688 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



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

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

 basidia are represented in fig. 389 2 , p. 684, and fig. 390 5 . 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 Ericaceae. 



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 Telephorece 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. Stereum, 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 7 ), laterally attached, is 



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



Hydnece 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. Hydnum imbricatum, fig. 390 8 ). The Polyporece 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 lacrymans. 



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. perennis (fig. 390 9 ) and the allied Boletus edulis; 



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 Trametes 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 



