VEGETABLE EXCRETIONS. 53 



immediately much augmented : but, even when 

 exposed to the light, there is always some exu- 

 dation, though in small quantity, going on from 

 the roots. 



That plants are able to free themselves, by 

 means of this excretory process, from noxious 

 materials, which they may happen to have im- 

 bibed through the roots, was also proved by ano- 

 ther set of experiments on the 3Iercurialis cuiniia, 

 the Senecio vulgaris, and Srassica campestris, or 

 common cabbage. The roots of each specimen, 

 after being thoroughly washed and cleaned, were 

 separated into two bunches, one of which was 

 put into a diluted solution of acetate of lead, and 

 the other into pure water, contained in a sepa- 

 rate vessel. After some days, during which the 

 plants continued to vegetate tolerably well, the 

 water in the latter vessel being examined, was 

 found to contain a very perceptible quantity of 

 the acetate of lead. The experiment was varied 

 by first allowing the plant to remain with its 

 roots immersed in a similar solution, and then 

 removing it, after careful washing, in order to 

 free the roots from any portion of the salt that 

 might have adhered to their surface, into a 

 vessel with rain water ; after two days, distinct 

 traces of the acetate of lead were afforded by 

 the water. Similar experiments were made with 

 lime-water, and with a solution of common salt, 

 instead of the acetate of lead, and were attended 



