224 
Journal of Agricultural Research voi. xxvi, no. 5 
observed were very fine, especially in the aspen blocks. They were 
hyalin in many cases before staining reagents were applied. The appear¬ 
ance of the blocks is shown in Plate i, H and I. The presence of a surface 
darkening is to be seen in the case of certain blocks in I. This darkening 
was especially marked on the ends of the blocks and the surfaces showed 
discolored streaks. The growth within the blocks was less abundant in 
the case of this mold than with the other four species. It tended to be 
localized near the surface especially. The vessels contained the most 
mycelium, but hyphae were also present to some extent in the rays and 
fibers of aspen and white oak. In spruce the development was chiefly in 
the tracheids, and the hyphae extended longitudinally near the surface. 
No such marked effects on the wood were produced in this culture as in 
those described and figured by Hubert (jo, 12) who observed cell walls 
that were bored through and also exhibited surface thinning in instances 
where hyphae developed along the wall in contact with it. 
MOLD 71218-1 (AN UNIDENTIFIED FORM COMMON ON SITKA SPRUCE ANP 
RED OAK) 
In the cultures of the unidentified mold No. 71218-1 the blocks showed 
a considerable dark discoloration on the surface. The development in 
aspen and spruce was not so vigorous as that of the other molds. The 
growth was chiefly longitudinal in the open cavities of the vessels, tracheids 
(PI. 2, A), and resin passages. Except near the surface, the traversing of 
cell walls appeared to be reduced to the lowest degree consistent with pro¬ 
gress from cell to cell. Mycelium was found, however, in apsen fibers, in 
spruce rays and in the rays and vertical parenchyma of the white oak 
specimens. 
MONILIA SITOPHILA 
The aspen blocks which had been inoculated with Monilia sitophila 
appeared clean for the most part, only slight darkening, probably due 
chiefly to water stain, occurring near the edges. The other species of 
wood showed dark spots, and here and there slimy mats of mycelium 
adhered to the blocks. The growth of mycelium within the blocks was, 
however, abundant. Large twisted hyphae were present, especially at the 
center of the aspen block. In this case the growth of the mold was not 
confined to the vessels but was abundant in the fibers, rays, and vertical 
parenchyma. Many of the hyphae bored through the cell walls and 
traveled across the grain as well as longitudinally. This was noted par¬ 
ticularly in the white oak specimens (PI. 3, A). The spruce, on the other 
hand, appeared to be attacked chiefly near the surface (PI. 2, B). In 
that region the hyphae were large and abundant and showed less boring 
action on the cell walls than this fungus exhibited in the case of the 
other species of wood. 
PENICILLIUM DIVARICATUM 
The external effect of Penicillium divaricatum varied considerably 
with the different species of wood. The aspen test specimens were fairly 
clean looking to the naked eye, except for some spots and end darkening. 
The spruce, although it showed only slight discoloration of the ends, 
seemed softer than the normal wood of the species when it was cut in 
preparing the sections for microscopic study. The red oak blocks showed 
considerable end discoloration or darkening, and the white oak specimens 
had this appearance in a still more marked degree. Mats of mycelium 
