ASCENT OF SAP. 49 



sink far down into the earth, leaving the surface at all 

 times as dry and unproductive as a desert ; vegetation 

 would cease ; brooks and rivers would lose the gradual 

 supplies which the earth affords them through tliis in- 

 fluence, and become dried up ; and all plants and all 

 animals die for want of drink and nourishment. Thus 

 the very existence of the whole human race evidently 

 depends on a law, apparently insignificant to the un- 

 thinking, but pointing the observing mind to a striking 

 proof of the creative design which planned all the 

 works of nature, and fitted them with the utmost ex- 

 actness for the life and comfort of man. 



ASCENT. OF SAP. 



The following interesting experiments serve to ex- 

 plain the cause of the ascent of sap in plants and trees : 

 Take a small bladder, or bag made of any similar 

 substance, and fasten it tightly on a tube 

 open at both ends {Fig. 17) ; then fill them 

 with alcohol up to the point C, and im- 

 merse the bladder into a vessel of water. 

 The alcohol will immediately rise slowly 

 in the tube, and if not more than two or 

 three feet high, will run over the top. This 

 is owing to the capillary attraction in the 

 Apparatus ex- mluute porcs of tho bladder, drawing the 

 lisingofsap. water within it faster than the same at- 

 traction draws the alcohol outward. One liquid will 

 thus intrude itself into another with great force. A 

 bladder filled with alcohol, with its neck tightly tied, 

 will soon burst if plunged under water. If a bladder 

 is filled with gum-water, and then immersed as before, 

 C 



