OF NATURAL HISTORY. 23 



Befide the leaves, plants tranfpire by the pores of the fkin. But 

 the quantity emitted in this manner is not nearly equal to that 

 which iffues from the leaves. The fame thing happens with regard 

 to man and quadrupeds. Though they likewife perfpire through 

 the fkin, yet by much the greater quantity of perfpirable matter is 

 difcharged by the lungs. Befide throwing out fuperfluous or noxi- 

 ous matter by the leaves, plants, by the fame organs, abforb from 

 the atmofphere, and perhaps from the fun's rays, fome unknown 

 matter, which is neceffary to their exiftence. The lungs of ani- 

 mals likewife derive, from the fame fources, a particular matter or 

 principle, without which life could not long be continued. 



Another analogy between the ftrudture of plants and animals me- 

 rits obfervation. The round bones of animals confift of concentric 

 ftrata or plates, which can be eafily feparated ; and the wood of 

 plants confift of concentric layers of hardened veflels, which feparate 

 when macerated in water. A tree acquires an additional ring every 

 year ; and, by counting thefe rings, a pretty exadl eftimation of its 

 age may be attained. 



The branches of plants have been confidered as analogous to the 

 arms or tentacula of animals. But this is one of thofe ftrained ana- 

 logies which fliould be carefully avoided. The great ufe of branches 

 is evident. By producing an amafing number of leaves, a large fur- 

 face is expofed to the air and fun, to anfwer the important purpofes 

 of tranfpiration and abforption. If there is any thing In plants ana- 

 logous to the arms or tentacula of animals, it muft be confined to 

 fuch fpecies as twift themfelves around poles or trees, as the ivy, 

 the vine, the convolvulus, &c. and to fuch as fupport their trunks 

 on other bodies by means of little hooks, as the goofe-grafs, and 

 many other kinds. 



All 



