138 INTRODUCTION TO THE STUDY OF FUNGI 



often zoned, and the tubes are typically stratose, each stratum 

 being the growth of a year, so that the species are truly per- 

 ennial. Some have a central, others a lateral stem, but most 

 commonly they are attached by a broad 

 base, where they are very thick, and not 

 uncommonly of the shape of a horse's 

 hoof, or more rarely several pilei grow 

 together in an imbricate manner. The 

 species of Polyporus, as now restricted, 

 generally shrink and become contorted 

 in the process of drying; but in Fomes 

 the substance is so rigid that no shrink- 

 ing or alteration of form takes place, 

 and, except for the depredation of in- 

 Pig. 52.-Poi yP orus, with sects might be preS erved unaltered for 



common stem. ° *■ 



a century. Such species as Fomes 

 comubovis, when sawn through, resemble sections of buffalo- 

 horn, although generally the internal substance is more 

 fibrous. 



Polystictus includes thinner, smaller, and more delicate 

 species, which are of a somewhat tough and leathery consist- 

 ency, usually flexible, and either hairy or velvety, or becoming 

 smooth. The surface of the pileus may be concentrically 

 sulcate, normally zoned, but not encrusted. The intermediate 

 stratum is fibrillose, passing down into the hymenophore, so 

 that the tubes are not separable. The latter are short, 

 and developed from the centre towards the circumference. 

 Commonly the whole thickness behind does not exceed a 

 quarter of an inch, often less, sometimes more ; but the pilei 

 may be confluent laterally, or densely imbricated, and the 

 hymenium may run down the matrix for a considerable dis- 

 tance. The habit and appearance often closely resemble 

 species of Stereum. Additional to the sessile species, there are 

 some which have a central stem, others with a very short 

 lateral stem, expanded at the base into a sort of disc, for attach- 

 ment to the matrix ; but most of the European species are 

 sessile, extended at the base, and more or less imbricate. The 

 pores are very variable in size in different species ; in some 

 they are so small as scarcely to be visible to the naked eye, 



