14 BULLETIN 1037, U. S. DEPARTMENT OF AGRICULTURE. 
layers, perhaps a few cells in thickness. H. Marshall Ward {55). 
however, in connection with certain experiments upon spruce blocks 
which had been artificially infected with Penicillium sp., notes that 
the examination of sections from cultures 3 months old showed that 
the hyphse of this fungus had entered the starch-bearing cells in 
the medullary rays of the sapwood and had consumed the starch. 
The hyphse were observed deep in the wood extending from tracheid 
to tracheid through the bordered pits. Miss A. L. Smith (46) notes 
the presence of a dark-brown hyphomycete in decaying timber. This 
mycelium had invaded the woody tissue and had apparently brought 
about a partial destruction of the medullary rays (see also Free- 
man, 12). 9 
During a series of experiments by the writer, cultures were taken 
from various points within red-oak blocks 2^ by 2& by 10 inches 
long which had been cut from green sapwood and then artificially 
infected with 15 different fungi including 13 of the common molds. 10 
The results obtained seem to confirm Ward's experiments, for posi- 
tive mold cultures were secured even from the center of these blocks. 
However, as far as known, the molds do not cause any serious disin- 
tegration of the cell walls in green timber and thus do not impair 
the strength of the wood to any appreciable extent. As in the case 
of the blue-stain fungus, it is the stored food within the cells that is 
the object of attack. 
The principal objection to the presence of mold lies in the dis- 
coloration due to the masses of mycelium and the luxuriant clusters 
of fruiting bodies which often develop upon green sapwood, and 
sometimes the heartwood, under conditions of high humidity and 
temperature resulting from poor ventilation. However, these super- 
ficial growths are readily removed during sanding or planing opera- 
tions. In many cases they can be readily brushed off. This is par- 
ticularly true of material which has become surface dried. 
An inspection of a carload of moldy timber is quite likely to pro- 
duce an impression that is liable to react unfavorably upon the 
shipper. Moreover, the presence of much mold or sap-stain in 
timber indicates the existence of conditions which are favorable to 
the development of decay. Such material, then, should be viewed 
with suspicion, but not of necessity with unfavorable discrimination. 
FACTORS WHICH FAVOR THE GROWTH OF SAP-STAIN AND MOLD 
FUNGI. 
The development of fungi is dependent upon four factors — a sup- 
ply of air, containing the essential element oxygen; the requisite 
McBcth and Scales (30) list a considerable number of molds that are apparently able 
to destroy cellulose, though they act differently toward different kinds of cellulose. 
10 See page 29 for the list of fungi used in this experiment. 
