218 



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 blackens and dies. The diseased part may 

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

 is checked by drought, or the blight may, in rainy weather, 

 rapidly proceed to transform the entire foliage into a moist, 



Fig. 119. — Potato late-blight. Eows at left sprayed with Bordeaux 

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

 Original. 



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 conditions 

 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 offensfve odor discernible 

 at consideral)le distance from the field. The disease usually 

 soon shows on the stems also, which in turn blacken and die. 



