Fig. 8.3-2b. Transverse section of phloem in a cactus (Espostoopsis dybowskii; native to Brazil with no common name). Unlike the Melocactus peruvianus in Fig. 8.3-2a, the phloem of this species is trapped between the expanding xylem (below the bottom of the micrograph) and a cap of phloem fibers (such caps are common in plants of many types). As the vascular cambium produces new sieve tube members and companion cells, the old ones collapse and accumulate interior to the fiber cap. Instead of producing a radial strip of collapsed cells as in Fig. 8.3-2, they form tangential arcs of collapsed cells.