J 920.] 



485 



Direct Injury by Salt. —The question ol' direct injui v to leaves 

 by salt may now bo considered. The leaves of most land plants, 

 such as can be wetted, are slightly permeable to water with dis- 

 solved salts.* Experiments were made by Lewis! on the effect 

 produced by immersing leaves of lilac, holly, arum and other 

 plants in sea-water or in salt water containing about the same 

 strengtli of sodium chloride. After immersion for 12 or 27 hours, 

 all the leaves showed an increase in salt-content and a higher 

 osmotic pressure of the cell-sap. In arum, lilac and Camellia 

 the first effect of immersion was loss of weight, indicating extrac- 

 tion of w^ater from the leaf, but after three to six hours a progres- 

 sive increase in weight began, while in holly and Caveiidishia 

 the increase began at once. Leaves of lilac and arum showed a 

 considerable wilting effect when sprayed with sea-water, thus 

 showing that water may be extracted from the leaf in this way 

 also. 



Before immersion of the leaves, the leaf-cells of all the plants 

 became plasmolysed w-hen sections were placed in sea -water 

 {i.e., the protoplasm of the cells became contracted), but 

 in most cases a stronger solution than sea-water wiis required to 

 induce plasmolysis of the cells in sections cut from leaves which 

 had been immersed for 12 to 27 hours, adaptability in the 

 osmotic pressure of the cells being thus shown. It is concluded 

 that the plasmolysis of cells and the wilting of leaves induced in 

 certain plants by the presence of salt spray on the leaves would, 

 at any rate in many cases, be a temporary effect if a supply of 

 water w^ere available for the regaining of turgescence. 



In all cases the cells of the leaves were found to be living at 

 the end of the experiments, hence one may say that no evidence 

 was obtained that the amount of salt taken up by the leaves in 

 these experiments would have any toxic action. 



In the case of the foliage of trees exposed to salt spray, a 

 certain amount of salt would at times pass into the leaves. t but 

 whether a toxic effect would be produced;:; in any case, unless 

 excessive loss of w^ater by transpiration should also occur, is 



* PfefEer. P/n/.<}ioJo(}i/ of Plants, Eiiir. ed.. Vol. 1. p. 100 : Dandi'iio, Tunis. 

 Cauad. Imt.. Vol. 7. part 2 : Boodle, Netr P/i i/folot/h'. Vol, 3 (1*>04). p. 81). 



t Lewis. On induced Variation'^ in tbe Osmotic IMessuro and Sodium Chloride 

 Content of the Leaves of Non-halophytes. JVfiir Pln/tnlofjist, Vol. 11 (li^l2). p. 2."».'). 



X Blackledge, Var'iatiitn.^ in jJie XaCl-ron^ont of non-lialophytts, Ann. Hot., 

 Vol. 27 (1018), p. 1(18. The observations in this paper are perhaps open to the 

 objection that a comparison of the proporti(ui of salt in the soil in ditYerent 

 1' icalities may irive little or no indication of the relative amounts of salt which 

 have soaked into the soil from time to time. 



§ The data given by Coupin (AVr. (iciu'rah' <le llnt..\\A. lo. l^«.iS. ]>. 117) as 

 to the strength of salt solution producing a toxic etfect when supplied to :he loots 

 are of no service for the present question. 



F 



