136 MICEOSCOPIC FUNGI. 



large number of oospores, each containing a hun- 

 dred zoospores. It can scarcely be considered 

 marvellous that the white rust should be so com- 

 mon on plants favourable to its development, the 

 marvel being rather that any plant should escape. 



Until recently it was doubtful whether more than 

 one or two species of Cystopus (white rust) were 

 known. It is now certain that we have four in 

 Great Britain, and three or four others are found 

 elsewhere. Of the British species one is found on 

 many cruciferous plants, as the shepherd's-purse, 

 garden-cress, mustard, radish, and plants of the 

 cabbage kind. This is the Cystopus candidus. 

 Another occurs on the goat's-beard, salsify, and 

 scorzonera, which is called Cyst opus cubicus. Both 

 have great external resemblances, but both possess 

 specific internal differences. In the Goat's-beard 

 rust (plate X. fig. 201) the terminal conidia in the 

 bunches or fascicles of conidia which are produced 

 within the pustules are spheroidal, large, and of a 

 yellow-brown tint, whilst the residue are cylindrical, 

 smaller (plate X. fig. 202), and more or less com- 

 pressed. In the crucifer rust the conidia are all 

 equal in the pustules and globose. The oospores 

 in the former of these are subglobose and the warts 

 on their surface are solid ; whilst in the latter the 

 oospores are truly globose, and the warts on the 

 surface are hollow (plate X. fig. 210). The third 

 species is the Sandspurry white rust (Cystopus 

 Lepji'joni), which was found on the common sand- 



