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to 100 pounds, directly down on to the young mustard and grain. Twenty- 

 five acres were easily covered in five hours, so that under favorable con- 

 ditions, 40 to 50 acres could be readily sprayed in one day. The spraying 

 is best done when the grain and weeds are from (i to 10 inches high, or 

 just before the mustard plants begin to bloom. 



Further, it is highly important that the spraying be done during favor- 

 able weather. The great importance of this will be seen when we come to 

 consider the physiological side of the problem. The best time for the most 

 successful work is just after the dew is off, on a bright, sunshiny day. A 

 little Dakota wind also helps the process; but if a rain soon follows, the 

 iron salt is washed off and the work comes to naught. 



Now if we keep close watch of the plants sprayed we can readily fol- 

 low the various steps of the destructive action of the salt. First, the 

 sulphate dries on the leaves, leaving minute, whitish flakes on the surface. 

 Next, we note after two or three hours, particularly in the case of such 

 succulent plants as mustard, the appearance of many scattered, more or 

 less translucent, sunken areas on the leaves. The leaves by this time ap- 

 pear to be somewhat wilted and the whole plant looks somewhat sick. 

 Two or three hours later, close examination reveals the next step of the 

 process, in the gradual blackening of the sunken areas. The microscope 

 shows this to be due to the blackening of the cell contents of the shrunken 

 cells. Further wilting and drying up of the leaves is soon followed, in 24 

 hours or so, by their complete death. In a few days to a week, most of 

 the mustard leaves have fallen off, or remain as dry, withered remnants 

 on the dead stems. Occasionally a leaf may make a weak revival ; or a 

 plant here and there may make a futile effort at flowering and seed pro- 

 duction. But if the work is thoroughly clone, but few weeds survive. 1 

 have seen mustard so thick as to approximate 100 plants to the square 

 foot, all totally destroyed by effective spraying. 



After following the above description of the various steps in the ap- 

 pearance of a sprayed leaf the interpretation of the physiological action 

 of the sulphate seems clear. First, the salt drying in minute flakes on 

 the surface of the leaf, undoubtedly acts as a strong plasmolyzing agent 

 to draw the water out of the cells with which it is in immediate contact. 

 Thus results the scattered, translucent, sunken areas, merely from plas- 

 molysis of those regions by the overlying salt. This plasmolysis is par- 

 ticularly striking in the case of the ragweed, which responds to the action 

 of the sulphate even more quickly than does mustard or other weeds in- 



