VEGETABLE EXCRETION. 47 



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 suit- 

 able 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 satis- 

 factory manner by the recent experiments of M. 

 Macaire.* The roots of the Clionchilla muralis 

 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 its smell and taste, the presence of a bitter 

 narcotic substance, analogous to that of opium ; a 

 result which was farther confirmed by the appli- 

 cation 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 immersed in water, could produce 

 this effect, which he therefore 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 



* An account of these experiments was first published in the fifth 

 volume of the " Memoires de la Societe de Physique et d'Histoire 

 Naturelle de Geneve," and repeated in the " Annales des Sciences 

 Naturelles," xxviii, 402. 



