WHEAT. 



[ 818 ] 



WOOD. 



(PI. 22. fig. 32). Chemically, it consists of 

 a proterue compound, and is therefore co- 

 loured by INIillou's and Pettenkofer's test- 

 liquids. 



AMialeboue polarizes light like horn. 

 BiBL. Runiev, Phil. Trans. 1787; Bonders, 

 IlidcJer's Phys. Chemie ; Lehmann, Phys. 

 Cliem. 



WHEAT.— The stabch of the grain of 

 wheat (Triticinn mlgare and other species 

 and varieties) presents itself in the form of 

 delicate little fiattish lenticular bodies, very 

 characteristic (PL 46, fig. 8). Wheat is 

 subject to various Blights, -which are re- 

 ferred to under that head, depending on 

 the groveth of parasitic Fungi, especially 

 TiLLETiA, attacking the ear, Pucci>^ia 

 attacking the straw, &c. In other cases the 

 ear is found infested with a minute worm 

 (Anguilli'la tritici) remarkable for its 

 tenacity of life. 



WINGS OF Insects. — The arrangement 

 of the veins or nerves of the anterior wings^ 

 of the Hymenoptera is sometimes used to 

 form the basis of systematic arrangement ; 

 and the several veins and interspaces have 

 received distinct names, which may be illus- 

 trated by reference to PI. 34. fig. 11, repre- 

 senting the anterior wing of the humble- 

 bee (L'otnbtts terrestris) : a, costal nerve ; 

 h, hind margin ; c, iimer margin of wing, 

 with the fold (k) for the attachment of the 

 hooks ; d, postcostal nerve ; e, externo-me- 

 dian;/, anal ; the nerve between 3 and 10, the 

 trausverso-median ; h, anterior or outer mar- 

 gin ; /, the subdiscoidal : s, stigma ; 1, costal 

 cell ; 2, externo-median cell ; 3, interno- 

 median ; 4, anal ; 5, radial or marginal ; 6, 

 first cubital cell ; vi, m, m, second, third, 

 and fourth cubital cells; 10, first discoidal 

 cell; 11, second ditto; 12, third ditto; 13, 

 first, and 14, second apical cell. 

 See Insects, ivini/s. 



liiBL. That of Insects ; Jurine, Kou- 

 velle Methode ; Shuckard, Tr. Eniom. Soe. 

 i. ; Staveley, Miss, Neurafio/t, Linn. Trans. 

 xxiii. 125 ; Semper, Sielold c^ KiJUikers 

 ZAtischr. viii. 320. 



WINTE'UE^.— A section of the Dico- 

 tyledonous family Magnoliacete (Dbiwys, 

 Tasmannia), remarkable for the character 

 of the elementary structure of the wood, 

 approaching closelj' to that of the Coniferpe, 

 It consists, as in that family, wholly of 

 pitted prosencliymatous colls without ducts, 

 the cells having two or three rows of bor- 

 dered pits as in Abaucabia. A distinc- 

 ion exists, however, in the character of the 



medullary rays, which are very numerous in 

 Wintereae, occiuTing 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 himdred cells ; the latter are very evident 

 on the sm-face of the wood when the bark 

 is removed. The meduUary rays here tra- 

 verse all the annual layers of wood, which 

 is not the case in the Ooniferae. 



BiBL. Goeppert, Linncea, xvi. 135 (1842) ; 

 Ann. Sc. Nat. 2. xviii. 317. 



WOOD. — The mode of origin of Avood is 

 explained in the articles Cambium, Me- 

 dulla, Medullary Kays, and Vascular 

 bundles, while the characters of the ele- 

 mentary organs of which wood is composed 

 are described under the heads of Cell ; 

 Fibrous, Pitted, and Spiral Struc- 

 tures ; and Secondary Deposits. Pe- 

 culiar composition of the wood in certain 

 classes, families, or genera of plants is also 

 noticed under their special heads, which 

 will be referred to presently. In this article 

 the principal modifications of the wood, as 

 a whole, occurring in these and certain 

 other cases, are to some extent classified, 

 in order to indicate 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-a'ascular 

 bundles, which in their most complete 

 form contain Spiral and other Vessels, 

 Pitted ducts, Prosenchymatous cellular 

 tissue with thickened walls {looody Jibre) ; 

 and in the Monocotyledons, vasa propria, 

 as they are called by Mohl, viz. elongated 

 tubular cells of membranous structure oc- 

 curring in the centre of the bundles. 2, 

 Medullary Rays in the Dicotyledons, or 

 a generally diftused medullary parenchyma 

 in the Monocotyledons. 3, Woody I'AREN- 

 CHYMA, which is foimd under difterent con- 

 ditions and in difterent quantities in difter- 

 ent cases. 



The GvMNOSPERMS may be considered 

 in the above enumeration as agreeiug with 

 the Dicotyledons. Tiie less-generiilly dif- 

 fused structures connected with Secretion 

 are here let^t out of \\e\\. 



In classifying the kinds of wood, we may 

 commence with the l^ss perfect forme. 



