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ON THE EXCRETIONS OF THE ROOTS OF PLANTS. 



dolle, undertook . to investigate chemically the nature of these excretions, the 

 particulars of which, have been published in the Transactions of the Physical and 

 Natural History Society at Geneva. On the commencement . of his experiments, 

 he obtained no result either by examining the roots taken from the soil, or by 

 the analysis of the pure silica in which the plants had grown ; but he found very 

 curious facts on the removal of plants by washing the roots of different species- 

 clean of all foreign matter, and placing the plants in clean pure water for some 

 hours. A plant of Chondrilla muralis, which had been placed in pure water for 

 about eight hours, excreted a small quantity of matter analogous to opium, which 

 was bitter and greenish ; this substance, dissolved in water, gave a precipitate in 

 brown flakes by the action of subacetate of lead, and acetate of lead. This 

 matter, mixed with a solution of gelatine and submitted to a gentle heat, left a 

 residue of a reddish-brown colour. 



A similar result has been observed in the kidney-bean. He took two plants 

 of the kidney-bean, and after well washing the roots, he placed one in a bottle of 

 water to stand during the day, the other he placed in a bottle of water to stand 

 during the night. On examining the bottles, there were evident signs of the 

 presence of excretory matter, but the plant which stood during the night con- 

 tained the larger quantity. The same thing occurred when the plants were 

 placed in the dark. These facts confirm the observations of Brugmans 

 before-mentioned. Mr. Macaire further observed that different plants excreted 

 different matter ; — that which he obtained from the Leguminosce was analogous 

 to gum, and contained a little carbonate of lime. He found that grasses deposit 

 a small quantity of matter which contains muriated and carbonated alkalies, 

 and earth, but very little gum : that the succories exude by their roots an abun- 

 dance of matter, which is brown, bitter, and analogous to opium, and which also 

 contains tannin, a brown, gummy, extractive substance, and some salts : that 

 poppies appear to exude a similar matter to the preceding, and the Euphorbias a 

 gum-resinous matter, of a whitish yellow colour, and very acrid. 



These excretions are evidently designed for the purpose of freeing the plant 

 from matter which is not congenial to it, and which must be injurious to its 

 health. Mr. Macaire has moreover ascertained, by experiments, that plants 

 may, by this process, discharge a .portion of such noxious substances as they may 

 have absorbed. 



He placed a plant of Mercurialis annua, (after having well washed the roots,) 

 in such a manner that one portion rested in a solution of acetate of lead, the 

 other in pure water. The water he found, at the end of some days, to contain 

 a quantity of acetate of lead, sensible to tests, and which, he considers, proves 

 that it was absorbed by the 'root in the acetate of lead, and being rejected by 

 the plant, was discharged into the pure water. According to the same observer, 

 different plants which were placed for some days in a mixture of water, chalk, or 

 acetate of lead, or nitrate of silver, or marine salt in small quantities, were 



