164 PART II. VEGETABLE HISTOLOGY. 



spiral ducts are often met with. For example, one end of the 

 duct may possess a spiral, while the other is annulate. 



e. The Reticulate duct is one in which the thickenings take 

 the form of a reticulum or network, as in Fig. 422. Intermediate 

 forms between this and the spiral are also sometimes seen, and 

 gradations occur between this and the dotted duct. 



f. The Trabecular duct is a rarer form, in which the thick- 

 enings cross the lumen of the cell. On either side of the 

 central fibro-vascular bundle in the leaf of the common Juniper 

 occur tracheids having thickenings of this character. Fig- 

 423 represents some of them as they appear in transverse sec- 

 tion, and Fig. 424 some of the same in longitudinal view. 



(10) Hard Bast or Liber fibers. These consist of greatly 

 elongated, usually taper-pointed, but sometimes forking or spar- 

 ingly branching, very thick-walled, tough and flexible cell-deriv- 

 atives. Their walls, when mature, are strongly lignified, fre- 

 quently unequally thickened, and often marked wiih delicate, 

 oblique, slit like markings. They are usually more highly refrac- 

 tive and lustrous than wood-fibers, and with saffranin stain a 

 brighter rose-red ; they are also, in the majority of cases, rela- 

 tively longer and thicker walled. Occasionally, though not 

 commonly, transverse septa may be observed in them, as in some 

 wood cells, dividing the narrow lumen into two or more com- 

 partments, and not uncommonly they may be observed to con- 

 tain crystals of mineral matter. 



Bast fibers proper constitute the tough and stringy tissues in 

 the liber or inner bark of Dicotyledons, such as the Bass-wood. 

 Flax and Leatherwood. The value of Flax for the production 

 of textile fabrics depends upon the presence of these fibers. 

 See Figs. 425 and 426. 



Though bast fibers, in the strict sense of the term, are con- 

 fined to the bast or phloem portion of fibro-vascular bundles, 

 fibers structurally indistinguishable from them often occur else- 

 where in the plant. Examples of these are the masses of brown 

 fibers found in the fundamental tissues of some Ferns ; the 

 isolated and very irregular, often branching, fibrous cells found 

 in the parenchyma of some leaves, as those of the Tea-plant; 

 the fibrous tissue that surrounds and strengthens some fibro 

 vascular bundles, as those of Maize ; the strengthening cylinder 



