88 MORPHOLOGY OF THE CELL. 



Occasionalh- fibres which are verj- much branched are met ilth, 

 notably in the leaves of Camellia, for instance common te\ j see 

 Fig. 68. Genei-allj- the walls are thickened unevenly, even form- 

 ing conspicuous projections into tlie cavity of the cell ; while 

 some fibres have regular and characteristic markings, a few 



111 



of which are shown in Fig. 6.5. Septate forms are occasionally 

 found. The change in the character of the cell-wall whicii ac- 

 comp.anies the thickening is essentialh' lignification, like that 

 observed in wood-cells and ducts. It is generally said that the 

 walls of liber-cells are less brittle than those of the elements 

 of wood, and this is commonl}- so ; but there are some flexible 

 wood-elements, and there are, on the other hand, some very 

 brittle fibres of sclerenchyma. The thickening of the wall in 

 liber-cells takes place not only in different degrees, but with va- 

 riations in the amount of infiltration of foreign matters, which 

 give rise to differences in the behavior of the fibres with reagents. 

 In a few cases the inner part of the wall is somewhat gelatinous 



Fig. 65. Fragments of some of the more common bast-fibres used in the arts. '^, 

 a. Flax. Linum ii.'^itatiFsimum. (Wiesner ) 

 6, Hemp, Cannabis sativa. (Scbaebt.) 



c, Jnte, CorchoruH capsnlaris. (Wiesner.) 



d, Cliina-grass, Boelimeria nivea. 



