INTBODUCTION TO CRTPTOQAMIC BOTANY. 861 



for food ; while a multitude of species are corky, and to a cer- 

 tain extent persistent. Woody species are very rare ; but I 

 have one species of Sistotrema perfectly ligneous, with enor- 

 mously developed teeth, and perhaps one of the finest of the 

 ligneous Fungi. In fact, so varied are they, that the species 

 differ from each other more than the lower genera. In all 

 these cases the hymenium is inferior, or merely resupinate ; 

 but in Hericium it is strictly amphigenous, insomuch that the 

 genus may be considered as a group of simple Glavarue 

 consolidated into a single mass. Sistotrema and Irpex are 

 approaches to the Polyporioid group, and are in their early 

 stage scarcely distinguishable. Radulum, however, connects 

 these with Hydnum, so that their association with the other 

 genera is not unnatural. 



394. The whole group affects temperate climes, and, with 

 one or two rare exceptions only, has representatives in the 

 tropics. One curious Hydnum occurs in Jamaica, and there 

 are a few sub-tropical species, differing, however, but slightly 

 from the forms of more temperate regions. There are some 

 representatives in the antarctic regions, but the species have 

 their centre in the northern hemisphere. The finest species 

 abound in Sweden. A few occur all over Europe. H. clou- 

 throides is abundant amongst the Himalayas. Numerous 

 species occur in Great Britain, but those of the mesopod 

 division are rare. H. repandum is one of our best esculent 

 Fungi, and I believe very safe ; and a few more are esculent. 



5. POLTPOEEI, Fr. 



Fructifying surface essentially porous, the pores constitut- 

 ing mere depressions in the substance, or formed by a folded 

 membrane, so as to be separable from each other, or from 

 the pileus. Substance various. 



395. The essential character of this important division is 

 the depression of the hymenium, in the form of more or less 

 perfect tubes. Now, if the hymenial surface of the indefinite 

 elevations of a granulated Gorticiuon be entirely depressed, 

 we have at once a Porothelium, of which an important Poly- 

 poroid form has lately been discovered by Mr. Spruce on 

 the banks of the Rio Negro, a tributary of the Amazon. If 



