HEART-ROT 93 
they make themselves bore-holes which are nearly circular 
and of the same size as the hyphae. These bore-holés are 
always exactly perpendicular to the surface of 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 lignase 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 1 to 5p. 
in diameter (fig. 35, 6). 
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 
