WOOD. 



[ 687 ] 



WOOD. 



It consists, as in that family, wholly of pitted 

 prosenchymatous cells without ducts, the 

 cells having two or three rows of bordered 

 pits, as in ARAUCARIA. A distinction exists 

 however in the character of the medullary 

 rays, which are very numerous in Wintereae, 

 occurring both large and small, six or seven 

 in the breadth of 1-12" in a vertical section 

 at right angles to the rays ; some of them 

 being thin, composed of one or two parallel 

 layers of cells, extending to a vertical extent 

 of about ten cells ; others much larger, ten 

 or twelve cells thick (or broad), and of a 

 vertical extent of eighty or a hundred cells ; 

 the latter are very evident on the surface of 

 the wood, when the bark is removed. The 

 medullary rays here traverse all the annual 

 layers of wood, which is not the case in the 

 Coniferae. 



BTBL. Goeppert, Linnesa, xvi. p. 135 

 (1842), Ann. des Sc. nat. 2 ser. xviii. 

 p. 317. 



WOOD. The mode of origin of wood is 

 explained in the articles CAMBIUM, ME- 

 DULLA, MEDULLARY RAYS, and VASCU- 

 LAR BUNDLES, while the characters of the 

 elementary organs of which wood is com- 

 posed are described under the heads of CELL, 

 PITTED and SPIRAL -FIBROUS STRUC- 

 TURES, FIBRES, and SECONDARY DEPO- 

 SITS. Peculiar composition of the wood in 

 certain classes, families, or genera of plants 

 is also noticed under their especial heads, 

 which will be referred to presently. In this 

 article the principal kinds of modification of 

 the wood (taken as a whole) occurring in 

 these said cases, and in certain others, are 

 to some extent classified, in order to indi- 

 cate their relations, and to furnish a guide 

 to microscopists seeking to observe the most 

 remarkable varieties of structure occurring 

 in this substance. 



The elements entering into the composi- 

 tion of wood are, 1. FIBRO-VASCULAR 

 BUNDLES, which in their most complete 

 form contain SPIRAL and other VESSELS, 

 PITTED DUCTS, PROSENCHYMATOUS cel- 

 lular tissue with thickened walls (woody 

 fibre) ; and in the Monocotyledons, * proper 

 vessels,' as they are called by Mohl, viz. 

 elongated tubular cells of membranous struc- 

 ture occurring in the centre of the bundles, 

 apparently corresponding to the CAMBIUM 

 at the outer surface in Dicotyledons. 

 2. MEDULLARY RAYS in the Dicotyledons, 

 or a generally diffused medullary parenchyma 

 in the Monocotyledons. 3. Woody PA- 

 RENCHYMA, which is found under different 



conditions and in different quantities in dif- 

 ferent cases. 



The GYMNOSPERMS may be considered, 

 in the above enumeration, as agreeing with 

 the Dicotyledons. The less generally dif- 

 fused structures connected with Secretion 

 are here left out of view. 



In classifying the kinds of wood, we may 

 commence with the less perfect forms. 



Monocotyledons. In our native plants of 

 this class the stem is mostly herbaceous, 

 and the woody structure then occurs simply 

 in the form of "fibres" (fibro-vascular bun- 

 dles) (fig. 460, p. 419), the structure of which 

 has been described elsewhere (fig. 7^6). 

 The same kinds of elements are arranged in 

 nearly the same way in most of the arbores- 

 cent plants of this class, such as Palms, for 

 example in the Cocoa-nut Palm, in the com- 

 mon Cane ( Calamus), or the various striped 

 solid canes (all Palms) used for walking- 

 sticks, &c. The solid woody texture depends 

 in these upon the interspace between the 

 fibro-vascular bundles being filled up with 

 woody parenchyma ; i. e. the general medul- 

 lary substance, which in such stems as that 

 of the White Lily is soft and spongy, in the 

 Palms &c. becomes solidified 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 lignified 

 forms of the structure which is exhibited in 

 a soft and herbaceous condition in our com- 

 mon Grasses. 



Certain Monocotyledons present a struc- 

 ture which differs from the above in the 

 appearance presented by transverse sections. 

 In the Smilacese, and some of the Diosco- 

 reacese, the fibro-vascular bundles are ar- 

 ranged 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 parenchyma, 

 and there is no cambium region be- 

 neath the rind. The anomalous growth 

 exhibited by the stems of other Monocoty- 

 ledons, such as Draccena, Yucca, &c., can- 

 not be regarded as depending on the forma- 

 tion of wood in the proper sense ; in them, 

 layers of fibrous structure are formed be- 

 tween the central region of the stem (con- 

 taining 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 



