VII] 



USTILAGINALES 



193 



uninucleate or binucleate (fig. 160), but it is not known whether fusion takes 

 place in them. The multinucleate character of the mycelial cells strongly 

 suggests that no preliminary pairing of the nuclei occurs. 



In Ustilago Zeae Lutman also observed a mycelium of multinucleate 

 cells ; at the time of spore-formation binucleate and uninucleate cells and 

 finally uninucleate spores 'appear. 



Tilletiaceae 



The principal genera of the Tilletiaceae are Tilletia, Entyloma, Ttiburcinia, 

 Urocystis and Doassansia. They have in common the continuous basidium 

 with a terminal group of spores. 



Tilletia Tritici and T.foetens are the stink brands of wheat, so called by 

 reason of the strong odour of trimethylamin or herring brine given out by the 

 brand-spores. The two species differ in the character of the epispore which 

 is smooth in T. foetens, reticulate in T. Tritici. In both cases spores are 

 produced in the ovaries of the host, all tissues of which, except the outer 

 coat, are destroyed. The spore masses are garnered with the crop, and 

 damage all grains with which they are threshed or ground. The infected 

 flour and contaminated chaff and straw are causes of disease in man and 

 animals. 



On the germination of the brand-spore of T. Tritici the nucleus passes 

 into the basidium and divides three times so that eight nuclei are formed. 

 Eight basidiospores are budded off in a 

 bunch at the apex of the basidium, and 

 each receives a single nucleus. Frequently 

 additional nuclear divisions take place 

 and ten, twelve, or sixteen uninucleate 

 spores may be produced. When the spores 

 are fully formed short conjugating tubes 

 grow out and connect neighbouring 

 spores, often while these are still attached 

 to the basidium (fig. 161). 



According to Rawitscher the nucleus 

 of one cell of the pair passes over into 

 the other and the nuclei lie near one 

 another but without fusion. After con- 

 jugation the spores may become septate; 

 from those which contain two nuclei fila- 

 ments of binucleate cells grow out, and 

 may give rise to conidia which are also binucleate. Under suitable conditions 

 the binucleate hyphae bring about infection by pushing between the cells 

 of the host seedling. In the cells of the sporogenous mycelium fusion of the 



13 



Fig 



61. Tilletia Tritici (Bjerk) Wint.; 

 a. basidium thirty hours after germination 

 of brand-spore; b. conjugation of basidio- 

 spores ; X3oo; after Plowright. 



