WOOD. 



[ 819 ] 



WOOD. 



Monocotyledons. — In our uative plants of 

 this class the stem is mostly herbaceous, 

 and the woody structure then occius sim- 

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

 bi'mdks, tig. 45G, 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 must 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 

 textm'e depends in these upon the inter- 

 space between the fibro-vascular bundles 

 being filled up with looody imrenchyma ; 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 tlie 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 lignified forms of 

 the structure which is exhibited in a soft 

 and herbaceous condition iu our common 

 Grasses. 



Certain Monocotyledons present a struc- 

 tm'e which differs from the above in the 

 appearance presented by transverse sec- 

 tions. In the Smilacese, and some of the 

 Dioscoreacese, the fibro-vascular bundles are 

 aiTanged in more definite order in one or 

 two cij'cles ; but there is no distinction of 

 pith, medullary rays, and bark here ; the 

 bundles are bound together by looody par- 

 enchyma, and there is no cambium-region 

 beneath the rind. The anomalous gTowth 

 exhibited by the stems of other Monoco- 

 tyledons, such as Draccena, Yucca, See., 

 cannot be regarded as depending on the 

 formation of wood in the proper sense ; in 

 them, layers of fibrous structure tire 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 bimdles 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 arc furnished by longitudinal and 

 transverse sections of the trunks of large 

 Palms and of the large woody leaf-stalks of 

 these, of canes of difterent kinds, of Bamboo 

 canes, the rliizome of Sarsaparilla plants 



(Smila.v), JRuscus, the harder parts of the 

 stem often found attached to imported 

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

 sil Palm-stems, prepared by the lapidary, 

 can also be obtamed 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 gi'owth of the 

 Fibro-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. 



Traus verse and Tex-tical section of a segment of a 

 shoot of the Maple in the early pai't of the second year 

 of itsage. T. spiral vessels; YP, pitted ducts; F, woody 

 fibre; C, cambium; Pc, cortical parenchyma; F, liber 

 fibres; Pc, cellular envelope of the bark ; S, corky layer 

 of ditto. Magnified 6U diameters. 



3g2 



