WHITE MILDEWS OR BLIGHTS. 169 



torted ; their petioles and tlie peduncles and calyces 

 of tlie flowers swollen^ distorted^ and grey with 

 mould ; and the whole plant looking so diseased 

 and leprous that it needs no mycologist to tell that 

 the rose is mildewed. The conceptacle in this spe- 

 cies is minute^ and contains but one sporangium, 

 which is one of the characters of the genus in which 

 it is now included, and a more justifiable distinction 

 than the ramifications of the appendages. The my- 

 celium is rather profuse, and the threads or appen- 

 dages which spring from the conceptacle are simple 

 and floccose (fig. 216). The sporangium contains 

 eight ovate spores. This species {Sphcerotheca 

 joannosaj Lev.), in its oidioid or conidiiferous form, 

 was for some time known under the name of Oidium 

 leucoconium. 



An allied species constitutes the hop-mildew, a 

 visitation with which some of our Kentish friends 

 are too familiar. This is not a prejudiced species 

 in the choice of its habitation, since it is found on 

 many other plants, where it flourishes with equal 

 vigour. The meadow-sweet, burnet, scabious, 

 teasle, dandelion, and other composite plants, plan- 

 tain, and plants of the cucumber family, all suffer 

 more or less from its roving disposition. The my- 

 celium of whitish threads is even more conspicuous 

 than in the last species, but the conceptacles are 

 often not to be found at all. These are also very 

 minute and most common on the under surface of 

 the leaves. The appendages, or fulcra, are simple. 



