LIFE OF THE ■S\'HOLE PLANT. 



'99 



h 



fliiid absorbed by the roots, the force with which it ascends to 

 the stem, and the amount transpired by the leaves, are directly 

 proportionate to one another. 



The force of the circulation was measured by Hales in the 

 stem of the Vine by the apparatus represented in Jiff, 1126, 

 where a represents a vine stock, to the transverse section of 

 which is attached a bent glass tube, d e f g, by means of a 

 copper cap, h, a piece of bladder, and a lute, c. The bent tube 

 being filled with mercury to the level, ef, at the commencement 

 of the experiment, the force of the sap was readily calculated 

 by the fall of the mercury in one leg of the tube d e g, and its 

 corresponding rise above /in the other leg of the tube. In this 

 way he found, that in one experiment, the force of the ascent 

 was sufficient to support a column of 

 merciuy 32|- inches in height. He also 

 calculated from his experiments on the 

 Vine, that the force with which it rises 

 in this plant is nearly five times greater 

 than that of the blood in the crural 

 artery of a horse, and seven times greater 

 than that of the blood in the same artery 

 of a dog. In some experiments of Brucke 

 on the force of the ascent of the sap in the 

 spring in the Vine, he found that it was 

 equal to the support of a column of mer- 

 cury 17^ inches high. Hales' experiment 

 is, however, a measure of the force of 

 absorption by the root rather than of 

 ascent of the sap (see p. 796). 



As the fluid rises in the stem it is of a 

 watery nature, and contains dissolved in pig. ii26. Apparatus em- 

 ployed hy Hales to show 

 tlie force of the ascent of 

 the sap. a. Cut vine stock ; 

 b, a copper cap, which is 

 secured to the stock by 

 means of a piece of l 'ladder 

 and lute, c ; d, e,f, g, bent 

 glass tube attached to the 

 copper cap, and contain- 

 ing mercury, the level of 

 which, at the commence- 

 ment of the experiment, 

 is marked by e, f, and at 

 the conclusion in one leg 

 of the tube by g ; and 

 hence the mercury in the 

 other leg must have risen 

 to a corresponding degree 

 to its depression in the 

 former. 



<^^\J^ 



it the various inorganic matters in the 

 same state nearly in which they were ab- 

 sorbed by the roots. It also contains 

 sugar, dextrin, and other matters which 

 it has dissolved in its course upwards to 

 the leaves, &c. In its passage upwards, 

 although it becomes more and more al- 

 tered from the state in which it was 

 absorbed by the roots; when it reaches 

 the leaves it is still unfitted for the 

 requirements of the plant, and is hence 

 called Crude Sap. It undergoes certain 

 changes in the leaves and other green 

 parts, by which it becomes altered in 

 several particular?, and is then adapted for the uses of the plant. 

 In this state it is termed Elaborated Sap. 



Changes of the Crude Sap in the Leaves^ ^'C. — The changes 



