76 FIBERS 



the walls of certain bast fibers is related to the greater tensile 

 strength and durability of such elements. 



4. Ontogeny of fibers. Regardless of their location in the 

 plant, fibers arise from initial cells which are very short as com- 

 pared with the length of the mature element. An impressive 

 example of this fact is furnished by Aldaba's (1927) work on 

 fiber development in Bochmeria. In this plant, the fiber initials 

 "are approximately 20 microns in length" and "the increase in 

 the longitudinal dimension of the longer bast fibers is of the order 

 of 2,500,000 per cent, but the process of elongation is gradual 

 and extends over a number of months." The mechanics of the 

 process of elongation in fibers and the accompanying development 

 of a thick secondary wall has attracted much attention as well 

 as speculation. The investigations of Aldaba (1927) and An- 

 derson (1927) on flax fibers have revealed many peculiarities 

 but our knowledge of fiber development in other forms is still 

 meagre. It is apparent that in certain bast fibers, the upper 

 end of the element remains delicate and active during the phase 

 of cell elongation. Whether the necessary adjustment between 

 such greatly extending cells and tiieir neighbors is achieved by 

 "sliding" growth or by "differential" growth, however, is not 

 clear. (Cf. Anderson 1927, Meeuse 1938 and Ilayward 1938, pp. 

 395-400.) The behavior of the protoplast during the growth 

 and differentiation of certain types of fibers offers a number of 

 points of interest. In a recent study, Esau (1938a) has shown 

 that during the elongation of the primary phloem fibers in tobacco, 

 the protoplasts become multinucleate as a result of repeated mi- 

 totic divisions of the nuclei. Cell plates, howevei-, do not form 

 at the end of the successive nuclear divisions and "the spindle 

 fibers are less persistent than in ordinary division figures." At 

 the final stages in fiber ontogeny, usually after secondary walls 

 have developed, the nuclei appear to fuse or clumii and in nearly 

 mature fibers "the nuclear material frequently occurs as one 

 large degenerating mass." The physiological significance of this 

 multinucleate condition in young phloem fillers is quite obscure. 

 Ilaberlandt (p. 154) wiio has observed a multinucleate protoplast 

 in the bast fibers of TAnmn and certain members of the Legu- 

 minosae maintains that "the presence of several nuclei appears 



