these fruiting bodies and the 1 to 7 celled spores they contain (fig. 10) readily distinguish this fungus from the blue-stain fungi.

Tests made to determine the sterilizing effect of heat upon the organism within 3/4-inch oak boards showed that it could resist a temperature of 170° F. for 24 hours at a relative humidity of 35 to 65 per cent. No doubt the formation of spores within the wood tissues, a characteristic of this fungus, had something to do with this unusual resistance to killing by heat.

YELLOW STAIN OF HARDWOODS

The principal loss due to this stain is in the discoloration of the finished product and has caused considerable uneasiness when discovered in oak stock used in the manufacture of airplane propellers.16 A study of the fungus in relation to the strength properties of yellowed oak has indicated that the mechanical properties of the wood are but slightly affected.

Yellow stain is often found in the products manufactured from hardwoods. The stain develops in the wood during the period

16 Colley, R. H., Wilson, T. R. C., and Luxford, R. F., The Yellow Stain Fungus and Its Effect on the Strength of White Oak: Final report. Forest Products Laboratory; 1924,

following the cutting of the tree and before the wood is worked up into the finished product. Improper storage of logs, lumber, or other wood products under conditions favorable to fungous growth may cause this stain to develop. A moldy appearance of the stock may be the first symptoms. Later the wood may show the characteristic yellow discolorations.

FIGURE 13.--Drawing showing fruiting stalk bearing spore chains (+300) and spores highly magnified (+1,600) of the yellow-stain fungus

The stain has been observed in birch veneer and airplane stock, hickory and maple handles, in oak laminations used in airplane propellers, in oak wagon felloes and spokes, and in oak lumber.

The stain is of a pale yellow color sometimes difficult to detect, usually in streaks or irregular areas, and is most easily detected when the wood is freshly surfaced. The fungus is found in areas of

the wood showing very faint to no discoloration. The stain often penetrates deep into the wood and can not be surfaced off. Thin sections of the yellowed wood observed under the microscope show numerous minute colorless fungous threads within the wood cells, occasionally penetrating the cell walls. (Fig. 11.)

Artificial cultures (fig. 12) using fragments of the yellowed wood produce a fungus which is moldlike in character, olive buff in color, and which grows rapidly under proper moisture conditions.

Taxonomic characteristics place the fungus in the Penicillium divaricatum group. (Fig. 13.)

RED STAIN OF BOX ELDER

A disease of the box elder characterized by a bright red stain in the wood has been under observation since 1920.17 The stain is very frequently met with and, therefore, popularly believed to be a fairly reliable character for the identification of box elder wood. This redstained wood has been found in many places in the United States, and what appears to be the same thing has been reported in a few places in Europe.

The discoloration is found in all parts of the tree, from the roots to the smaller branches. (Figs. 14 and 15.) Its vivid color lends some poetic faith to the belief held by the ancient Greeks that it represented the heart blood of the dryads, tree spirits, or wood nymphs, who were killed with the cutting of the tree. Scientific curiosity and the use of the microscope have disclosed this “dryad blood" to consist of something very different.

It has been found that this red discoloration of a light coral red to hellebore red or carmine color, common in heartwood and to some extent in sapwood, is due to the presence in the wood of a soluble red pigment produced by the colored threads of a fungus new to science and named Fusarium negundi Sherb. This fungus develops within the wood and derives its nourishment therefrom, but no evidence has yet been found to indicate that it decays the wood. It is classed as a wood-staining organism.

The fungus appears to be weakly parasitic, since it is found developing in the sapwood of living trees, following entrance through wounds principally caused by sapsuckers-birds resembling the wellknown woodpeckers. The sapsuckers appear to be agents in spreading the disease from different parts of a tree or from tree to tree. Associated at times with the red-stain fungus in the same tree are to be found various rot-producing fungi. This necessitates caution in the use of red-stained wood where strength and durability are important.

The geographical distribution of the red-stain disease is assumed to coincide with the range of the box elder. It has been found in many places in the United States, and what appears to be the same disease has been reported in a few places in Europe.

As means of reducing the spread of the red stain and as a preventive measure in case the organism develops greater parasitic tendencies, sanitary measures in regard to the proper care of wounds are suggested for shade trees; and for forest trees the burning of

17 Hubert, E. E.. The Red Stain in the Wood of Box Elder: Jour. Ag. Research 26: 447-457; 1923.

FIGURE 14.-Transverse sections of a box-elder branch 2 inches in diameter

showing the central portion stained by the red-stain fungus (Fusarium negundi)

42717-29-3

FIGURE 15. Transverse section of box elder cut down in November, 1922, showing the heart rot of Fomes applanatus in the central heartwood surrounding this is a dark band of red stain with five projecting areas all halting abruptly on the same annual ring. The sapwood shows scattered individual infections by the red-stain fungus which entered through injuries produced by sapsuckers. At the division line between the two annual rings last formed are found eight of these infections. One of these injuries had not been healed and the direct relation is shown between the red-stain area and the cavity in the bark and cambium, produced by the bird