INFLUENCE OF DRAINAGE AND CHEMICAL FACTORS. 475 



In the exceptional cases noted above, easily recognizable changes in 

 the vegetation coincide with important differences in the chemical 

 quality of the soil. Near the sea, in what we call the maritime for- 

 mations, the soil contains a much larger percentage of common salt 

 (Nad) than is present in ordinary soils. This substance acts upon 

 the great majority of plants as a poison if it occurs in the soil in 

 considerable quantity — 1 per cent or, for many species, even less. 

 Consequently the vegetation of the dunes and beach is sparse and is 

 composed of but few species, most of which are peculiarly adapted to 

 salt-impregnated soil and air, and are not found in normal inland soils. 

 Even more strikingly is this the case with the salt marshes, where the 

 soil is overflowed with brackish water at every high tide. Their vege- 

 tation is extremely different from that which occupies ordinary, 

 moderately well drained soils which contain but a small trace of salt. 



Peculiar chemical conditions are also found in the soil of the 

 swampy forests so long as they remain in their natural condition. 

 Chief among these peculiarities are exceeding richness in vegetable 

 matter and poverty in oxygen, to which is due the presence of much 

 humic acid. The soil is sour, in addition, we have the physical 

 peculiarity of a very high water content, the soil being normally satu- 

 rated. Given such conditions and it is not strange that the vegeta- 

 tion, notably the forest growth, of these swamps is sharply differen- 

 tiated from that on adjacent, not swampy soils, even where the latter 

 are moderately moist. 



Both the maritime and the swamp soils are agriculturally worthless 

 in their natural condition. It is not likely that any treatment could 

 be devised which would render arable the salt marshes or the beach 



sometimes ••lime-avoiding'' in another. Some of the principal works dealing 

 with the subject are: 



Unger. Uber den Einfmss des Bodens auf die Verteilung der Gewiichse. 1886. 



Tliurnian. J. Essai de phytostatique applique a la chaine du Jura et aux con- 

 trees voisines. 1849. 



DeCandolle. A. Geographiebotaniqueraisonne. Vol. 1, pp. 264. 422-447. 1855. 



Bonnier, G. Quelques observations sur les relations entre la distribution des 

 phanerogames et la nature chimique du sol. Bull. Soc. Bot. de France, vol. 26, 

 pp. 338-841. 1879. 



Contejeau. C. Geographic botanique. Influence du terrain sur la vegetation. 

 1881. 



Vallot, J. Recherches physico-chimiques sur la terre vegetale et ses rapports 

 avec la distribution geographique des plantes. 1883. 



Fliche et Grandeau. Recherches chimiqnes et physiologiqnes sur la bruyere 

 commune. Ann. de la Science Agrom unique (1S84), vol. 1, 394-411. (Two other 

 papers by the same authors are there cited— De rinrluence de la composition 

 chimique du sol sur la vegetation du pin maritime. Ann. de Chimie et de 

 Physique, ser. 4. vol. 29. 1873, De 1'inrluence de la composition chimique du sol 

 sur la vegetation du chataignier, op. cit. , ser. 5, vol 2. 



Ramann. E, Forstliche Boden-Kunde und Standortslehre. pp. 365. 366. 1893. 



Warming. E. Lehrbuch der okologische Planzengeographie. pp. 63, 75. 1896. 



Schimper. A. F. W. Pfanzengeographie. 105-118 (1898.) 



