298 



DISEASES OF CULTIVATED PLANTS 



Mint rust, caused by Puccinia menthae (Pers.), often com- 

 pletely destroys entire beds of mint. All stages of the fungus 

 are produced on the same host. The cluster-cup condition 

 of the fungus appears first somewhat early in the season, and 

 is most abundant on the stems, which become much twisted, 

 distorted, and swollen, and more or less covered with the 



FIG. 87. Puccinia asparagi. i, aecidium stage on a young 

 shoot of asparagus ; 2, teleutospore stage on a summer plant ; 

 3, aecidiospores; 4, uredospores ; 5, teleutospores. Fig. 2 

 reduced remainder variousl ma. 



bright orange spores. The pustules of summer-spores and 

 winter-spores develop at a later stage, and are mostly con- 

 fined to the leaves, where they appear under the form of 

 minute brown or blackish pustules which soon become 

 powdery. 



I. Forming large orange patches on stem and leaves. 

 Spores subglobose, minutely warted, pale yellow, 35-45 X 

 18-25 P" 



II. Small brown pustules on leaves mostly, spores sub 

 globose or elliptical, pale brown, minutely warted, i8-28x 

 15-20 p. 



III. Blackish pustules on the leaves, spores elliptical or 

 almost cylindrical, scarcely constricted, end rounded, thick- 

 ened, minutely warted, brown, with a pale papilla, 2 5-3 5 X 

 18-23 //,, stem larger than spore. 



The mycelium of the aecidium stage is perennial in the 

 creeping underground portion of the stem, hence when a 

 plant is once infected it produces the disease every season. 



