1 66 



Minnesota Plant Diseases. 



mous number of rust fungi, constituting" many of the most im- 

 portant diseases of cultivated crops. Wheat rusts have been 

 mentioned. The cluster-cups of the cedar apple fungus are 

 often destructive to pear and apple trees. Of great importance 

 are also the asparagus rust and mallow rust and the numerous 

 rusts of beans and clover. The great rust disease of the coffee 

 plant, though not, of course, directly affecting Minnesota plants, 

 has been of enormous importance in its devastation of the 

 coffee crops of India and Ceylon. In 

 addition to these might be mentioned a 

 host of parasitic rusts which yearly levy 

 a tax on field and garden crops, on wild 

 plants and greenhouse plants in fact, 

 they are almost universal in their distri- 

 bution. (Figs. 2, u, 23, 26, 29, 73 to 

 77, 136 to 145, 160 to 162, 181, 182, 199 

 to 201, 205 to 209.) 



Jews' ear fungi (Auricular line a). 

 This group of fungi derives its name 

 from the name of a common member of 

 the group a very widely distributed 

 fungus. The nearest relatives of the 

 Jews' ear fungi are the rusts, though at 

 first sight this fact is not apparent. 

 These fungi are almost all saprophytic, 

 growing chiefly on wood, but one spe- 

 cies is apparently a parasite upon 

 mosses. Unlike the rusts, winter spores 

 are not produced, but a basidium very 

 similar to that of many rusts is formed 

 directly on threads of the fruiting' body. 

 The basidia are long cylindrical bodies of 

 four cells, and they stand side by side in a dense palisade, form- 

 ing one surface of the fruiting body. The latter is variously 

 shaped : club-, spoon-, shelf-, or ear-like, and is found at the 

 surface of the log or whatever substratum may furnish the 

 nutrient material. The vegetative mycelium is found in the 

 log just as is the mycelium of the pore or shelf fungus in wood- 

 inhabiting saprophytes. The fruiting body of the Jews' ear 



FIG. 78. Various basidia and 

 spores of the lower basid- 

 ium-bearing fungi. 1. 

 Jew's-ear fungus; a, a 

 basidium; b stalk with 

 basidiospore. 2. Trembling 

 fungus; the basidium is 

 longitudinally divided. 3. 

 Weeping fungus; has an 

 undivided and forked basid- 

 ium. Highly magnified. 

 After Brefeld. 



