Cystopus candidus, Lév. Crucifer White Rust; conidia equal, globose; membrane equal, ochraceous; oospores subglobose, epispore yellowish-brown, with irregular obtuse warts; warts solid.—On Shepherd’s-purse, Cabbages, and other Cruciferæ. Summer. Very common. ([Plate X.] figs. 198-200, 205-207.)
Cystopus cubicus, Str. Goatsbeard White Rust; conidia unequal; terminal cell sterile, larger than the rest; membrane thickened, ochraceous, rarely yellowish; fertile cells shortly cylindrical; membrane hyaline; oospores globose; epispore brown, verrucose; warts hollow, round, or irregular.—On goatsbeard, salsify, and scorzonera. Summer and autumn. Common. ([Plate X.] figs. 201, 202, 210.)
Cystopus Lepigoni, De By. Sandwort White Rust; conidia unequal; terminal cell sterile, globose; membrane thickened; fertile cells subglobose or cylindrical; membrane hyaline; oospores globose; epispore brown, tubercles minute, irregular, very convex, often resembling spines.—On Spergutaria rubra. Swanscombe Marshes, September, 1864. (R. G. Keeley.)
PERONOSPOREI, De By.
Peronospora, Casp.
Parasitic threads mostly inarticulate. Spores of two kinds:—1. Acrospores on the tips of the branchlets; 2. Oospores large, globose, on the creeping mycelium.
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; apex furnished with a prominent papilla.—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 to four horizontal branches near the summit, once, twice, or three times bifurcate; acrospores subglobose or ovoid, with an obtuse papilla at the apex.—On various Umbelliferæ. Common and variable.
Peronospora pygmæa, Ung. (P. curta, 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 gangliformis, Berk. Lettuce Mould; threads of the mycelium stout, now and then torulose; suckers vesicular, obovate or clavate; fertile threads 2-6 times dichotomous, 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, subglobose; apices with broad depressed papillæ, produced on the spicular processes, On Lettuces and other Compositæ. Frequent. ([Plate XIV.] fig. 265.)