132 PHYCOMYCETES. 



may cause considerable damage to the lettuce (Lactuca saticn], 

 this being especially the case in France. The parasite is most 

 dangerous in forcing-houses during winter or early spring, and 

 spreads rapidly, favoured by the damp atmosphere. The young- 

 diseased plants are stunted, and take on a pale colour. Early 

 removal and destruction of diseased plants is to be recommended; 

 also abandonment for lettuce-cultivation of infected houses or 

 frames. 



In addition to lettuce, this fungus attacks a number of 

 Compositae, e.y. Cineraria, Sonckiis, etc. 



Peronospora. 



The mycelium is intercellular in living plants. The haustoria 

 may be simple, button-shaped, or thread-like, or may branch 

 inside the host-cell. The long and much-branched conidiophores 

 produce conidia singly at the ends of their branches. The 

 conidia produce a germ-tube. The oospores are brown-coated 

 and are formed singly in the oogonia ; they germinate in spring. 



Peronospora Schachtii, Fuck. 1 is injurious to the inner 

 leaves of sugar beet and mangold (Beta vulgaris), while young 

 seedlings are killed by it. The mycelium hibernates in the 

 roots ; as yet oospores have not been found. 



P. effusa (Grey.) This causes injury to spinach (Spinai-'m) 

 oleracea) and other Chenopodiaceae (Britain arid U.S. America). 



P. Schleideni, Ung. Kills the leaves of cultivated and wild 

 species of onion (Allium) (Britain and U.S. America). 



P. dipsaci, Tul. Injures stems and leaves of Dipsacus syli;^t<T 

 and D. Fullonum. 



P knautiae, Fuck., of Knautia and Scaliosa, is probably identi- 

 cal with last. 



P. viciae (Berk.) (Britain and U.S. America). A dangerous 

 species to many Papilionaceae (especially peas, beans, tares, 

 lentils, etc.), often causing great damage to field crops. In 

 recent years the new fodder-plant L11ii/nis syh'cstris has bcm 

 frequently attacked. 2 



P. trifoliorum, De Bary 3 (Britain and U.S. America). Dis- 

 tinguished from the preceding form by its irregularly marked 



1 Kiihn, Botan. Zeituny, 1873. 



-Zritx<-li riff f. PflanzenJerankheiten, 11., p. 'J'2.3 and 283. 



"Smith, Dii*<* of Crops, London. lss|. 



