68 



acidity was due to the presence of hj^drochloric acid. It is intended 

 that some experiments in this direction shall soon be made in the 

 laborator3\ 



A somewhat simpler explanation than the one just described may 

 be offered — simpler because it does not require that the plant must 

 first take up the acid radical and then go through the reverse process 

 of exuding it again. It is known with reasonable certainty that a 

 certain amount of hydrolysis takes place in aqueous salt solutions, 

 although the absolute amount maj^ be, and with ordinary strong elec- 

 trolyses usually is, very small indeed; nevertheless, it does take 

 place to some extent, and it seems not impossible that the x^lants 

 might show their selective j)roperties in the solution, taking uj) the 

 base more rapidly than the acid", the latter in consequence being left 

 in greater proportion in the culture or soil solution. Of classical 

 importance in this connection is the work of Kuhn,^ who found that 

 when maize was grown in a solution containing ammonium chloride, 

 the ammonium residue was partly taken up by the plant and hj^dro- 

 chloric acid remained in the solution. In fact, there does not seem 

 to be any inherent difficulty in supposing that the plant might selec- 

 tivelj^ absorb au}^ ion for which it might have a special predilection. 

 As soon as this ion is removed from the solution the corresponding 

 ion with its opposite charge of electricity must either be removed 

 from the solution by precii)itation or volatilization, for example, or it 

 at once reacts with the water. Supposing the ion removed by the 

 plant to be a base, the action of the remaining acid ion on the water 

 must necessaril}^ be accompanied by the liberation of oxygen from 

 the water of the solution. Whether or not any observation of this 

 kind has been made I do not know, but the liberation of the oxygen 

 might ver}^ well take place so slowly as to escape detection. The 

 question as to what becomes of the electrical energy on the ion which 

 the plant absorbs will be answered in a consideration of the work 

 energy, heat energy, or other equivalent forms of energy involved in 

 the mechanism of the absorption process, and does not necessarily 

 demand further consideration at this point. ^ 



It must be admitted in all frankness that the known facts in our 

 possession are not sufficient to justify a positive opinion as to the 

 views just presented. They seem, however, to be founded on a 

 rational basis and are put forward tentatively as suggestive of possi- 

 ble lines of investigation and the justification for formulating them 

 here will be found in the results of future work. Whatever maj' be 

 the bearing of this work on the ideas here presented, it can not fail 

 to be of the utmost importance in throwing light upon the difficult 

 problem of plant nutrition. 



1 Henneberg's Journal, pp. 116 and 135 (1864). 



- These views are not intended to imply that salts can not be taken up as such, 

 even by nonhalophilous j)lants, under certain conditions. Wolf (loc. cit. ) has 

 long since shown that this may be done, and that, moreover, in such cases the 

 process can not be a simple ditf usion phenomenon. 



