16 BULLETIN 871, IT. S. DEPARTMENT OF AGRICULTURE. 
certain time produce conditions unfavorable for their further develop- 
ment and are forced to seek another field. 
In the wood the hyphae are hyaline, varying in diameter from 
0.8 to 3.3 fi but being most commonly 0.8 to 1.7 /i, branching and 
rebranching into the finest threads, anastomosing, sparsely septate, 
rarely constricted at the septa, and sometimes having clamp connec- 
tions. They never become so abundant as to fill the tracheids 
completely. Usually the hyphae pass from the lumen of one tracheid 
into that of an adjoining tracheid and then extend up or down 
the lumen, but occasionally a single hypha may cross several 
tracheids in a radial or tangential direction without extending up or 
down their lumens or giving off any branches. The holes in the 
walls of the tracheids made by the hyphae are very small, particularly 
so since the hyphae are often sharply constricted when passing through 
the walls. Karely the hyphae are irregular in shape. 
The hyphae composing the cobwebiike and feltlike masses of 
mycelium in the badly decayed wood (see p. 13) are usually 
hyaline, but sometimes have granular contents. They vary in diam- 
eter from 0.8 to 40 p } are richly branched, more commonly septate 
than the hyphae found in tne wood cells, and sometimes constricted 
at the septa. No clamp connections were found. They frequently 
anastomose. They were often very irregular in shape, and globose 
or spindle-shaped swellings were frequent. 
OTHER FORMS OF DECAY. 
Besides the typical decay already described, two other very 
characteristic forms were found. One of these is characterized by 
small spots or pockets of brown decayed wood varying in width from 
0.5 to 2 mm. (0.02 to 0.08 inch) and in length from 1 to 4 mm. 
(0.04 to 0.16 inch), with the long axis running vertically in the wood. 
In some cases larger decayed spots are formed by the joining of two 
or more smaller ones. The tiny decayed spots are separated by 
apparently sound wood. As for the structure of the decayed wood 
and its reactions with various reagents, these agree exactly with the 
typical form of dry-rot (see p. 14), and this decay is very probably 
an abnormal form of the typical decay caused by Polyporus amarus. 
The other form of decay consists of very small white spots (measure- 
ments as given above) in which the wood has been reduced to cellulose, 
separated by apparently sound wood. The structure of the decayed 
wood is practically as described by Hartig (8, p. 53-54; 9, p. 36-37) 
for decay caused by the ring-scale fungus (Trametes pini), and the rot 
under consideration is undoubtedly caused by this fungus, since, 
through the courtesy of Dr. James K. Weir, the writer has been 
privileged to examine sporophores of Trametes pini with the typical 
