140 Vegetable Physiology. 
____ proof that this matter was the result of excretion from the roots, it 
was found that neither pieces of the root nor of the stem, when ma- 
cerated in the water during the same time, occasioned either — 
smell, or precipitate. 
To determine at what period, whether night or day, this cadagee 
from the roots takes place, a plant of common bean (Phaseolus vul- 
garis) was carefully cleaned, placed in rain water and kept a week 
during the day time in. one vessel, and during the night in another, 
being well wiped at each transfer. In both the fluids there were ev- 
ident marks of excretion from the roots, but that in which the roots 
were immersed during the night contained a very notable excess of 
the transpired matter. Numerous other experiments gave the same 
result. As it is well known that the light of day causes the roots to 
absorb their juices, it is natural to suppose that during aie 
a. takes plates so 283 
2 , (if we may so speak,) the excreto- 
r of their roots in order to get rid of hurtful substances which 
hey may have imbibed, the following experiments were made. Some 
plants of Mercurialis annua, were well washed in distilled water, and 
placed so that one portion of their roots dipped into a weak solution 
of acetate of lead, and another branch of the same root into pure wa- 
ter. Having vegetated in this manner very well for several days, 
the water was tested by hydro-sulphuret of ammonia, whieh pre 
by the black precipitate which it formed, that a notable powtidir of 
the lead had been absorbed and deposited by the branch which dip- 
ped in the pure water. Groundsel, cabbage, and other plants gave 
the same result. Some plants grew very well for two days in ace- 
tate of lead. ‘They were then withdrawn, their roots well washed 
with distilled water, carefully wiped, again washed in distilled water, 
(which being afterwards tested, was found to contain no lead,) and 
then placed to vegetate in a seni of rain water. In the course of 
two days, this water was found to contain a small ary of —— 
of lead. 
- The same experiments were made with lime water, which, being 
less injurious to plants, is preferable to lead. The roots being 
partly placed in lime water and parily in pure water, the plants lived 
well and the pure water soon shewed the presence of lime by ox@ 
late of ammonia,—and plants which had grown in lime and then 
transferred with every precaution to pure water, soon disgorged§ = 
it a portion of lime. 
