WOOD. 



[ 819 ] 



WOOD. 



Monocotyledons. In our native plants of 

 this class the stem is mostly herbaceous, 

 and the woody structure then occurs sim- 

 ply in the form of u fibres " (Jibro-vascular 

 bundles, fig. 456, p. 495), the structure of 

 which has been described elsewhere (fig.791, 

 p. 800). The same kinds of elements are 

 arranged in nearly the same way in most of 

 the arborescent plants of this class, such as 

 Palms for example, in the Cocoa-nut Palm, 

 in the common Cane (Calamus), or the 

 various striped solid canes (all Palms) used 

 for walking-sticks, c. The solid woody 

 texture depends in these upon the inter- 

 space between the fibro- vascular bundles 

 being filled up with woody parenchyma ; i. e. 

 the general medullary substance, which in 

 such stems as that of the White Lily is soft 

 and spongy, in the Palms &c. becomes soli- 

 dified by the great deposition of secondary 

 layers upon the walls of the cells ; thus 

 the bundles, at first "fibres," are bound 

 together into a solid wood. The thick 

 woody walls of the hollow Bamboo cane 

 are constructed on the same plan, being 

 highly developed and lignifiea forms of 

 the structure which is exhibited in a soft 

 and herbaceous condition in our common 

 Grasses. 



Certain Monocotyledons present a struc- 

 ture which differs from the above in the 

 appearance presented by transverse sec- 

 tions. In the Sniilaceae, and some of the 

 Dioscoreaceae, the fibro -vascular bundles are 

 arranged in more definite order in one or 

 two circles ; but there is no distinction of 

 pith, medullary rays, and bark here; the 

 bundles are bound together by woody par- 

 enchyma, and there is no cambium-region 

 beneath the rind. The anomalous growth 

 exhibited by the stems of other Monoco- 

 tyledons, such as Draceena, Yucca, &c., 

 cannot be regarded as depending on the 

 formation of wood in the proper sense j in 

 them, layers of fibrous structure are formed 

 between the central region of the stem 

 (containing the original vascular bundles) 

 and the rind, which take their origin from 

 the ends of the vascular bundles at the 

 periphery of the stem beneath the rind, and 

 extend down in a kind of false cambium 

 layer beneath the rind. 



Interesting objects illustrating the above 

 structures are furnished by longitudinal and 

 transverse sections of the trunks of large 

 Palms and of the large woody leaf-stalks of 

 these, of canes of different kinds, of Bamboo 

 canes, the rhizome of Sarsaparilla plants 



(Smilax), Ruscus, the harder parts of the 

 stem often found attached to imported 

 Pine-apples, &c. Sections of silicified fos- 

 sil Palm-stems, prepared by the lapidary, 

 can also be obtained from the dealers in 

 objects. 



Dicotyledons. In this class we meet with 

 a remarkable diversity in the character of 

 the wood, which moreover here exhibits, 

 from the indefinite power of growth of the 

 FLBRO-VASCULAR BUNDLES, a much more 

 extensive and perfect development than in 

 the Monocotyledons. In the articles ME- 

 DULLA (fig. 455, p. 495), MEDULLARY RAYS 

 (fig. 457, p. 496), and VASCULAR BUNDLES 

 (fig. 792, p. 801) are described the condi- 

 tions of ordinary Dicotyledonous stems in 

 the first year of their growth ; it is stated 

 in the account of the vascular bundles, that 

 a new layer of wood is developed in the 

 cambium layer in each succeeding season 

 (fig. 457, p. 496). The nature of the ele- 

 mentary structures in such cases is illus- 

 trated by the accompanying figures from the 

 Maple (Acer campestre, figs. 807 & 808), 



Fig. 807. 



Transverse and vertical section of a segment of a 



fibres; PC, cellular envelope of the bark; 8, corky layer 

 of ditto. Magnified 60 diameters. 



3G2 



