LINUM USITATISSIMUM 397 



and Tammes (ii), extremes of i to ixo mm. with averages approxi- 

 mating those of other investigators. The extreme lengths of the 

 individual fiber cells are based upon their continued independent 

 growth. Tammes (ii) points out that the pericyclic cells which 

 differentiate into fibers do not undergo any transverse division, 

 or at least not as frequently as adjacent cells, and continue to 

 elongate without cross wall formation. This general growth 

 proceeds until the basal portion of the cell is below the region of 

 axial elongation of the meristematic portion of the stem tip, 

 and then that part of the fiber ceases to elongate, further increase 

 in length being restricted to the upper portion of the fiber. Theo- 

 retically, the pericyclic cell may continue to elongate as long as the 

 adjacent cells are dividing transversely and the axis in that locus 

 is undergoing internodal elongation; but, actually, there are 

 occasional transverse divisions. In connection with secondary 

 wall thickening, there may be a peculiar separation of portions of 

 the protoplast by secondary layers of cellulose which results in local 

 dilations in the fibers. (Fig. 2.03, D, 1-4.^ 



In addition to the method of fiber elongation described by 

 Tammes (2.1), Anderson (2.) believes that there is a sliding action 

 by which the tips of the elongating pericyclic cells push past one 

 another. It seems likely that this phase of elongation accompanies 

 general cellular enlargement. The tips of the fibers are not trans- 

 verse, but taper gradually to a very acute point, and the length of 

 the tapered portion of the fiber may indicate the approximate 

 amount of sliding that has occurred. (Fig. 2.03, D, /.) 



Growth and Wall Formation of the Fiber. — The wall 

 structure of the flax fiber has been the subject of intermittent inves- 

 tigation since Nageli (16) observed the concentric lamellae and 

 alternating light and dark bands in its secondary walls. Subse- 

 quently, Krabbe (14), Correns (6), Tammes (ii), Nodder (17), 

 Aldaba (i), Anderson (i), and others have each added something 

 to an understanding of fiber structure and development. 



The middle lamella consists of pectic materials deposited by the 

 split halves of the cell plate when wall formation is initiated. Her- 

 20g (11) and others interpret it as being intercellular substance, 

 applying the term primary wall to the first deposits of material 

 against the middle lamella and using the term secondary wall in 

 referring to the lamellated structures deposited later. (Fig. 103, 

 A-C.^ There has been some confusion in cell wall terminology 



