. IV. ABSORPTION IN VEGETABLES. 97 



presence in the vegetable tissue of a certain quantity of 

 water, which perhaps acts by adhesion to the new water 

 which should rise, just as occurs with a sponge which is 

 more rapidly impregnated with water when it has been pre- 

 viously moistened than when it has been dried. Dutrochet 

 also tried the effect of drying a plant, of allowing it to re- 

 cover the water it had lost, and of plunging it again into 

 that liquid ; and he found that, although the water was re- 

 stored, the ascent took place only when the plant had re* 

 gained its original degree of turgescence. This turgescence 

 of the leaf-cells takes place, according to Dutrochet, by an 

 action of endosmose, in consequence of which the liquid 

 is transpired by the leaves in an active manner, very different 

 to that of a liquid which evaporates in the air. Lastly, I 

 must remind you, that Dutrochet has demonstrated that the 

 influence of light on the ascent of the sap in plants is exer* 

 cised in respiration and in the fixation of oxygen in the 

 vegetable tissue. 



The phenomenon of the ascent of liquids in plants does 

 not, therefore, depend, solely on capillarity and imbibition. 

 The cause resides principally in the roots, and in the next 

 place in the leaves. It is probable that an action of endos- 

 mose occurs in the extremity of the roots; and it is not 

 unnatural to suppose that a similar cause acts in the move- 

 ments of the chyle and lymph in the lymphatic and chyli- 

 ferous vessels a movement which continues some time 

 after death. 



