CHAJ*. III. ELEMENTARY ORGANS. 347 



pbere so as to exhibit symptoms of incipient putre- 

 faction, the orifices of the tubes may be distinctly 

 perceived. They are particularly apparent on the 

 horizontal section of decayed trunks of the Elm- 

 tree, in which they are arranged in circular rows in 

 the direction of the concentric layers. In this case, 

 however, they exhibit merely a skeleton ; but Hed- 

 wig observed them in the transverse section of a 

 branch of the Pear-tree detached even in the spring, 

 while the sap was yet flowing. They were largest 

 and most distinct in the layers immediately under 

 the bark, but diminishing in their diameter towards 

 the centre.* 



It has been maintained, however, that the cavities Ohjec- 

 observable in the horizontal section of the wood 

 are not the orifices of tubular fibres, but of spaces 

 formed by the circular disposition of sets of fibres 

 closely united together, but leaving a tubular open- 

 ing in the centre. But if this were even the fact, 

 still these openings are as completely a vessel as if 

 the fibres themselves were tubular; and it is but 

 of little consequence in the mean time to know how Answered, 

 the tubes are formed, if they are but acknowledged 

 to exist. Regarding it therefore as certain that 

 plants are furnished with longitudinal tubes, as well 

 as with cells or utricles for the purpose of conveying 

 or containing their alimentary juices, I shall pro- 

 ceed to the specific illustration of both together with 

 their peculiarities and appendages. 



* DC Fibrac Vegetables Ortu, i. 



