CLOVE-RRUST. 



419 



The clover-rust bears its clus- 

 ter-cups on the same plant with 

 the other forms. They appear 

 in early summer, in small clus- 

 ters, especially on the stalk and 

 veins of the leaves. The later 

 cluster-cups are accompanied or 

 followed by small round or oval 

 pustules of rough brown uredo- 

 spores, that are partly covered 

 by the torn, lead-colored epider- 

 mis of the leaf. Both of these 

 forms immediately reproduce a mycelium, 

 similar to that from which they originated, 

 in other leaves. The winter spores oc- 

 cur in slightly darker clusters in the fall, 

 and germinate the following spring. They 

 differ from the corresponding spores of 

 Puccinia in being one-celled, and resemble the uredospores of 

 the same species, except that they are somewhat darker brown, 

 smooth, and often furnished with a blunt point at the end. 



U. medicaginis falcatae (D. C), is a related rust, found in all 

 its stages on alfalfa and none-such, and on the wild rabbit's-foot 

 clover and hop-clover. Its winter spores are striped by longi- 

 tudinal ridges. Other species of Uromyces are found on differ- 

 ent grasses. U. dactylidis (Otth.) occurs, in Europe, on orchard 

 grass, the taller fescue, etc., and is represented in this country by 

 several forms on a number of grasses. Its cluster-cups are found 

 on the butter-cup. U. acuminatus (Arthur) is common on fall- 

 marsh grass ; U. spartinae (Farlow) on rush-salt grass ; and U. 

 Pechianus on the smaller salt grass {Distichlis maritima). These 

 species are not known to have a cluster-cup stage. 



Burning over meadows and fields covered with rusty stubble ; 

 a propel succession of crops ; and the destruction of plants that 



Fig. 164. 



