*4t THE DATE PALM. 



the two liquids and the mode of interchange of the liquids is 

 known as "osmosis." 



Plants require a constant supply of water and salts for the 

 elaboration of their food and to enable them to carry on their 

 vital functions. The supplies of water and salts are obtained 

 in solution from the soil through the cell walls of the roots by 

 osmosis ; these cell-walls acting as the permeable membranes. 



As soon, therefore, as a solution of salt in the soil becomes 

 more dense than that of the cell sap in the plant, the flow of water 

 aiad salts into the plant becomes inhibited or reversed, and if 

 the solution is strong enough, and its action continues suffi- 

 ciently long, the state of plasmolysis is produced and the plant 

 dies. 



Great damage has frequently been done to date plantations 

 in the Sahara by heavy rains and floods where the surface soil 

 has T^een covered with a thick layer of salt. When such a layer 

 accumulates, one way of getting rid of it is to scrape it off and 

 cart it away. If only the layer of salt on the surface of the soil 

 is taken away, this costs little and may be done repeatedly if 

 necessary . In the attempt to get rid of these salts, people some- 

 times cart away the surface soil to a depth of 6 inches or more, 

 but as will be seen from Table I page 21 it will be as effective and 

 much less expensive to merely scrape the surface whenever a 

 crust of salt forms. If, before a crust of salt has formed on the 

 land, ordinary farm crops can be grown between the trees, and 

 the land is irrigated for these in the usual manner, or if the land 

 is simply flooded occasionally, the upward current of water due 

 to evaporation from the surface of the land is reversed, the salts 

 are carried down and to some extent redistributed in the soil and 

 a large accumulation of salts at the surface of the soil is retarded 

 or prevented. 



Possibly one variety of date-palm may resist more alkali 

 than others, just as one variety ripens later than another, and it 

 may be possible, therefore, to obtain a variety specially suited 

 for growing on salty lands. 



