Heart Bot of Ptseroxylon 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 hoUowness 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) Schulze's Soln. (Chlorozinc Iodide). — The rotten wood takes the blue 

 colour characteristic of cellulose. 



(2) Phloroglurin and Hydrochloric 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 Sulphuric 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 



