OOMYCETES 



323 



Reess — Ueber d. Entstehung d. Flechte Collema glaucescens (Monber. Berl. Acad. , 



1871). 

 Reess— Ueber d. Natur d. Flechten (Samml. wiss. Vortrage von Virchow u. v. 



HoltzendorfiF, 1879). 

 Schwendener — Die Algentypen d. FlecHengonidien (Basel, 1869). 

 Schwendener — Erorterungen z. Gonidienfrage (Flora, 1872). 

 Schwendener — Die Flechten als Parasiten d. Algen (Verh. d. Basel, naturf. Ges. , 



1873). 

 Stahl — Beitr. z. Entwickel. d. Flechten, ii. (Leipzig, 1877). 

 Treub — Lichenencultur (Bot. Zeit., 1873). 

 Treub — Onderzoek. over d. Natuur d. Lichenen (Diss.) (Leiden, 1873). 



Special literature is quoted under each group. 



GROUP I.— PHYCOMYCETES. 



Class XVIII.— Oomycetes. 



Order i. — PERONOSPOREiE. 



The thallus of the Peronospores consists of irregularly and copiously 

 branched hyphae inhabiting for the most part the living, and especially 

 the chlorophyll-bearing, tissues of terrestrial flowering plants of different 

 natural orders. The 



mode of life in this case _ I '^ -^ 



is parasitic, and the 

 hyphse usually follow 

 the intercellular spaces, 

 .and in many cases send 

 ■short processes termed 

 haustoria into the ad- 

 joining cells. These 

 haustoria are variously 

 formed according to the 

 species. They are gene- 

 rally branched in Pero- 

 nospora (Corda) and glo- 

 bular in Cystopus (Lev.). 

 The hyphae of other 



species (PhytOphthOra, ^^^^ 285. — intercellular mycelial hypha: (m\ with haustoria 



Aa J3v.^ traverse the cells penetrating into cells (z), A^ oi Cystopus ccindidus L6v. ; B^ of 



■'*'' /'eronaspora catotAeca de'By. (x ^go). (After de Bary.) 



of the host- plant. Trans- 

 verse walls do not commonly appear in the hyphae until the period of the 

 formation of reproductive organs. The effect of this parasitic mode 



