202 ASCOMYCETES. 



The disease spreads through fields in a centrifugal direction 

 from a starting-point. Besides the above plants, it is also 

 said by Kiihn to attack carrots, sugar-beet and mangolds, 

 fennel and potatoes ; and Tulasne gives asparagus and red 

 clover as hosts. Prunet l believes that the fungus remains 

 three years in the soil, and recommends that diseased fields 

 should not be cropped with lucerne or clover for several years. 

 He also advises the isolation of infected land by surrounding 

 it with a deep trench in which sulphur is strewn, then covered 

 over with soil. The enclosed plot should next be deeply 

 trenched between June and August, and all plant-remains 

 removed and burnt. 



Rh. crocorum D. C. 2 The Saffron destroyer. This parasite 

 attacks and kills corms of the saffron (Crocus sativus). The 

 mycelium finds entrance by the stomata of healthy corms, 

 and covers them externally with a web of violet- coloured 

 mycelium. 



Rh. solani Kuhn. occurs as black sclerotia on the skin of 

 potato-tubers. 



Rh. batatas Fr. occurs in America on sweet potato. 



Rh. allii Grev. occurs on tubers of shalot (Allium, ascalonicum) 

 and onion (A. sativum). 



Rh. betae Kiihn is said to attack beet-root in America. 3 



We may also consider at this place : 



Dematophora necatrix Hartig. 4 The vine-root fungus. 

 This parasite causes a very destructive disease of the vine, 

 and is often confused with attacks of the Phylloxera-insect. 

 It occurs in the United States, and is common throughout 

 France, Switzerland, Italy, and South-west Germany, being 

 known under a variety of names. 5 Occasionally it has been 

 known to attack the roots of fruit trees and other plants 

 cultivated in vinevards. 



t/ 



1 Prunet, " Sur le Rhizoctone de la Ltizerne." Compt. rend., Paris, 1893. 



Fr. Wagner, " Das Vorkommen des Wurzeltoters d. Luzerne." Zeitsch. d. 

 Landwirth. Verein in Bayern, 1894. 



- Prillieux, "Sur la maladie des Safrans." Compt. rend., xciv. and xcv. 

 Tulasne, Fungi hypogaei, PI. VIII., 1851. 

 ''-Iowa Afjric. Exper. Station, Bulletin 15, 1891 ; with illustrations. 



4 R. Hartig, Untersuchwngen aus d. forsfbotan. Institut zu JUiinchen, in., 1883. 



5 Wurzelpilz, Weinstockfaule, Pourridie de la Vigne, Pourriture, Blanc des 

 llacines, Blanquet, Champignon blanc, Aubernage, Mai nero, Morbe bianco, etc. 

 (Hartig's Lehrbwh). 



