Minnesota Plant Diseases. 



145 



cup fungi, and in particular parasitic forms, build storage or- 

 gans, often as large as a small filbert nut, and the cups are 

 produced in clusters upon this 

 storage organ in the follow- 

 ing spring. Wild anemones, 

 cultivated clovers and plant 

 bulbs are often attacked by 

 such storage-organ-forraing 

 cup fungi, as are also plants of 

 the blueberry family. In the 

 latter case the storage organ 

 replaces the fruit of the host 

 plant and cases are known 

 where the same fungus lives on 

 two different hosts in its life- 

 time just as do many of the 

 rust fungi; i. e., the fungus 

 produces accessory spores on 

 one host and sac spores on the 

 other. A common disease of 

 certain coniferous trees in the 

 northern part of the state is 

 due to one member of the cup 

 fungus group. Compared 

 with other disease-producing 

 groups, however, the tree cup- 

 fungi are not of very great 

 economic importance, and this 

 is especially noticeable since 

 the cup fungi constitute such 

 a very large group of plants. 

 (Figs. 4, 10, 14, 61 to 65.) 



Lichen-forming fungi. It 

 has already been stated that 

 lichens are equal-partnership- 

 organisms consisting of an alga and a fungus. In a vast ma- 

 jority of cases, the fungi are members of the cup-fungus group, 

 as is seen by the production of cups. In some lichens, how- 

 ever, black fungi participate and in a very few stalked fungi 

 10 



Fig. 65. — Cup fungus (Helotium citrinum) 

 on decaying wood. Slightly magnified. 

 Original. 



