CLASSIFICATION OF FUNGI 39 



Albugo Candida, (P.) Rou., is widely distributed 

 throughout the world, and attacks many of our cruciferous 

 vegetables, such as radishes, horse radish, cress, cabbage, 

 etc. These host plants are frequently very much 

 deformed by the mass of mycelium which accumulates 

 within the tissues. 



The second family, Peronosporaceae, is distinguished 

 from the first by the conidia, which are always pro- 

 duced singly and aerially. It includes the following 

 important and destructive genera : Plasmopara, 

 Sclerospora, Peronospora, Bremia, and Phytophthora, 

 which are usually referred to as downy mildews, blights, 

 etc. 



The species of the genus Peronospora, are widely 

 distributed throughout the world, and are the cause of 

 many of our most troublesome diseases. Peronospora 

 Schleideni, Unger, the onion blight (Fig. 24, and page 

 234), has proved very destructive in the Bermudas 

 and the United States, and is no doubt much more 

 widely distributed. The mycelium penetrates the leaf 

 and eventually gives rise to the conidiophores, which 

 come out through the leaf. The conidia are elliptical 

 and germinate by the formation of a tube which enters 

 the new host through a storna. The fungus also 

 produces oospores very freely and spreads rapidly. 

 P. parasitica, (Pers.) De Bary, is a well-known, widely 

 distributed fungus, which causes the mildew of the 

 cabbage and allied plants. P. trichotoma, Massee, is 

 the cause of a disease on the malaga (see page 234), and 

 P. Nicotianae, Speg., attacks the tobacco. 



Bremia is another well-known genus containing 

 B. lactucae, Reg., which is widely distributed and well- 

 known as downy mildew of the lettuce. 



The species belonging to the genus Plasmopara 

 are also very abundant and destructive in both tropical 

 and temperate regions. Among the most common 

 are P. cubensis, (B. & C.) Humphrey, on the cucumber, 

 and P. viticola, (B. & C.) Berl. & De Toni, on the 

 grape. 



