The Ascent of the Sap 



severed vessels. This bleeding is seen 

 abundantly in the vine. 



Now what should we expect to find in this 

 fluid pouring either from the vine or from a 

 fruit tree ? Many things, no doubt ; for 

 this fluid is the principal substance from 

 which all that the plant contains is to be 

 derived. Well, we should be mistaken : the 

 rising sap is scarcely anything but pure water. 

 It is with great difficulty that science has 

 succeeded in determining some substances in 

 solution, because their amount is so small. 

 The most frequent among these substances 

 are compounds of potash and lime and of 

 carbonic acid gas, traces of phosphates and 

 of nitrogenous or ammoniacal compounds. 

 The fluid from which the plant is to derive its 

 food is a very thin broth, composed of an 

 enormous quantity of water and a very small 

 amount of matter in solution. But these 

 scanty materials are the only portion utilised 

 by the plant, and the water that collected 

 them from the ground, and then transported 

 them from the roots to the leaves ; the water 

 which makes up almost the whole of the rising 

 sap, leaves the plant as soon as the journey is 

 accomplished, and returns as vapour to the at- 

 mosphere, whence it originallydescended as rain . 



119 



