350 



FUNGI 



<:uous as causing diseases of grasses. As a rule the attack of the para- 

 site is limited to one special region of the host, e.g. the ovary, or the 

 whole flower, or the leaf, or the stem, or even, in a few cases, the root ; 

 and when the fungus has attained its maturity, the result commonly is 

 that the part affected has been destroyed with the exception of the epi- 

 derm or integument and the remains of vascular tissue, and is replaced 

 by a powdery mass of brown or black resting-spores. The mycele sends 

 its long thin hyphae mostly along the intercellular spaces, in many cases 

 emitting branched haustoria into the adjoining cells, and the resting- 

 spores are formed either on all parts of 

 the hyphae or on particular branches. 

 The life-history, briefly stated, 

 begins with the production from the 

 resting-spore of a promycele which 

 bears sporid-like gametes ; these 

 gametes conjugate in pairs, and the 

 united pair either directly produce 

 a new mycele, or sporids which do 

 so. This mycele then bears resting^ 

 spores again in another host. Varia- 

 tions on this course of life-history 

 will be mentioned later on. Though 

 these conjugating gametes differ from 

 those of Protomyces in their acro- 

 genous origin on a promycele, they 

 may yet be considered homologues of 

 those, just as the acrogenous spores 

 of Chaetocladium are undoubtedly 

 homologous with the endogenous 

 spores of Mucor. 



In Entyloma (de By.) the resting-spores are borne interstitially at 

 indefinite intervals on the mycele, as in Protomyces ; in Tilletia (Tul.) 

 they occur singly, and only terminally on the spore-bearing hyphae ; 

 while in Geminella (Schroet.) they are borne, two together, in series 

 throughout the length of the special hyphae. In Urocystis (Rabenh.), 

 Sorosporium (Rudolphi), and Tuburcinia (Berk.) they are united, 

 several together, into a kind of coil, which is invested with a transitory 

 or a persistent integument. With the exception, perhaps, of Graphiola 

 (Port.), the exact relationship of which to the Ustilagineae has yet to be 

 determined, Sphacelotheca Hydropiperis (de By.), formerly Ustilago 

 Hydropiperis, according to de Bary's description, affords the best 

 example of a well-developed stroma. This fungus attacks the ovule of 



FIG. 299. Tilletia caries Tul., germinating. 

 In , gametes on promycele,/. In b, ga- 

 metes, s, conjugate in pairs. In c, a germ- 

 tube proceeding from pair of gametes, s. 

 A', a. sporid ( x 460). (After Tulasne.) 



