10 BULLETIN 1037, U. S. DEPARTMENT OF AGRICULTURE. 
leaves a tube, with a cross section having the shape of the cross sec- 
tion of the ray, extending into the trunk from the bark. This tube 
is sometimes filled entirely with a mass of brown hyphae, the larger 
number of which extend in the direction of the ray (PL I, figs. 1 
and 2). From the ray cells some hyphae make their way into adja- 
cent wood cells (fig. 2, 2\ PL I, figs. 1 and 2). 7 They grow along 
these, both up and down (fig. 2, 1) , giving off branches to other wood 
cells. In this manner the whole wood body becomes penetrated by 
the brown hyphae in a very short time after the first infection. The 
number of hyphae in the wood cells proper, excluding the medullary 
ray cells and the cells of the wood parenchyma, is very small indeed. 
This is probably due to the fact that the fungus finds scant material 
upon which to live in the wood cells. The hyphae are apparently 
able to puncture the unlignified walls here and there, but they stop 
at that point. The writer was not able to demonstrate that the hyphae 
could attack the lignified walls. In other words, the ' blue ' fungus 
is one which confines its attack to the food substances contained in the 
storing cells of the trunk and to the slightly lignified walls of these 
storing cells." According to the same authority (41, p. 19), the resin 
ducts may be attacked in like manner (fig. 2, S\ PL I, fig. 2). 
In the case of sawed timber it is quite probable that the fungous 
spores falling upon the surface of the sapwood find there the mois- 
ture and food material necessary for germination. Subsequently they 
give rise to a mass of mycelium, many of whose hyphae enter the 
wood through the exposed medullary or pith rays and then probably 
invade the surrounding tissue, as explained by Von Schrenk. 
SUSCEPTIBILITY OF VARIOUS WOODS TO SAP-STAIN FUNGI. 
The sapwoods of many kinds of timber are susceptible to sap-stain, 
though the degree of susceptibility varies considerably. Among the 
conifers southern yellow pine, western yellow pine, sugar pine, and 
the spruces seem to be readily stained and in the case of the broad- 
leaved trees, red gum, red oak, white oak, and hackberry seem to be 
particularly susceptible. 
Often there is a considerable difference between a species when 
grown on the dry uplands and the same species when grown under 
the moist conditions characteristic of the lowlands (Von Schrenk and 
Spaulding, 4-4)- This difference in woods of the same species may be 
even more marked when grown in essentially different climates 
(Spaulding, If.8) . It seems to be the opinion of many lumbermen that 
timber grown in the South is more susceptible to fungous attacks 
than timber grown in the North. If differences in susceptibility do 
7 E. E. Hubert (21) observed in the wood of scrub pine and northern white cedar 
hyphae of Ccratostomella sp., which had ponotrated tracheids and wood fibers for a dis- 
tance of several cells from the medullary rays. 
