LINUM USITATISSIMUM 399 



flax fiber. Aldaba states that these may be formed by transforma- 

 tions of successive telescoping hyaline membranes which later 

 differentiate into cell wall lamellae. According to this explana- 

 tion, the lamellae are initially formed as a series of tubular mem- 

 branes which overlie one another. Each successively formed mem- 

 brane arises at the base of and centripetal to the previous one, 

 growing upward toward the tip of the elongating fiber. These 

 hyaline structures resemble plasma membranes, and are gradually 

 transformed into lamellae which become thickened by a process 

 suggestive of intussusception. 



Anderson's explanation of the formation of the secondary layers 

 agrees in many respects with that of Aldaba (i). He notes, that 

 the first evidences of deposition of the lamellae occur at the basal 

 portion of the fiber following the period of rapid elongation, that 

 these layers are in contact with the remainder of the wall at only a 

 few points or not at all, that the first cellulose deposited is much 

 hydrated and in a state of viscosity that seems almost gelatinous, 

 and that there is evidence to indicate that the wall formation 

 actually occurs in the living cell free from adjacent walls of the 

 same cell, later becoming coherent with them. 



The process of secondary wall thickening is not a uniform one in 

 which there is a steady increase in the thickness of the wall, but 

 takes place as a series of periodic additions of new layers of cellu- 

 lose. Each additional increment is deposited by the protoplast and 

 appears in a transectional view of the fiber as a much involved and 

 wrinkled layer which is apparently in contact with the previously 

 formed secondary wall only at widely separated points or in some 

 instances not at all. Later, it is pushed closely against this wall, 

 but it does not adhere to it nor is there any welding material 

 between them. The lamellae can be separated from one another, 

 which indicates that they are not cemented together and empha- 

 sizes their independent origin. The force which causes the flatten- 

 ing out of the infolded layers is probably turgor pressure; and as a 

 result of its action, the secondary wall loses its wrinkled appear- 

 ance and becomes firm and more rigid. (Fig. i03, E-G.') Several 

 lamellae are added in this manner, but they are not laid down with 

 regularity and the number varies in different fibers. 



The secondary wall is usually divided into two to five major 

 layers, and these in turn may consist of many minute lamellae. 

 The lines marking the limits of the major layers, as well as those 



