THE VEGETABLE CELL. 69 



taken up by tlieir roots, but tbis means can only act in perennial plants, 

 and not in annuals. 



Since tbe roots undoubtedly possess tbe power of separating a saline 

 solution into a dilute and a concentrated, and absorbing tbe thinner ; and 

 since, according to TrincMnetti's experiments, certain plants absorb par- 

 ticular salts oidy in very small quantity^, tbe question arises wbetber, in 

 particular cases, tbe plants are in a condition to take up from a solution 

 water alone, witb tbe total exclusion of tbe dissolved substance. We 

 Lave no definite experience on tbis point, but sucb a thing is not impro- 

 bable. I may mention bere tbat formation of Pungi lias been observed 

 even in arsenical solutions, for arsenic is a substance so hostile to vege- 

 table life, tbat it can scarcely be supposed tbat any plant could maintain 

 its existence when it contamed arsenic in its sap. It was also observed 

 hj Yogel (-Erdman and Marcliand. ''Journ,,'' Bd. 25, 209), tbat Cereus 

 variabilis bad taken up no copper after having been watered for ten 

 weeks with solution of sulphate of copper, that the copper penetrated 

 just as little into the leaves of Stratiotes ahides, and that Chara vulgaris 

 vegetated for three weeks ui a solution of sulphate of copper without 

 taking up this metal. 



If the experiments mentioned in the foregoing cannot be ex- 

 plained in every single detail through the laws of endosmose, yet 

 there is a great probability that this will be possible in time. 

 "We must not forget, in considering this absorption, that in the 

 majority of plants we have to do with an apparatus in wliich the 

 laws of endosmose cannot display themselves clearly. These can 

 only be seen undisturbed v/here no other force is acting upon the 

 two fluids separated by a partition. But only the comparatively 

 few plants growing totally under water occur in this condition, 

 while the physical conditions in which the great majority of plants 

 are placed, must give rise to impoitant modifications in those of 

 their phenomena depending upon endosmose. Since the leaves 

 have a large surface with a comparatively small mass, and are 

 provided with numerous stomates on the under side, they are 

 fitted to evaporate a great quantity of water. This does occur 

 in a surprising degree when external circumstances do not repress 

 the foi*mation of vapour; thus, for example;, in Hales' experi- 

 ments, a sun-flower 8| feet high lost on an average a pound and 

 four ounces of water daily in this way, the loss rising to a pound 

 and fourteen ounces on a warm and dry day, from which Hales 

 reckoned that in comparison of the surfaces, the evaporation 

 was some three times as strong in this plant as in man, and in 

 comparison of volume seventeen times as strong. So consider- 

 able a loss of water cannot remain without re-action upon the 

 absorption of the root-cells. For since the sap in the cells of the 

 leaves becomes so much more concentrated through the loss of 

 water, their power of inducing endosmose will increase in propor- 

 tion, they replace the water taken from them, from the cells of the 

 stem, and so tliis action is continued through the whole tissue of 

 the plant down to the i-oots, which strive to absorb water from 



