Fig. 15.3-8a – c. Tangential and transverse sections of a climbing, vine-like cactus (Acanthocereus columbianus). The low magnification tangential section shows that a very high percentage of the volume of this wood is composed of ray cells: this cactus is able to store a large amount of water directly in the wood, close to its vessels. But the high magnification tangential section shows that these ray cells have stained red – they are lignified. This is another of the problems with terminology for wood cells: these are isodiametric cells with thick (but not very thick) lignified secondary walls, so it seems like they should be called sclereids. But their walls are so thin they really have the look of being parenchyma cells, and they remain alive, storing water and starch – something that sclereids do not typically do. We just avoid the terminology problem by using adjectives: these are sclerified ray cells.