Explanation:
In Strychnos bredemeyeri small segments of the cambium cease to produce secondary xylem temporarily and produce more phloem centrifugally. A new segment of the cambium differentiates outside to this phloem, which unite with the regular cylinder to form a complete ring by leaving the cambium segment in the furrow. Such repeated activity of cambium results in inclusion of phloem islands within the secondary xylem called intraxylary phloem. Beside interxylary phloem, intraxylary phloem is added from the marginal pith cells.