VEGETABLE TISSUES '. WOODY FIBRE. 401 



of Rice-paper (§ 284), by first filling these with Lime-water by 

 means of the air-pump, and then placing the paper in weak solu- 

 tions of Phosphoric and Oxalic acids. The artificial Eaphides of 

 Phosphate of Lime were rhombohedral ; while those of Oxalate of 

 Lime were stellate, exactly resembling the natural Eaphides of the 

 Rhubarb.* 



294. A large proportion of the denser parts of the fabric of the 

 higher Plants is made-up of the substance which is known as 

 Ligneous Tissue or Woody Fibre. This, however, can only be 

 regarded as a very simple variety of Cellular Tissue ; for it is com- 

 posed of peculiarly-elongated Cells (Fig. 216), usually pointed 

 at their two extremities so as to become spindle-shaped, whose 

 walls have a special tendency to undergo consolidation by the 

 internal deposit of Sclerogen. It is obvious that a tissue consist- 

 ing of elongated cells, adherent together by their entire length, 

 and strengthened by internal deposit, must possess much greater 

 tenacity than any tissue in which the cells depart but little from 

 the primitive spherical form ; and we accordingly find Woody 

 Fibre introduced wherever it is requisite that the fabric should 

 possess not merely density, but the power of resistance to ten- 

 sion. In the higher classes of the Vegetable Kingdom it consti- 

 tutes the chief part of the Stem and Branches, where these have a 

 firm and durable character ; and even in more temporary struc- 

 tures, such as the Herbaceous Stems of annual Plants, and the 

 Leaves and Flowers of almost every tribe, this tissue forms a more 

 or less important constituent, being especially found in the neigh- 

 bourhood of the Spiral Vessels and Ducts, to which it affords 

 protection and support. Hence the bundles or fasciculi composed 

 of these elements, which form the ' Veins ' of Leaves, and which 

 give ' stringiness ' to various esculent Vegetable substances, are 

 commonly known under the name of Fibro- Vascular tissue. In 

 their young and unconsolidated state the Ligneous cells seem to 

 conduct fluids with great facility in the direction of their length ; 

 and in the Coniferous tribe, whose Stems and Branches are des- 

 titute of Ducts, they afford the sole channel for the ascent of the 

 sap. But after their walls have become thickened by internal 

 deposit, they are no longer subservient to this function ; nor, 

 indeed, do they then appear to fulfil any other purpose in the 



* The materials of the above paragraph are derived from the excellent 

 section on this subject in Prof. Quekett's "Lectures on Histology." — 

 Besides the vegetables therein named as affording good illustrations of 

 different kinds of Eaphides, may be mentioned the parenchyma of the 

 leaf of Agave, Aloe, Cycas, Encephalartos, <fec; the cuticle of the bulb of 

 the Hyacinth, Tulip, and Garlic (and probably of other bulbs) ; the bark 

 of the Apple, Cascarilla, Cinchona, Lime, Locust, and many other trees ; 

 the pith of Eleagnus, and the testa of the seeds of Anagallis and the Elm. 

 — The Raphides characteristic of the different Natural Orders of Plants 

 have been carefully studied by Mr. Gulliver ; who has given an account 

 of them in successive Papers in the "Annals of Natural History." 



D D 



