Vegetable Physiology for the Year 1836. 535 



in four ounces of water in which three grains of sugar of lead 

 were dissolved; so soon as on the eighth day they became paler, 

 and here the decoloration began from the root. From the 

 third day these plants were placed in pure water, but the poi- 

 soning was so complete that they began to die as early as the 

 fifth day. Repeated experiments showed that even within 

 twenty-four hours so considerable a quantity of the salt of lead 

 had been imbibed that sulphuret of ammonia indicated the 

 presence of the metal by the brown tint. It was thus proved 

 that in Lemna not only the little roots imbibe but also the 

 leaves, and indeed the under surface in as high a degree as 

 the upper one. This phenomenon is, however, as I think, 

 quite common, even in the most perfect terrestrial plants, in a 

 higher degree, however, in the imperfectly organized aquatic 

 plants, which consist solely of parenchyma, and in which this 

 has been demonstrated by various experiments. Unger thinks 

 rather that the foreign substances which are taken in pass 

 through the cellular partitions than that they mix with the 

 cellular sap; on the other hand, however, my own experi- 

 ments made on Lemna with salts of iron, as also on plants of 

 balsam and maize with prussiate of potash, show that the dis- 

 solved substance imbibed mingles with the cellular sap. But 

 if we act with reagents on such cells, the coloured substances 

 proceeding from the action are almost all precipitated upon 

 the partitions of the cells and on the molecules of the cellular 

 sap. 



These experiments on the reception of dissolved foreign 

 matters through the cellular tissue were performed by Unger 

 chiefly in order to see whether a secretion of the imbibed sub- 

 stances again took place through the root. Various experi- 

 ments decidedly proved that the Lemna plants secreted nei- 

 ther the metallic salt nor the sulphuret of ammonia which 

 they had taken up, and I can state the same thing of the im- 

 bibed sulphate of iron and the prussiate of potash. Plants 

 of Lemna trisulca which were charged with one of these sub- 

 stances, and plants which had taken up the other, were placed 

 in a glass with clean water : they continued to grow for some 

 days, but exhibited no reaction in the water. 



It is well known that the experiments of Macaire and Dau- 

 beny* went to prove such a secretion of the foreign substances 

 imbibed by means of the root, yet in all their experiments we 

 are left in uncertainty as to whether the roots were uninjured; 

 the contrary must even be supposed. 



In all these experiments, especially when acrid substances 

 such as vitriol are given to the plant to imbibe, they suffer 



[• A notice of Prof. Daubeny's experiments will be found in Lond. and 

 Edinb. Phil. Mag., vol. iv., p. 52.— Edit.] 



