392 BRITISH FUNGI 



Forming extended crusts on wood ; warts more or less elongated, 

 with a cavity or depression at the tip. Porothelium. 



Forming subgelatinous crusts, the surface covered with radiating, 

 irregular wrinkles or veins, which are sometimes covered with 

 warts. Phlehia. 



NOTES ON THE GENERA 



Hydnum 



So long as we have to deal with species having a regular cap 

 and a central stem, with spines on the under surface of the cap, in 

 place of gills, there can be no mistake as to the genus Hydnum. 

 The same is true of those stemless species growing out of wood. 

 It is when we come to the truly adnate species, of which there are 

 many, forming a thin crust, everywhere attached to the sub- 

 stratum by the under surface, and covered by spines on the free, 

 upper surface, that the trouble commences. It is characteristic of 

 the genus Hydnum that the spines are free from each other at the 

 base, and that they spring from a flat surface ; that is, they do 

 not originate from wrinkles or ridges, as in Irpex. In Grandinia, 

 which might be mistaken for a reduced, adnate species, the out- 

 growths are rounded and wart-like, as they are also in Porothelium, 

 where each minute wart has a little indentation at its tip. It is 

 important to remember that in Hydnum the spines should be sharp- 

 pointed and should spring from an even surface. One of the larger 

 species, H. repandum, is edible. vSome species are destructive para- 

 sites on timber and fruit trees. 



So far as at present known, the head-quarters of this genus is in 

 Sweden. More species are known from that country than from all 

 the rest of the world combined. 



Irpex 

 In this genus the teeth are coarser, often flattened, and not ro 

 uniformly sharp-pointed as in Hydnum. The most important 

 point of distinction between the two genera, however, consists in 

 the origin of the spines from the cap. As already pointed out, in 

 Hydnum the spines originate from a flat surface ; whereas in Irpex 

 they either arise from slightly raised ridges, when they are arranged 

 in irregular rows, or from ridges anastomosing to form an irregular 

 network. There are no species with a central stem ; the highest 

 forms are more or less resupinate and free above, an adnate portion 

 running down the matrix, or altogether adnate. All grow on wood. 



Caldesiella 

 Our single species is entirely adnate throughout, forming a very 

 thin layer of loose texture, densely covered with erect or oblique, 

 acute or compressed, slender spines. Cannot be mistaken for any 



