400 THE UNIVERSE. 



powers, that certain plants vegetate in soil stufFed Avitli 

 deadly substances without suflfering in the least from it. 

 In the countries Avhere arsenic abounds there are some 

 which brave its action. Hence, when everything else is 

 dying round them, certain leguminous plants cover with 

 verdure the rocky soil of Cornwall, Avhich contains fifty per 

 cent, of arsenical srdphuret, and the rest of which is only 

 composed of silica and snlphuret of iron. ^ 



By means of very simple experiments it can be demon- 

 strated that absorption by the roots is a vital act. If, on 

 the one hand, a root be plunged uninjured into a saline 

 solution, and on the other a similar plant be immersed, 

 after having its members cut short off, it will be seen at 

 the end of a certain time that the uninjured plant has not 

 absorbed the salt in the same proportion as it is found in 

 the solution, whereas that which has had its roots divided 

 has l^een abandoned to the dominion of physico-chemical 

 causes, and has pumped up the liquid without making 

 any selection." 



Water is the principal food of the plant, but the radi- 

 cles also take up other substances from the earth. They 



iJt is true that the experiments of Messrs. Saussure, De Caudolle, and Macaire 

 have shown that certain salts of copper, mercury, and iron, which kill plants, 

 are yet absorbed by them. But this takes place equally in animals, and in no 

 way disproves the vital nature of the absorption by the roots. On the other 

 hand, again, it has been observed that certain plants do not absorb these salts 

 at all. If we plunge the Chara vulgaris and the Stratiotes aloides into salts of 

 copper, we do not perceive that their roots absorb a particle of them. According 

 to Dr. Daubeny, professor at Oxford, the sulphuret of arsenic contained in small 

 quantities in the soil produces no injurious effect upon mustard, beans, and 

 barley. He concludes that, to a certain extent, plants possess the power of select- 

 ing from the constituents of the soil in which they live, — Daubeny, British Asso- 

 ciation. 



- The sea, which contains thirty times as much sodium as potassium, furnishes 

 to some of the Algre, di-awiug all their mineral matter from it, ecjual quantities of 

 these two metals, and to many others half as much potassium as sodium. — 

 Popular Science lievieit; vol. vii. p. 67.— Tii. 



