132 



SCLERENCHYMA. 



iibreS of Corchorus spec, Abelmoschus tetraphyllus, Sida retusa, Sec'} The thick- 

 ening mass is either continuous, as for instance in most fibres used in manufacture, 

 according to Wiesner ^ or in many . cases provided with narrow pit-canals, which, 

 especially in the fibres associated so as to form bundles, have almost always the form 

 of narrow, rectilinear, longitudinal, or parallel oblique slits like a left-handed screw * 



Fig. 34.— Pteris aquilina. Ahzlfoia. 

 brown-walled sclerenchyinatous fibre 

 from the stem ; B piece of one of these 

 more highly magnified (550) ; p profile 

 view of the slit-like pits ; C transverse 

 section; a limiting lamella; b,c inner 

 layers of the wall. From Sachs' Text- 

 book. 



Fig. 53,— Half of a thick 

 sclerenchyniatous fibre, with 

 crystals of calcium oxalate im- 

 bedded externally in the wall, 

 from the stem of Welwitschia 

 mirabilis. From Sachs" Text- 

 book, 



(Pig- 54)- Still exceptions to this occur in the short fibres, as the simple ones of 

 the Quinine bark, and the branched ones of the leaf of Camellia: here there are 

 narrow canals, not slit-shaped, but round in section. The sclerenchymatous fibres 

 described by Milde * as being spirally thickened, which form a many-layered closed 

 -covering on the upper side and on the nerves of the under side of the leaf of Acro- 

 pteris radiata, would be better described as having slit- like pits. Their membrane, 

 which is thickened till the lumen is almost obliterated, has very numerous, regularly 



' Compare Wiesner, /. c. 



' Mohl, I.e. p. 876.— Schwendener, I.e. p. 8, 



^ Rohstoffe, p. 305. 



' Fjlices Europae et Atlantidis, p. 40. 



