390 



Minnesota Plant Diseases. 



remain in the cells of the host. The cluster-cups are found on 

 the leaves of some coniferous tree. Spruces in the neighbor- 

 hood of affected cow- 

 berry plants often show 

 an abundance of cluster 

 cups and are usually most 

 seriously attacked in the 

 lower branches. It has 

 not been proven in our 

 American plants that 

 these two stages are con- 

 nected, but there seems 

 to be considerable proba- 

 bility that such is the 

 case. 



Rust of a n emon e 

 (Puccinia fusca Relh.). 

 Anemone, Thalictrum 

 and allied genera are sub- 

 ject to the attack of 

 anemone rust. In this rust 

 only the winter spores 

 are produced. The af- 

 fected plants are consid- 

 e r a b 1 y deformed. The 

 leaf stalks are longer and 

 the leaf blades are thick- 

 ened. The spore groups 

 are found on the lower 

 surface of the leaves. The winter spores of the anemone rust 

 pass the winter in a resting condition on the dead leaves of the 

 host and germinate in the spring. 



Rust of wild sarsaparilla (Triphragmiuvi davellosum Berk.). 

 Although found only rarely in some places, this rust is very com- 

 mon in others. It is particularly abundant in the northern part 

 of the state, but is exceedingly rare or entirely wanting in the 

 middle and southern parts. It forms blackish, winter-spore 

 groups on the under surface of the leaf. These groups are 

 almost smut-like in their appearance. The spores are com- 



FlG. 207. — The stem rust of cowberry (a plant of 

 the blueberry group). The fungus spores are 

 formed in the skin cells of the host, several in 

 each cell; they have germinated sending out 

 short, divided threads, each division of which 

 produces a short-stalked basidiospore. Highly 

 magnified. After Hartig. 



