POLYPORUS. 



441 



stems of oak-trees. At first they are soft, later hard and brown 

 with grooves on the upper side. The dark heart-wood of the 

 oak exhibits white or yellowish longitudinal stripes of rotten 

 wood converted into cellulose (Fig. 272). In the white portions 





Fig. 272. — Potyporus drpadeus. The mycelium forms longitudinal stripes 

 in the Oak-wood. (v. Tubeuf phot.) 



the destruction is more complete than in the yellow, where dis- 

 solution of the lamellae has not as yet taken place (Fig. 273). 



A simultaneous destruction of the wood by F. dryadeus and 

 P. igniarius may occur (Fig. 274); in this case, the medullary 



