688 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



fertile surface (the hymenium) consisting of basidia with 4 processes (or sterig- 

 7)iata) from each of which a conidium (or basidiospore) is abstricted. Typical 

 basidia are represented in fig. 389 -, p. 684, and fig. 390 ^. The hymenium in this 

 group is exposed at the time when the basidiospores are produced. 



As in the Ascomycetes, so here, there is an extensive range of forms from simple 

 to complex. Simplest of all are the Exobasidece, mostly parasites on Ericacese. 

 Exobasidium Rhododendri, which causes the Alpine Rose apples, has already been 

 mentioned (p. 520), as also E. Vaccinii and E. Lauri (p. 526). The hymenium in 

 these simple forms is produced over the whole surface of the hypertrophy or 

 blister caused by the Fungus. In the Telepltorece a definite tissue bearing the 

 hymenium is developed; this is termed the hymenophore or fructification. In the 

 simple Corticium this forms smooth sheets of waxy nature everywhere encrusting 

 the substratum. The basidia occur over the free surface. Stereuvi, also very 

 common on old trunks, forms leathery plates usually attached laterally or stalked. 

 The hymenium is on the smooth under surface, whilst the upper surface of the 

 fructification is more or less velvety. Craterellus (fig. 390 "), laterally attached, is 

 hollowed out above; the under surface is the fertile one. In the Clavarim the 

 fructification is club-shaped and fleshy, and covered externally by the hymenium — 

 as in the sulphur-yellow Clavaria incequalis very common on grass lawns and 

 pastures — or it is branched and coral-like as in Clavaria aurea (fig. 390 ^). In the 

 Hydneoe there is a well-marked distinction into a stalk and cap (known as the 

 pileus); the hymenium is on the under surface, and is in the form of a number of 

 crowded spines or teeth (e.g. Hydnu7)% imbricatum, fig. 390 '^X The Polyporeoi form 

 a large and important group, characterized by the fact that the hymenium has the 

 form of a number of pits, tubes, or meshes, usually on the under surface of the 

 fructification. The simplest of these is the Dry-rot Fungus, Merulius lacryman-^. 

 The mycelium of this Fungus penetrates the substance of ill-preserved woodwork 

 in houses, disintegrating it and reducing it to a brittle consistency. At places it 

 produces fructifications, flat irregular bodies whose under surface, the hymenium, 

 consists of a honeycombing of shallow depressions. The property which these 

 fructifications possess of excreting drops of water has given to this Fungus the 

 name lacrymans. In Polyporus the hymenium has the form of numerous fine 

 tubes lined with basidia. The fructification may be either bracket-like, as in 

 Polyporus fomentarius, or it may have the cap-like form of a mushroom mounted 

 on a central stalk, e.g. P. p)erennis (fig. 390^) and the allied Boletus edidis: 

 in both the cases cited the hymenial surface is, of course, directed towards the 

 ground. To these Polyporuses belong some of the most destructive diseases 

 of timber, their myceliums penetrating the wood everywhere, softening and 

 disintegrating it (e.g. Polyporus igniarius, P. fomentarius, P. sulphureus, and 

 P. annosus — otherwise known as Tranietes radiciperda). The last-named P. 

 annosus causes a well-known disease of coniferous timber, the wood coming out 

 in white spots before it is finally disintegrated. It is of interest because the 

 fructifications are produced on the roots of the trees attacked. Allied to Polyporus' 



