LIGNIFIED TISSUES 



249 



A 



A 



13 4 5 



Fig. 83. — Diagrams representing various stages in the differentiation of bast 

 fibre in Bcehmeria nivea. (1) Young fibre enclosed by single, closed, 

 tenuous hyaline membrane. (2) Later stage in enlargement of fibre 

 and shows an inner secondary hyaline membrane which originates as an 

 ingrowth of basal portion of primary membrane and grows upward 

 towards the elongating apical portion. (3) Still later stage, showing 

 a number of inner telescoping open tubular membranes, each of which 

 has originated as an ingrowth from the preceding one. (4) More 

 advanced stage of fibre development. (5) Nearly mature fibre. The 

 fibre has practically ceased longitudinal growth and the upper extremity 

 of the first tubular membrane has reached the upper end of the fibre. 

 The walls of the compartments are forming and several successively 

 formed tubular membranes are growing upward within the dilated 

 portions of the fibre. (After Aldaba, Amer. J. Bot.) 



become transformed into cell-wall lamellae. Cell-wall formation 

 may therefore be visualised as a telescoping of a series of succes- 



