174 ASCOMYCETES. 



Sph. epilobii Lk. occurs on Epilohium (U.S. America). 

 Sph. Niesslii Thiira. on Sorbus {Pyrus) Aria. 

 Sph. pminosa C. et Pk. on Rhiis in America. 



KR9Pp 



Fio. 71. — Sphaerotheca castagnei. Epiphytic mycelium on epidermis of S'piraea 

 ULmaria. Three haustoria are embedded in epidermal cells. Two conidiophores 

 are shown, from one of which a conidium has become detached. A hair of 

 Spiraea is shown at one side. (v. Tnbeuf deL) 



Podosphaera. 



This genus is distinguished from Sphaerotheca by its upright 

 perithecial appendages, which branch dichotomously towards their 

 extremities. 



Podosphaera oxyacanthae D. C. Apple powdery mildew, 

 also occurring on pear (Pyrus), hawthorn {Crataegus), mountain 

 ash (Fyru^ Au^ijparia), and medlar {Mespilus). In America 

 this disease is very injurious to apple-cultivation.^ It attacks 

 chiefly young seedling plants, stunting their growth and causing 

 them to lose their leaves. 



P. tridactyla "Wallr. This causes injury to leaves of various 

 species of Prunus (cherry, plum, and sloe)^ (Britain and U.S. 

 America). 



"Account 'by M. B. Waite (U.S. Department of Agriculture, Report for 

 1888) ; notes on treatment in Fairchild's experiments (Journal of Mycology, vii. 

 p. 256), and elsewhere (Edit.). 



3 Halsted Zeitschrift f. Pflanzenkrankheiten, 1895, p. 338) gives as additional 

 hosts: Apple, Crataegus Oxyacantha, Amelanchier canadeiisis and Spiraea (Edit.). 



