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 120C. 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 a heart-rotted spruce tree for the presence of 

 soluble gum and was unable to obtain any trace of it. 



