VEGETABLE EXCRETION. 4.9 



might have adhered to their surface,) into a vessel 

 with rain water; after two days, distinct traces 

 of the acetate of lead were afforded by the water. 

 Similar experiments were made with hme- water, 

 and with a solution of common salt, instead of 

 the acetate of lead, and were attended with the 

 like results. De Candolle has ascertained, that 

 certain maritime plants which yield soda, and 

 which flourish in situations very distant from the 

 coast, provided they occasionally receive breezes 

 from the sea, communicate a saline impregnation to 

 the soil in their immediate vicinity, derived from 

 the salt which they doubtless 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 supplying salutary 

 nourishment to other kinds of plants : thus it 

 has been observed that the Salicaria flourishes 

 particularly in the vicinity of the willow ; and 

 the Orobanche, 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 different kind. 



This fact is of great importance in the theory of 

 agriculture, since it perfectly explains the advan- 

 tage derived from a continued rotation of different 

 crops in the same field, in increasing the produc- 



VOL. II. E 



