Microscopical Essays. 



66 6 



the nature of this fubftance. it's form and ftruclure, are at prefent 

 but very little known. It is floccofe, and varies in colour in 

 different fpecies. 



Of the Vasa Propria Interiora. 



Befides the lymphatic veflels and the cellular fubftance, we 

 find the juice veflels, or vafa propria, in the bark. In thofe trees 

 which are famous for medicinal virtues, they are ufually very 

 large ; they carry the milky juices of the fumaeli, and in them is 

 lodged the fineft and higheft-flavoured turpentine in all the kinds 

 of pine. Dr. Hill thinks that a tree of that genus exhibits them 

 beft, and the more, as the turpentine which fills them may be 

 perfectly diflblved in fpirit of wine. The pinus oriental is is the 

 fpecies in which thefe veflels are moll diftin&ly feen. 



Of the Blea. 



This is that part of the tree which is forming into wood, and 

 therefore lies between it and the bark, and may be feparated from 

 them by maceration. 



A longitudinal piece of the blea, when examined by the 

 microfcope, exhibits a number of veflels running parallel to each 

 other, the inter flitial fpaces being filled with a floccofe, white, 

 formlefs fubftance, of which Dr. . Hill fufpecls even the veflels 

 themfelves to be formed/ Innumerable fmall openings, or 

 mouths, may be difcovered in thefe veflels, fuited to imbibe the 

 xnoifture which is fo eflential to the life and health of plants. 

 Thefe mouths cannot be \yell difcerned, except when they are 



4 M opened 



