ELECTRIC RESISTANCE OF PLANTS. II 



cent. ; very fine sand, 17.0 per cent. ; fine sand, 23.5 per cent. ; 

 medium sand, 2.6 per cent.; coarse sand, 2.0 per cent.; fine 

 gravel, o.i per cent. Chemical analysis, — MgSO^, 3.38 per 

 cent.; NagSO^, 70.78 per cent.; KCl, 4.42 per cent.; 

 NaHCOg, 15.48 per cent. During the dry seasons the salts 

 appear at the center of the spot as a rather heavy white 

 encrustation. 



The salts are not uniformly distributed in the soil. The 

 total soluble salts in the first foot, as determined by electric 

 resistance tests made by the Bureau of Soils, was 1.72 per 

 cent; In the second foot, i.o per cent; and In the third foot, 

 1.3 per cent. Tests made by the writer with a standardized 

 Instrument of the type used by the Bureau of Soils* showed 

 that the salts are also unequally distributed horizontally. 

 Following Is given the resistances In ohms of soil solutions 

 from the three plant zones of the salt spot; the results were 

 not reduced to per centages. 



Canescens zone, 1350 ohms. 



Polycarpa zone, 350 ohms. 



Niittallii zone, 3 1 ohms. 

 The field tests show thus that the salts are most abundant in 

 the Niittallii zone and least abundant in the canescens zone, 

 and that they are intermediate in amount in the intermediate 

 zone. A detailed study of the spot would show a secondary 

 variation in the distribution of salts as the washes which run 

 through it are flooded with each considerable rain and carry 

 away the salts of the banks to so great an extent that as 

 noted above plants which are not highly salt resistant may 



grow along them. 



With the establishment of certain definite relations be- 

 tween the relative amount of salts in the soil and the kind 

 of halophytes occurring on them it seemed desirable to study 

 somewhat more closely the nature of the plants so sharply 

 contrasted with one another. Analyses of salt loving plants 

 show that chlorine is present in large quantities as the foUow- 



♦Kindly loaned by Prof. R. H. Forbes, Arizona Experiment Station. 



