SECT. I. ORGANOGRAPHY AND GLOSSOLOGY. 13 



are found to be the sections of tubes, which are often 

 variously marked by dots, lines, and, in some instances, 

 are composed of a spirally twisted filament. These 

 appearances evidently show us that the vegetable struc- 

 ture is composed of polygonal cells and cylindrical 

 tubes, so arranged that they lie with their greatest 

 lengths parallel to the axis of the part in which they 

 are found. Among the lowest tribes of flowerless plants, 

 which form an extensive class, no tubes are observable, 

 and their whole mass is composed of cells alone. 



(13.) Elementary Textures. If we now examine the 

 materials of which these cells and tubes are constructed, 

 we find them to consist of a delicate, homogeneous 

 membrane, of extreme tenuity, generally colourless, and 

 without any distinct traces of organisation. Besides 

 this, there is a fine cylindrical fibre, which might be com- 

 pared to transparent catgut ; and this is often spirally 

 twisted and variously ramified upon the surfaces of the 

 cells and tubes, in a manner which we shall presently 

 describe. It is supposed that all the modifications ob- 

 servable in the internal organisation of plants result 

 from the various combinations which take place be- 

 tween these two elementary textures, " Membrane " and 

 " Fibre." 



(14-.) Chemical Composition. It has not been ascer- 

 tained whether these two organic elements of the vege- 

 table structure are identical in chemical composition, or 

 whether, indeed, the membrane and fibre which com- 

 pose the cells and tubes in different parts of plants are 

 always of the same kind. The inquiry would be one 

 of extreme difficulty, if not of absolute impossibility, 

 with the present resources of chemistry. All that is 

 known of the composition of these textures has been 

 derived from experiments made upon the gross mate- 

 rial, imperfectly separated from the various matters 

 which the cells and tubes contain. In this state it is 

 found to be composed of the three elements, oxygen, 

 hydrogen, and carbon ; but the exact proportion in 

 which these are united is uncertain, if, indeed, it be 



