TO 



THE PLANT. 



It might be supposed that plants become saturated 

 with the substances absorbed from the air and from the 

 soil ; and that all materials offered by the soil in solu- 

 tion, or made soluble by the cooperation of the roots, 

 are absorbed without distinction. Upon this assump- 

 tion, only that substance in the plant could of course 

 pass into it from without, which is withdrawn from the 

 solution within for a formative purpose. 



The investigations made by Schultz-Fleeth show 

 that Nymphcea alba and Arundo phragmites absorb 

 from the same soil and water, the former nearly 13 per 

 cent., the latter 4*7 per cent., of ash constituents ; and 

 of these silicic acid in the most unequal proportion ; 

 the ash of Nymphcea alba containing less than \ per 

 cent, of that substance, while in the ash of 'Arundo 

 phragmites there are above 71 per cent. Upon the 

 supposition just made, an equal amount of silicic acid is 

 offered to the roots of both plants, and they both take 

 up an equal quantity of it in proportion to the volume 

 of the sap respectively. In the reed plant the silicic 

 acid is incessantly withdrawn from the sap, and depos- 

 ited in a solid state in the leaves, the margins of the 

 leaves, the sheaths, &c. As the sap within contains 

 less silicic acid than the solution without, fresh quanti- 

 ties of it are absorbed from the latter ; but not so with 

 the Nymphcea) because the silicic acid taken up by that 

 plant is not consumed in it. 



If we accept the same reasons for the passage into 

 the plant of carbonic acid and phosphoric acid, then it 

 can possess no actual power of selection, but the per- 

 meation of the nutritive substances will depend upon 

 osmotic conditions. 



It certainly cannot be denied that the absorption of 

 nutritive substances depends upon growth or increase 



approved practice to steep grains of wheat, intended for sowing, in a solu- 

 tion of sulphate of copper. The usual explanation of this practice is, that 

 sulphate of copper destroys the sporules of blight to which the wheat plant 

 is liable, an explanation which it is not my intention to dispute. Still it 

 might also be held, supposing copper to be an essential constituent of 

 wheat, that the practice in question serves to supply the copper necessary 

 for the vigorous growth of the plant.' 



