| Two species of Rhamnus: Rhamnus davurica and Rhamnus ussuriensis were used as experimental materials,their phenological periods and habitats were investigated.The anatomical structures of vegetative organs of two species were systematically studied by paraffin section,three-cut wood,wood segregation and scanning electron microscope.The differences in the structural evolution of the two species were observed,and the relationship between structure and environment was analyzed,in order to provide anatomical basis for the wood identification and development and utilization of Rhamnus species in the future.The results were as follows:(1)The results showed that the leaf-unfolding period of R.davurica was similar to that of R.ussuriensis,while the bud bursting,flowering,fruiting,and deciduous periods were all later than those of R.ussuriensis.R.davurica mostly growed in the hillside forests,dark and moist places of shrubs or forest borders and ditch edges;while R.ussuriensis mostly growed in the riverside,mountain forests or hillside shrubs.(2)The leaves of R.davurica and R.ussuriensis were bifacial leaf,and the type of stomata was irregular.The shape of epidermal cells was irregular,the upper epidermal cell anticlinal walls of R.davurica had the inlaid G type while the lower epidermal cell anticlinal wall had the inlaid D type.The upper epidermal cell anticlinal walls of R.ussuriensis had the inlaid A type while the lower epidermal cell anticlinal walls had the inlaid G type.The palisade tissues of both the two species had two layers,and the spongy tissues were loose.Comparing with R.davurica,the palisade tissues of R.ussuriensis were more developed.The main veins of the leaves of R.davurica and R.ussuriensis were well-developed and consisted of mechanical tissues,ground tissues,and vascular bundles.The vascular bundles of leaves were open collateral vascular bundles with semilunar shape.The xylem was close to the adaxial side,while the phloem was close to the abaxial side,and there was a weak cambium zone between them.The vascular bundles of R.ussuriensis were surrounded by large number of exotic tannin cells,druses,and a small number of mucous cells.There were cellular gaps between the cells near the abaxial side,forming aerenchyma,which had a strong resistance to corrosion,drought,and cold.Only a few druses and mucous cells were distributed around the vascular bundle of R.davurica,and the resistance to corrosion and cold was weak,but the resistance to drought was strong.The petioles of R.davurica and R.ussuriensis were composed of epidermis,ground tissues and vascular bundles.The transverse sections of the petioles of both species were nearly round and concave in the middle.The epidermal cells were oval,closely arranged,and covered with epidermal hair.The epidermis of R.davurica had outer epidermal hair,while that of R.ussuriensis had no epidermal hair.The vascular bundles in both species were open collateral vascular bundles,which were composed of the xylem,cambium zone,and phloem in a semicircular arrangement.The xylem vessel molecules of R.ussuriensis were abundant and tightly arranged,while the xylem vessel molecules of R.davurica were fewer in number and loosely arranged.A large number of exotic tannin cells and a small number of mucous cells and druses were distributed in the petiole of R.ussuriensis.There were no exotic tannin cells in the petiole of R.davurica,but only a small number of mucous cells and druses.(3)Anatomical structure of the stems: the stem primary structures of both R.davurica and R.ussuriensis were composed of the epidermis,cortex,and vascular cylinder.The epidermis consisted of oval cells with a single layer,tightly arranged and surrounded by the cuticle.The cortex was located on the inner side of the epidermis,between the epidermis and the vascular cylinder.It had multiple layers of cells with tightly arranged thick cell walls.The outer side of the cortex was the thick collenchyme with 3-4 layers.There were 6-8 layers of parenchyma cells in the mediopellis of the primary stem of R.davurica and 8-10 layers of parenchyma cells in the mediopellis of the primary stem of R.ussuriensis,but the inner cortex of the two species was not obvious.The vascular cylinder of the primary stem of the two species consisted of three parts: vascular bundle,pith,and pith ray.The vascular bundle of the two species was the open collateral vascular bundle,which consisted of the primary xylem and fascicular cambium and primary phloem.The development type of the primary xylem was endarch.3-5 vessels of the primary stem of R.davurica lied in a row,and each vascular bundle had 2-5 rows of pore chains.3-4 vessels of the primary stem of R.ussuriensis lied in a row,and each vascular bundle had 2-6rows of pore chains.The main vessels in the primary stems of the species were the annular vessel and spiral vessel.R.davurica and R.ussuriensis had well-developed pith,compose of nearly round parenchyma cells,with the largest cells in the center and strong resistance to drought.The stem secondary structures of R.davurica and R.ussuriensis were composed of periderm,secondary vascular tissue,and pith.The periderm was brown and consisted of the cork layer,phellogen and phelloderm.Lenticels were distributed on the periderm.The secondary vascular tissues consisted of the secondary phloem,vascular cambium,secondary xylem,and vascular ray.In the secondary xylem of the stem,the vessels were mostly the multiple pore type and pore clusters.The vessels of the secondary stem of R.davurica were spiral vessels.The vessels in the secondary stems of R.ussuriensis were the pitted vessel and the spiral vessel,and there were oval-bordered pits on the walls and the pits were elliptic shaped.The secondary stems of the two species were ring-porous wood with obvious growth rings,which were composed of vessels,tracheids,wood rays,wood fibers and wood parenchyma cells.The pith was well-developed and consisted of tightly arranged hexagonal parenchyma cells.The wood rays of R.davurica and R.ussuriensis were all heteromorphic type II,and the ray cells were composed of horizontal and vertical cells.(4)Anatomical structure of the roots: the root primary structure of both R.davurica and R.ussuriensis consisted of three parts: epidermis,cortex,and stele.The epidermal cells had 1 layer and a tight arrangement.The cortex was composed of the outer cortex,cortical parenchyma cells and inner cortex.The cortex of the primary root of R.davurica had 6-7 layers,while that of R.ussuriensis had 5-7 layers.The stele consisted of the pericycle,primary xylem,primary phloem,and parenchyma cells.The primary xylem was interspersed with the primary phloem.The primary xylem of R.davurica was tetrarch,while that of R.ussuriensis was diarch.The development type was both external.The root secondary structures of both the two species were composed of the periderm,cortex,secondary phloem,cambium zone,secondary xylem,and rays.The periderm was brown and consisted of the cork layer,phellogen,and phelloderm.The vessels of secondary roots of the two species were pitted vessels,and there were marginal pits on the tube walls.The pits were oval shaped.The growth rings of secondary roots of the two species were blurred,which were composed of vessels,tracheids,wood rays,wood fibers and wood parenchyma cells.The vessels were mostly solitary pore type,and the pores were round.The wood rays in the secondary roots of both species were heteromorphic type II,and the ray cells were composed of cells of horizontal and vertical types.In conclusion,in the same environment,there were many differences in the structure of the two species,and the two species had adaptability to the arid environment.In the process of evolution,R.ussuriensis showed more developed,while R.davurica presented to be more primitive. |
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