124 INTRODUCTION TO THE STUDY OF FUNGI 



which is not in harmony with the general conception that the 

 hymenium is from the first exposed. In the Thelephoreae, 

 Clavarieae, and Hydneae the hymenium is exposed from the 

 earliest stage ; whereas in the Polyporeae and the Agaricineae 

 the hymenium, in the higher forms, is completely differentiated 

 while yet concealed by a structure known as the veil, which in 

 many species is only ruptured by the expansion of the pileus 

 when the spores are mature. The idea of concealing the 

 hymenium from the light is equally apparent in the various 

 orders enumerated, except in the Clavarieae. In the Thele- 

 phoreae the simplest genera — Corticium, Coniophora, and Penio- 

 phora — have the hymenium covering the whole of the upper- 

 most or free surface of the hymenophore, and consequently, 

 from the earliest period of development, exposed to the light ; 

 whereas in the genera Stereum and Thelephora a portion of 

 the hymenophore becomes free from the substratum and bends 

 over, thus turning the hymenium away from the light ; and, by 

 a series of transitions we find the higher species of the two 

 last-named genera assuming umbrella -shaped forms with a 

 central stem and inferior hymenium, but not at any period 

 covered by a veil. In the Agaricineae we meet with the same 

 sequence of the evolution. In such low forms as Cantharellus 

 retirugis and Agaricus (Pleurotus) hypnophilus the plants are 

 fixed to the substratum by the pileus with the hymenium 

 uppermost, and may be compared to a Corticium, with the 

 hymenium imperfectly broken up into gills ; whereas in such 

 species as Agaricus (Pholiota) praecox and Agaricus (Amanita) 

 muscarius the hymenophore is supported on a stem with the 

 hymenium on the under side, and concealed by a veil until the 

 spores are mature." It might also have been urged here, in 

 confirmation, that specimens of Fomes and Polystictus from 

 tropical or sub-tropical regions, where the light is strong, 

 are constantly to be met with, in which the log has become 

 turned and the hymenium of the Polypores growing thereon 

 exposed to the full light. In such cases, and especially 

 in such common species as Polystictus sanguineus and 

 Polystictus occidentalis, the old hymenium gradually becomes 

 obliterated, and a new hymenium is formed upon what previ- 

 ously was the upper surface, but accidentally inverted so as to 



