«t> ITSES OF THE 



Before we take leave of the secreted fluids of vegeta- 

 bles, a few more remarks upon their direct utiii;.y to the 

 pkmts themselves may not be superfluous. Mal]>ighi 

 first sufrgested that these secretions might nourish the 

 plant, and our latest inquiries confirm the suggestion. 

 Da Hamel compares them to the blood of animals, and 

 so does Durvvin. But the analogy seems more plain 

 between the sap, as being nearly uniform in all plants, 

 and the animal blood, as in that particular they accord, 

 while the secreted fluids are so very various. Mr. 

 K light's dieory confirms this analogy, at the same time 

 that it establishes the opinion of Malpighi. The sap 

 returning from the leaf, where it has been acted upon by 

 the air and light, forming ntw wood, is clearlv the cause 

 of the increase of the vegetable bodv. But it is not so 

 clear how the resin(jus, gummy or other secretions, laid 

 aside, as it were, in vessels, out of the great line of cir- 

 culation, can directly minister to the growth of the tree. 

 I conceive they may be in this respect analogous to ani- 

 mal fat, a reservoir of nourishment whenever its ordina- 

 ry supplies are interrupted, as in the winter, or in seasons 

 of great drought, or of unusual cold. In such circum- 

 stances the mucilaginous or saccharine secretions espe- 

 ciall} , perhaps the most general of all, may be absorbed 

 into the vegetable constitution ; just as fat is into the 

 animal one, during the existence of any disease that in- 

 terrupts the ordinary supplies of food, or interferes with 

 its due appropriation. It is well known that such ani- 

 mals as sheep through the winter, grow fat in the autumn 

 and awake veiy^ lean in the spring. Pcihaps the more 

 recent layers of wood in a Plum- or Cherry-tree, if they 



