CHAP. IV. 
THE ROOT. 
307 
have been made by Macaire, who, in a paper in the Trans- 
actions of the Physical Society of Geneva, has given an ac- 
count of his important experiments, of which the following is 
an abstract : — He found that Chondrilla muralis, and Cicho- 
raceous plants in general, secreted a matter analogous to 
opium; Leguminous plants, a substance similar to gum, with 
a little carbonate of lime ; Grasses, a minute quantity of 
matter consisting of alkaline and earthy muriates and car- 
bonates, with very little gum ; Papaveraceous plants, a matter 
analogous to opium ; and Euphorbias, a whitish yellow gum, 
and resinous matter of an acrid taste. 
He also found that plants actually possess the power of 
freeing themselves from matter that is deleterious to them, 
by means of their roots. Acetate of lead is a well-known 
active vegetable poison ; he took two bottles, one of which. A, 
was filled with pure water, and the other, B, with water 
holding acetate of lead in solution. He placed a plant of 
Mercurialis annua with half its roots plunged in A, and the 
other half in B. After a short time the water in the bottle A 
contained a notable proportion of acetate of lead, which must 
have been carried into the system by the roots in bottle B, 
and thrown off again by those in bottle A. He also states 
that various plants which had lain several days in water 
charged with lime, or acetate of lead, or nitrate of silver, or 
common salt, in small quantity, having been carefully washed 
and placed in pure water, gave back from their roots the 
deleterious matter they had absorbed. 
It is difficult to speculate upon the results to which this 
curious discovery may lead. It is perhaps an explanation of 
the necessity of the rotation of crops, of the action of what 
are called weeds, of the utility of changing the earth of plants 
.growing in pots, and of other phenomena which could not 
previously be accounted for. It requires, however, a great 
deal of ulterior examination ; but as the enquiry has been 
taken up by Dr. Daubeny, the learned Professor of Botany 
and Chemistry at Oxford, at the instance of the British Asso- 
ciation, it is not to be doubted that a few years will throw 
much additional light upon the subject. 
M. Payen has ascertained (Ann. des Sc., n. s., iii. 18 .) that the 
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