ALKALI RESISTANCE OF DATE PALM. 119 



by the date palm which was seen growing at Chegga, Algeria, in a soil 

 containing about 0.8 per cent of chlorids, while amounts of chlorids 

 as great as 0.2 per cent were apparently entirely without effect on the 

 date palm at Ourlana, Algeria. 



RESISTANCE OF THE DATE PALM TO SULPHATES. 



Sulphates, such as Glauber's salt (sodium sulphate), are still less 

 injurious than chlorids to the date palm, which, when well estab- 

 lished, is able to withstand enormous amounts of these salts probably 

 from 2 to 5 per cent. Roots of the California fan palm, which is 

 probably no more resistant to alkali than the date palm, were found 

 at Palm Springs in the Salton Basin, California (see p. 112), rami- 

 fying abundantly in a layer of subsoil 6 feet below the surface, where 

 there was 4.52 per cent of Glauber's salt and 0.26 per cent of magne- 

 sium sulphate present. Allowing 0.02 per cent as the amount of 

 g}^psum (calcium sulphate) that would go into solution in the soil 

 moisture, the total sulphates would amount here to 4.80 per cent of 

 the weight of the soil. Even greater amounts of sulphates were 

 observed in the surface soil at Chegga, Algeria, where they amounted 

 to 5.11 per cent of the weight of the soil, 4.89 per cent being Glauber's 

 salt; the subsoil here contained 1.82 per cent of sulphates, which rep- 

 resents more nearly what the roots had to withstand, although in 

 addition there was 0.88 per cent of chlorids. It is clear that, like 

 other plants, the date palm can resist sulphates much better than 

 chlorids. 



RESISTANCE OF THE DATE PALM TO CARBONATES (BLACK ALKALl). 



Whether the date palm can resist the dreaded " black alkali," a the 

 soluble carbonates, is not settled as yet, for none of the soils from the 

 Sahara contained any appreciable amount of these very poisonous 

 salts. At Tempe, Ariz., a soil obtained from the vicinity of the 

 Cooperative Date Garden, where date palms grow luxuriantly, con- 

 tained some 0.06 per cent of sodium carbonate in the surface foot. 

 Well-drained soils containing an excess of gypsum, such as was 

 observed in all the Saharan samples, can not contain any considerable 

 amounts of soluble carbonates, for if any such salts existed they 

 would immediately react with the gypsum present, and as a result 

 inert calcium carbonate (limestone) and comparatively harmless sodium 

 and potassium sulphates would be formed. 



Professor Hilgard has demonstrated the possibility of reclaiming 

 black alkali lands by the application of sufficient amounts of gypsum 



a The name " black alkali " is applied because the soluble carbonates change the 

 usually gray desert soils to black, as a result of their action in dissolving the humus. 

 In contrast to black alkali, other soils are called "white alkali," from the color of 

 the surface crusts that form in very alkaline spots. 



