APPENDIX. 215 



PEROI^OSPOIIEI, DeBy. 

 PeronosporAj Casp. 



Parasitic threads mostly inarticulate. Spores of two kinds : — 

 1. Acrospores on the tips of the branchlets ; 2. Oospores large, 

 globose, on the creeping myceHum. 



Peronospora infestans, Mont. Potato Mould ; threads 

 of mycelium slender, always destitute of suckers ; fertile threads 

 thin, gradually 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 ; apcK furnished with a prominent papilla,— On 

 leaves, stems, and tubers of the Potato, causing the potato- 

 murrain. Very common since 18i5. (Plate XIV, fig. 264.) 



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

 Mould ; threads of mycelium stout, often tomlose ; suckers 

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

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

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

 once, twice, or three times bifiucate ; acrospores subglobose or 

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

 Common and variable. 



Peronospora pygmsea, Ung. {P.curta,^QYk). 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 diehotomous, 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. INot 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 dieho- 

 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 Composite. Frequent. 

 (Plate XiV. fig. 265.) 



