LIFE OF THE WHOLE PLANT. 



'83 



The force of the circulation was measured by Hales in the 

 stem of the Vine by the apparatus represented in fig. 1118, 

 where a represents a section of a vine stock, to the upper end 

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

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

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

 of the experiment, the force of the sap Avas 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 suflScient to support a column of 

 mercury upwards of 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 mercury 17i 

 inches high. 



As the fluid rises in the stem it is of a 

 watery nature, and contains dissolved in 

 it the various inorganic matters in the 

 same state nearly in which they were ab- 

 sorbed by the roots. It also contains 

 some sugar, dextrine, and other matters 

 which it has dissolved in its course up- 

 wards to the leaves, &c. In its passage 

 upwards, although it becomes more and 

 more altered from the state in which it 

 was absorbed by the roots; when it 



Fig. 1118. Apparatus em- 

 ployed by Hales to show 

 the force of the ascent of the 

 sap. a. Cut vine stock, b. 

 a copper cap, winch is se- 

 cured to the stock by means 

 of a piece of bladder and 

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

 glass tube attached to the 

 copper cap, and containing 

 mercury, the level of which, 

 at the commencement of 

 the experiment, is marked 

 by e, /, and at the conclu- 

 sion in one leg of the tube 

 by g ; and hence the mer- 

 cury in the other leg must 

 have risen to a correspond- 

 ing degree to its depression 

 in the former. 



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 particulars, 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, Sfc. — The changes 

 which the crude sap undergoes in the leaves by the action of 

 ;light and air, and by which it becomes transformed into the 

 elaborated sap, have been already particularly alluded to 

 in treating of the Functions of Leaves (p. 734); it Avill ba 

 3 E 



