Earlywood Vessels Research Articles

FLUID FLOW IN THE OUTERMOST XYLEM INCREMENT OF A RING‐POROUS TREE, ULMUS AMERICANA

Hydraulic conductivity through the outermost growth ring of Ulmus americana was quantified to determine the significance of this single growth increment to fluid flow in xylem of a ring‐porous tree. Gravity flow rates through trunks deprived of the outermost growth ring dropped to 8% of the rate achieved in control trunks whose cross section was intact. However, colored dye, fed through stem segments, appeared in up to 4‐yr old wood, corroborating earlier reports that fluid flows through more than just the outermost growth ring of ring‐porous trees. Finally, the pathway of flow through older rings was shown to consist of narrow latewood elements while the wider and more hydraulically significant earlywood vessels came into play only in the outermost growth ring of U. americana. These data indicate that the outermost growth ring of Ulmus is responsible for over 90% of xylem transport in this ring‐porous tree, because wide earlywood vessels function only for one growth season.

Wood Anatomy of the Styracaceae: Evolutionary and Ecological Considerations

Woods of over 40 species representing nine genera of Styracaceae were studied. Features present in most taxa include growth rings, diffuse porosity, combinations of both solitaries and pore multiples, exclusively scalariform perforation plates, opposite to alternate intervessel pitting, imperforate tracheary elements with indistinctly bordered pits, both uniseriate and multiseriate heterocellular rays, and axial parenchyma distributed as a combination of diffuse, diffuse-in-aggregates, and scanty. Prismatic crystals occur in species of the genera Bruinsmia, Halesia, and Styrax, and silica is present in a few Neotropical species of Styrax. The characteristic solitary pore distribution and high scalariform perforation plate bar number of Huodendron are of potential evolutionary significance. The xylem of Lissocarpa differs from the Styracaceae in possessing more highly evolved vessel elements with both simple and scalariform perforations and prominently banded axial parenchyma. The occurrence of simple perforation plates in the wider, earlywood vessel elements, along with an increased pore frequency and decreased vessel element length, in Styrax platanifolius and S. texanus is documented. Both species inhabit seasonally dry habitats of the southwestern United States, thus supporting similar specialisations observed in other plants growing in xerophytic conditions. The apparent variation in perforation plate condition within different geographic varieties of S. officinalis is discussed. Significant correlations of wood anatomical characters and latitude of provenance are present among species of Styracaceae. Increasing latitude is strongly correlated with increased pore and multiseriate ray frequency, and decreased vessel element length and wall thickness. Increasing latitude is less strongly correlated with an occurrence of decreased pore diameter, increased bar number per perforation plate, increased fibre-tracheid and intervessel pit diameter, and increased frequency of uniseriate rays. Weak correlations are also evident between increasing latitude and shorter ray height and narrower, shorter, and thinner-walled fibre-tracheids.

Improved Trunk Injection for Control of Dutch Elm Disease

Conventional preventative injections into healthy trees overlook the properties of elm's ring-porous wood. The new injector described here forces fungicide into the large earlywood vessels of the outermost growth ring. Only these vessels can conduct fungicide to the entire tree. Older vessels, tapped by conventional injectors actually reduced spread of injected fluids in the outer growth ring in our dye experiments. Of the 55 elms treated with Lignasan by our method for three years, none developed disease symptoms while 11 of the 15 control trees in the same area died.

Xylobolus frustulatus Decay of Oak: Patterns of Selective Delignification and Subsequent Cellulose Removal

Xylobolus frustulatus caused a distinct pocket rot in decorticated oak. Polymerization products appeared to accumulate in advance of delignified wood to form barriers to decay. Medullary ray parenchyma and earlywood vessels were not readily degraded and remained between pockets of decay. Chemical analyses indicated that 97% lignin, 96% xylose, and 69% mannose were removed from pockets of wood during incipient decay. Although 53% of the cellulose was removed from these areas, the remaining white tissues were composed of relatively pure cellulose. Hyphae became abundant as the released cellulose was subsequently removed. In the most advanced stages of decay, hyphae were absent from pockets, and only a sparse lining of crystals, found to contain a high concentration of calcium, remained.

Vessel Grouping in Dicotyledon Wood

A hitherto unappreciated correlation exists between nature of vessel grouping and nature of imperforate tracheary elements in wood of dicotyledons at large: families and genera with true tracheids (large fully bordered pits common on both radial and tangential walls) have solitary vessels. Presence of true tracheids as a subsidiary conductive system is hypothesized to render vessel grouping a superfluous adaptation. Vessel grouping does occur to various degrees in taxa with fiber-tracheids or libriform fibers; the degree of grouping is related to likelihood or seriousness of vessel failure by air embolisms because of either drought or frost. Grouping of vessels is regarded as a way of providing alternate conduits whereby water can be carried in the same pathways in case one or several vessels in a group are incapacitated by air embolisms. Presence of vascular tracheids, if sufficiently abundant, is held to be correlated with smaller degree of vessel grouping because vascular tracheids can form a subsidiary conductive system; small numbers of vascular tracheids do not affect vessel grouping patterns. Species which possess vasicentric tracheids possess a subsidiary conductive system ideally located around vessels and have solitary vessels or else (ifvasicentric tracheids are less common) a low degree of vessel grouping. Species with very large vessels at the beginning of growth rings tend to have little grouping in the earlywood vessels but more grouping in latewood vessels; this dimorphism is held to relate to enhanced safety oflatewood vessels, since earlywood vessels have little safety and the latewood is thereby the wood portion where safety mechanisms are concentrated. Fiber-tracheids do not have sufficient conductive capabilities to form a subsidiary conductive system; borders on pits of fiber-tracheids are rapidly lost during evolution, and such loss generally pr~cedes appearance of septate or nucleated conditions or is simultaneous with it. Relative selective value of the various vessel grouping types (clusters, radial multiples, diagonal bands, tangential bands) as well as of larger aggregations remains a topic for more investigation, as does significance of grouping of primary xylem vessels.

Ultrastructural cell wall modifications in secondary xylem of American elm surviving the acute stage of Dutch elm disease: vessel members

Modified vessel wall layers and their ultrastructural characteristics in branches of artificially inoculated elm (Ulmus americana L.) trees surviving the acute disease stage and of naturally infected, chronically diseased trees are described. Walls of large early-wood vessels in zones where disease action was prevalent have a strong stain reaction and may be uniformly or locally three to four times thicker than normal.In smaller vessels (some including vessel tracheids), an extra lignified-like, often discontinuous layer may be present. This layer is generally demarcated from the normal by a dense band. Pit membranes and vessel end plates are likewise much thickened through the presence of an opaque material similar to that of the pit membrane. This material differs from that forming the coating layer which like tyloses is generally present inside the thickened or extra vessel wall layer.The possible significance of these observations, particularly in relation to disease development and tree resistance, is discussed.

Vessel-length distribution in stems of some American woody plants

Vessel-length distributions in some trees, shrubs, and a vine have been calculated from measurements of particle penetration and of air-volume flow through the xylem. In shrubs and diffuse-porous species, longest vessels were about 1 m long, but most of them were much shorter, the largest percentage in the 0–10 cm length class. In the two ring-porous species investigated (Quercus rubra and Fraxinus americana), the longest vessels often were as long as the tree's stem, but most of them were much shorter. In the grapevine (Vitis labrusca) which has large-diameter vessels (ca. 300 μm) a small percentage of the vessels was 8 m, but most of them were less than 5 m long. In a given species, lengths of the longest vessel were quite variable, but the distribution of the short lengths was more constant. In general, vessel lengths are correlated with vessel diameters: wide vessels are longer. Even in diffuse-porous species, the slightly narrower latewood vessels are somewhat shorter than the wider early wood vessels. The method is a simplified version of that described by Skene and Balodis, but using a programmable desk calculator. It works best with diffuse-porous species in which vessels are randomly distributed in the stem, and less well in species with wide vessels, because as vessels reach the length of the stem itself, they cannot be randomly distributed.

Vessel element development in the earlywood of red oak (Quercus rubra)

Earlywood formation was observed in 60-year-old forest-grown red oak trees in southern Michigan. Extreme care in removing samples from the cambial region of the main stem at 1.4 m and 18 m, and from small branches at about 24 m, permitted the following conclusions. First vessel elements were initiated in the second or third xylem derivative radially removed from the previous year's latewood, possibly in overwintering derivatives, simultaneously throughout the bole and branches of the tree, some 2 weeks before bud enlargement. Vessel elements enlarged first in the tangential dimension (to about 200 μ.) within a few days after initiation of differentiation. Enlargement in the radial direction required up to 2 weeks to grow 300 μ, occurring as the entire xylem mother cell zone was displaced outward by cambial growth to either side—tangentially—of the vessel element. The duration of earlywood formation was about 10 weeks, while the duration of shoot elongation was less than 2 weeks. First earlywood vessels were fully mature about 5 weeks after initiation, coinciding with the unfolding of first leaves. All foliage was mature several weeks before complete maturation of later formed earlywood vessels. Detailed stem analysis and bark peeling studies revealed that stem sections clear of branching contained few lateral junctions between axial vessels. There were many such junctions where twigs joined larger limbs and where limbs joined the main stem; all such junctions were between adjacent vessels from the same limb.