234 MICROSCOPIC FUNGI. 



of mycelium slender, always destitute of suckers ; fertile threads 

 thin, gradually attenuated upwards, with oue 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.) 



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

 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 

 trifurcate, with one tofour horizontal branches near the summit, 

 once, twice, or three times bifurcate ; acrospores sub^lobose or 

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

 Common and variable. 



Peronospora pygmsea, Ung. (P. cK/-fo,Berk.). Anemone 

 Mould ; threads of mycelium thickeucd, 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 gangliformis, Berk. Lettuce Mould; 

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

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

 tomous, sometimes trichotomous ; stems and primary branches 

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

 the apex into a turbinate or subglobose vesicle bearing from 

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

 bose ; apices with broad depressed papillae, produced on the 

 spicular processes.— On Lettuces and other Composites. 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 trichotomous; branches always repeatedly trifurcate; 

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

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

 company with Gystopus candidus. Summer and autumn. Common. 

 (Plate XIII. fig. 262.) 



