20 Bi'ilish Fnnn. 



to the inside to siicli an extent tliat the lumen or 

 cavity is almost obliterated. This is accompanied by- 

 partial gelification, and subsequent cementing to- 

 gether of the hypho3 into a compact woody mass. The 

 result of this differentiation is a thin hollow cylinder 

 of rigid tissue extending throughout the length of 

 the stem and just witinn the circumference, the 

 central portion of the stem consisting of unmodified 

 hyphce. At the apex of the stem the woody ring 

 expands into the pileus in the form of numerous 

 tapering rays of the same consistency as the stem 

 cylinder, and modified from the original soft tissue of 

 the pileus. When the soft portions of the pileus and 

 stem decay, the hardened portion described above 

 remains in the form of a hollow stem with a trumpet- 

 shaped terminal portion formed of radiating tapering 

 ribs. A few other allied species of Polyporus present 

 a similar marked differentiation of tissues in the 

 sporophore. 



Coloration in fungi is often very pronounced. De 

 Bary considers that the colours are as a rule present 

 only in the substance of the walls of the hyphae, and 

 not in the cell-contents, and more especially after the 

 walls have undergone some modification, as in the 

 deep red of the pileus of the poisonous fly agaric, 

 Amanita muscarius, where the brilliant colour is con- 

 fined to the thin gelatinized layer on the surface of 

 the pileus. In the genus Calostoma again, the bright 

 vermilion colour of a specialized zone of tissue in the 

 sporophore is produced by the disintegration of the 

 hyphae, which results in a dry powdery mass. Light 

 appears in some cases to be an indisjDensable factor in 



