ORDER AGARICALES 499 



arise from a dicaryon mycelium with normal nuclear phenomena in the 

 basidium and yet produce only two spores on the basidium with two 

 nuclei passing into each. In some members of the family, as occurs fre- 

 quently on other Eubasidiae a mitotic division subsequent to the second 

 meiotic division results in the production of eight nuclei in the basidium 

 of which four may enter into the basidiospores and four remain behind, or 

 two proceed into each spore. In a stained specimen of Coprinus sp. studied 

 by the author each basidium possessed eight nuclei but after spore dis- 

 charge four still remained in the basidium. With the exclusion of Cantha- 

 rellus all Agaricaceae are chiastobasidial. 



The hymenium may consist entirely of basidia or there may be cystidia 

 of various types. In Coprinus the basidia are separated by large sterile 

 cells called paraphyses, not so tall as the basidia but much broader so that 

 the latter are arranged in squares, one at each corner where four para- 

 physes meet. Such paraphyses are not produced in most of the genera of 

 the family. The cystidia may differ in appearance from the basidia only in 

 the absence of sterigmata or they may be elongated, pointed, or forked, or 

 knobbed so as to resemble a tenpin. The upper portion of the cystidium is 

 often covered with crystals. Some cystidia are the terminal cells of laticif- 

 erous hyphae or of hyphae containing mucilaginous substances. The 

 cystidia occurring at the edge of the lamellae are called cheilocystidia and 

 may resemble or differ from those borne on the faces of the gills, the 

 pleurocystidia. Where, as in some species of Coprinus, the large, stout 

 pleurocystidia extend across the space between two gills and assist in 

 holding them apart they are sometimes called trabecular cystidia. 

 (Fig. 166.) 



Fayod (1889) distinguished several types of gills by their tramal struc- 

 tures. Other mycologists since then have recognized the value of these 

 distinctions in the classification of the Agaricaceae. The outer surface 

 always consists of the vertically standing basidia (and cystidia if present) 

 arising from a subhymenium, a thin or thick layer immediately below the 

 basidia. This may be indistinguishable. In the mixed or irregular trama 

 the hyphae are arranged without apparent order, being sinuous or inter- 

 laced. The regular trama consists of elements clearly parallel. In the 

 bilateral trama the trama proper is reduced to a thin median plane from 

 which the hyphae diverge obliquely in a curved line toward the strongly 

 developed subhymenium. In the inverse trama the young lamella has the 

 "regular" structure with a distinct subhymenium. As maturity ap- 

 proaches hyphae grow from the subhymenium obliquely inward, filling 

 the space formerly occupied by the vanished median portion of the trama. 

 It must be recognized that these four types grade into one another and 

 that at times it is difficult to decide which type is present, especially if 

 the gill that is being studied is a little too young or too old. 



