VEGETABLE ORGANIZATION. 75 



ferent portions of the same vessel, when followed 

 by the eye throughout a great extent of its length. 

 Thus, in the course of the same tube, (as seen in 

 Fig 17), we find parts exhibiting spiral fibres, 

 which, in other parts, bifurcate and again unite ; 

 and in others, again, form rings : these may 

 afterwards, by a closer junction, present a reti- 

 culated appearance, or a series of transverse 

 lines, which, becoming smaller and smaller, are 

 at length mere points, arranged in circular rows 

 around the cylindrical surface of the vessel.* 



What are called the ivoody fibres have their 

 origin, like all other parts of plants, in cells. 

 These are generally fusiform, that is, of the 

 shape of a double cone, very greatly elon- 

 gated, and placed close and parallel to one 

 another, with the narrow extremities of one set 

 wedged in between those of another set (Fig 18). 

 Their coats are more firm and elastic than those 

 of ordinary vessels, but do not appear to con- 

 tain any internal fibres, although they receive, 

 in the progress of their developement, large 

 additions of solid matter. These fibres are gene- 

 rally collected together into bundles or layers, 

 and are accompanied by cells and vessels of 



* Many distinguished botanists, such as Rudolphi, Link, 

 Treviranus, and Dutrochet, consider these spots as being pro- 

 duced not by the deficiency of the internal coating, but by the 

 addition of granular bodies. See De Candollc's Organographie 

 Vegetale, torn. 1, p. 56. 



