EDAPHIC OR SOIL FACTORS: CHEMICAL 193 



increased salt supply. The researches of Harris et at. (1924) ou 

 Atriplex confertifolia showed extraordinarily high values of osmotic 

 concentration.^ The osmotic concentration attained no less than 150 

 atmospheres, the electric conductivity 0.129 mho. ; the chloride content 

 exceeded 100 g. per liter of cell sap. On mangroves of the Indian coral 

 islands, Faber (1925) measured at the end of ebb tide 148.4 atmos- 

 pheres in the leaves of Rhizophora and 163.2 atmospheres in the 

 leaves of Avicennia officinalis. Besides, most of the halophytes are 

 equipped with an unusually high regulative power against osmotic 

 changes. According to Gola, these are anastatic species. The 

 mangroves, as facultative halophytes, thrive in ordinary soil, but they 

 can stand a salt solution of 8 to 12 per cent. 



Juncus suhulatus of the Mediterranean coast, one of the species 

 which tolerates the highest concentrations of salt, develops only in a 

 humid habitat. When the soil dries, it begins to suffer and increase its 

 osmotic concentration from 19.6 to 50 atmospheres, at which point the 

 plant yellows and dies. These species can by no means be regarded as 

 xerophytes, as Schimper assumed. In Faber's experiments the man- 

 groves gave evidence of the fact that the increase of osmotic pressure in 

 plants grown in highly concentrated nutritive solutions (NaCl, 

 MgS04, KNO3) is alone sufficient to cause an increase of water-storage 

 tissue and thereby a thickening of the leaves. Accordingly, the suc- 

 culence of the mangrove w^ould be a case of hypertrophy caused by high 

 turgor pressure. Keller (1925) arrives at similar results in experiments 

 with S. herhacea. An addition of very small quantities of sodium and 

 potassium chloride to the nutritive solution brought about a more 

 vigorous growth as well as an increase of succulence. Sodium sulphate 

 has a similar effect, while magnesium sulphate, according to the experi- 

 ments of Batahn (cited in Keller, 1925), caused no noticeable increase 

 of succulence as compared with plants of unsalted soils. 



The experiments of Lesage (1890) have shown that sodium chloride 

 soils induce a certain degree of succulence in many species. Numerous 

 observations on the conduct of non-halophytic, inland species in shore 

 regions agree with this. Upon saline soils quite a few non-halophytic 

 species develop special, more or less succulent varieties: Tetragonolobus 

 siliquosus var. maritima, Plantago major var. carnosa, P. coronopus var. 

 maritima, etc. Crossing between genotypes of a population of salt- 

 favoring species, with extinction of unfit descendants, seems to have 



1 In their studies in Tooele valley, Utah, Harris et al. (1924) found distinct 

 relations between soil conditions and the physicochemical behavior of cell content 

 (osmotic pressure, electric conductivity, chloride content) of the most important 

 indicator plants. 



