368 CLASS BASIDIOMYCETEAE 



discharge of basidiospores and its relation to the distribution of the spores 

 by air currents. (Figs. 120, 121.) 



In all cases where the basidiospores are expelled violently Buller has 

 pointed out that they seem to be attached somewhat obliquely to the 

 sterigmata. Just before the spore discharge a drop of liquid begins to 

 appear at one side of the point of attachment, attaining full size in 5 to 

 20 seconds. It is worthy of note that in Sporoholomyces the spores are 

 discharged in the same way. This mode of attachment and release is 

 entirely different from that of true conidia (except conidia of Tilletiaceae) . 



In the Ascomyceteae the vegetative mycelium is mainly of the mono- 

 caryon type, with the haploid nuclei one to a cell or at least not closely 

 associated by twos. The ascogenous hyphae on the contrary have two 

 nuclei to each cell, i.e., they are dicaryotic. These alternating types of 

 mycelium may be called primary and secondary respectively. Mainly the 

 latter is short-lived and limited in growth. However, in the Taphrinales 

 the main vegetative mycelium is of the secondary type, the primary 

 mycelial stage being very much abbreviated. In the Basidiomyceteae the 

 secondary "dicaryon" type of mycelium is more often the preponderating 

 stage, the primary mycelium usually being of much shorter life than the 

 secondary mycelium. 



In very many of the Ascomyceteae there are definite male and female 

 reproductive structures (antherids and oogones, respectively). Yet in 

 some groups sexuality is on the decline and then these special reproductive 

 organs may be substituted for by the union of vegetative cells. This.latter 

 condition is the more frequent in the Basidiomyceteae where only in the 

 Rusts (Uredinales) are special female receptive hyphae produced. Even 

 in this group contact of vegetative hyphae of compatible types is suffi- 

 cient for sexual reproduction. In the Rusts special male gametes (sperm 

 cells or spermatia) are formed in definite organs called spermogonia, 

 but only on monocaryon mycelium. In many other members of the 

 Basidiomyceteae there are produced small hyaline, one-celled and uni- 

 nucleate spores called oidia. They arise on oidiophores and as they are 

 set free they cling together in a drop of sticky liquid, forming little shining 

 balls. The oidiophores may be simple or branched. The branches or the 

 apical portions of the unbranched oidiophores break up into oidia succes- 

 sively from the tip toward the base, leaving eventually only a short stub. 

 Brodie (1931), Vandendries (1924), and others have shown that mostly 

 the oidia arise only from primary mycelium. Long ago Dangeard (1894- 

 1895) described the formation of uninucleate oidium-like cells from the 

 dicaryon mycelium of Dacrymyces and more recently Vandendries and 

 Martens (1932) have demonstrated their occurrence on the dicaryon 

 mycelium of Pholiota aurivella (Batsch ex Fr.) Quel. In this species from 

 the same secondary mycelium may be produced thick-walled binucleate 



