60 INORGANIC CONSTITUENTS. 



the water, which is essential to living plants, may be charged with 

 them ; for it is within what may be called common experience, that 

 saline solutions of certain degrees of concentration, oftentimes act 

 injuriously on vegetation. 



The spongioles which terminate roots have too close a tissue to 

 allow any thing but fluids to pass through them. All attempts to 

 make them absorb solid bodies in a stale of minute division, and held 

 in suspension in water, have been ineffectual. In these attempts the 

 spongioles have acted precisely like perfect filters, with which those 

 that we employ in our laboratories cannot be compared. Further, 

 the weakest solutions are not entirely absorbed by certain roots ; a 

 kind of separation takes place ; a portion of the dissolved salt ap- 

 pears to abandon the water at the moment of its penetrating the 

 spongiole. This follows from the researches of M. de Saussure, 

 instituted with a view to ascertain, 1st. If plants absorb substances 

 dissolved in water in the same proportion as they absorb water ;* 

 2dl.y. If plants make a selection among diflferent substances held in 

 solution in the same liquid. t 



In solutions severally containing eight ten-thousandths (0.0008) 

 of each of the following substances — chloride of potassium, chloride 

 of sodium, nitrate of lime, sulphate of soda, hydrochlorate of ammo- 

 nia, acetate of lime, sulphate of copper, sugar-candy, gum arabic, 

 and extract of humus,J — several entire plants with their roots, of 

 the polygonum persicaria^ (lakeweed or redshanks,) which had lived 

 for some time in distilled water, until their roots had commenced 

 growing, were immersed. 



The plants lived in the shade during five weeks, throwing out roots 

 in one of the solutions mentioned. They languished, without show- 

 ing any appearance of growth in the solution of hydrochlorate of 

 ammonia, and could only be kept alive in the sugared water, which 

 soon became changed, by renewing it frequently. They died at the 

 end of from eight to ten days, in gum water, and in the solution of 

 acetate of lime. They held out but for two or three days in the 

 water which contained sulphate of copper. 



Observations precisely similar made on the bidens cannabina pre- 

 sented the same results, with the sole difference, that this plant lived 

 for much shorter times than the redshanks. 



To estimate in what proportion the substances dissolved were ab- 

 sorbed, relatively to the water, M. de Saussure made use of the 

 solutions previously employed ; but he brought the experiment to a 

 close when the plants had taken up precisely half the liquid which 

 was feeding them. Each solution fed a suflfieient number of plants 

 to allow of this condition being fulfilled in two days. Half of the 

 liquid remaining after each experiment was analyzed, and the quan- 

 tity of salt found therein, showed, by the difference between this 

 and the quantity originally contained, the amount which had pene- 

 trated the vegetable. Representing by one hundred parts the whole 



* Siuspure, Rocherches chimiques, &.c. p. 247. t Ihid. rage 253. 



i This entered into the solutions only in the proportion of t\\ o ten-thousai^dtht 

 0.0002.) 



