266 Dr. Daubenv on the Degree of Selection exercised by Plants, ^x. 



But in all these instances the poisonous quality of the substance was evinced 

 by the more or less rapid decay of the plant that had imbibed it ; whereas, 

 where nitrate of strontian was employed, the functions of life appeared to go 

 on for a considerable time without material obstruction. 



Upon the whole, then, I see nothing, so far as experiments have yet gone, 

 to invalidate the conclusion, to which the preceding facts appear to lead, 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. 



