Ethrel (2 - chloroethylphosphonic acid) applied in lanolin paste at eoneentrations of 0.01, 0.10, or i % to stems of 12-month-old Pinus halepensis seedlings greatly altered the rate of growth and anatomy of stems within 60 days. Height growth was not affeeted but growth of bark and xylem tissues was greatly increased after treatment with ethrel at 0.10 or 1%. The thick bark was the result of inereased phloem production and more intercellular spaee. Increase in the amount of xylem resulted from production of more tracheids per radial file rather than an inerease in traeheid size. The highest coneentration of ethrel applied (1 %) stimulated inerease in the amount of ray tissue and production of longitudinal resin duets in the xylem. The role of ethylene in regulating differentiation of stem tissues is discussed.
F. Yamamoto and T. T. Kozlowski
F. Yamamoto and T. T. Kozlowski
Flooding of soil for 66 days decreased the rate of dry weight increment and induced stem hypertrophy and abnormal cambial growth in 3-year-old Thuja orientalis seedlings. The rate of dry weight increase of seedlings was reduced largely because of root decay and a decrease in root growth and in initiation of new roots. Diameters of the submerged portions of stems increased as a result of accelerated growth of bark as weil as xylem increment. stem diameters also increased above the water level but alm ost en tirely because of an increase in tracheid production. The xylem of submerged portions of stems was characterised by wide variations in tracheid size (with many largediameter tracheids), lack of arrangement of tracheids in orderly radial rows, and an increased number of xylem rays and large ray cells. Flooding also stimulated ethylene production in stems but did not affect formation of resin ducts in the bark and did not induce formation of compression wood. Ethylene appeared to play a role in regulating cambial growth of flooded plants.
F. Yamamoto, G. Angeles and T. T. Kozlowski
Ethrel (2-chloroethylphosphonic acid) applied in lanolin paste at concentrations of 0.4, 1.6, 6.2, or 10.8% to stems of 3-month-old Ulmus americana seedlings greatly altered stem anatomy within 41 days. Application of ethrel at 1.6% or higher concentration was followed by greatly increased bark thickness primarily as a result of an increase in the amount of phloem and intercellular spaces. Xylem increment was increased following treatment with 0.4 or 1.6% ethrel and reduced by 6.2 or 10.8% ethrel. All concentrations of ethrel increased the number of vessels, reduced vessel diameters, and induced an increase in ray width and size of the individual ray cells. Ethrel at 6.2 or 10.8% inhibited differentiation of fibres, many of which were poorly developed and contained protoplasm and nucleL Ethrel also stimulated accumulation of dark-staining organic deposits in the ray parenchyma cells, axial parenchyma cells, and immature fibres. The data indicate a role of ethylene in control of growth and anatorny of stems.
T. O. Siddiqi
In Ficus religiosa (Moraceae) extension and radial growth occurs in late July and early August, respectively, under the local climate of Aligarh. The derivative tissue differentiates into xylem and phloem simultaneously in August. The phloem production stops late in August, restarts early October and then continues up to November. The xylogenesis continues up to November without interruption. Formation of the precursor phloem is observed in March. Cell size and the relative proportion of fusiform and ray initials vary with season.
M. T. M. Bosman
Effects of decay and weathering on the stems of Phragmites australis Trin. ex Steud. were studied on material used for thatching. Decay appeared to be mainly a result of fungal attack and ultra-violet radiation. Biological degradation by soft-rot fungi causes a considerable loss of cell wall constituents towards the exposed basal part of the stems. In sclerenchyma and parenchyma (excl. the subepidermal tissues) this effect is visible as diamond-shaped cavities, spirally arranged in the central part of the secondary cell walls (following the microfibrillar arrangement). A second type of fungal attack is observed in stems obtained from a byre. Here the cell walls are thinned from the lumen side towards the external wall layers, showing in longitudinal section cells with locally enlarged lumina. At the exposed parts of the stem superficial weathering by ultra-violet radiation causes degradation of lignin. Thus the middle lamella region disintegrates and the outer cell layers peel off.
Joanna T. Tippett
Kino veins, generally referred to as gum veins, are formed in Eucalyptus spp. in response to injury. Although they are retained as defects in the wood of many species, in some they become inc1uded in the phloem, then the rhytidome and are eventually shed. Ninety-three Eucalyptus spp. were sampled to determine whether they had xylem or phloem (bark) veins. The species which exhibited kino veins in the phloem were all members of three sections of the subgenus Symphyomyrtus. All species examined of the subgenera Monocalyptus and Corymbia had xylem veins. Kino veins are formed by the lysigenous breakdown of parenchyma bands produced by the cambium. The difference which results in the veins either being shed in the bark or inc1uded in the xylem is determined at the time of their initiation. The parenchyma bands may be produced on either the xylem or on the phloem side of the cambium. The fate of the veins becomes apparent once normal cambial divisions resurne the production of xylem and phloem.
Monique T. M. Bosman
Radial and longitudinal variation in fibre wall percentage, area percentage of vessels and resin canals and specific gravity was studied in five superior six-year-old plantation grown trees of red meranti (Shorea leprosula, S. parvifolia and S. pauciflora). In another 23 trees of these species specific gravity was measured at breast height.
Monique T. M. Bosman
Longitudinal variation in fibre wall percentage, area percentage of vesse ls and resin canals and specific gravity was studied at three to five height levels in three naturally and five plantation grown trees of Light Red Meranti (Shorea leprosula and S. parvifolia).