OOMYCETES 



2-23 



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



1871). 

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



Holtzendorff, 1 879). 

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

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

 Schwendener — Die Flechten als Parasiten d. Algen (\'erh. d. Basel, naturf. Ges. , 



1873); 

 Stahl — Beitr. z. Entwickel. d. Flechten, ii. (Leipzig, 1S77). 

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

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



Special literature is quoted wider each group. 



GROUP L— PHYCOMYCETES. 



Class XVIII.— Oomycetes. 



Order i. — Peronospore^e. 



The thallus of the Peronosporese consists of irregularly and copiously 

 branched hyph^e 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 ! A 



is parasitic, and the 

 hyphae 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 hyph^ of other 

 species (Phytophthora, 

 de By.) traverse the cells 

 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 



Y 2 



Fig. 285. — Intercellular mycelial hyphae (;«), ^vith haustoria 

 penetrating into cells (2), A , of CystopJis candidiis L6v. ; B, of 

 Peronospora calotheca de By. ( x 390). (After de Bary.) 



