352 PLANT DISEASES 



Peronosporaceae. — Conidiophores usually branched; 

 conidia generally producing zoospores ; sometimes directly 

 forming a germ-tube ; sexual reproduction by antheridia 

 and oosphores producing oospores. 



Cystopus, Lev. — Conidia concatenate, chains vertical, 

 numerous, forming a sorus, which remains covered by the 

 epidermis of the host until the conidia are mature, and 

 then bursts through. Conidia all alike, producing zoo- 

 spores ; or the terminal conidium thicker walled, giving 

 origin to a germ-tube, or sterile and protective in function. 

 Oospores globose, epispore usually ornamented. 



Cystopus candidus, Ldv., Ann. Set. .Nat., ser. in. vol. 

 viii. p. 371. — Sori white, shining, then powdery, often 

 large and confluent, conidia all similar, globose, smooth, 

 15-17 /u, diam. Oospore subglobose, 28-50 /i, epispore 

 yellowish-brown, with blunt warts, which sometimes pass 

 into short, crooked ridges. 



Cystopus tragopogonis, Schroet., Krypt.-Flor. SMes., 

 in. i. p. 234. — Sori white, globose or oblong, flat, often 

 concentrically arranged ; terminal conidium largest, thick- 

 walled, sterile, remainder shortly cylindrical, thin-walled, 

 with an equatorial thickened ring, 16-22 /z. Oospores 

 globose, 45-65 ju., brown, with large, hollow warts, which 

 are themselves minutely warted. 



Phytophthora, De Bary. — Mycelium spreading in the 

 tissues of the host, haustoria few or wanting ; gonidio- 

 phores generally sparingly branched, gonidia at first 

 terminal on the branches, then apparently lateral also, 

 owing to continuation of growth of apex of conidiophore 

 beyond the point of origin of the first conidium, elliptical, 

 apex papillate, usually producing zoogonidia on germination. 

 Oospores globose, epispore smooth, rather thin, brown. 



