62 British UrediiiecB and UstilannecE. 



Ustilago. — The spore-forming hyphse enlarge and 

 branch in various ways. The gelatinization of their in- 

 terior takes place to such an extent as to almost obliterate 

 their lumen, which, however, may frequently be seen as a 

 narrow shining line in the middle of the hyphas (Plate V. 

 Fig. 7). At certain points the surface of these hyphae en- 

 large, so that they appear nodose. The increase in size 

 of the hypha continues, so that adjacent hyphae become 

 variously tangled and intertwined together, and eventually 

 many of the hyphae appear glued together, or to have 

 coalesced. The irregularities of the hypha; become more 

 marked, and it is obvious that each tumefaction will even- 

 tually become a spore, inasmuch as they gradually get 

 more and more rounded (Plate V. Fig. 8). It is in the 

 interior of these distended hyphae that spore-formation 

 takes place. It is, however, always found that the external 

 spores are the most developed, the formation being, in 

 fact, centripetal. The commencement of the differentiation 

 of the protoplasmic contents is at the exterior of the mass, 

 and it gradually proceeds inward towards the centre. The 

 spores when first formed have gelatinous envelopes, and 

 gradually become more or less polygonal from mutual 

 compression. The interior of the spore is now seen to 

 have a distinct contour, and to contain fatty granules. 

 The outer edge of this contour darkens, and even while it 

 is still surrounded by a thin gelatinous envelope the 

 irregularities of the epispore begin to be apparent. As 

 the spores ripen this gelatinous membrane disappears, so 

 that at their maturity they have no remnant of it ; nor are 

 any remains of the mycelial hyphae attached to them, as is 

 often seen in Tilletia. 



Spliacelotheca. — This genus differs from Ustilago in the 

 spore-mass being developed in a receptacle. De Bary thus 

 describes its development : " The vegetative mycelium. 



