16 BULLETIN 1037, TJ. S. DEPARTMENT OF AGRICULTURE. 
tacks recently felled trees, but does not penetrate deeply, owing to the 
high water content of the wood. He also states that the mycelium of 
the fungus readily penetrates throughout the sapwood of winter- 
felled wood when the loss in water content amounts to 10 to 20 per 
cent. Moreover, the growth in moist wood takes place for the most 
part in the older layers of the sapwood, or those in proximity to the 
heartwood. Finally, Munch concludes that the sap-stain fungus is 
capable of infecting the living tree, thus becoming parasitic, provided 
the fungous spores find entrance to the sapwood through injuries to 
the bark, such as those produced by bark-boring beetles ; and that con- 
ditions favorable for fungous growth, namely, a reduction in the 
water content and a corresponding increase in the air content of the 
sapwood, are brought about through disturbances in the root system 
of the tree. 
In this connection certain investigations by Snell {^7) on the rela- 
tion of the amount of decay to the density of the wood should be men- 
tioned. Five fungi which had been found to cause the rotting of 
structural timber in Xew England cotton mills were grown upon 
blocks of loblolly-pine sapwood and Sitka spruce. Several series of 
these blocks, each series containing a different percentage of moisture, 
were used in these experiments. The results obtained with loblolly 
pine agreed in the main with those of Munch (32) upon Scotch pine, 
a wood of about the same density. In the case of Sitka spruce, a wood 
of considerably less density, however, it was found that the limits of 
moisture content favorable for fungous growth were raised. In other 
words, " the values representing the upper limits for decay will vary 
inversely with the density of the wood." 
Temperature. — It has been clearly demonstrated in a number of 
temperature tests 13 upon some of the molds derived from infected 
timber that these fungi grow readily between certain limiting tem- 
peratures. Beyond these, they cease to show any signs of activity. 
The optimum temperatures are commonly those which obtain during 
the late spring and summer months in certain parts of the country. 
particularly in the South, i. e., 80° to 85° F. It is probable, how- 
ever, that each species has its own characteristic range. 
Food. — Sap-staining fungi and molds have been shown in cultures 
to live upon quite a variety of foods. Being devoid of chlorophyll 
they can not, like the higher plants, manufacture their own food, but 
must depend upon that already available. The medullary rays and 
wood parenchyma 'of green sapwood often contain certain starches, 
sugars, and oils which represent the stored food of the tree. These 
are the substances upon which sap-staining fungi probably depend 
for their existence. 
13 These tests were conducted at the Forest Products Laboratory, Madison, by Mrs, 
Rose Harsch Lvnwalter. 
