274 



A TEXT-BOOK OF BOTANY. 



RETICULATED TRACHEAE, and those with spherical or oblique slit 



pores are known as POROUS TRACHEAE or vessels (Figs. 142-144). 



In those vessels in which but few of the transverse walls are 



obliterated, the walls are marked by both simple and bordered 



- @g u 



FIG. 144. Types of tracheae or vessels. A, vessels with annular and spiral thickenings 

 in Phlox Carolina; B, longitudinal section through fibrovascular bundle in aconite, showing 

 porous (p) and spiral tracheae (t), bast fibers (b), and some of the collenchyma cells (c) ; 

 C, longitudinal section showing reticulate tracheae in scopolia; D, longitudinal section of 

 the woody part of the rhizome of Spigelia, showing tracheae (t), tracheids (h), tracheae (r) 

 with yellowish-brown, gum-like masses; E, portion of xylem of stem showing in Hyos- 

 cyamus tracheae (t) with bordered pores and wood fibers (w), with simple oblique pores. 



.pores, which latter are described under tracheids. Vessels contain 

 water, water-vapor, and air ; in some cases they contain sugar, 

 tannin, mucilage, or resin. 



