LESSON 9.] 



VASCULAK TISSUE. 



31 



185. From this point the absorptive process continues, until every 

 particle of ligneous matter is removed from the tube, which is now 



FIG. 51. 



FIG. 50. 



Annular rings. 



FIG. 52. 



Scalariform v 



Old vessel. 



called an old vessel (Fig. 52) ; this either continues permanently 

 empty, or becomes filled with a bundle of woody fibre. 



186. Spiral vessels are nearly round, F IG . 53. 

 annular vessels are more or less com- 

 pressed tubes, but scalariform vessels 



preserve a beautifully symmetrical figure, 

 while an old vessel returns to the origi- 

 nal rounded form. 



187. The figure of the scalariform^ 

 as compared with the annular, vessel, 

 seems to arise from the fact of the annu- 

 lar rings being broken up, and the tube 

 of cellulose readily yielding, between the 

 ligneous particles, to the pressure which 



Uniformly Surrounds it. A beautiful Scalariform vessels, from stem of fern. 



view of Scalariform vessels, from the stem of a Fern, is given in 

 Fig. 53, in which it will be seen that they form groups, of variable 

 size, in the midst of the cellular tissue. There cannot be a finer ex- 

 hibition of these vessels, than a transverse section of the stem of a 

 fern discloses. 



