POLYPORACEAE 487 



pore into the open air, where they are carried off by currents of air. 

 Cystidia of various types may be present in the hymenium and in some 

 species stiff, pointed, brown setae similar to those in Hymenochaete of the 

 Thelephoraceae. This has led to the suggestion that the various species 

 with setae now distributed among several genera, but especially in 

 Phellinus, in the Polyporaceae, should be placed in the same group as 

 the above mentioned genus. With very few exceptions the hymenium is 

 confined to the sides of the pores, not usually being formed on the edges 

 as in Meruliaceae. Conidiophores are produced on the upper surface of 

 the sporophore in some species. Under certain environmental conditions 

 a large portion of the tissue of the spore fruit may be converted into 

 chlamydospores, a condition upon which were based the genera Cerio- 

 myces and Ptychogaster. 



The vegetative mycelium is slender and branching, the individual 

 cells often being rather long. Some species of Polyporaceae produce large 

 tuber-like subterranean sclerotia the size of a man's head (e.g., Pachyma 

 cocos Fr.). From these the spore fruits arise when conditions are favorable. 



The processes of sexual reproduction are known in only a few cases in 

 the family. The mycelium of the spore fruits of many species appears 

 mostly to have clamp connections as does to a large degree the vegetative 

 mycelium growing in the wood. The basidia eventually have four or eight 

 nuclei, four of which pass into the four basidiospores whose nuclei in 

 some cases divide so that the spores become binucleate. In such species 

 the germ tubes show by the presence of clamp connections that secondary 

 or dicaryon mycelium is produced immediately upon germination of the 

 spores. Cultures of uninucleate basidiospores produce monocaryon 

 mycelia which lack clamp connections. When compatible mycelia come 

 into contact diploidization occurs and the dicaryon mycelium may de- 

 velop clamp connections, or in rarer cases they may fail to develop 

 although the mycelium is dicaryotic. 



Mounce and Macrae (1936) showed that in Gloeophyllum saepiarium 

 (Wulf.) Karst. {Lenzites saepiaria), Coriolopsis trabea (Pers.) B. & S. 

 (L. trahea) and Trametes americana Overh. the monocaryon mycelia 

 arising from germination of the basidiospores fall into only two mutually 

 compatible classes, therefore these species are of ''bipolar" sexual be- 

 havior. However, there is complete compatibility between all monocaryon 

 mycelia derived from sporophores collected in different geographic 

 regions. This indicates that geographical races exist in these fungi as has 

 been demonstrated in the Ustilaginales (see p. 378) and some of the 

 Heterobasideae (see p. 453). Robak (1936) reported that Hirschioporus 

 abietinus (Dicks, ex Fr.) Donk (Polystictus abietinus) is, on the contrary, 

 quadripolar in its sexual behavior. He also showed that the monocaryon 

 mycelium of Coriolellus serialis (Fr.) Murr. {Trametes serialis), a bipolar 



