RESISTANCE OF PLANTS 



381 



not accumulate them in their stems and leaves, possessing special 

 adaptations for removing them. They are provided for this 

 purpose with numerous secretive glands covering the surface of 

 their stems and leaves. Statice and the shriib Tamarix, widely 

 distributed in the steppes and deserts, belong to this group. 

 In dry weather, a deposit of salts completely covers their surface 

 and is partly blown away ]:)y the winds and partly washed off 

 by rain. 



Fig. 120. — Salicornia plants growing without sodium chloride, on the left; and 

 with the addition of sodium chloride, on the right {after Keller). 



Among the crop plants, true halophytes are not found, just as 

 true xerophytes are not met with, but there are more or less salt- 

 tolerant forms among them. Cotton, alfalfa, beets, tomatoes, and 

 water melons, for instance, tolerate -a certain accumulation of 

 salts in their tissues. Soft wheat varieties are more salt resistant 

 than hard wheats. Flax, oats, and buckwheat are not salt 

 resistant. Within the limits of each crop, more and less resistant 

 varieties can be found; but this feature has been very little 

 studied, and no systematic work has been done as yet on selection 

 of salt-tolerant varieties. 



The harmful effect of soil alkaH is manifested on the plant in 

 different ways. The high concentration of the soil solution 

 impedes the swelling and germination of seeds as well a.s the 



