OF NATURAL HISTORY. 31 



being only more clofe and compa<Sl in the bark and wood than 

 in the pith. It is well known that the pith of plants dimin- 

 iflies in proportion to their age. The reafon is obvious *, 

 every year the ring of veflels, which lies contiguous to the 

 wood, dries, condenfes, and becomes wood. 



The leaves of vegetables conlifi: of a fine lldn,which inclo- 

 fes the parenchyma or pulp. This {km, like that of animals, 

 is an organic body, furniflied with an immenfe number of par- 

 enchymatous and ligneous fibres, and interwoven in a manner 

 precifely fimiiar to that of the trunk and branches. When 

 the ikin is removed, the pulp appears, and is every where 

 interfperfed with imall cylindrical fibres, wound up into mi- 

 nute bladders. A large nerve runs along the middle of every 

 leaf, and continually fends off branches, which gradually de- 

 creafe in magnitude, till they reach the edge or difc. This 

 principal nerve is a colledtion of fmall tubes, which, at proper 

 diftances» go off, and are diftributed over the leaf in a man- 

 ner precifely fimiiar to the diftribution of the nerves over 

 the human body. 



With regard to flowers and fruits, their general texture is 

 the fame with that of the parts already delcribed, differing 

 only in various proportions of the ligneous veiTeis and paren- 

 chymatous or pulpy fubftance. That vegetables are pcirelTed 

 of fecretory glands, is apparent from the almofl infinite va- 

 riety of their taftos, odours, and colours. Thefe fenfible 

 qualities differ even in different parts of the fame plant. 

 But the glandular fecretion of vegetables is mofl confpicuous 

 in the flowers and fruit. Many flowers fecrete a ne(Slareous 

 fluid, which is more grateful to the palate than the fineft 

 honey. The glands of fome fruits, as thofe of the lemon and 

 orange, fecrete liquors of very different qualities. The vef- 

 fels of the rhind contain an acrid effentlal oil, while thofe of 

 the parenchyma or pulp fecrete an agreeable acid. 



