16 



EFFECT OF SOLUBLE SALTS UPON PLANTS. 



degree to produce any material influence on the loss of water through 

 the leaf. 



The following table gives the amount of water transpired by wheat 

 plants in soils containing these two concentrations of alkali salts 

 and by the controls in each case, the amount of water transpired 

 being expressed in milligrams per square centimeter of leaf surface 

 per hour: 



Table V. — Amount of water transpired by wheat plants grown in soils containing dif- 

 ferent concentrations of soluble salts and by control plants grown in nonsaline soils. 







Soil contain- 





Soil contain- 







ing 0.09 per 





ing 0.12 per 







cent total 





cent total 



Series of experiments. 



Control. 



salts (esti- 

 mated 0.06. 

 per cent 

 sodium 

 chlorid) . 



Control. 



salts (esti- 

 mated 0.08 

 per cent 

 sodium 

 chlorid). 





mg. 



mg. 



mg. 



mg. 



No. ] 



2.16 

 3.27 



4.21 



3.98 



2.35 



3.01 



2.80 





3.35 







The results show that transpiration is stimulated by the presence 

 of amounts of soluble salts too small to produce any perceptible 

 modification of structure. The stimulation was greatest in the soil 

 containing the smaller amount of alkali, the amount of water trans- 

 pired by the plants in the 0.09 per cent soil having been in the two 

 series of experiments, respectively, 94 per cent and 21 per cent greater 

 than in the corresponding controls, while in the 0.12 per cent soil it 

 was only 19 per cent and 11 per cent greater. 



GENERAL SIGNIFICANCE OF RESULTS. 



It is not improbable and in fact these experiments seem to demon- 

 strate that plants that are not halophytes when grown in saline soils 

 undergo modifications of structure of a kind that are believed to 

 reduce transpiration. It is a well-known fact that most xerophytes — 

 i. e., plants growing naturally in dry situations — differ in many points 

 of structure from mesophytes and hydrophytes (plants whose natu- 

 ral habitats are, respectively, moderately moist and very wet situa- 

 tions). Some of these characteristics of xerophytic plants, such as 

 the reduction of the number of stomata, the situation of the latter 

 in pits or furrows, the development of a covering of hairs on the leaf 

 surface, etc., are doubtless efficacious in diminishing transpiration. 

 Other means of protecting against excessive loss of water are thicken- 

 ing of the cuticle and its reenforcement by the secretion of wax or 

 bloom which is deposited on its surface. Most halophytes (plants 

 growing naturally in saline or "alkali" soils) exhibit similar pecul- 

 iarities of structure. 



134 



