16 BULLETIN 1037, U. S. DEPARTMENT OF AGEICULTUEe. 



tacks recently felled trees, but does not penetrate deeply, owing to the 

 high Avater content of the wood. He also states that the mycelium of 

 the fungus readily joenetrates 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. Finall}^, Miinch 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, nameh% 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 {If.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 ISTew 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 Miinch {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." 



Tem'perature.^^i has been clearly demonstrated in a number of 

 temperature tests ^^ 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, 

 particular!}^ 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 varietj^ 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. 



^^ These tests were concluotecl at the Forest Troducts Laboratory, jSIadison. by Mi-s. 

 Rose Harsch Lynwalter. 



