414 CLASS BASIDIOMYCETEAE 



case the antherid from the cell below does not fertilize it but degenerates, 

 unless it finds an adjacent hypha one of whose cells it can fertilize. Liro 

 calls the receptive cells "oogones," and suggests the similarity to the 

 sexual process in the Peronosporaceae. Oudemans (1895) saw these bridg- 

 ing branches and called them clamp connections, but that can hardly be 

 correct since they grow upward from the base toward the apex, and con- 

 nect two dicaryon cells. 



Occasionally more than one promycelium may grow from a single 

 teliospore. This has been observed by Brefeld (1895) and by Yen (1937), 

 both in Sphacelotheca schweinfurthiana (Thiim.) Sacc. Yen observed a 

 similar development of two promycelia from a teliospore of Sorosporiuni 

 consanguineum E. & E. On dilute beer malt the sporidia are produced in 

 clusters terminally (as in Tilletia) and in lateral groups, not one at a time 

 from each cell of the promycelium. The sporidia in liquid media often 

 bud in the manner of yeasts, forming a monilioid chain or a cluster of 

 yeast-like cells. (Fig. 139.) 



Hiittig (1933) has shown that in Ustilago avenae (Pers.) Jens, the 

 temperature has considerable effect upon the proportions of disjunction 

 in the first and second meiotic divisions. Disjunction in the first division 

 (called by him pre-reduction) occurred in 14 per cent of the cases at 9° C, 

 17.4 per cent at 19°, 31.5 per cent at 25.5°, and 18.7 per cent at 29.5°. 

 Various chemicals also modify these proportions. 



Union of opposite sexual strains may take place by the conjugation of 

 two sporidia, the nucleus of one passing into the other sporidium. When 

 this germinates it gives rise to a dicaryon mycelium. Both Dickinson 

 (1927, 1928) and Boss (1927) showed that the dicaryon phase initiated by 

 the union of two sporidia is often only transitory in cultures of the fungus, 

 the further growth of the mycelium consisting of monocaryon hyphae, 

 some of one, some of the other sexual phase. For such species it seems 

 probable that only when the union occurs in the tissues of the host is the 

 dicaryon phase permanent. The binucleate sporidium may produce a 

 binucleate conidium. Rawitscher (1912) and others have shown that 

 instead of producing sporidia the promycelial cells of the opposite sexual 

 phase may conjugate by short conjugation tubes, through which the 

 nucleus of one of the cells passes into the other. This latter then produces 

 binucleate sporidia. It may happen that uninucleate sporidia germinate 

 and produce monocaryon mycelium. When two hyphae of such mono- 

 caryon mycelia of opposite sexual phases meet they unite and a dicaryon 

 mycelium results. A uninucleate conidium from one mycelium may unite 

 with a hypha of a mycelium of opposite sexual phase, etc. Bauch (1922) 

 showed that in Ustilago violacea (Pers.) Fuckel, the two sexual phases of 

 mycelium differ in their reaction to various nutrients present, as evinced 

 by the degrees of growth and distribution of the mycelia in various culture 



