SUBSIDIAKY CULTURES ON ALKALINE SOILS. 115 



SUBSIDIARY CULTURES TO FOLLOW IN CONNECTION WITH DATE PLANTA- 

 TIONS ON ALKALINE SOILS. 



Although no other profitable crop plant can stand as much alkali as 

 the date palm, there are a number which can endure considerable 

 amounts of alkali and which could be set out on the less alkaline parts 

 of the tract to be planted or under the date palms after much of the 

 excess of salts had been washed out of the soil by several years' irri- 

 gation, accompanied by drainage. The grape, the olive, the pome- 

 granate, the jujube, and the fig are commonly grown in the partial 

 shade of the date palm in the Saharan oases. (See PL V, fig. 1, 

 and PI. XII.) All of these plants can endure more alkali than can 

 most fruit trees, though the almond and pear resist considerable 

 amounts. Barley is one of the crops that can stand much alkali, and 

 it is commonly grown in winter between the rows, especially of } r oung 

 date plantations. Sorghum is equally resistant. Asparagus is found 

 to do very well in the salty soils of the Oued Birh country, and it may 

 prove a profitable minor culture. Cotton is alkali-resistant in Egypt 

 and is grown in the oases in the interior of the Sahara. 



Since a species of pistache, which could be used for stock on which 

 to graft the pistache of commerce, occurs in the northern Sahara, 

 where it is the only tree that grows wild, it is not impossible that this 

 choice nut may be grown to advantage on alkaline soils. Carobs can 

 stand the heat and dry air of the desert very well, yielding fruit valu- 

 able for horse and cattle food in place of grain, and are at the same 

 time very ornamental evergreen shade trees, suitable for street plant- 

 ing. The Casuarina, the Tamarix, and some of the acacias and Euca- 

 lypti are trees well adapted to endure desert climates. Among forage 

 plants the Australian saltbush deserves first mention, for it can endure 

 very large amounts of alkali. Sorghum is another useful forage plant 

 for such land. Saharan alfalfa will prove of great value for the less 

 alkaline soils those having 0.5 per cent of alkali or less. It is not 

 unreasonable to hope to find a whole series of crops which can endure 

 a considerable amount of alkali in the soil, and which will permit some 

 diversification of agriculture even on the most alkaline tracts that are 

 first put under culture by planting date palms. 



LIMITS OF ALKALI RESISTANCE OF THE DATE PALM. 



It is naturally of very great importance to determine as nearly as 

 possible the limits of alkali endurance of the date palm, as it is the 

 most profitable crop than can be grown in very alkaline lands, and on 

 large areas in the hotter arid regions of the Southwest it is the only 

 paying crop that can succeed. A careful study of the growth and 

 fruitfulness of the date palm at various points in the Sahara desert 

 shows that although this plant can grow in soils containing from 3 to 



