PHYCOMYCETES 353 



Phytophthora phase oli, Thaxter,^/. Gaz., vol. xiv. p. 273 

 (1889). Mycelial hyphae branched, rarely penetrating the 

 cells of the host by irregular haustoria. Conidiophores 

 strongly swollen at their point of exit through the stomata, 

 arising singly, or one to several in a cluster; simple, or 

 once dichotomously branched, and once to several times 

 successively inflated below the apices; conidia oval or 

 elliptical, with truncate base and papillate apex, 35-50 x 

 20-24 p. Germination by zoospores, usually fifteen in 

 number, or rarely by a simple hypha of germination. 

 Oospores unknown. 



Phytophthora infestans, De Bary, Journ. Bot., n. ser. vol. 

 v. p. 149 (1876). Mycelium slender, haustoria absent; 

 conidiophores solitary, or in clusters of 2-5, emerging 

 through the stomata, simple or sparingly branched up- 

 wards, tapering upwards, above with scattered, swollen 

 portions, corresponding to the points of origin of conidia, 

 up to i mm. high, 10-12 p thick below, hyaline, forming 

 a very delicate mould on the leaf ; conidia lemon-shaped, 

 colourless, with a prominent papilla, 25-30 x 15-20 ft, pro- 

 curing on germination 6-16 swarmspores; oospores un- 

 known. 



Phytophthora cactorum, Schroeter, Krypt. FL Schles., 

 p. 236 = Phytophthora omnivora^ De Bary. Hyphae vari- 

 ously branched, haustoria absent; conidiophores slender, 

 simple, or sparingly unilaterally branched, often nodulose 

 at intervals below the apex; conidia lemon-shaped, 

 50-60x35-40 /*, liberating on germination up to 50 

 zoospores ; oospore globose, smooth, yellowish-brown, 

 24-30 p diam., often conglomerated. 



Plasmopara, Schroeter. Mycelium stout, furnished with 



