HEART-ROT 93 



they make themselves bore-holes which are nearly circular 

 and of the same size as the hj^hae. These bore-holes are 

 always exactly perpendicular to the surface oi the walls, 

 and thus follow the line of the shortest distance from the 

 lumen of one tracheide to that of the next. To make these 

 bore-holes the hyphal tips must excrete the necessary 

 enzymes (presumably a hgnase and a cytase). When once 

 a hypha has gained a passage from one tracheide to the 

 next, the hole which it occupies ceases to enlarge, and it 

 may reasonably be deduced from this that the enzymes are 

 only secreted by the apices of the hyphae, since, if they 

 were also secreted by the sides of the hyphae, the holes 

 would continue to enlarge when the hyphae had grown 

 through. Bore -holes may be seen cut through the curved 

 side -walls of a bordered pit while the actual pore of the pit 

 is left intact. These bore-holes are often extremely numerous, 

 and I have counted as many as thirty-five in 0'002 sq. mm. 

 of tracheide wall. 



The fungal hyphae may be seen in all kinds of elements 

 of the wood^ — tracheides, resin ducts, resin cells, medullary 

 ray tracheides and parenchyma. The hyphae in the 

 tracheides are of all sizes, and generally run along the 

 elements in a longitudinal direction and often clinging to 

 the sides. Either large or small hyphae may bore through 

 the tracheide walls ; thus the bore-holes vary from I to 5 /x 

 in diameter (fig. 35, b). 



The resin ducts often become entirely filled with a mass 

 of hyphae which are nearly always fine : the broad hyphae 

 do not commonly appear in the resin ducts. In the medullary 

 ray parenchyma it is otherwise, for here only the coarser 

 hyphae are found, and these run generally along the medul- 

 lary rays, passing through the end walls of the ray cells by 

 holes which they bore through the simple pits. 



The decomposition of the wood by the hyphae in this 

 stage is very slight, and, apart from the bore-holes, there is 

 no apparent delignification. But in certain places an 

 entirely different development of the hyphae occurs, which 

 causes black specks in the wood. These black specks are 



