SECT. IV. ELABORATION OF THE SAP. 135 



supposed that the action of the plates will be uni- 

 form throughout the whole plant ; or rather, it must 

 be supposed that it will often be directly in oppo- 

 sition to that which is necessary to the propulsion 

 of the sap. But admitting that the sap is pro- 

 pelled by the agency of the plates in question, and 

 admitting that it has been thus raised to the ex- 

 tremity of the woody part of the plant, how are 

 we to account for its ascent in such parts as are 

 yet higher the leaf-stalk and leaf, the flower- 

 stalk and flower ; as well as in the herb also, and 

 in the lofty Palm, in which no such plates exist ? 

 Here it .will be necessary to introduce the agency 

 of a new cause to complete the work that has been 

 thus begun, and of a new set of machinery to 

 supply the deficiency or absence of the machinery 

 that has been already invented. In short the theory 

 of Mr. Knight is beset with so many difficulties, and 

 the agency of the alleged cause so totally inadequate 

 to the production of the effect to be accomplished, 

 that of all theories on the subject it is perhaps the 

 least satisfactory, 



SECTION IV. 

 Elaboration of the Sap, 



THE moisture of the soil is no sooner absorbed Com- 

 into the plant than it begins to undergo a change, the root 

 This is proved by the experiment of making a bore OI 

 or incision in the trunk of a tree during the season 



