PERONOSPORA in 



B. Wall of oospore wrinkled. 



Poppy mildew {Peronospora arborescens, De Bary) often 

 proves very destructive to cultivated poppies, and is also not 

 uncommon on our wild species. On the larger cultivated 

 species its effects are very evident ; the mildew often almost 

 entirely covers the under surface of the leaves with a thin, 

 whitish, fluffy mildew. The stem and petals are also often 

 attacked. Diseased plants soon change to a sickly yellow, 

 and the leaves curl and eventually fall to the ground. 



Conidiophores slender, repeatedly forked; ultimate branch- 

 lets very slender, pointed and curved, conidia subglobose, 

 15-24x15-20 p.. Oospores globose, wall brown, minutely 

 striate, 25-35 /j. diam. 



I have proved by experience that no benefit is derived from 

 spraying with either Bordeaux mixture or potassium sulphide. 

 The only means of preventing an epidemic is to remove 

 plants as soon as the disease is observed. 



Wallflower mildew {Peronospora parasitica, De Bary) often 

 exterminates whole beds of wallflowers, and also attacks many 

 other cruciferous plants, both wild and cultivated. When 

 wallflowers are attacked, every part of the plant soon changes 

 to a sickly yellowish-green colour, the stem is usually swollen 

 and more or less curved, as are also the leaves, and every 

 part is more or less covered with a delicate white mildew. 

 Oospores are formed in profusion in the tissues. 



Conidiophores thick, soft, wavy, repeatedly branched, ulti- 

 mate branchlets fine pointed, curved, conidia broadly ellip- 

 tical, 20-25x16-20 /x. Oogonia angularly globose, wall 

 tinged yellow, very thick, slightly wrinkled, 25-45 /x diam. 



Diseased plants can be readily recognised by the characters 

 indicated above, and all such should be promptly removed 

 and destroyed. When the disease has been present the land 

 should not be planted with cruciferous plants for two or three 

 years, otherwise infection would probably follow. 



Spinach mildew {Peronospora effusa, Rab.) attacks culti- 

 vated spinach, and is also not uncommon on wild plants 

 belonging to Chenopodiaceae, as goosefoot {Chenopodiiim), 

 also on members of the dock {Polygonaceae) and violet 

 ( Violaceae) families. 



