THK ''BLUE FUNGUS. 19 



(PI. VII. 1). giving- oil Itrunches to other wood cells." In this manner 

 the whole wood body becomes penetrated by the In-own hyphte in a 

 very short time after the iirst infection. The number of hyphie 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 thc^ fungus finds scant material upon which to 

 live in the wood cells. The hyplue are apparently al)le to puncture 

 the unlignitied walls here and there, but they stop at that point. The 

 writer was not a])le to demonstrate that the hyph<\3 could attack the 

 lignitied walls. In other words, the '* blue *" f ung-us is one which confines 

 its attack to the food substances contained in the storing cells of the 

 trunk and to the slightly lignitied walls of these storing- cells. The 

 best instance of the resistance which the lignified walls offer to the 

 dissolving action of the hypha? 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 liber. 



The resin ducts are attacked in much the same manner as the medul- 

 lary rays. (PI. VII, 3; PI. VIII, iig. 2.) The walls of the component 

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

 them considerablv in advance of the hvpha? in the wood cells and also 

 of the blue color which follows the appearance of the hypha? in the 

 rays. When the hyphtv have reached the heartwood they cease grow- 

 ing inward. One reason for this ma}^ 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 hyphse do not 

 flourish in the heartwood, neither in the medullar}- 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 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 hyph^. In the top of the tree the 



"The hyphw growing out from the metlullary rays, as shown in PI. VIII, fig. 2, 

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



