41 2_ Dr. Bell on the Vhyfiology of Plants. 



The true bark may be confidered as a congeries 

 of cellular fubftance, in which are placed two 

 kinds of organb, the vafa propria, or the veflels 

 peculiar to the plants, and the longitudinal fibres. 

 Of the ufe of thefe, nothing can be faid at 

 prefcnt. 



n. On removing the bark, the wood appears. 

 Its fubftanc" is denfer than the bark, and its 

 ftrufture more difficult to be demonftrated. But 

 it has been diicovered iikev/ife to contain vafa 

 propria, and longitudinal fibres, and, befides 

 thefe, large veficls with fpiral coats, which run 

 from one end of the tree to the other, and are 

 denominated vafa aena. Between the wood and 

 the pith lies a green coloured fubftance, firft 

 accurately defcribed by Dr. "John Hilly and by 

 him affirmed to contain all the parts of the plant 

 in embryo; he gave it the name of Corona. 



3. In the centre of the tree refides the pith, 

 ■which, in young plants, is very abundant. As 

 they approach to maturity it grows drier, and 

 appears in a fmaller quantity ; and, in very aged 

 trees, it is entirely obliterated. Its fubftance is 

 cellular, and, according to the author juft men- 

 air. In this he was mlftaken, becaufe it is f jund in the 

 heart of fruits, covering the feed, and becaufe J)u Hamel, 

 and Dr. Hope found, that, when the cuticle is removed, 

 and the acceflion of the air prevented by wax-cloth, thif 

 covering is neverthelefs in a little while reftored. 



tioncd? 



