THE '"BLUE" FUNGUS. 19 



(PL VII, 1), giving off branches to other wood cells. a In this manner 

 the whole wood body becomes penetrated by the brown hyphae in a 

 very short time after the first infection. The number of hyphae in the 

 wood cells proper, i. e., excluding the medullary ray cells and the 

 cells of the wood parench} T ina, 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 hyphae 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 hyphae 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 hyphae 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. (PL VII, 3; PL VIII, fig. 2.) The walls of the component 

 cells are dissolved, leaving a tube filled with brown hyphae. 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 hyphae advance in the medullary rays keeps 

 them considerably in advance of the hyphae in the wood cells and also 

 of the blue color which follows the appearance of the hyphae in the 

 rays. When the hyphae 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 lignifica- 

 tion of the heartwood cells. It is very certain that the hyphae do not 

 flourish in the heartwood, neither in the medullary rays and resin ducts 

 nor in the wood cells proper. Hartig 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 hardh r 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 hyphse. In the top of the tree the 



The hyphse growing out from the medullary rays, as shown in PI. VIII, fig. 2, 

 make the wood cells appear septate. This, of course, is not the case. 



