SALT PLANTS AND SALT-SPOTS CANNON 



125 



salts are likewise unequally distributed horizontally. Following is presented 

 the typical resistance of soil solutions for different portions of the salt-spot; 

 the results have not been reduced to percentages : 



Table 2. Resistance in ohms of soil solutions of salt-spot near Tucson. 



The field tests show, then, that the salts are most abundant in the nut- 

 talli zone, and least abundant in the canescens zone, and in the zone between 

 the two they are intermediate in amount. A detailed study of the salt-spot 

 would show a secondary variation in the quantities of salts in the soil, as 

 where the washes, which are flooded with each heavy rain, run into and 

 through the spot. In such places the soil is leached and, as above stated, 

 makes possible the invasion of less resistant salt plants and even of non-salt 

 plants. 



CHEMICAL ANALYSES OF SALT PLANTS. 



The observed zonal distribution of the salt plants taken in connection 

 with the marked vertical and horizontal distribution of the salts in the soil, 

 suggested the desirability of conducting an inquiry into the character of the 

 constituents of the plants themselves. This was done along two lines, namely, 

 by chemical analysis 4 , and electric resistance. 



3 This anomalous condition is not explained in the notes. In dry seasons the 

 ground at this place is covered with an incrustation of salts. 



4 The chemical analyses were made by Mr. William H. Walker, Laboratory of 

 Physiological Chemistry, Columbia University, and through the kindness of Pro- 

 fessor Wm. J. Gies. 



