518 



EXPERIMENTS ON THE ROOTS OF PLANTS. 



When speaking to M. De Candolle of these results, he related to me a 

 curious fact which he had himself observed. The plants that are cul- 

 tivated near the sea for the produce of soda, sometimes thrive very well 

 at a great distance from the ocean, provided they are placed within the 

 influence of the sea air, which, it is well known, transports the particles 

 of salt with which it is charged to a great distance. M. De Candolle 

 was persuaded that the land where the kali thus placed had grown, con- 

 tained more salt than the land adjoining, so that, instead of extracting 

 it from the earth, these plants appeared to have furnished it by the 

 exudation of their roots. Reflecting on this experiment, I imagined 

 that I could perform it myself on a small scale with common plants, 

 and I placed the roots with the plants of the groundsel, swine thistle, 

 (Sonchus oleraceus,) mercury, &c. in rain water, and proceeded to 

 bathe the leaves with a solution of sea salt. My solution being too 

 concentrated acted forcibly on the leaves, I diluted it with water, and 

 with a pencil touched the lower part of the leaves and stalks, I even 

 moistened all the green part of the plant, but the reactives never indi- 

 cated any trace of salt rejected by the root, although the plants had 

 flourished. Hence it appears, that either solutions of salt cannot imitate 

 the proceedings of nature, or that perhaps the soda vegetables alone 

 have the power of absorbing the marine salt, and of rejecting a portion of 

 it by their roots. I should like very much to be able to repeat my 

 experiment on a Mesembryanthemum or a Salsola. There is then no 

 doubt that the plants have the power of rejecting by their roots those 

 soluble salts injurious to vegetation, which are found in the water 

 which they absorb ; though but a small portion of these salts appeared 

 in the residuum which I obtained in my own experiments, because the 

 plants, imbibing only pure water and carbonic acid, could reject by their 

 roots only the small quantity of salt which they contained at the time 

 they were taken out of the earth. I could gather little more than the 

 result of the action of their organs on the aliment, not of foreign bodies, 

 which only spread through the vegetable system without being decom- 

 posed. I shall now enter into some details on the small number of 

 families which I have examined ; each of them has produced results 

 nearly similar in the divers individuals or kinds under experiment, but 

 unhappily the number is very small. 



Leguminosce. — The only plants examined of this family were kidney 

 beans, peas, and beans of the species generally cultivated in this country. 

 These plants exist and develope themselves extremely well in rain 

 water. After they have vegetated in it some time, the liquid, when 

 examined, has but little taste, and the smell is slightly herbaceous ; it is 



