Fig.
15.3-17. Transverse section of wood of a cactus (Acanthocereus
columbianus). This wood has scanty
paratracheal parenchyma. It is paratracheal because each
parenchyma cell is in contact with a vessel, and it is scanty because it
does not completely ensheath the vessel (arrows indicate three fibers that touch
the vessel). Notice also that this vessel is close to a ray: the water that the
cactus stores in its thick, succulent cortex can travel easily through the ray
and then to the vessel.