250 BOTANY 



sively-formed tubular membranes within an elongating closed 

 tubular membrane. 



The bast fibres of Linum usitatissimum were also investigated 

 by the same inethod. Although less extensive in length than those 

 of Bcehmeria, the mode of formation was found to be very similar. 

 The first-formed basal telescoping membranes originate in the 

 basal extremity of the cell and grow upward, ultimately reaching 

 the apical end of the fibre. 



The phenomenon of cell wall formation in bast fibres of both 

 Boehmeria and Linmn obviously cannot be accounted for solely on 

 the basis of the theories of apposition and intussusception. The 

 growth of successive telescoping tenuous membranes, which sub- 

 sequently differentiate into cell wall lamellae, is more suggestive of 

 transformation. The phenomenon of growth and differentiation 

 in the bast fibres of these plants raises the question of whether 

 the mode of formation of cellulose walls is fundamentally similar 

 in all types of plant cells. In other words, is the cell wall formed 

 in all cases by the continued growth and transformation of the 

 plasma-membrane ? It should be noted in this connection that 

 it is not essential to assume that the successively-formed portions 

 of the plasma-membrane arise invariably by a telescoping process, 

 since the latter phenomenon may be a specialised one, only 

 characteristic of certain types of elongated cells. 



The statements regarding the nature of flax fibre are very 

 conflicting, and the whole subject of the chemistry and formation 

 of these fibres has recently been reinvestigated by Anderson. 

 The work was mainly carried out with fresh sections, cut freehand 

 from the plant, and microchemical tests were applied for the 

 identification of the cell wall material in situ. 



An important method of studying the fundamental structure of 

 the cell wall was also worked out. The flax fibre was placed on a 

 slide in a 1 per cent, solution of iodine in potassium iodide and 

 50 per cent, sulphuric acid slowly added at the side of the cover- 

 slip. Marked swelling of the cellulose wall of tlie fibre now 

 occurred. When the fibre reached the swollen condition, the 

 cover-slip was pressed down immediately over the fibre with a 

 needle, and considerable enlargement of the fibre took place, thus 



