i66 British Fimo^i. 



'i> 



appears and the mature spores form a drj^ powdery 

 mass. In the genera Urocystis, Tuhurcinia, and 

 Sorosporium the spores are compacted into per- 

 manent clusters, and surrounded by a special envelope 

 which either soon disappears, or persists as a protec- 

 tive coat until the spores germinate. In Urocystis 

 this envelope consists of sterile cells which surround 

 the central cluster of spores. In Doassansia the 

 clusters of spores are enclosed in receptacles consist- 

 ing of closely compacted, dark coloured, sterile cells 

 arranged in a single layer like the palisade cells of a 

 leaf. De Bary has shown that in Sphacelotheca 

 hydro piper is, which infests the ovules of Polygonum 

 hydropiper, the sporophore is still more complex, 

 being furnished with a thick outer wall, and a central 

 axis or columella, the spores being formed in the 

 space between the two. The spores at maturity are 

 generally some shade of brown^ and often opaque, and 

 the epispore in many species is ornamented with 

 warts, spines, or ridges which are often combined to 

 form a network. The spores described above are 

 resting-spores, but gonidia are also produced by some 

 species. The details of germination of the resting- 

 spores furnish important systematic characters, and 

 will be described under the several generic diagnoses ; 

 in the present place it is sufficient to state that the 

 first product of germination is a short germ-tube, the 

 jjro mycelium, which soon gives origin to small spore- 

 like bodies called primary sporidia. A very remark- 

 able feature about these primary sporidia is that they 

 almost invariably conjugate in pairs ; that is, ad- 

 jacent pairs become organically united by a short tube 



