378 



DISEASES OF ECONOMIC PLANTS 



visible from both sides. They are about 1-2 mm. in di- 

 ameter, and are not sharply bordered, but shade off grad- 

 ually into the surrounding tissue. With a hand lens very 

 small, spore-bearing organs may be seen in the centers of 

 the older spots, first as shiny amber-colored elevations. 

 These elevations soon crack open and expose very small, 



4^ 



Fig. 162. — Four alfalfa leaf spots; 1, ascochytose ; 2, pseudopezizose ; 3, cerco.s- 

 porcse; 4, stagonosporose. After Stewart and others. 



disk or cup shaped sporiferous bodies, which remain sur- 

 rounded by portions of the ruptured epidermis. Badly 

 diseased leaves usually turn yellow and fall off. Spots 

 upon the stems show the same general character as those 

 upon the leaves. 



The lower leaves, and the leaves of older plants, are most 

 subject to the leaf spot. Plants late in the season, as of 

 the second and third cuttings, suffer much more than earlier 

 in the season. These crops, especially if allowed to stand 

 a little too long before cutting in a dry season, may be badly 



