14 BULLETIN 1037, U. S. DEPARTMENT OF AGEICULTUEE. 



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 PenicUUum sp., notes that 

 the examination of sections from cultures 3 months old showed that 

 the hypha? of this fungus had entered the starch-bearing cells in 

 the medullary rays of the sapwood and had consumed the starch. 

 The hyphas were observed deep in the wood extending from tracheid 

 to tracheid through the bordered pits. Miss A. L. Smith (4^) 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).'' 



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." 



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 



' McBeth and Scales (30) list a considerable number of molds that are apparently able 

 to destroy collulosp, though thoy act (liEferently toward difffrent kinds of cellnlose. 

 ^^ See page 29 for the list of fuiigi used in this experiment. 



