STRUCTURE.] BARK IS EVASCULAR. 195 



among the liber, the result of which is the throwing off the 

 parts of the bark lying over it as soon as they die. 



So long as the parts of the bark remain alive, they give 

 way to the expansion of the wood within it, by adding new 

 tissue to themselves, as has been already stated : but when 

 they die, they are necessarily torn into clefts, rents, or ribands, 

 as we find in the trunks of trees. 



These statements, taken from the writers above referred to, 

 although valuable as far as they go, by no means lead to satis- 

 factory general conclusions, and demand much more investi- 

 gation. The bark has never, in fact, received the attention 

 which its great importance demands. 



When stems are old, the bark usually bears but a small 

 proportion in thickness to the wood ; yet in some plants its 

 dimensions are of a magnitude that is very remarkable. For 

 instance, specimens of Abies Douglasii have been brought to 

 Europe twelve inches thick, and these are said not to be of 

 the largest size. 



Air cells and Vasa propria are exceedingly common in the 

 bark, but there is no authenticated instance of any spiral or 

 other vessels having been found in it ; except in Nepenthes, in 

 which they occur in almost every part, and exist in no incon- 

 siderable numbers in the bark. 



* * * Liber. 



It will have been seen that the only part of the bark in 

 which woody or longitudinal tissue occurs is the liber or 

 endophloeum. Here it is often very abundant, and exceed- 

 ingly tough and thick-sided ; in consequence of which it is of 

 great value for many useful purposes. When freed from the 

 cellular tissue adhering to it, it is often manufactured into 

 cordage, especially in trees and shrubs of the natural order 

 Malvacea3. The Russia mats of commerce are manufactured 

 from the thin laminae into which the endophloeum of the 

 Lime Tree (Tilia europasa) readily separates. The Lace bark 

 of Jamaica, remarkable for its beautiful lace-like appearance 

 when gently pulled laterally, and for its great toughness, 

 whence it is twisted into whip-lashes, is the laminated liber 

 of Lagetta.lintearia. 



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