PERONOSPORALES 



221 



spores. The genus may be regarded as intermediate between 

 Plasmopara and Bremia, but the enlarged tips of the branches of 

 the sporangiophore are not disc-Uke as in Bremia. Each bears 

 but a single sporangium. 



7. Peronospora Corda (1837: 20). 



Mycelium intercellular; haustoria in a few species short and 

 knob-like but in the majority filamentous and more or less 

 branched; sporangiophore consisting of an erect trunk several 

 (approx. 2-10) times dichotomously branched, the branches 



Fig. 80. — Peronospora effusa (Grev.) Rab. Sporangiophore and sporangia. 

 {After Schwarze 1917.) 



more or less reflexed and the terminal branchlets sharp pointed; 

 the habit consequently more graceful than in Plasmopara; spo- 

 rangia typically larger than in that genus, colored, lacking an 

 apical papilla and germinating from an indeterminate point on 

 the side by a germ tube; oospores more or less globose, smooth 

 or variously marked, germinating by germ tubes. 



Eriksson (1918 h: 19) states that in P. spinaciae Laubert 

 [ = p. effusa (Grev.) Tub] the oospore is not a hibernating spore, 

 but germinates in situ in the green leaf by several germ tubes 

 which push out through the stomates and develop an aerial 

 mycelium from which sporangia are cut off (Fig. 80). He says 

 further that these sporangia germinate by swarmspores. His 



