EDAPUIC OR SOIL FACTORS: CHEMICAL 201 



are known, it is easy to calculate the quantity of NaCl dissolved in 

 the soil. 



Example. — 100 g. of dry earth contains 0.53 per cent of NaCl; the moisture in 

 the soil is determined as 20 per cent. Thus the moist earth contains dissolved in 

 it 



0.53 X 100 .^^^ ^ .^ ^, 



■ ^7^ = 2.65 per cent Nad. 



The mere notation of the sodium chloride content, on the basis of 

 a dry soil, is not very significant ecologically, without the simultaneous 

 determination of the moisture in the soil. 



Vegetation of Sulphate Soils. — Sulphate soils cover vast areas of the 

 dry regions of southeastern Europe, Persia, Central Asia, the western 

 states of North America, Northern Africa, and other regions. In 

 places they have a desert-like character, and often they are covered 

 by a snowy- white crust of salt. 



The sulphates occur mostly as sodium sulphate, Na2S04, or as 

 magnesium sulphate, MgS04; calcium sulphate, CaS04, occurs more 

 rarely, and sometimes the chlorides predominate. 



The solontschak soils of southeastern Russia and Transcaspia have 

 been studied by the Russian soil specialists. B. Keller (1923, 1926) 

 deals mostly with the vegetation. In this region succulent Cheno- 

 podiaceae of the genera Suaeda, Salsola, Anabasis, and Halimocnemis 

 display the greatest number of species. Characteristic among non- 

 succulents are Statice, Frankenia, and Cressa, whose glands give off 

 large quantities of highly soluble salts (Na2S04, NaCl). Similar 

 discharges of salts have also been observed on leaves of Statice, Limo- 

 niastrum, Frankenia, Tamarix, and Cressa, of the south European and 

 north African salt steppes and in species of the mangrove, such as 

 Avicennia and Aegiceras, as well as in Armeria, Statice, and Glaux 

 maritima of the north German coast. Fitting (1911, p. 267) observed 

 this "salt lye" upon leaves in the morning and explained it as due to 

 osmotic action by the solid salts already excreted. The experiments 

 of Ruhland (1915), however, show that it is due to nightly secretions 

 of aqueous solutions which are supposed to free the living cells from a 

 harmful excess of salts. The osmotic value of the epidermal cells of 

 S. gmelini rises as high as 165 atmospheres. Montfort (1922, p. 156), 

 who has closely followed the salt secretions of S. limonium and Armeria 

 maritima, sees in this function an indication of uninterrupted absorp- 

 tion of water by strong osmotic action of the roots. 



The dominant succulents of the solontschak soils of western Asia 

 and along the Mediterranean Sea are arranged in various communities, 

 frequently in belts, according to salt concentration and moisture. 



