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.