WOODY AND VASCTJLAR TISSUE. 



33 



which are simply open membranous tubes containing spiral 

 fibre lying together in close coils in the tube, or with the coils 

 more or less separated, or broken into rings or bars, hy the 

 elongation of the tube after the formation of the spiral. All 

 these different forms of the spiral deposit may be seen in the 

 common garden balsam, very frequently in the same duct. 

 This form of vascular tissue is called Trachenchyma (trachea, 

 the windpipe), on account of its resemblance in appearance 

 and in functions to the trachea or air-tubes of animals. 



The annexed illustrations are taken from the Botanical Text- 

 Book of Dr. Gray : — 



16. 



Figs. 10. 11. 



12. 



13. 



14. 



15. 



Fig. 10. A simple splial vessel, torn across, with the thread uncoiling. 



Elg. 11. Two such vessels joined at their pointed extremities. 



Fig. 12. A compound spiral vessel, partially uncoiled, firom the Banana. 



Fig. 13. A portion of a duct from the leafstalk of Celery ; the lower part anmJar, 

 the middle retmdated, and the thread at the upper part broken up into short pieces. 



Fig. U. Duct from the Wild Balsam or Jewel-weed ; the coils of the thread distant; 

 a portion forming separate rings. 



Fig. 15. Scalariform ducts of a Fern, rendered prismatic by mutual pressure. 



Fig. 16. Similar duct of a Fern, torn into a spiral band. 



