94 ORGANS AND FUNCTIONS OF PLANTS. 



the minute cells. He fancies (for it is quite a fancy) 

 that every cell has the power of alternately expanding 

 and contracting, and by that means the fluid, not in 

 the cells, but between and among them, is pushed 

 along. It is thus carried up, not in any sort of vessel, 

 but between the cells directly to the leaves, without 

 undergoing any other change than that of mixing with 

 the juices it may meet with in its course. 



Professor Henslow says ' ' the particular route which 

 the ascending sap takes, has often been matter of 

 dispute, but it has been clearly ascertained by repeated 

 experiments, that it ascends along that portion of the 

 cellular tissue that constitutes the woody fibre and not 

 through the vascular tissue ; with respect to the mode 

 in which this sap is conducted along this cellular 

 tissue, there is still much uncertainty." 



Dutrochet explains it on the principle of experi- 

 ments made in 1827-8, with various membranes. He 

 filled with milk the large gut of a fowl, tied it at 

 each end, and placed it in water, when in twenty-four 

 hours he found seventy-three grains of the water had 

 got through and mixed with the milk, and in twelve 

 hours more the gut became tensely swelled out with 

 water. But what was remarkable, the passing of 

 water after that time was reversed, and in thirty-six 

 hours fifty four grains had oozed outwards. By filling 

 the gut with a solution of gum arabic, inserting in its 

 upper orifice a glass tube, placed perpendicularly, 

 and plunging the other tied end into rain water, the 

 water, by passing in, forced the thicker fluid up through 

 the glass tube. He thence concluded that a thinne 



