LECTURE IV. 157 



the vessels of plants should imbibe the raw 

 juices of the earth, however impregnated, 

 and so suddenly convert them into sap, 

 which is a very peculiar fluid ; for it seems 

 a more wonderful kind of digestion than 

 that which takes place even in the stomachs 

 of animals. Here, however, the experi- 

 ments of Mr. Knight seem to aid our con- 

 ceptions, by shewing, that the returning 

 vessels impregnate the plant with juices, 

 which concrete, and are probably dissolved 

 in the ascending watery sap, enriching it 

 with nourishment, and it may be, chemi- 

 cally aiding in its formation. Mr. Knight 

 finds that the specific gravity of the wood 

 of trees, is diminished by the ascent of 

 the sap. Thus, when the genial warmth 

 of the spring excites those actions which 

 imbibe the juices of the earth, and cause 

 the ascent of the sap, the plant seems 

 bursting with life and nutriment. The 

 leaves bud in every part, and are formed 

 with surprizing celerity. When, however, 

 the tree has attained its full extent of an- 

 nual growth, the returning sap is more 

 especially employed in storing the inter- 



