E DAP III C OR SOIL FACTORS: CHEMICAL 



195 



other plants. Halophytic vogptation taken as a whole should permit 

 of classification into various types according to the presence or absence 

 in the soil solution of certain of the ions of sodium chloride, or of 

 sulphates of potassium, calcium, or magnesium. The specific ionic 

 effect should be reflected by the floristic composition of the vegeta- 

 tion, even though, as Gola (1910) states, a partial substitution of 

 NaCl by MgCl2 or CaClo may be possible. 



Vegetation of Sodium Chloride Soils. — Few reliable facts are known 

 in regard to the limitation of plant communities to certain types of 

 saline soils, but the vegetation of sodium chloride soils has received 

 most attention. High concentrations of pure sodium chloride are 



y!6 'U ''2 



Fig. 103. — Growth rate of marine aigao and strand plants in various concentra- 

 tions of sea water. A, Salicornia herhacea seedlings; B, Fucus serratus sporlings; C, 

 Nitschia putrida; and D, Aster tripoHum seedlings. (After Montfort and Brandup.) 



deadly to all plants. In mixed solutions the harmful effects of the Na 

 and CI ions are counteracted by the antagonism of the Ca ions, and 

 along with Na and CI the soil usually contains a considerable quantity 

 of CaCOs and MgCOa together with varying amounts of sulphates in 

 dry areas. In places the sodium chloride soils of the Mediterranean 

 are rich in ferric oxide. A sample from the lagoon of Venice near 

 Mestre, according to Begiiinot (1913, p. 46), gave these figures: NaCl 

 1.10 per cent; CaCOg 6.08 per cent; MgCOs 6.87 per cent; FegOs + 

 AI2O3 11.25 per cent; organic matter 3.00 per cent; and insoluble 

 residue 69.62 per cent. 



The average sodium chloride content of the Mediterranean Sea 

 ranges around 3.8 per cent and is subject to only minor variations. 

 But the salt concentration of lagoon water and of soils which are 

 occasionally flooded will vary greatly. During the summer drought 

 sodium chloride concentrations of 8 to 10 per cent in the uppermost 

 layers of tho soil occur frequently, while after the autumn rains the soil 



