THE HELVELLACEAE. 275 



The Helvellaceae. 



This family is well known, some as poisonous, others as 

 edible fungi (morel, etc.), and a few are suspected of being para- 

 sites. The ascogenous layer occupies the upper surface of the 

 sporophores, which grow on the earth and assume many various 

 forms. As a rule they are erect and fleshy, and more or less 

 lobed, wrinkled, or folded. 



USTILAGINEAE. 



The Ustilagineae or Smut-fungi are distinguished by their 

 dark-coloured or black chlamydospores, which, on germination, 

 produce some form of promycelium capable of giving rise to 

 an indefinite number of conidia or sporidia.^ The chlamydospores 

 themselves are produced in large numbers from a mycelium, 

 and serve as resting-spores to carry the fungus through the 

 winter, being often, in fact, the only part which persists. An 

 endogenous formation of spores in sporangia as in the lower 

 fungi, or in asci as in the Ascomycetes, does not occur in 

 the Ustilagineae, Uredineae, or Basidiomycetes. 



The resting-spores of the Ustilagineae contain only one 

 nucleus, the result of copulation of two nuclei ; their formation 

 thus marks the end of one generation, and their germination 

 the beginning of a new. In the case of the Uredineae, Basidio- 

 mycetes, and Ascomycetes, the beginning of the new generation 

 is indicated by the germination of the teleutospore, the formation 

 of basidiospores on the basidium, and the germination of the 

 ascospore respectively. 



All the Ustilagineae are parasitic on higher plants, the 

 mycelium growing intercellularly and nourished by means of 

 haustoria sunk into the host-cells. The mycelium itself causes 

 neither disease nor deformation of plants, and it is only when 



^ Brefeld regards the promj'celium of the Ustilagineae not, like De Bary, as 

 a mycelial structure, but as a conidiophore or basidial structure. In accordance 

 with this view he has founded his intermediate group, the Hemibasidii corre- 

 sponding to the Ustilagineae. Brefeld then subdivides this group into («) Ustila- 

 gineae {Usfi/ago, Sphacdothf.ca, ScJiizoiiella, To(ypospo)-ium), which as a rule 

 have a septate promycelium ; and {h) Tilletieae ( TiUttia, Enfyloma, Melanotaenium, 

 Schroetcria, Theraphora, Sorosporium), with non-septate promycelia. {Schimmel- 

 pilze. Heft v., IS83, and Heft xi., 1895.) 



