128 British Fungi. 



Peronosjjora sparsa, Berk. Gard. Cliron. 1862, p. 

 308, with fig.; Cke. Hdbk. n. 1790; Sac. Syll. vii. 

 n. 884. 



On under surface of living rose leaves. Rare. 



Gonidiophores scattered or aggregated and fomiing 

 an almost imperceptible grey film. The type speci- 

 men in Berkeley's herbarium is on the leaves of 

 some large cultivated rose. 



Fam. 3. Sapeolegniace^. 



Asexual mode of reproduction by zoogonidia that 

 are generally biciliate ; the hyph^e becoming partly or 

 entirely transformed into zoosporangia ; sexual mode 

 by oogonia and antheridia. 



Analysis of the Genera. 



A. Zoosporangia formed from the terminal portions 

 of the hyphge. Antherozoids not formed from proto- 

 plasm of antheridia. 



§ Filaments more or less constricted at intervals. 



Leptomihis. Zoogonidia biciliate. 



§§ Filaments not constricted. 



* Zoogonidia always destitute of a membrane. 



Saprolegnia. Zoogonidia evolved within the zoo- 

 sporangia ; oogonia generally polysporous. 



Pijthium. Zoogonidia evolved after escaping from 

 the zoosporangia ; oogonia monosporous. 



** Zoogonidia at first with a distinct membrane 

 from which they escape before leaving the zoo- 

 sporangia. 



Dityuchus. Oogonia not perforated. 



Bijjlanes. Oogonia perforated. 



