44 TERRESTRIAL ADAPTATIONS. 



chine ill regulated ; every thing would go wrong ; 

 repeated collisions and a rapid disorganization 

 must be the consequence. We will, however, 

 attempt to illustrate one or two of the cases in 

 which this would take place, by pointing out 

 forces which act in the organic world, and which 

 are adjusted to the force of gravity. 



1. The first instance we shall take, is the force 

 manifested by the ascent of the sap in vegetables. 

 It appears, by a multitude of indisputable experi- 

 ments, (among the rest, those of Hales, Mirbel, 

 and Dutrochet,) that all plants imbibe moisture 

 by their roots, and pump it up, by some internal 

 force, into every part of their frame, distributing 

 it into every leaf. It will easily be conceived 

 that this operation must require a very consider- 

 able mechanical force ; for the fluid must be 

 sustained as if it were a single column reaching 

 to the top of the tree. The division into minute 

 parts and distribution through small vessels does 

 not at all diminish the total force requisite to 

 raise it. If, for instance, the tree be thirty-three 

 feet high, the pressure must be fifteen pounds 

 upon every square inch in the section of the 

 vessels of the bottom, in order merely to support 

 the sap. And it is not only supported, but pro- 

 pelled upwards with great force, so as to supply 

 the constant evaporation of the leaves. The 

 pumping power of the tree must, therefore, be 

 very considerable. 



