200 Parasitic Moulds and Mildews. [Sess. 



Phytophthora infestans (Mont.) De Bary, the fungus of the 

 potato-disease, is too well known in its effects, and too widely 

 distributed, to need more than a passing notice. The conidia 

 are produced on the under surface of dark or withered spots 

 on the living leaves. 



Plasmo'para pygmcea (Ung.) Schrot. — Not uncommon on 

 leaves of Wood-Anemone. 



P. nivea (Ung.) Schrot. — Common on leaves of various 

 species of Umbelliferse, especially on Goutweed, where it pro- 

 duces pale yellowish spots, on the under surface of which the 

 white conidiophores are thinly developed. 



P. densa (Pers.) Schrot. — Common on leaves of Yellow- 

 rattle, and less frequently on those of Eyebright and Bartsia. 

 Owing to deficiency in chlorophyll, the affected leaves are 

 conspicuous by reason of their pale yellow colour. The under 

 surface bears a dense felt of whitish conidiophores. 



Bremia lactitcce Eegel. — Common on leaves of Groundsel 

 and various other wild and cultivated species of Compositse. 



Peronospora calotheca De Bary. — Frequent on various species 

 of Eubiaceae, such as Lady's-Bedstraw, Goose-grass, Wood- 

 ruff, &c. 



P. vicice (Berk.) De Bary. — Frequent on various wild 

 species of Vetch (especially Vicia sepium) and allied Legu- 

 minosse, also occasionally on leaves of Garden Pea, where it 

 usually forms on the under surface dense clusters of violet- 

 grey conidiophores. 



P. alsineaQntm Casp. — Not unfrequent on leaves of Chick- 

 weed and Mouse-ear Chickweed. 



P. arenarice (Berk.) Tul. — Frequent at the sea-coast, and 

 usually very abundant where it occurs, on the terminal leaves 

 and stems of Sea- Purslane. 



P. parasitica (Pers.) De Bary. — Very common on many 

 wild and cultivated species of Cruciferse, such as Shepherd's- 

 purse. Water-cress, Wallflower, Stock, &c., to which it often 

 occasions considerable injury. It is frequently found on 

 plants which are also infected with Cystopus candidus. 



P. ficarice Tul. — Common on various species of Buttercup, 

 sometimes covering the whole under surface of the leaves with 

 a grey flocculence. The affected leaves are also stunted in 

 size and paler in colour. This must be carefully distinguished 



