56 BULLETIN 1296, U. S. DEPARTMENT OF AGRICULTURE 
stances the more isolated spots were selected. The outer layers of 
the pulp were carefully folded back with a sterile needle, and some 
of the infected pulp from the interior of the sheet was transferred to 
plain malt and acidified plates. Usually three of each kind of plates 
were inoculated, but when the infection of the pulp was unusually 
heavy many more were used. If the spots were produced by molds, 
single spore cultures were made as soon as the fungus sporulated. 
The hymenomycetes were much more difficult to isolate. The 
plates were observed frequently, and as soon as the transfer grew 
sufficiently other plates were made from the mycelial growth around 
it. Great care was taken to avoid the mycelia of any molds which 
might be present. It is seldom indeed that a piece of pulp is infected 
with a hymenomycete without being also more or less infected with 
various molds, and vice versa. It is frequently necessary to make 
many transfers before microscopic examination shows a pure culture. 
Welcome exceptions were several hymenomycetes which produce 
oidia, chlamydospores, or basidiospores; from these, single spore 
cultures coulcl be made almost as easily as from the molds. 
In working for pure cultures of pulp fungi, the greatest difficulty 
was caused by an overrunning of the plates by rapidly growing molds 
before other fungi could start growth. The most troublesome of 
these molds were species of Trichoderrna and Mucor, which accounted 
for the loss of hundreds of plates. Some species of the former genus 
were almost invariably present and in a sporulating condition on 
deteriorating pulp. 
Although bacteria probably play some part in the decay of wood 
pulp, it is quite evident from the studies made that they are not 
as important a factor as might be expected. There are perhaps 
two good reasons why this is true. Most cellulose-dissolving bacteria 
require (1) an abundance of moisture, and (2) a slightly alkaline 
medium. Ordinary pulp storage conditions would not satisfy the 
first condition, and ground-wood and sulphite pulps, which are 
slightly acid, do not afford the second. 
FUNGI OBSERVED 
Although molds, by which term all fungi except the hymenomycetes 
are referred to here, are more numerous and occur more frequently, 
they cause much less damage to pulp than do hymenomycetes. 
When molds are present, however, hymenomycetes are very likely 
to be found. 
The most common of all the fungi observed are molds with large, 
dark-brown mycelia which interlace the wood fibers and produce 
a neutral gray or olive-black blotch in the pulp. At times the infec- 
tion spots coalesce, and large gray or blue-black areas are formed. 
Several species of fungi produce such spots, and it is impossible to 
distinguish between them except bv cultural methods. Blotches 
Eink to purple in hue are found less frequently. They are produced 
y species of Penicillium and Fusarium. Only rarely have these 
molds been found sporulating on the pulp. Large yellow blotches are 
frequent in occurrence, most of them being indicative of some species 
of Trichoderrna. Pinkish cinnamon spots are quite common, and are 
caused either by a mold or by any of several wood-destroying fungi 
(hymenomycetes). It is often difficult to distinguish between the 
two types, especially in the early stages of infection. From small 
