THE '"BLUE" FUNGUS. 21 



attacked by the beetles. Why this should be so it is difficult to explain 

 satisfactorily. The spores must enter the region between the wood 

 and the bark through the beetle holes and burrows, for there is no 

 other way for them to get through the bark. Cracks in the bark are 

 practically entirely wanting in the living trees. The only explanation 

 possible is that the h} T phae start their growth in the bark and cambium 

 layer, the parts richest in food materials, and then grow inward at one 

 or more points independent of the beetle holes. 



As soon as the living bark and wood die, a wood-boring beetle enters 

 the wood and makes numerous small holes all through the sapwood 

 (see PL IX). It enters felled trees within a few days after the tree is 

 cut. The holes which it makes extend radially into the trunk, some- 

 times with great directness, then again obliquely. The beetles bore 

 with great rapidity, so that they may have reached the heartwood in 

 the course of a few months. These holes form very convenient chan- 

 nels for the entrance of the hyphse of the "blue" fungus, and the^ 

 take advantage of their opportunities. Before they appear in the 

 wood cells surrounding the holes made by the wood-boring beetle, 

 one finds great masses of another fungus in the open ends of the wood 

 cells bordering the hole. This is the so-called " ambrosia" fungus, 

 which the beetles carry into the holes with them, and upon the spores 

 of which they feed. The hyphse of this fungus are colorless and 

 thick walled. They extend into the wood cells away from the holes 

 only a short distance, but near the holes they grow into dense mats, 

 which practically plug the lumen of the wood fibers toward the beetle 

 hole. The bunches of sporophores with the round pores project into 

 the beetle hole from these mats. 



The hyphse of Ceratostomella can be distinguished readily from those 

 of the " ambrosia" fungus. They are thin walled, full of vacuoles, and 

 turn brown very soon. There seems to be no relation between the 

 two, although such a relation is not impossible. The development of 

 the "ambrosia" fungus is now being investigated, and it is hoped that 

 this study will throw more light on any possible relation. 



This class of beetle probably carries the spores of Ceratostomella 

 with it into the holes it makes, much as it carries the "ambrosia " spores. 

 This seems probable from the fact that the " blue " fungus seems to start 

 at various points along a beetle hole ; in other words, it does not grow 

 down into the hole from the outside. Sections made at right angles to 

 the hole show that the fungus starts to grow on all sides of the hole, 

 and that it makes most rapid headway in a direction parallel to the long 

 axes of the wood fibers (PI. IX). When once the hyphse have reached 

 the medullary rays from the wood fibers, progress in all directions 



Hubbard, H. G. The Ambrosia Beetles of the United States. Bull. 7, n. s., 

 Division of Entomology, U. S. Dept. of Agriculture, 1897, pp. 9-30. 



