94: PLANT PHYSIOLOGY 



conditions of the laboratory seems to be facilitated by the 

 addition of a small amount of common salt to the culture. 

 The ash of strand and marine plants contains a larger per- 

 centage of sodic chloride than that of inland plants. This 

 is due simply to the presence of so much salt where they 

 grow. Strand plants do not need salt, as is proved by 

 cultures.* Inland plants are unfavorably influenced by a 

 percentage of salt, in the soil or in water, which strand 

 plants bear without injury. These last have succeeded in 

 becoming adapted to conditions which preclude or minimize 

 competition from more sensitive forms. The adaptations 

 are discussed in the rapidly increasing literature on the 

 ecology of the so-called halophytes.t Although the common 

 salt in sea water is needed as food only in the smallest 

 quantities if at all by the marine algae, they will bear only 

 the most gradual transfer to fresh water. This is probably 

 due, however, to the greater density of the sea water, and 

 this depends upon the other salts dissolved in it as well as 

 upon this single one. 



An interesting experimental study of strand and other 

 plants with relation to common salt and sea water has re- 

 cently been made by Coupin.I He finds that 1.5% of com- 

 mon salt in soil or in water is poisonous to plants which 

 do not naturally grow on the sea-shore. Since sea 

 water contains about 2.5% of common salt and the soils 

 bathed hj the sea contain still more than this proportion, 

 we can readily understand the sharp line which separates 

 the marine and strand floras from those of the interior. 

 Coupin attributes the poisonous property of sea water for 

 inland plants mainly to its content of common salt, for the 

 two salts next to this in abundance, magnesium sulphate 

 and chloride, are present in quantities which he says are 

 below the toxic proportions. Magnesic sulphate is poison- 



* See Nobbe in Versuchsstationen, Bd. 13, 1870, the literature there 

 cited, and Pfeffer, Pflanzenphysiologie, I., p. 424, etc., Engl, transl. I. 

 pp. 429, 30, etc. 



f For example, Schimper, A. F. W. Pflanzengeographie auf physiolo- 

 gischer Grundlage, Jena, 1898. 



t Coupin, H. Sur la toxicite du chlorure de sodium et de I'eau de mer 

 a, I'ggard des vegetaux. Rev. gener. de Botanique, T. X., 1898. 



