528 SOILS. 



succulence of the characteristic plants. This " incrassation " 

 belongs not only to the saline flora proper, but is acquired to a 

 greater or less degree when plants not ordinarily at home on 

 saline ground are transferred to it artificially, or by saline 

 overflows; while at the same time the leaves usually become 

 smaller, and the growth more compact. Correspondingly, 

 when saline plants are transferred to non-saline ground, the 

 leaves generally become thinner and larger, and the growth 

 more slender. The well-known " Russian thistle " is a case 

 in point, as is also its close relative, the soda saltwort (Sal- 

 sola soda) ; although the latter does not often venture as far 

 from the saline lands as does the former (Salsola kali tragus), 

 which now seems to have become a world-wide weed, with 

 only a shade of preference for alkali lands. 



Structural and Functional Differences Caused by Saline 

 Solutions. It has been definitely shown by the investigations 

 of Schimper, Brick, Hoffmann, Lesage, Rosenberg and 

 others, that the peculiarities or changes of structure brought 

 about by saline solutions are essentially those pertaining to 

 xerophile (drought-enduring) vegetation; which in general 

 tend to the diminution of evaporation from the plant surfaces. 

 It may be said, roughly speaking, that the absorption of water 

 by the roots begins to diminish so soon as the concentration 

 of the saline solution approaches or exceeds one-half of one 

 per cent; while when it rises as high as three per cent., water- 

 absorption by the roots ceases even in the wettest soils, and the 

 plant suffers from drought quite as much as from any di- 

 rectly injurious effects of the salts. Different plants of 

 course differ in the measure of concentration which brings 

 about these phenomena, which vary also with the character of 

 the soluble salts. It is stated that injurious or useless salts 

 like common salt act at lower concentrations than e. g., salt- 

 peter, which is useful. The difference in external structure 

 are : diminution of the size of leaves, assumption of cylindrical 

 or spinous forms, sinking-in of the breathing pores below the 

 outer surface, dense hairy covering, resinous exudations, etc. 

 Internally we find that xerophile plants have developed on 

 their upper or outer leaf-surfaces instead of one, several lay- 

 ers of "palisade" (long and erect, closely-packed) cells, 

 through which transpiration is extremely slow, as is also the 



