LACK OF ANNUAL PERIODICITY IN CAMBIAL PRODUCTION OF PHLOEM IN TREES FROM MEDITERRANEAN AREAS

Annual periodicity of cambium production of xylem and phloem cells has rarely been compared in trees from different environments. We compared the structure of cambium and the youngest xylem and phloem increments in four tree species, Fagus sylvatica, Picea abies, Pinus sylvestris and Pinus halepensis, from nine temperate and Mediterranean sites in Slovenia and Spain. In Picea abies, Pinus sylvestris and Fagus sylvatica from temperate locations in Slovenia, xylem and phloem growth ring boundaries could be identified. In Fagus sylvatica growing at two elevations on Moncayo mountain, Spain, phloem increment consisted of only early phloem. In Pinus sylvestris from the same two sites, growth ring boundaries were not as clear as in temperate Slovenian sites. In some cases we could identify phloem growth ring boundaries but in others it was very doubtful, which could be explained by collapse of the outermost early phloem sieve cells. In Pinus halepensis from all sites, we could only distinguish between collapsed and non-collapsed phloem, while phloem rings could not be identified. Widths of the youngest phloem and xylem annual increments could only be compared when phloem increments could be clearly defined, as with Picea abies, Fagus sylvatica and Pinus sylvestris from temperate sites. The visibility of the growth ring boundary in phloem was not related to the width of annual radial growth. The correlation between xylem and phloem ring widths was high, but moderate between the number of dormant cambial cells and xylem ring and phloem ring widths. Based on the structure of the youngest phloem increments, we concluded that there is no typical annual periodicity in cambial production of phloem cells in trees from certain Mediterranean sites. This may be due to continuous yearlong cell production and the absence of true cambium dormancy, at least on the phloem side, under mild winter conditions.

The Measurement and Process of Aeroengine Inlet Total Pressure Field

It’s important to measure inlet total pressure field for aeroengine. Firstly, test scheme is discussed. Three pectinate total pressure probes, which can be rotated with an additional straight ring segment around the engine axis, are used to measure the total pressure field. The radial distribution of test points is designed via Tchebycheff integral method. Radial average and circumferential average are calculated according to the field data via area averaging method. At last the total pressure field is visualized via mapping the data to colors. Test results show that the total pressure distribution in main airflow is evener than that in boundary layers and the thickness of inner and outer ring boundary layer can be estimated.

Microcracks Occurring During Drying Visualized by Confocal Laser Scanning Microscopy

The microcracks occurring during drying of wood were visualized under confocal laser scanning microscopy (CLSM). Precise control of relative humidity and temperature in a specialized environment chamber made it possible to acquire sequential images of the wood of Cryptomeria japonica during drying from the water-saturated condition. The images indicated that the microcracks occurred between tracheid and ray parenchyma in the latewood region and the crack tip advanced in both the bark and pith directions. Subsequently, the crack tip expanding towards the bark stopped at the earlywood region through the growth ring boundary. The other tip toward the pith stopped at the earlywood region before reaching the growth ring boundary. Our technique made it possible to generate microcracks and discuss the relationship between moisture content and microcrack formation during drying. We found the CLSM technique to be an effective method for visualizing microcrack propagation with time.

BIFURCATIONS IN DYNAMICS OF SHEPHERD SYSTEMS

A small moon orbiting near the edge of a ring of particles can act as a "shepherd", keeping errant ring particles from drifting away and keeping the ring boundary sharp. This phenomenon was predicted before it was observed [Goldreich & Tremaine, 1979] and has been successfully modeled by many authors, see [Murray & Dermott, 1999]. In this paper we focus on the bifurcations that occur in the motion of a ring particle as the mass of the moon and the distance between orbits of the moon and the particle are adjusted.

INTERVASCULAR PITTING ACROSS THE ANNUAL RING BOUNDARY IN BETULA PLATYPHYLLA VAR. JAPONICA AND FRAXINUS MANDSHURICA VAR. JAPONICA

The structure of intervascular pits, located at the boundary between the outermost and the second youngest annual rings in Betula platyphylla var. japonica and Fraxinus mandshurica var. japonica was examined by field-emission scanning electron microscopy. Unilaterally compound pits were present in the intervascular common wall at the annual ring boundary in both species. On the outer annual ring side of the unilaterally compound pits, outlines of pit membranes were curved or trifoliate, and each pit aperture was often elongated and curved. The porosity of the intervascular pit membranes differed between the two species. In B. platyphylla var. japonica, microfibrils were loosely packed in the peripheral region of each pit membrane, and openings of up to 300 nm in width were observed. By contrast, microfibrils were densely packed throughout the entire pit membranes in F. mandshurica var. japonica, and no openings perforating the pit membranes entirely were found. In addition, each species exhibited some unique features. In B. platyphylla var. japonica, extensive ethanol-soluble material was detected not only in the intervascular pits but also on scalariform perforation plates. In F. mandshurica var. japonica, we observed fine curly fibrils of unkown chemical composition in the intervascular pit membranes.

CONDUCTIVE FUNCTION OF INTERVESSEL PITS THROUGH A GROWTH RING BOUNDARY OF MACHILUS THUNBERGII

Vessels in some species are connected by intervessel pits on the tangential walls of radial multiples, which may allow the radial flow of sap. This network was investigated in Machilus thunbergii Sieb. et Zucc., a diffuse-porous wood with radial multiples extending through growth ring boundaries. Air permeability measurements suggest radial flow paths exist through a growth ring boundary. Flow paths were pressurestained with reduced basic fuchsin solution. Observations of serial cross sections confirmed the flow paths to be via vessels and intervessel pits in radial multiples of vessels on growth ring boundaries. Resin casts of low-density polyethylene, viewed by scanning electron microscopy, showed the vessel network extending through a growth ring boundary as well as the branching of vessels.