264 



DISEASES OF ECONOMIC PLANTS 



spots generally show first near the tip or margin, probably 

 because surface water remains longer on these parts. The 

 diseased area soon dies and blackens. It may temporarily 

 dry out and curl up if the progress of the fungus is 

 checked by drought, or it may, in rainy weather, rap- 



FiG. 119. — Potato late blight. Rows at left sprayed with Borde:iux 

 mixture and Paris green ; rows at right received Paris green only. 

 Original. 



idly proceed to transform the entire foliage into a moist, 

 putrid mass. In the earlier stage the blackened part is 

 bordered by a narrow region of light green, characterized 

 by a slightly watery, flaccid appearance. Under con- 

 ditions of especially humid atmosphere a fine, white down 

 may be seen upon the more recently invaded parts. This 

 affection of the leaves is accompanied by an offensive odor 



