THE DIAGNOSTIC CHARACTERS OE SOME 

 SUPERFICIAL FUNGI. 



Bv Ethel ]\Iary Doidge, M.A., D.Sc, F.L.S. 



(Read, July lo, 1918.) 



Of the large group df Asconiycetes with a superficial 

 mycehum known as the Perisporiales only the family Erysiphacea? 

 has until recently received much attention from systematists ; 

 this is probably due not only to fche economic importance of the 

 powdery mildews, but to the fact that the other two ifaniilies 

 which were placed in the group comprise almost exclusively 

 tropical and sub-tropical fungi ; but the whole group is a very 

 interesting one, and well repays study. 



Before referring to recent work on the classification I should 

 like to discuss the peculiarities of the fungi, formerly classed to^ 

 gether as the Perisporiales. 



The Erisyphacecc, the family causing the well-known powdery 

 mildews, are more or less familiar to every student of botany : 

 the colourless superficial mycelium and the oidial form of the 

 conidia are common to all the genera, and the classification is 

 based solely on the characters of the perithecia and spores. 



Unfortunately, although the Oidiiim stage occurs on a large 

 variety of hosts, these fungi very rarely form perithecia in this 

 country ; this is especially true of mildews occurring on cultivated 

 plants, and I can only think of three which commonly produce 

 perithecia, Erysiphe (jraminis. Spluerotheea humuli on Cosmos, 

 and Podospbcrra leucotricha the cause of the apple mildew. 



One of the most beautiful genera is Uncinula with uncinate 

 perithecial appendages, of which there are several South African 

 representatives : the most common is the cosmopolitan species, 

 Uncinula polychceta, which occurs on Celtis phamnifolia; two 

 other species with less numerous appendages occur on Ficus and 

 on Pterocarpus. 



The genus Phyllactinia differs slightly from the rest of the 

 family in not being entirely superficial ; it sends special branches 

 of limited length into the intercellular spaces of the leaf through 

 the stomata, and on these branches the haustoria are produced. 

 which penetrate the cells olf the mesophyll. 



The perithecial appendages are e(|uatorial, and are straight 

 and rigid, with a bulbous base. The appendages exhibit striking 

 hygroscopic movements, and aid in dissemination by bending 

 backwards and prizing the perithecium away from the leaf sur- 

 face when it is mature. 



Only one cosmopolitan species, Phyllactinia corylea, is recog- 

 nised, occurring on a large number of hosts, and this has been 

 collected in the Transvaal on species of Combretum, Rhus, and 

 Vigna. 



