow from one tracheide to another. But it is 
possible that some slight delignification takes place through 
the whole region surrounding the hyphae. 
As the rot advances this gum disappears. As shown in 
the next section it is probable that some of it becomes con- 
verted into an insoluble gum, but what happens to the rest 
is obscure. It does not seem in any way to impede the growth 
of the fungus, and it is possible that the fungus even feeds 
on it, either in its original state or after hydrolysis. I have 
examined aheart-rotted spruce tree for the presence of 
soluble gum and was unable to obtain any trace of it. 
