LECT. IV. ABSORPTION IN VEGETABLES. 95 



larity and imbibition. But there is also something more. 

 You have all, doubtless, seen, that in cutting across a vine 

 stem in the spring, there runs out an enormous quantity of 

 liquid. Hales, by fixing to the top of the stem (Fig. 6. a, b) 

 a mercurial guage (a, y) consisting of a curved glass tube 

 (a, x, y, z,) containing mercury, and open at the other ex- 

 tremity, observed that the mercury rose 38 inches (equal to 

 43 feet 3J inches of water) higher in the longer open leg 

 (y, z) of the tube than in the other leg (x ;) and this he 

 ascribed to the force of the sap which came out of the 

 stem and forced up the mercury. 



This force of impulsion, and the discharge of the liquid 

 of the plant from a cut, are facts incompatible with the ef- 

 fects of capillarity and imbibition. A liquid rising in a 

 capillary tube, cannot overflow the tube by the effect of the 

 same force which raises it. 



Dutrochet has demonstrated by a very simple experiment, 

 that the force of impulsion which produces the ascension of 

 the juice of a plant, has its seat in the ultimate extremities 

 of the roots. This distinguished physiologist made succes- 

 sive sections of the trunk of a vine, approaching each time 

 nearer the roots ; and finally, he cut even the roots them- 

 selves contained in the ground, and he observed that the 

 flow of sap continued. One of the ultimate filaments of the 

 rootlet, when plunged in water, also allowed the juice to 

 escape from it. It is then in the spongelets that the force 

 of impulsion resides. Dutrochet adds that he has disco- 

 vered in the cortical cellules of the spongelet a liquid 

 denser than water, and coagulable by nitric acid. He 

 therefore, fancied that he had discovered in the spongelet, 

 or rather in its cells, filled with a liquid denser than the 

 water which surrounds them, a group of endosmometers ; 

 hence the phenomenon of the ascent of the liquid in 

 the plant becomes a case of endosmose. It is desirable, 



