1910-T911.] Notes on Parasitic A scomycetes, 335 



K potentillce Sadeb. attacks the stalks, and occasionally 

 some of the leaves, of Potentilla Tormentilla, which it causes 

 to become distended to several times their normal thickness, 

 and to assume a pale yellowish-green colour. It appears to 

 be a common species in most districts. 



Taphrina aurea Sadeb. occurs on leaves of poplar, where it 

 forms conspicuous blisters which become golden-yellow on 

 their concave side, owing to the presence of abundance of 

 yellow- spored asci. This species also seems to be widely 

 distributed. 



T. Tosqicinetii (West.) forms large blisters on alder leaves, 

 the upper surface of which assume a somewhat glaucous 

 appearance, on account of the presence of innumerable asci. 

 It appears to be common throughout the country. 



T. Sadebeckii Johans. also occurs on leaves of alder, where 

 it produces smaller blisters than those caused by the last- 

 mentioned species. They are whitish or yellowish in colour, 

 and are formed mostly on the lower side of the leaf, and less 

 commonly on the upper surface. This species seems to be 

 less frequent than T. Tosquinetii. 



T. bullata Tul. forms convex, thickish blisters on leaves of 

 pear and hawthorn. These are green at first, but afterwards 

 become brown, and bear whitish asci on their lower surface. 

 This species is somewhat rare or locally distributed. 



We now come to the second of the five families of parasitic 

 Ascomycetes — viz., the Perisporiacese, the species of which 

 present several well-marked characteristic features. In the 

 early stage of development of many fungi of this family a 

 mycelium is formed on the surface of the leaves of the host- 

 plant, so as to produce one of the numerous " mildews " 

 which so often prove injurious to growing plants, and 

 which were referred to in a paper formerly read to the 

 Society.^ At this stage the fungus is regarded as belonging 

 to the Hyphomycetes, and usually produces its conidia in 

 abundance. At a later period the parasite reaches its 

 ascigerous condition, and develops on the mycelium numerous 

 minute perithecia, which become dark-brown or black when 

 mature, and are very often furnished externally with special- 

 ised threads or appendages. These perithecia are destitute 

 1 See the Society's 'Transactions,' vol. vi. pp. 198, 201, 202. 



