BARK— LEAF. 



157 



cellular tissue). They lie next the cambium, and are active 

 in the work of circulation. They belong to the pith- 

 system. 



2. Fibrous cells, sometimes called Bast-cells, though bast 

 is merely a German word meaning the same thing. They 

 belong to the wood-system. In gymnogens, as we know 

 (81), there is little difference between the wood and the 

 barli, though the stem is exogenous in structure. In the 

 fully-developed exogens, however, the liber is composed of 

 fibres much longer, finer, and stronger than those of the 

 wood ; they are also of dazzling whiteness and extreme 

 flexibility. 



The liber abounds in hemp and flax, furnishing the well-known 

 staples. The liber of the linden, or lime-tree (sometimes called bass- 

 wood, a cor- 

 ruption of 

 bast), is 

 used to 

 make Rus- 

 sia matting. 

 The 1 a c e- 

 bark-tree of 

 the West 

 In dies (Fig. 

 230) gets 

 its names 

 from its 

 abundant 

 and exqui- 

 sitely fine 

 liber, al- 

 ready 

 woven into 

 lace in the 



tree, which needs only to be removed and made up into shapes. It is 

 more durable than lace, and more easily laundried. Our leatherwood 

 (Dirca) belongs to the same Order; its liber is made into thongs. 

 These fibrous liber-cells are not essential to the life of the plant. In 

 the beech-bark few fibrous cells are produced after the first year. In 

 the linden and lace-bark they continue, increasing each year by a 

 layer applied to the inner surface of the older liber. They grow 

 longitudinally, like the wood. 



385. Green, or Middle, Bark (Fig. 229, g) is purely cel- 

 lular, full of parenchyma, and abounding in chlorophyl. 

 It does not increase after the first year, and is finally 

 obliterated. 



14 



Fig. 229. — TraiiBverse section of part of a trunk of Cork Oak (Quer- 

 cus Suber), 6 years old; showingGlayeraofwood and 6 layers of cork : 

 m, medulla, or pith; Tns^ medullary- sheath; hiu, heartwood ; nw, new 

 wood, or sapwood ; ca, cambium layer ; 7, liber ; g, green bark ; co, 

 corky bnrk, in 6 layers, 1 for each year; sb, surface-bark, consisting of 

 broken cork-flakes. 



