234 



MICEOSCOPIC FUNGI. 



of mycelram slender, always destitute of suckers ; fertfle threads 

 thin, graduallj; attenuated upwards, with one to five branches ; 

 one or more inflated vesicles near the apices of the branches ; 

 branches either simple or with short branchlets; acrospores 

 ellipsoid or ovoid; apex furnished with a prominent papilla: 

 oogonia globose, epispore brown, warted.— On leaves, stems, and 

 tubers of the Potato, causing the potato murrain. Very common 

 since 1845. (Plate XIV. fig. 264.1 



Peronospora nivea, Ung. (P. macrospora, B.). Paksnip 

 Mould ; threads of mycelium stout, often torulose ; suckers 

 numerous, vesicular, obovate ; fertile threads fasciculate, dwarfish, 

 tapering or subulate, or once or twice shortly bifurcate, rarely 

 trilurcate, with one to four horizontal branches near the summit, 

 once, twice, or three times bifurcate ; acrospores snbglobose or 

 ovoid, with an obtuse papilla at the apex. — On various TJmbeUifercB, 

 Common and variable. 



Peronospora pygmsea, Ung. (J". c»rfo,Berk.). Anemone 

 Mould ; threads of mycelium thickened, often constricted and 

 varicose; suckers minute, obovate, or pear-shaped: fertile threads 

 fasciculate (2-5 or more), simple above or divided at the apex 

 into 2-4 short simple branches, or shortly twice dichotomous, or 

 all simple, obtuse, surmounted by 2-4 short spicules ; acrospores 

 ovoid or ellipsoid, variable in size; apices broadly and obtusely 

 papillate.— On Wood-anemone. Not uncommon. (Plate Xv. 

 fig. 267.) 



Peronospora ganglifonnis, Berk. Lettuce Mould; 

 threads of the mycelium stout, now and then torulose ; suckers 

 vesipular, obovate. or clavate; fertile threads 2-6 times dicho- 

 tomous, sometimes tricbotomous ; stems and primarjr branches 

 slender, dilated or inflated above ; the ultimate ramuli inflated at 

 the apex into a turbinate or subglobose vesicle bearing fiom 

 2-8 subulate processes or spicules ; acrospores minute, subglo- 

 bose; apices with broad depressed papillae, produced on the 

 spicular nrooesses. — On Lettuces and other Compositte. Frequent, 

 (Plate XIV. fig. 265.) 



Peronospora parasitica, Pers. Cabbage Mould; 

 threads of the mycelium thickened and much branched ; suckers 

 numerous, branched ; branches clavate, obtuse ; fertile threads 

 thick, soft, flexile, equal or unequal, 5-8 times dichotomous, 

 rarely tricbotomous; branches always repeatedly trifnrcate; 

 acrospore broadly elliptical, very obtuse at the apex, white. — On 

 Cabbages, Shepherd's-purse, and other Cruciferse, sometimes in 

 company with Oystopas candidm. Summer and autumii. Common, 

 (Plate XIII. fig. 262.) 



