— =. 
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 hyphe 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 P]. TX). 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 hyphe of the **blue” fungus, and they 
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 hyphe 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 hyphe of Ceratostomel/a 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 Czratostomella 
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 (Pl. IX). When once the hyphe 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. 
