Minnesota Plant Diseases. 387 



Cluster-cup of gooseberry and currant (Aecidium grossn^ 

 laricB Schum.). This is very common on wild gooseberries and 

 currants. See Diseases of Garden Crops. See also Rust of 

 Sedges (this chapter). 



Cluster-cup rust of composites {Species of Aecidium). A 

 number of cluster-cup rusts attack wild and cultivated plants be- 

 longing to the composite family, e. g., sunflowers, asters and 

 goldenrods. Very little is known of their relationships with the 

 other spore-forms. They occur in abundance, throughout early 

 summer and midsummer, and are usually found on yellow spots, 

 accompanied by the pycnidia or accessory spore capsules, as in the 

 rusts of wild spring flowers. These cluster-cup rusts must be 

 distinguished from the golden-rod rust, which is caused by a dif- 

 ferent fungus and is even a different spore-form. A close ex- 

 amination, even with the aid of a hand lens, will serve to dis- 

 tinguish between them. The cluster cups are very easily recog- 

 nized. 



Leaf rust of golden rod and aster. See Diseases of Green- 

 house and Ornamental Plants. 



Rust of sunflowers (Ptfcama tanaceti DC). See Diseases of 

 Greenhouse and Ornamental Plants. 



Rusts of ferns [Hyalopsora polypodii (P.) Magn.]. Our 

 common wild ferns are subject to a rust disease, which is not un- 

 common in this state. The fragile fern is frequently attacked. 

 Summer spores are produced on the under surface of the leaves. 

 The winter spores are scattered through the fern tissues. They 

 are not as conspicuous as the summer spores. The latter occur 

 in dark, rust-like patches, often covering considerable areas. 



Stem and leaf rust of cowberry (Calyptospora goeppertiafia 

 Kuhn). An interesting disease of plants of the blueberry family, 

 similar in some of its effects to those of the fungus leaf gall of 

 the same plants, is caused by a rust fungus. This attacks 

 chiefly the cowberry and other related species. The young 

 shoots are attacked and the affected branches become much 

 larger than the healthy and are swollen to several times their 

 normal thickness. This swelling takes place the year following 

 the infection of the plant. The parasite lives in the tissues 

 for several years and the formation of fruits is usually pre- 

 vented on such affected shoots and the latter are finally killed. 



