200 



PLANT SOCIOLOGY 



A/a a % 



; 2 



Depth of water below the .surface, meters Percentage of salts 



1 or less 3 or more 



2 1 to 3 



3 or more . 25 to 1 



Wiiter brings salt to the surface so that in areas of shallow water 

 table are found the highest concentrations. The contour of the land 

 also has much to do with the salt content. The playas being depres- 

 sional areas are naturally closer to the ground water and have the 

 highest salt concentration. 



Determination of Chloride Content. — According toLagatu and Sicard 



(1911), the fluctuations of the chlorine 

 content of the soil calculated on the 

 basis of 100 parts of air-dried or moist 

 soil give consistent results. Calcu- 

 lated on the basis of dry or moist 

 earth, the sodium chloride content of 

 the lagoon soils near Montpellier 

 increases constantly down to a depth 

 of 2.5 m., as is shown in the accom- 

 panying figure (107). 



However, these two authors rightly 

 call attention to the fact that plant 

 roots absorb their nutrition from the 

 soil solution. For this reason the 

 sodium chloride content of the solution 

 must be examined, and in each sample 

 the amount of soil moisture must also 

 tent with increasing depth of the soil, be determined. Soil Samples for the 



near Rieueouion, France, on June 6 determination of Sodium chloride COn- 



i:jrl,™ISa'«' """""• ''""t<=°t ''■•'' Pl^x^ed m closed containers 



at the collecting places. The deter- 

 mination of moisture (see p. 213) should be performed as soon as 

 possible. Then 50 g. of soil are dried, and the determination of 

 chlorine is made in the usual manner by leaching out the chlorides with 

 distilled water and titrating the dissolved chlorides with accurately 

 standardized silver nitrate, with potassium chromate as indicator. 



Should the soil contain organic admixtures, the filtrate is to be 

 evaporated to dryness, and the residue carefully heated until all carbon 

 is burned off. The sodium chloride content is calculated by multiply- 



, . ,, , , c ..o/NaCl 58.5 



ing the weight of chlorme by the factor 1.648 [ 



so 



.•^ /so 

 o 



200 



250 



Fig. 107. — Increase of NaCl con- 



= ^= = 1.648 



CI 35.5 

 If the moisture of the soil and the NaCl content of the dry soil 



