40 ORGANOGRAPHY. 



fibres. DeCandolle has given the following Table of the relatiye 

 strength of some of these fibres as compared with silk, thus: — 



Silk supported a weight of . . . . 34 



New Zealand Flax 23| 



Common Hemp . , . . . . Ifi^ 



Common Flax llf 



Pita Flax 7 



Other fibres brought recently from India and other countries are 

 even stronger than the aboA^e. While woody tissue is thus 

 shown to possess great strength when \ised in the form of what 

 are called fibres, these also, when macerated sufficiently, form a 

 pulp from which paper is chiefly manufactured. 



All articles manufactured from cotton, which is composed of 

 long tubular parenchymatous cells placed end to end, with very 

 thin walls, are by no means so strong as those made fi'om woody 

 tis.'iue. 



The different kinds of woody tissue are commonly associated in 

 the plant with other organs, which are also of an elongated tubu- 

 lar character, but larger than the prosenchymatous cells of which 

 the woody tissues are composed. These constitute the 



3. Vessels or Vascular Tissue. — These names were origi- 

 nally given to these organs from an erroneous idea of their re- 

 semblance to the vessels of animals, with which, however, they 

 have no analogy. The name of duct is also frequently applied to 

 them by authors. There are several varieties of vessels or ducts, 

 the nature of which depends upon the modifications which their 

 walls undergo by secondary deposits in their interior. Thus we 

 have pitted, spired, anmdar, rcticidated. and scalariform dnct.-^, 

 or vessds as we shall in future call them, as more in accordance 

 with general custom. 



a. Fitted or Dotted Vessels. — These constitute '^y their com- 

 bination Pitted Tiss7(,e, the Porous Tissue of some authors, or the 

 Vasiform Tissue, Bothrcnchj/ma, or TapknnchT/ina oi others ; the 

 two latter names being derived from Greek words signifying pits. 

 They either consist of elongated pitted cells with pointed ends 

 (Jig. 25); or, as is generally the case, of a row of cylindrical 

 pitted cells placed end to end, the intervening partitions of which 

 have become more or less absorbed, so that their cavities form a 

 continuous canal (fiffs. 75 and 76). The origin of pitted vessels 

 from a row of cells of a similar pitted nature, is clearly shown 

 in many instances by the contractions which their sides exhibit 

 at various intervals, by which they acquire a beaded or jointed 

 appearance {fffs. 75 and 76) ; for these joints evidently corre- 

 spond to the points where the component cells come in contact, 

 and in some eases even we find the intervening membrane not 

 completely absorbed between the cavities, but remaining in the 

 form of a network or sieve-like partition {fcf. 77). Pitted vessels 



