FIBRES. 



131 



into account in the statements of average, which require confirmation throughout. 

 The published measurements of simple bast-fibres give for the shortest forms, such as 

 those of Peruvian bark, a relation of about 1:10 to i : 20 ; for the longest, found 

 among the Urticacese, a length exceeding the greatest breadth two or three thou- 

 sand times (to i : 4000). The branched forms are as a rule relatively short and 

 broad, e.g. Fig. 53, but much-elongated specimens also occur. 



As examples we may cite the following few measurements found by Mohl ^ and 

 Wiesner", and in the Quinine bark by VogF, for fibres of bast and bundles; for 

 further details we must refer to Wiesner's summary. I.e. Where only the length is 

 given, the medium of the measurements of breadth given may serve as the breadth. 



The considerable length of many fibres, together with the occurrence of. the 

 chambered fibres to be described below, has given rise to the view that a fibre does 

 or may arise by the coalescence of several meristematic cells disposed in a longi- 

 tudinal series '- More exact investigation however can find a priori no sound ground 

 for this, and all minute observations have shown that each simple or branched 

 fibre results from the metamorphosis of one cell ^. 



The wall of the sclerenchymatous fibres is thickened to an extent which differs 

 according to each special case, and usually so that the lumen is greatly reduced 

 (centripetal) ; the thickening mass is nearly equally thick all round, or in many cases 

 it projects inwards much more strongly at certain points than at others, e.g. bast- 



• Bolan. Zeitg. 1855, p. 876. 



° Mikroskop. Untersuchungen im Laborat. d. polyt. Inst. Wien ; and Rohstoffe, d. Pflanzen- 

 reichs, cap. 11. 



' Die Chinarinden des Wiener Grosshandels, &c. 1867. 



* Meyen, in Wiegmann's Archiv, 1838, 1, p. 297.— Schacht, in Berl. Acad. Monatsber. 1856, p. 

 517: Lehrb. II. p. 567. — Hanstein, Milchsaftgef. p. 45. 



= Compare Unger, Wachsthum d. Stammes u. Bildg. d. Bastzellen, Wiener Acad. Denkschr. 

 Bd. XVI; Boehra, Wien. Acad. Sitzungsber. Bd. 53; Sanio, Botan. Zeitg. i860, p. 210. Further, 

 the statements in Chapter VII upon the intercellular fibres of the Aroidese, and Chapter XIV. 



K 2 



