VEGETABLE EXCRETIONS. 43 



§ 7. Excretion in Vegetables. 



It had long been conjectured by De Candollc, that the 

 superfluous or noxious particles contained in the returning 

 sap are excreted or thrown out by the roots. It is evident 

 that if such a process takes place, it will readily explain why 

 plants render the soil where they have long been cultivated 

 less suitable to their continuance in a vigorous condition, 

 than the soil in the same spot was originally; and also why 

 plants of a different species are frequently found to flourish 

 remarkably well in the same situation where this apparent 

 deterioration of the soil has taken place. The truth of this 

 sagacious conjecture has been established in a very satisfac- 

 tory manner by the recent experiments of M. Macaire.* 

 The roots of the Chondrilla muralifi were carefully cleaned, 

 and immersed in filtered rain water: the water was changed 

 every two days, and the plant continued to flourish, and put 

 forth its blossoms: at the end of eight days, the water had 

 acquired a yellow tinge, and indicated, both by the sm.ell 

 and taste, the presence of a bitter narcotic substance, analo- 

 gous to that of opium; a result which was farther confirmed 

 by the application of chemical tests, and by the reddish 

 brown residuum obtained from the water by evaporation. 

 M. Macaire ascertained that neither the roots nor the stems 

 of the same plants, when completely detached, and im- 

 mersed in water, could produce this effect, which he there- 

 fore concludes is the result of an exudation from the roots, 

 continually going on while the plant is in a state of healthy 

 vegetation. By comparative experiments on the quantity 

 of matter thus excreted by the roots of the French bean 

 {Phaseotus vulgaris) during the night and the day, he found 

 it to be much more considerable at night; an effect which it 

 is natural to ascribe to the interruption in the action of the 

 leaves when they are deprived of light, and when the cor- 



• An account of these experiments was first published in the fifth volume 

 of the "Memoires de la Society de Physique ct d'Histoire Naturelle dc Ge- 

 neve," and repeated in the " Annales des Sciences Naturclles," xxviii. 402. 



