PLEURENCHYM. 



[BOOK I. 



acutely to each end, lying in bundles, and, like the cellular 

 tissue, having no obvious communication with each other, 

 except by invisible pores. Slack states, that the tubes are 

 often met with open at their extremities ; " which probably 

 arises either from the membrane being obliterated where it 

 was applied to another fibre, or ruptured by the presence of 

 an adjoining tube, as we sometimes find the conical extremity 

 of another tube inserted into the aperture." 



Many vegetable anatomists consider it a mere form of cel- 

 lular tissue, in a lengthened state. However true this may 

 be in theory, woody tissue may be known by its toughness 

 and extremely attenuated character. The distinction between 

 cellular and woody tissue is particularly well seen in the long 

 club-shaped aerial radicle of Rhizophora Candelaria. It there 

 consists of large, very long, transparent tubes, lying imbedded 

 in fine brownish granular matter, which is minute cellular 

 tissue (fig. 7.) 



Usually it has no markings upon its 

 surface, except occasionally a particle 

 or two of greenish matter in its inside; 

 but sometimes it is covered with spots 

 that have been mistaken for pores, and 

 which give it a peculiar character (Plate 

 II. fig. 3. 5. and 20.) ; and I have re- 

 marked an instance, in Oncidium altis- 

 simum, of its having tubercles on its 

 surface. It often contains amylaceous 

 granules in abundance. Generally, 

 while cellular tissue is brittle, and has 

 little or no cohesion, woody tissue has 

 great tenacity and strength ; whence 

 its capability of being manufactured 

 into linen. Every thing prepared from flax, hemp, and the 

 like, is composed of woody tissue ; but cotton, which is cellular 

 tissue, bears no comparison as to strength, with either flax or 

 hemp. 



Alphonse De Candolle gives the following as the result ob- 

 tained by Labillardiere, as to the relative strength of different 



