80 PLANTS MAY ABSORB POISONOUS SUBSTANCES. 



were the same in all. — [Meyen Jdlireshericht, 1839, p. 1.] Provided, 

 therefore, the substances which plants prefer be present in the soil, the 

 kind of inorganic matter they take up, or of ash they leave, is not mate- 

 rially affected by the presence of other substances, even in somewhat 

 larger quantity. 



These facts all point to the same conclusion, that the roots have the 

 power of selecting from the soil in which they grow, those substances 

 which are best fitted to promote the growth or to maintain the healthy 

 condition of the plants they are destined to feed. 



6°. It has been stated above that the roots of certain plants refuse to 

 absorb nitrate of strontia and acetate of lime, though presented to them 

 in a state of solution — the same is true of certain coloured solutions which 

 have been found incapable of finding their way into the circulation of 

 plants whose roots have been immersed in them. On the other hand, 

 it is a matter of frequent observation that the roots absorb solutions con- 

 taining substances which speedily cause the death of the plant. Arsenic, 

 opium, salts of iron, of lead, and of copper, and many other substances, 

 are capable of being absorbed in quantities which prove injurious to the 

 living vegetable — and on this ground chiefly many physiologists refuse to 

 acknowledge that the roots of plants are by nature endowed with any 

 definite and constant power of selection at all. But this argument is of 

 equal force against the possession of such a power by animals or even by 

 man himself; since, with our more perfect discriminating powers, aided 

 by our reason too, we every day swallow with our food wliat is more or 

 less injurious, and occasionally even fatal, to human life.* 



On the whole, therefore, it appears most reasonable to conclude that 

 the roots are so constituted as (1°) to be able generally to select from the 

 soil, in preference^ those substances which are most suitable to the nature 

 of the' plant — (2°) where these are not to be met with, to admit certain 

 others in their steadf — (3°) to refuse admission also to certain substan- 

 ces likely to injure the plant, though unable to discriminate and reject 

 every thing hurtful or unbeneficial which may be presented to them in 

 a state of solution. 



The object of nature, indeed, seems to be to guard the plant against 

 the more common and usual dangers only — not against such as rarely 

 present themselves in the situations in which it is destined to grow, or 

 against substances which are unlikely even to demand admission into its 

 roots. How useless a waste of skill, if I may so speak, would it have 

 been to endow the roots of each plant with the power of distinguishing 

 ant? rejecting opium and arsenic and the thousand other poisonous sub- 

 stances which the physiologist can present to them, but which in a state 

 of nature — on its natural soil and in its natural climate — the liviaig vege- 

 table is never destined to encounter ! 



• I may here remark that it is by no means an extraordinary power which these circum- 

 stances seem to show the roots of plants to possess. In the presence of oxygen, nitrogen, 

 and carbonic acid, in equal quantities, water will prefer and will select the latter. From a 

 mixture of lime and magnesia, acetic or sulpliuric acid will select and separate the former. 

 Is it unreasonable to suppose the rooisof plants— the organs of a living being— to be endowed 

 with powers of discrimination at least as great as those possessed by dead matter? 



t This conclusion is not strictly contained in the premises above stated, but the facts from 

 which it is drawn will be fully explained in treating of the inorganic constituents of plants. 

 It is introduced here for the purpose of giving a complete view of what appears to be the 

 true powers of discrimination possessed by the root. 



