396 THE STRUCTURE OF ECONOMIC PLANTS 



While some investigators have expressed doubt regarding the 

 second type of growth, critical experiments by Tammes (ii) indi- 

 cate that as the stem increases in length, there is also an increase 

 in fiber diameter. This increase does not occur at a uniform rate, 

 being much more rapid in the initial stages of fiber development 

 than during the later phases of maturation. She found that as the 

 stem increased from i mm. up to a h:^ight of 77 cm., the average 

 diameter of the fiber increased from 11.6 ^ to 31.0 /-i. Anderson (x) 



a b c d e f g h i j k 



Fig. 2.02.. Semi-diagrammatic longisection of portion of nearly mature flax stem : a, pith 

 cells including thick-walled connective cells adjacent to xylem; b, protoxylem elements and 

 xylem parenchyma ; c, metaxylem ; d, secondary xylem ; e, cambium ; /, phloem zone in- 

 cluding secondary and primary phloem ; g, pericyclic fibers ; h, endodermis ; /, chloren- 

 chyma ; /, hypodermis ; k, epidermis. 



compared measurements of young and mature fibers and concluded 

 that developmental increases in fiber size were not common for all 

 fiber cells, occurring more conspicuously in some than in others. 

 He states that there is no doubt but that fibers do undergo "a slow 

 increase in diameter during their development until the time that 

 deposition of cell-wall material ceases." 



The length and diameter which the fiber attains are variable, 

 depending upon variety and cultural conditions. Diameters range 

 from IX to X5 m- Matthews (15) and Cross and Bevan (8) have 

 reported average lengths of 15 to 30 mm., Haberlandt (9) lo to 

 40 mm., Wiesner (2.7) xo to 50 mm., Herzog (10) 1.7 to 53.9 mm.. 



