Abstract:Ligustrum lucidum and Fraxinus chinensis are two species of the major host trees for wax insect (Ericerus pela). From external to internal pets, the bark structure of both species includes periderm, cortex, fibre bundles of primary phloem and secondary phloem. Their sieve tube members eaist with compound or simple sieve plates, and they all contain P-protein and sieve tube scorch. Companion cells arranse in a row or single cell as long as the sieve tube member. The longevity of sieve tube in Ligustrum lucidum lasts 12 months, while in Fraxinus chinensis 8 months at the most. Obvious division of cambia in both species begins in mid to late March, but euds in mid November in Ligustrum lucidum and in late Novembe in Fraxinus chinensis. The differentiation of xylem and phloem of both species begins in mid March,but ends in mid November and late December in Lingustrum lucidum, and in late September and late November in Fraxinus chinensis. In winter, there are partially differentiated sieve elements in phloem of both species. Thais partinlly differentiated sieve elements in Fraxinus chinensis appear in autumn, mature in mid March of next year, and collapse during September and October. In branches of Ligustrum lucidum there is a overwintering and functional zone with average thickness of 170. 2μm in phloem, while the zone in Fraxinus Chinensis only several cell rows thick.