438 CLASS BASIDIOMTCETEAE 



or epibasidia (Juel, 1898; Neuhoff, 1924; Rogers, 1934). These are then 

 homologized with the tehospore and promycehum (as hypobasidium and 

 epibasidium respectively) of the Uredinales and Ustilaginales. Onto- 

 genetically, where this distinction can be made, the hypobasidium is a 

 more or less spherical dicaryon cell within which the fusion of the nuclei 

 occurs. It may remain thin-walled and proceed immediately with the 

 formation of the epibasidium or may develop a thicker wall and become a 

 resting cell with diploid nucleus, from which, under proper conditions the 

 epibasidium then grows. 



The difficulty with the foregoing interpretation is that in some of these 

 fungi there is no such distinction in some species of a genus while it is 

 pronounced in other species. Furthermore, different structures have been 

 designated as hypobasidium and epibasidium. In the Auriculariales, in the 

 genus Auricularia, the somewhat elongated dicaryon basidium primor- 

 dium elongates after the nuclei have united and then meiosis occurs and 

 the four nuclei become separated by septa. There is no hypobasidium nor 

 epibasidium that can be distinguished. In some species of Septohasidium 

 the basidium primordium becomes a somewhat thick-walled resting cell, 

 and when favorable conditions come on this sends out a short stout hypha 

 like the whole basidium of Auricularia, within which meiosis occurs and 

 septa are formed. In other species no hypobasidium is formed at all and 

 within the basidial primordium occur the union of the two nuclei, and 

 their meiotic division, followed by septation to form the four celled 

 basidium. In still other species of this genus Avhether the resting stage, 

 usually interpreted as a hypobasidium, develops or not depends upon the 

 environment. Thus it is apparent that this is perhaps not such a funda- 

 mental character as has been supposed. In other words in the development 

 of the basidium in this group the presence or absence of a hypobasidium 

 and consequently of an epibasidium depends upon whether the ontogeny 

 of the basidium is interrupted or not. 



In the type of basidium found in the Dacrymycetales the basal portion 

 is interpreted as the hypobasidium and the two arms as epibasidia. But 

 here the meiotic divisions occur in the "hypobasidium," not in the "epi- 

 basidium" as in Septohasidium. In Tremella the "hypobasidium" is the 

 rounded basal portion within which meiosis occurs before the vertical 

 walls divide it cruciately into four cells. The four arms at whose tips the 

 sterigmata produce the basidiospores are interpreted as "epibasidia." In 

 TulasncUa the same structures are found, except that the "hypobasid- 

 ium" is not septate but is separated from the four epibasidia by septa. 



Order Auriculariales. The fungi included in this order are some of 

 them cosmopolitan but many are confined to the Tropics. They are largely 

 saprophytes on wood. A few are true parasites, such as some species of 

 Eocronartium and Jola, occurring on mosses; Septohasidium and Ured- 



