47 



stitute the white spots and also the white ))ands spoken of. The 

 various steps leading to the complete separation of the cellulose fibers 

 are exactly those which have been described for a similar process 

 caused by the hyphee of Trametes pini 

 forma abietln. 



A xc^vj different change is going- on at 

 the same time in the spring wood, and 

 gradually spreads from this to the sum- 

 mer wood. This change may be likened 

 to the one which Hartig has described as 

 taking place in pine wood attacked })y 

 PoJyjyortis horealix..^ The hypha? of the 

 fungus develop in the wood cells with 

 great rapidity, filling them completely. 

 Numerous hyph« pass through the walls 

 in all directions, making large irregular 

 holes many times the diameter of the 

 hypha^ which pass through them. The 

 secondary walls of the Avood cells are 

 gradually dissolved; a faint granular 

 appearance of the walls is seen at first, 

 and little by little the walls become thin- 

 ner. At last only the primary lamelhi is 

 left, and in the bordered pits the torus 

 (PI. XI, fig. 3). The whole wall finally 

 disappears, leaving simply that part of 

 the wall belonging to two or three cells, 

 namely, the portion having a triangular 

 cross section. This solution of the walls 

 goes on sinudtaneously throughout large 

 areas. The medullary rays disappear 

 completely, long before the wood cells are 

 entirely gone. The spaces left by the 

 dissolved cells are rapidly filled with 

 hypha^ and these hold poi'tions of the cell 

 walls not yet destroyed in place, and 

 give consistency to the mass, which thus 

 retains th(> shape of the wood befoi-e the 

 attack. The whole mass can be compressed by slight pr(\ssurc and 

 will not return to its original size. This accounts for the extremely 

 light weight of wood thus decayed. In PI. XI, fig. 2, a radial view 

 of wood in an advanced stage of decay is shown. The straight black 

 lines indicate groups of wood vessels, two or more; the hyphai between 



Fig. 8.— Baso of spruce brnnoli, sliowing 

 its resistance to the attack of tlie my- 

 celium of Polyporus subacidug Fk. 



' Hartig, R. Zeraetzuiigserscheinungeii dcs Ilolzes, etc. 



