362 



BOTANY 



of the stink-brand of wheat. The brand spores of these species are also produced 

 in the ovaries, from which, however, they do not escape, but remain enclosed within 

 them, filling the apparently healthy grains with black brand spores, smelling like 

 decayed fish. In the first-named species the brand spores are provided with a 

 reticulately thickened epispore ; those of T. lacois, on the other hand, are smooth- 

 walled. Unlike the Ustilagin- 

 aceae, the germ-tube gives rise 

 only at its apex to filiform con- 

 idia, which are disposed in a 

 whorl, and consist of four to 

 twelve spores (Fig. 285, 1). 

 The conidia also exhibit the 

 peculiarity that they coalesce 

 with one another in pairs in an 

 H-form. In this process two 

 conidia come into open com- 

 munication by means of a 

 bridge-like connection extend- 

 ing from the middle of the two 

 cells, a form of coalescence 

 which frequently takes place 

 between the mycelial hyphae 

 of the higher Fungi. The fili- 

 form conidia germinate readily, 

 and produce sickle-shaped con- 

 idia at the apex of the germ- 

 tubes. When abundantly sup- 

 plied with food material, the 

 germ - tubes grow into large 

 mycelia, from which such 

 sickle - shaped conidia are so 

 abundantly abstricted that • 

 they have the appearance of a 

 growth of mould. Thus Tilletia, unlike Ustilago, produces conidia of two forms ; 

 but in other particulars the development of both groups is the same. 



To the Tilletiaceae belongs also Urocystis occulta, Rye -stem blight, whose 

 brand spores are formed in Rye haulms. 



The transversely septate conidiophores of the Ustilaginaceae, and the unsep- 

 tate conidiophores of the Tilletiaceae, produce an indefinite number of conidia. 

 In the group of the Basidiomycetcs, although both types of conidiophores occur, 

 the number of spores produced is definite, and the conidiophores are then termed 

 basidia. 



The formation of conidia in the Hemibasidii represents an original form of 

 asexual spore-formation, while the development of brand spores is to be regarded as 

 an interpolated, more recently acquired mode of spore-production. 



Fig. 285. — Tilletia Triiici. 1, Germinating brand spore, with 

 unseptate conidiophore (t) and apical filiform conidia (c) 

 (X 300) ; 2, a germinating filiform conidium bearing a 

 sickle-shaped conidium ( x 400) ; 3, portion of mycelium 

 with sickle - shaped conidia ( X 350). (After Brefeld, 

 from v. Tavel.) 



Sub-Class 6. Basidiomyeetes 



Like the Ascomycetes the Basidiomyeetes form an extremely variable 

 group of Hyphomycetes, with septated mycelium and devoid of 

 sexual reproduction. They are specially characterised by the forma- 



