i i i i 
THE ‘‘BLUE”’ FUNGUS. 19 
(Pl. VII, 1), giving off branches to other wood cells.“ In this manner 
the whole wood body becomes penetrated by the brown hyphe ina 
very short time after the first infection. The number of hyphe in the 
wood cells proper, i. e., excluding the medullary ray cells and the 
cells of the wood parenchyma, is very small indeed. This is proba- 
bly due to the fact that the fungus finds scant material upon which to 
live in the wood cells. The hyphe are apparently able to puncture 
the unlignified walls here and there, but they stop at that point. The 
writer was not able to demonstrate that the hyphe could attack the 
lignified walls. In other words, the ** blue” fungus is one which confines 
its attack to the food substances contained in the storing cells of the 
trunk and to the slightly lignified walls of these storing cells. The 
best instance of the resistance which the lignified walls offer to the 
dissolving action of the hyphe is found in the outer walls of the medul- 
lary rays, which are composed in part of the more heavily incrusted 
walls of the adjacent wood fiber. 
The resin ducts are attacked in much the same manner as the medul- 
lary rays. (PI. VII, 3; Pl. VIII, fig. 2.) The walls of the component 
cells are dissolved, leaving a tube filled with brown hyphe. When 
looked at with a low-power magnifying glass, a cross section of the 
wood shows the resin ducts as black spots in the wood ring. 
The rate at which the hyphe advance in the medullary rays keeps 
them considerably in advance of the hyphe in the wood cells and also 
of the blue color which follows the appearance of the hyphe in the 
rays. When the hyphe have reached the heartwood they cease grow- 
ing inward. One reason for this may be the absence of food materials 
in the rays of the heartwood, and another may be the greater lgnifica- 
tion of the heartwood cells. It is very certain that the hyphe do not 
flourish in the heartwood, neither in the medullary rays and resin ducts 
nor in the wood cells proper. MHartig ascribes the restriction of the 
fungus to the sapwood to the smaller amount of water in the heart- 
wood, but it would seem to the writer that there would hardly be so 
very sharp a line between the points where growth does take place 
and where it does not, if it were a matter of water supply alone. 
The readiness with which the fungus can enter heartwood and sapwood 
cells and the presence or absence of food substances would seem to be 
factors of more importance in determining the regions where the 
fungus could or would not grow. 
The growth in the medullary rays comes to a stop within six months 
after the first infection, and perhaps earlier. This applies to such 
wood as is infected in July or August. By December or January the 
whole sapwood will be filled with hyphex. In the top of the tree the 
“The hyphe growing out from the medullary rays, as shown in Pl. VIII, fig. 2, 
make the wood cells appear septate. This, of course, is not the case. 
