60 



BOTANY. 



Closely related to the species above described is another one 

 (C. candidus), which attacks shepherd's - purse, radish, and 

 others of the mustard family, upon which it forms chalky 

 white blotches, and distorts the diseased parts of the plant 

 very greatly. 



For some reasons this is the best species 

 for study, longitudinal sections through the 

 stem showing very beautifully the structure 

 of the fungus, and the penetration of the 

 cells of the host 1 by the suckers (Fig. 34). 



Very similar to the white rusts in 

 most respects, but differing in the 

 arrangement of the non-sexual spores, 

 are the mildews (Peronospora, Phyto- 

 phthora). These plants form mouldy- 

 looking patches on the leaves and 

 stems of many plants, and are often 

 very destructive. Among them are 

 the vine mildew (Peronospora viti- 



cola) (Fig. 35), the potato fungus (Phytophthora infestans), 



and many others. 



spoi 



of the vine mildew (Pero- 

 nospora viticola), x 150. 



ORDER III. Saprolegniuceai (WATER MOULDS). 



These plants resemble quite closely the white rusts, and are 

 probably related to them. They grow on decaying organic 

 matter in water, or sometimes on living water animals, fish, 

 crustaceans, etc. They may usually be had for study by throw- 

 ing into water taken from a stagnant pond or aquarium, a dead 

 fly or some other insect. After a few days it will probably be 

 found covered with a dense growth of fine, white filaments, 

 standing out from it in all directions (Fig. 36, A) . Somewhat 



Host," the plant or animal upon which a parasite lives. 



