in Relation to Rotation of Crops. 21T 



the test of experiment. After various attempts to raise plants 

 in pure siliceous sand, pounded glass, washed sponge, white 

 linen, &c., he decided upon pure rain water. After cleansing 

 and washing the roots thoroughly, he placed them in vials with 

 a certain quantity of pure water. After they had put forth 

 leaves, expanded their flowers, and flourished for some time, he 

 ascertained, by the evaporation of the water, and the use of 

 chemical reagents, that the water contained matter which had 

 exuded from the roots. He satisfied himself that this is the fact 

 with respect to nearly all the phanerogamous plants. 



Several plants of Chondrilla muralis, perfectly clean^ were 

 placed with their roots in pure water. At the end of a week, 

 the water was yellowish, and emitted an odour like opium, and 

 had a bitter taste. Subacetate and acetate of lead produced a 

 brownish flocculent precipitate, and a solution of gelatine dis- 

 turbed its transparency. As a 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 macerated in the water 

 during the same time, occasioned either taste, smell, or preci- 

 pitate. 



To determine at what period, whether during night or day, 

 this discharge from the roots takes place, a plant of common 

 bean {Phaseolus vulgaris) 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 evident 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 absorption 

 ceases and excretion takes place. 



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

 tory power of their roots, in order to get rid of hurtful sub- 

 stances which they may have imbibed, the following experiments 

 were made. Some plants of the 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 

 aqother branch of the same root into pure water. Having ve- 



