SALINE AND ALKALI LANDS. 



531 



always moist to the touch, containing ordinarily over 15% 

 of moisture. It is therefore much liked by stock when fed 

 intermixed with other hay, and thus supplies all the salt 

 needed by cattle. The greasewood is much less liked by stock, 

 and bushy samphire is wholly rejected by them. Comparing 

 with these fleshy plants the ash of the two grasses, the first a 

 world-wide " salt grass," the other a common grass of the 

 American arid region, we note that not only do they contain 

 much less soluble ash than the saltbushes, but especially much 

 smaller amounts of sodium salts ; proving that even when 

 growing in company with the saltbushes on strongly impreg- 

 nated land, they can repel from absorption these to them use- 

 less or injurious salts. But in the case of the " shad scale," 

 also a " saltbush ' of the Great Basin, the ash-content is 

 remarkably low only about one-fifth of that of its Australian 

 relative and it differs widely from the latter in having but 

 a very low proportion of soda, and a very high one of lime 

 and potash, approaching in these respects to our usual forage 

 crops ; and being also fairly rich in nitrogen, it forms accept- 

 able browsing when other pasture plants are scarce. It there- 

 fore does not exert the laxative action produced by the exclu- 

 sive feeding on the more saline herbages. 



The exceptionally high ash-content of the cactus or prickly 

 pear, also given in the table, arises, it will be noted, not from 

 the soluble salts but from the absorption of extraordinarily 

 high proportions of lime and magnesia. Owing probably to 

 the latter substance, and also the oxalate form in which lime 

 is usually found in the cactus tribe, this plant when used as 

 forage is also somewhat laxative. 



Altogether, this table offers remarkable examples of wide 

 differences in the kind and amount of ash ingredients ab- 

 sorbed by plants growing upon similar soils and under identi- 

 cal climatic conditions ; indicating a selective power which no 

 merely physical theory of soil-action in plant growth can ex- 

 plain. 



Injury to Plants from the Various Salts. The early ob- 

 servers, especially Contejean, were predisposed from their 

 observations of lime on vegetation to ascribe the action of salt 

 upon marine vegetation to the sodium component. But the 

 wide differences in the effects of different sodium compounds, 



