288 THE BASIDIOMYCETES 



pearance to the hymenium of Hydnum. In Gyrocephalus the 

 infundibuliform fruiting body suggests that of Craterellus; in 

 ProtomeruHus the convolutions and folds of the honeycomb-like 

 hymenium resemble those of the dry-rot organism Merulius. In 

 certain genera the hymenia include various sorts of sterile struc- 

 tures (cystidia, paraphyses). 



Asexual reproduction occurs in Tremella and Sebacina but is 

 not known in most of the remaining genera. In some cases co- 

 nidia are formed on branched conidiophores; or the terminal por- 

 tions of the hyphae may fragment to form oidia, which may be 

 either uninucleate or binucleate [Dangeard (1895)]. 



Although mycelium derived from a germinating basidiospore 

 is composed of uninucleate cells, the cells of hyphae composing 

 the fruiting bodies are invariably binucleate. Since the recent 

 genetical studies of Barnett (1937) have disclosed that several 

 species of Exidia are heterothallic, presumably the dicarvotic 

 condition originates shortly after germination of the basidiospore. 

 The exact manner of origin of the dicaryon has not been satis- 

 factorily explained. Clamp connections are present in a consid- 

 erable number of species but are lacking in others. Hyphal fu- 

 sions are also of frequent occurrence. 



Development of the basidia and basidiospores has been studied 

 cytologically in a considerable number of genera and species 

 [Juel (1898), Neuhoff (1924), Kiihner (1926), Whelden (1934, 

 1935, 1935a, 1937)]. The investigations of Whelden on Tre- 

 mella, Exidia, Sebacina, Protodontia, and Tremellodendron have 

 disclosed a surprising uniformity in details of basidial develop- 

 ment. The young hypobasidium contains 2 nuclei, which unite. 

 The fusion nucleus, which is very large, sometimes appearing to 

 occupy more than half the volume of the hypobasidium, di- 

 vides in a plane transverse to the longer axis of the hypobasidium, 

 and a longitudinal septum then is formed, separating the 2 hemi- 

 spherical cells. A second nuclear and cell division, in a plane 

 at right angles to the first, results in a 4-celled, cruciate, longi- 

 tudinally septate hypobasidium. Meanwhile the 4 epibasidia 

 elongate and project to the surface of the gel layer. The nuclei 

 migrate through the epibasidia and become incorporated into 

 the spores which are formed at the epibasidial apices. 



Germination of the basidiospores may occur by repetition and 

 formation of secondary spores. In Tremella the secondary spores 



