74 



ASCOMYCETES. 



Sph. epilobii l.k. 

 Sph. Niesslii Tliii 

 Sph. pruinosa ( '. 



L-uis on E/nloJninn (t-.S. Aiueiica). 

 on Sin-bu.'i {Pi/rtiK:) Aria. 

 l'l<. on /i/<».s in America. 



9QQad6 



Fio. 71. — Spkaci-otkeca castagnei. Epiphytic mycelium on epidermis of Spiraea 

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

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

 Spimea is shown at one side. (v. Tubeuf del.) 



Podosphaera. 



This genus is distinguished from Spluu: rotheca by its upriglit 

 perithecial appendages, which branch dichotomously towards their 

 extremities. 



Podosphaera oxyacanthae J). C. Apple powdery mildew, 

 also ocruriing on pear (/'//r//.s), hawthorn {Crataegus), mountain 

 cish (Pi/ras Aaciiparia), and medlar (Mesjnhts). In America 

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

 rhit'Hy young seedling plants, stunting tlieir growth and causing 

 them to lose their leaves. 



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

 species of rni/ias (cherry, plum, and sloe)^ (Britain and U.S. 

 America). 



-Account by M. B. Waite (U.S. Department of Arjriculture, Report for 

 1888); notes on treatment in Fairchild's experiments {Journal of Mycolofjy, \IU 

 p. 2.56), and elsewliere (Edit.). 



3 Halsted Zei/ichrift f. Pflanzenkrankheiten, 1895, p. 338) gives as additional 

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



I 



