54 THE VITAL FUNCTIONS. 



with the like results. De CandoUe has ascer- 

 tained, that certain maritime plants which yield 

 soda, and which flourish in situations very distant 

 from the coast, provided they occasionally re- 

 ceive breezes from the sea, communicate a saline 

 impregnation to the soil in their immediate vi- 

 cinity, derived from the salt which they doubt- 

 less had imbibed by the leaves. 



Although the materials which are thus excreted 

 by the roots are noxious to the plant which rejects 

 them, and would consequently be injurious to 

 other individuals of the same species, it does not 

 therefore follow that they are incapable of sup- 

 plying salutary nourishment to other kinds of 

 plants : thus it has been observed that the Sali- 

 caria flourishes particularly in the vicinity of the 

 willow ; and the Orohanche, or broom-rape, in 

 that of hemp. This fact has also been established 

 experimentally by M. Macaire, who found that 

 the water in which certain plants had been kept 

 was noxious to other specimens of the same 

 species ; while, on the other hand, it produced a 

 more luxuriant vegetation in plants of a difterent 

 kind. 



This fact is of great importance in the theory 

 of agriculture, since it perfectly explains the 

 advantage derived from a continued rotation of 

 different crops in the same field, in increasing 

 the productiveness of the soil. It also gives a 

 satisfactory explanation of the curious pheno- 



