Heart Hot of Ptxroxylon utile (Sneezewood) . 
219 
Fig. 6 shows practically in the centre of the diseased stem a dark brownish 
mass composed of fungous threads closely matted together and also enclosing 
some wood. If this mass was to be removed, the hollowness of the trunk 
would be complete. 
Action of the Fungus on the Wood. 
The diseased wood is bounded from the healthy by a dark Vandyke brown 
ring, darker in colour than the normal wood. 
In the decayed wood the mycelium of the fungus is abundant in the 
vessels (Figs. 7 and 8), wood prosenchyma, and medullary rays (Fig. 9). 
In transverse section the vessels frequently appear completely blocked, and 
in addition to the mycelium they may contain a dark colouring matter, 
evidently composed of decomposition products of the fungus. 
The fungus secretes an enzyme which converts the lignin of the wood cells 
into cellulose ; the middle lamellae of the cells are destroyed, and as a result 
the cells easily separate. 
The destruction of the lignin results in the attacked wood frequently 
showing as white areas or patches (Fig. 6), where the elements consist of 
practically pure cellulose and are readily crumbled between the fingers. 
The enzyme would appear to diffuse from the region where the mycelium is 
abundant, and wood elements of which the walls consisted of cellulose were 
observed where there was little trace of fungoid hyphae. 
The following reactions were tried to show that the lignin of the wood 
is destroyed, and that these elements, therefore, give reactions for cellulose. 
(1) Scliulzes Solri. (CMorozlnc Iodide). — The rotten wood takes the blue 
colour characteristic of cellulose. 
(2) PhlorogJucin and HydrocJiJoric Acid. — The healthy xylem stains red- 
violet, characteristic of lignin, whereas the decayed xylem, since the lignin 
has been destroyed, does not give this reaction, but those for cellulose. 
(3) Iodine and Sulphuric Acid. — The healthy wood stains yellowish and 
the decayed gives the blue cellulose reaction as would be expected. 
(4) Aniline Sulphate and Sulpliuric Acid. — The normal wood takes a 
bright yellowish colour characteristic of lignin, whereas, again, the decayed 
does not, but would give reactions with reagents for cellulose. 
The action of the fungus on the wood may therefore be briefly summarized 
as follows : 
(1) The fungus secretes an enzyme which reacts on the lignin of the 
wood elements and converts it into cellulose. 
(2) The middle lamellae of contiguous cells are destroyed and the cells 
therefore easily separate. 
(3) Ultimately the remaining, now cellulose, walls of the xylem are 
(destroyed, and the fungus forms yellowish masses of matted fungoid threads 
