RKSISTANCK TO ALKALI. 73 



of water, from good drinking water to veritable brine containing 1 

 per cent of saline matters. It is the custom to provide for drainage, 

 usually by means of open ditches, in the oases having much alkali in 

 the soil or in the water. If the drainage is good, abundant irrigation 

 has the effect of washing the excess of alkali out of the soil. . However, 

 even in such situations there has been little study of the best means of 

 preventing the accumulation of alkali or of washing it out of the soil, 

 and many of the planters have no comprehension of its action on the 

 date palm. 



INVESTIGATION OF THE ALKALI-RESISTING POWER OF THE DATE PALM 



IN THE SAHARA. 



In view of the entire absence of trustworthy data as to the alkali 

 resistance of the date palm, the writer determined on the occasion of 

 his last visit to the Sahara Desert in 1900 to make a study of the soils 

 in the date plantations in order to determine the amount of alkali these 

 soils contain and what effect it had on the growth and fruiting of the 

 date palm when present in excessive quantities. Samples of soils were 

 secured in five different regions in the Algerian Sahara (see map, PI. 

 II, p. 76), representing several different methods of culture and drain- 

 age and showing all degrees of alkalinity. Through the kindness of 

 Prof. Milton Whitney, Chief of the Bureau (then Division) of Soils of 

 the Department of Agriculture, who also furnished instruments for 

 collecting and studying the soils on the spot, these samples were ana- 

 lyzed by Mr. Atherton Seidell in accordance with the methods usually 

 followed in the Bureau of Soils, namely, by digesting 50 grams of soil 

 in a liter of water for twenty-four hours and then analyzing the super- 

 natant solution. The analyses made in this manner do not represent 

 accurately the conditions existing in the soil water, since the amount 

 of the slightly soluble salts, especially gypsum, reported is far in excess 

 of what could dissolve in the soil moisture, which in the rather sandy 

 loam of most of the Sahanin oases would constitute about 8 to 15 per 

 cent of the weight of the soil, whereas in the method followed in mak- 

 ing the analyses about 150 to 200 times as much water was used. In 

 this bulletin, therefore, the analyses of Mr. Seidell have been recalcu- 

 lated in order to represent more nearly the conditions existing in the 

 soil. The amount of calcium sulphate' thai goes into solution in the 

 soil moisture has been estimated at 0.05 per cent in all the analyses, 

 except where large amounts of other sulphates were in solution, when 

 it was estimated at 0.02 percent. The amount that dissolves undoubt- 

 edly varies somewhat, depending on the quantity and nature of the 

 other salts present in solution. However, the amount here e>timat-d 

 is not far from the quantity actually present, and its inclusion in the 

 analyses renders them much more useful than to omit the gypsum 



