88 MORPHOLOGY OF THE CELL. 



Occasionally fibres which arc very ranch branched are met with, 

 notably in the leaves of Camellia, for instance common tea ; see 

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

 ing conspicuous projections into the cavity of the cell ; while 

 some fibres have regular and characteristic markings, a few 



of which are shown in Fig. 65. Septate forms are occasionally 

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

 companies the thickening is essentially lignitication, 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 commonly 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 arta. 

 a. Flax. Linum usitatissimum. (Wiesner ) 

 6. Hemp. CaTinabis saliva. (Schaoht.) 



c, ,Tnte, Corchorus capstans. (Wiesner.) 



d, China-grass, Boehmeria nivea. 



