22 



DKSCRIPTIVE BOTANY. 



length. When the stems of the Plantain and Banana 

 are cut into slices, the tracheae in which they abound 

 unravel before the edge of the knife, and form floc- 

 culent masses, which may be collected, and wrought 

 into a material possessing certain advantages superior to 

 those of cotton, for the manufacturer. The expense, 

 however, of collecting this delicate substance has been 

 found too great to admit of its being applied to any 

 really useful purpose ; as an entire plantain does not 

 yield above a drachm and a half of tracheae. 



Tracheae have been detected in a very few of the flower- 

 less plants, and only among the higher tribes of them, 

 such as ferns and club-mosses. 



(24.) Ducts. The elementary fibre divides and 

 ramifies on the inner surface of some tubes which com- 

 pose the vascular, just as it does on the vesicles which 

 compose the cellular tissue (art. 18.), and forms linear, 

 dotted, and reticulated markings upon them. Some 

 tubes are true trachea? in one part of their course, 

 whilst in another the fibre becomes ruptured at intervals, 

 and the detached portions, uniting at their extremities, 

 form rings ; and where the ruptures are more fre- 

 quent, these fragments of the fibre present linear and 

 dotted markings adheriug to the surface, and following 

 a spiral course (fig. 13.). 

 The name of ducts, is gene- 

 rally given to all varieties of 

 tubes composing the vas- 

 cular tissue, which are not, 

 strictly speaking, true trachee; 

 and they are separately named 

 according to the appearances 

 which the markings on their 

 surface assume ; such as 

 dotted,striped, and reticulated 

 ducts. Some authors, how- 

 ever, include all the marked 

 tubes, together with the spi- 

 ral vessels, under the general 



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