44 



THE ELEMENTARY STRDCTUEE OF PLANTS. 



i ' 55. Bast Tissue, or Woody Tissue of the Liber. The hast or 5ass, 

 fibrous inner bark, or liber, as it is variously termed, of those plants 

 that have a true bark separable from 

 the wood of the stem, usually consists of 

 or contains much longer, very thick-sided, 

 and tougher, but more soft and flexible 

 cells, than those of the wood itself. These 

 properties are " probably given them that 

 they may possess the strength, combined 

 with flexibility, which their position near 

 the circumference of a branch renders 

 necessary." These especially adapt them 

 to the useful purposes they so largely 

 subserve for clothing and cordage. The 

 textile fibres of flax, hemp, &c. are all de- 

 rived from this woody tissue of the bark, 

 separated from the brittle cells of the 

 wood itself, and freed from the surround- 

 ing thin-sided parenchyma by macera- 

 tion (which soon decomposes the latter) 

 and by mechanical means.* The length 

 of bast-cells as compared with wood-cells 

 is exemplified in the accompanying figures 

 of the two, from our Basswood (Fig. 49 

 — 51). The difference in the thickness 

 > of the walls in this case is also great ; the cells of the soft wood hav- 

 ing rather thin waUs even when old (Fig. 52), while those of the 



* Cotton differs from linen in many respects, and is of a Tcry different origin. 

 It consists of hairs, or long tubular cells, growing on the seeds of the plant. 

 These have very thin walls, which collapse so that the tube flattens, and then 

 twists spirally, which gives them a peculiar adaptation to be spun, or drawn out 

 together by torsion into a thread, contiguous fibres thus moderately clinging to 

 each other as they are drawn out. But they have not such thick and tough 

 walls as liber-cells ; so a cotton fabric is not so heavy nor so durable as linen. 



FIG. 49. Ono bast-cell, and part of another, from the bark of American Basswood. 50. 

 Some woody tissue from the wood of the same, with, a, upper end of a spirally-marked duct. 

 51. A separate cell from the wood. All magnified to the same degree. 



PIG. 62. Transverse section of some wood-cells of the Basswood, highly magnified. 63. 

 Similar section of some bast-cells from the bark of the same tree, equally magnified. 



no. 64, 55. Ends of bast-cells from the bark of the Leather-wood (Dirca palustris), mag- 

 nified. 



