EI-EMEXTARY STEUCXrEE. 



39 



1 



3000' 



-^ of an inch 



7'' 



P 



their walls, renders this tissue very strong and tough, and thus 

 admirably adapted for those parts of plants in which it is found, 

 and where such qualities are especially required. 



b. Disc-bearmg Woody Tissue.— Th.i's tissue is composed of those 

 wood-cells called Disc-hearing Wood-ccUs, which have been already 

 described. This tissue constitutes generally nearly the whole 

 of the wood of the Coniferse and other G-jnunospermous plants, 

 as well as a portion of the wood 



of some other plants, as Wintera Fig, 72. Fig. 73. Fig. 74. 

 aromatica, Illiciu7n anisahivi, &c. 

 The disc-bearing wood-cells, how- 

 ever, in the latter cases, are some- 

 what modified, the discs being 

 here found without the central 

 pit or dot {fig. 41). These disc- 

 bearing wood-cells are much 

 larger than the other kinds of 

 wood-cells, being often as much 



^S 3^0 ^^ 2M °^ ^^ ^^^^ ^^ ^^^' 

 meter, while the latter are fre- 

 quently not more than ttt^, or on 

 an average about 

 in diameter. 



c. Woody Tissue of the Liber. — 

 This consists of cells much longer 

 than ordinary wood-cells {fig.72), 

 with very thick walls {fig. 74), 

 and tougher, but at the same 

 time softer and more flexible; 

 hence these are a peculiar kind 

 of cells, and have received the 

 distinctive name of Liber-cells, 



from their common occurrence in the inner bark or liber of Dico- 

 tyledonous stems. This inner bark is also commonly termed 

 bast, hence the tissue formed by the combination of such cells is 

 also called Bast Tissue. The liber-cells are sometimes branched 

 {fig. 73). Besides the common occurrence of this tissue in the 

 liber, it also occurs as a constituent of the vascidar bundles of 

 Monocotyledonous stems, and also on the outside of many stems 

 in the same class of plants, and in the stems of Mosses. The 

 veins which form the framework of all leaves are also in part 

 composed of this kind of tissue. 



From the peculiar qualities of woody tissues or fibres, and 

 especially of the ivoody tissue of the liber, the latter is admirably 

 adapted for various manufacturing purposes ; thus. Hemp, Flax, 

 New Zealand Flax, Pita Flax, Sunn, Jute, and Chinese Grass 

 Fibre, are all composed of the liber tissue of diflPerent plants, 

 and will afford good illustrations of the value of such liber 



Fig. 72. Upper end of a liber-cell. 



Fig. 73. Branched liher-celi. 



After Sclileideu. Fig. 74. 



Transverse section of liber-cell*, 

 showing the thickness of their 

 ■walls. 



