SALT PLANTS AND SALT-SPOTS CANNON 129 



carries the most sodium salts, is inhabited by the species, A. nuttallii, which 

 contains the largest amount of soluble salts and also the largest proportion of 

 sodium. It has also the least amount of calcium. The species which occupy 

 the outer portion of the salt-spot, where the salts are least in amount, are 

 those which contain the least amount of sodium and the largest of calcium. 

 From these facts it is inferred that there is probably an increase in the 

 osmotic pressure in the different species as one goes from the periphery of the 

 salt-spot to the center, and that among the substances which contribute to 

 this effect the salts of sodium may find an important place. Whether there 

 is also an increase in such osmotically active organic substances as are not 

 electrolytes, the inference necessarily leaves out of consideration. 



It has already been stated that the relative amounts of sodium and cal- 

 cium in the different species of salt plants are unlike, Na being most abun- 

 dant in such species as contain the lowest proportion of Ca and vice versa. 

 These facts are so striking that they may have a special bearing beyond the 

 well known facility of plants of storing up in insoluble form certain salts. 

 There may be some relation, also, with the occurrence of salts in the soil 

 solution. It is known 8 that lime, when applied to certain alkali soils, serves 

 as a correction, making such soils more tolerable for mesophytes. It should 

 be noted that in such conditions the soil solution is probably made more dense. 

 Osterhout 9 has shown that calcium holds an antagonistic relation to sodium 

 by which the latter may be prevented from entering the protoplast. Applying 

 these findings to the case in hand, it may be concluded that the salt-spot in 

 question, if treated with a proper amount of calcium salts, might support an 

 entirely different type of vegetation, or that the kinds of salt plants inhabit- 

 ing it would be different than at present, owing probably to the absence of 

 the more intensely halophytic species. In such a case, the density of the soil 

 solution would play a minor role. The findings of the present study also 

 indicate that the most intense halophytes absorb salts of sodium in large 

 amounts without injury, and that it is due to this that such species can sur- 

 vive where such salts constitute the leading features of the substratum. 



8 Some mutual relations between alkali soils and vegetation. Kearney and 

 Cameron. U. S. Dept. Agric. Rep. No. 71, 1902. 



9 The permeability of protoplasm to ions and the theory of antagonism, Science, 

 N. S., Vol. 35, page 112, 1912. The permeability of living cells to salts in pure 

 and balanced solutions, Science, N. S., Vol. 34, page 187, 1911. 



