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 taste, 

 smell, or precipitate. 



To determine at what period, whether night or day, this discharge 

 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 the night ab- 

 sorption ceases and excretion takes place. 



To prove that plants employ, (if we may so speak,) the excreto- 

 ry power of their roots in order to get rid of hurtful substances which 

 they 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, which proved, 

 by the black precipitate which it formed, that a notable portion 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 They were then withdrawn, their roots well washed 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 vessel of rain water. In the course of 

 two days, this water was found to contain a small quantity of acetate 

 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 partly in pure water, the plants lived 

 well and the pure water soon shewed the presence of lime by oxa- 

 late of ammonia, — and plants which had grown in lime and then 

 transferred widi every precaution to pure water, soon disgorged into 

 it a portion of lime. 



