466 CLASS BASIDIOMYCETEAE 



The sterigmata may be long in proportion to the length of the basidium 

 or short, stout or. slender, straight or curved. In some species they are 

 hardly different from those of Ceratobasidium, tentatively placed in the 

 Tulasnellales (see Chapter 13) . Indeed these may represent transition forms. 



In a great many forms some of the potential basidia do not develop 

 far enough to produce sterigmata and spores. When they otherwise re- 

 semble not much modified basidia they are often spoken of as paraphyses. 

 It must be noted however that they arise from the same type of hyphae 

 that give rise to the basidia, so that in normal cases the paraphyses as 

 well as the young basidia are binucleate. In the Ascomyceteae, on the 

 contrary, the asci normally arise from dicaryotic hyphae and the para- 

 physes from monocaryotic hyphae. Thus the term paraphysis in the 

 Hymenomycetes is based on morphology and location of the structure, 

 not upon its phylogenetic implications (Ktihner, 1925a). 



Besides the paraphyses some of the hyphae underlying the basidial 

 layer may insert themselves between the basidia in the form of much 

 modified terminal cells. Except for the fact that in some cases they come 

 from hyphae more deeply located than those from which the basidia arise 

 they differ from the paraphyses mainly by their greater differentiation. 

 They are called cystidia. These are given special names depending upon 

 location, shape, contents, or function. They may be simple or branched, 

 colorless or colored, thin-walled or with thick walls, obtuse or pointed, 

 barely projecting from the hymenium or far exserted. In some species of 

 Coprinus they serve to hold the gills apart (trabecular cystidia) while in 

 Hymenochaete the stiff, sharp-pointed, bristle-like cystidia probably pro- 

 tect the hymenium from snails, slugs, or other soft bodied animals that 

 otherwise might destroy the basidia. The term gloeocystidium is given to 

 cystidia containing mucilaginous or oleaginous contents, usually at the 

 ends of conducting hyphae underneath the hymenium. In a few Hymeno- 

 mycetes there are produced in the trama or in the hymenium stellately 

 branched, thick-walled cells which may be considered as being specially 

 modified cystidia. By their location cystidia may be called cheilocystidia, 

 when they develop at the edges of the pores or lamellae, or pleurocystidia 

 when they occur in the hymenium that lines the pores or the surfaces of 

 the lamellae. Sometimes cystidium-like structures that develop on the 

 upper side of the pileus are called pileocystidia and similar structures on 

 the stipe caulocystidia. It must be recognized that these last two cate- 

 gories although resembling cystidia are perhaps better considered special 

 types of pubescence, confining the use of the term cystidium to structures 

 in the hymenium. 



The spore fruits show a very great variability of size and complexity 

 of structure. It seems probable that the simple forms in many cases repre- 



