Introduction 5 



roots perforce take in everything that is presented to their surfaces, or 

 have they the power of making a selection, absorbing the useful and 

 rejecting the useless and harmful ? 



Daubeny (1833) described experiments in which various plants, as 

 radish, cabbage, Vicia Faba, hemp and barley were grown actually on 

 sulphate of strontium or on soils watered with nitrate of strontium. 

 No strontium could be detected in the ash of any of the plants save 

 barley, and then only the merest trace was found. Daubeny concluded 

 that the roots were able to reject strontium even when presented in 

 the form of a solution. "Upon the whole, then, I see nothing, so 

 far as experiments have yet gone, to invalidate the conclusion... that 

 the roots of plants do, to a certain extent at least, possess a power of 

 selection, and that the earthy constituents which form the basis of their 

 solid parts are determined as to quality by some primary law of nature, 

 although their amount may depend upon the more or less abundant 

 supply of the principles presented to them from without." Some 

 years after, in 1862, Daubeny reverted to the idea, stating " I should 

 be inclined to infer that the spongioles of the roots have residing in 

 them some specific power of excluding those constituents of the soil 

 that are abnormal and, therefore, unsuitable to the plant, but that 

 they take up those which are normal in any proportions in which they 

 may chance to present themselves^" This, however, was not held to 

 apply to such corrosive substances as copper sulphate. De Saussure 

 had found that Polygonum Fersecaria took up copper sulphate in 

 large quantities, a circumstance which he attributed to the poisonous 

 and corrosive quality of this substance, owing to which the texture 

 of the cells became disorganised and the entrance of the solution 

 into the vegetable texture took place as freely, perhaps, as if the plants 

 had been actually severed asunder^- Daubeny concluded that a plant 

 is unable to exclude poison^ of a corrosive nature, as this quality of the 

 substance destroys the vitality of the absorbing surface of the roots 

 and thus reduces it to the condition of a simple membrane which by 



^ This idea of a selectivity of the roots has been recently revived by Colin and Lavison 

 (1910) who found that when peas were grown in the presence of barium, strontium or 

 calcium salts no trace of barium could be found in the stem, strontium only occurred 

 in small quantities, while calcium was present in abundance. They concluded that 

 apparently salts of the two latter alkaline metals could be absorbed by the roots and 

 transferred to the stem and other organs, but that this is not the case with salts of 

 barium. They obtained similar results with other plants, beans, lentils, lupins, maize, 

 wheat, hyacinth. Their proof is not rigid, and exception could be taken to it on chemical 

 grounds. 



' Vide Daubeny, Jcmm. Chem. Soc. (1862), p. 210. 



