Roger Heady

Effect of boiling water, seed coat structure and provenance on the germination of Acacia melanoxylon seeds

Acacia melanoxylon (Mimosoideae or Mimosaceae) is a high quality timber tree with an extensive natural distribution in Australia and a wide genetic and phenotypic diversity. Seeds from three widely differing provenances in Tasmania were tested to determine whether they had different responses to various dormancy-breaking treatments. All provenances had limited germination (<11%) if seeds were untreated and between 85% and 91% germination after 40 days if the seeds were nicked. For all provenances short (≤60 s) exposure to boiling water gave high germination percentages. These values were generally lower, although usually not significantly so, than the germination percentages following nicking. Germination percentages decreased with increasing time of exposure to boiling water, although one provenance had a significantly greater tolerance to one of the longer (20 min) treatments. Nicked seeds germinated quickly and uniformly, whereas those subjected to the boiling-water treatments germinated after a longer period and more gradually. In untreated seeds, the lens was a low, elliptically shaped dome (~110–135 µm wide, 140–190 µm long). In more than 99% of the seeds examined, the structure of the lens was markedly altered after a 10-s exposure to boiling water. A wide diversity of altered lens structure was found, from a circular hole between the macrosclereids, to a short fissure where the macrosclereids did not separate to their bases. Nicked seeds had a 200–375 times greater area for water uptake than a fully disrupted lens and this was probably the principal reason why the nicked seeds germinated sooner and more rapidly.

Wood anatomy of Wollemi Pine (Wollemia nobilis, Araucariaceae)

The wood anatomy of the recently-discovered conifer Wollemia nobilis (Wollemi pine) is described for the first time. Its mature heartwood is light brown in colour and has an air dry density of 0.57 g /cm3. Growth ring boundaries are distinct and the transition from earlywood to latewood is gradual. Average tracheid length is ~ 3.4 mm. Bordered pits are one-, two- or three-seriate and the double and triple rows of pits are ‘alternate’. In the bordered pits there is a flat transition from torus to margo. A warty layer lines tracheid walls and pit cavity surfaces. Resin plugs are common in tracheids that are adjacent to rays. Helical thickenings and crassulae are absent. Rays are uniseriate, low, and are composed entirely of parenchyma cells whose walls are thin and unpitted. Cross-field pitting is ‘araucaroid’ and the number of pits per cross-field ranges from 3–11 (av. 7). Resin canals and axial parenchyma cells are absent. The differences between normal mature wood compared to compression and juvenile wood are consistent with those of most other conifer genera. The anatomical features of wood of W. nobilis strongly support its classification as a member of the Araucariaceae, but show no major differences that distinguish it as a monotypic genus. On the basis of its wood anatomy, it is not possible to state whether W. nobilis is more closely related to Agathis or to Araucaria.

Intrusive trichome bases in the leaves of silverleaf nightshade (Solanum elaeagnifolium; Solanaceae) do not facilitate fluorescent tracer uptake.

PREMISE OF THE STUDY Solanum elaeagnifolium (silverleaf nightshade), having originated in the Americas, is now a serious summer-growing, perennial weed in many countries, including Australia. Most surfaces of the plants have a dense covering of trichomes, giving them a silvery-white appearance, hence the common name. We aimed to identify structural and functional properties of its leaves, especially the trichomes, that may affect the uptake of foliar-applied tracer dyes. METHODS The structure of leaves of Solanum elaeagnifolium was examined by light and scanning electron microscopy. The potential for transport of materials between trichomes and veins was studied with symplastic (carboxyfluorescein diacetate) and apoplastic (lucifer yellow) tracer dyes. KEY RESULTS Mature leaves had a dense covering of complex, stellate trichomes on both surfaces, particularly the abaxial. The basal cells of Solanum elaeagnifolium trichomes penetrated into the underlying palisade mesophyll layers. The innermost lobes of these basal cells sometimes contacted the bundle sheath of the veins, but were not observed to directly contact the xylem or phloem. We found that neither symplastic nor apoplastic dyes were transferred between the basal cells of the trichomes and the vascular tissues. The trichome layer repelled water-based tracer dyes, while one of four adjuvants tested facilitated entry of both symplastic and apoplastic dyes. CONCLUSIONS Our results did not support a transport function for the trichomes. The trichomes may protect the mesophytic leaves from invertebrate herbivory, while also probably decreasing radiation absorbed resulting in cooler leaves in this summer-growing species.

Callitroid (callitrisoid) thickening in Callitris.

In softwood tracheids, callitroid thickening is the term given to raised bars located above and below individual bordered pit apertures. Although most well developed in the Australasian genus Callitris, callitroid thickening is reported to be absent from six Callitris species and to vary in its frequency and prominence. An SEM study of callitroid thickening was carried out on multiple wood samples of each Callitris species, taken from trees growing in the wild. The aims of the study were to determine the occurrence, frequency, visual prominence and morphology of callitroid thickening in all Callitris species and to determine whether it could be used taxonomically. Callitroid thickening was found in all (19) species of the genus, in contrast to previous reports of its absence in some species. In general, callitroid thickening occurred at higher frequencies and was more prominent in species from dry habitats than in those from wet habitats. The frequency of thickening varied between and within samples and, for example, it was always more frequent on pits in narrow rather than in wide tracheids. Callitroid thickening varied in its morphology, and types consisting of one to four bars, extending completely or only partially across the inner radial wall of the tracheid, were observed. Thickening on tracheid-ray pits within cross fields occurred in all species, and with similar frequency and morphology to thickening of bordered pits. Our findings suggest that frequency of callitroid thickening is useful taxonomically in separating four groups of Callitris species and in assisting in the identification of certain individual species.

Identification of the woods used to make the Riley Cabinet: A historically-significant example of early Australian, convict-built, furniture

The Riley cabinet is a historically-significant piece of Australian furniture built by convict artisans in 1817–1820, only 30 years after colonisation of Australia began. The timber species used to make the cabinet were hitherto unknown. This paper describes the novel use of a truncated veterinary syringe needle as a minimally-invasive tool for obtaining very small wood-identification samples from the cabinet. We also describe how, using utmost economy of sample material, we identified the different cabinet woods, with varying levels of precision. Identification of the thirteen species encountered relied on macroscopic and microscopic features of the woods and consideration of the availability of different timbers to the cabinet-maker at the time the cabinet was made. We conclude that the early British settlers of Australia rapidly gained knowledge of the wide variety of indigenous woods suitable for cabinet manufacture, and suggest that the methods used to sample and identify the woods in the Riley cabinet may have wider application for identifying woods found in other historically-significant wooden objects.

Differences in the ultrastructure of their large warts allow white cypress pine (Callitris glaucophylla) to be distinguished from black cypress pine (C. endlicheri)

White cypress pine (Callitris glaucophylla) wood is durable enough to be used outdoors, but occasionally there are reports of its premature failure in ground contact, which may be due to its substitution by the less durable species, black cypress pine (C. endlicheri). It has been difficult to prove this, however, because the woods of both species are very similar in structure and cannot be separated using conventional anatomical features. This study examined whether differences in the size and morphology of warts on tracheid walls in the two species could be used to identify them. There were significant differences in the height, width and shape of warts in the two species, but there was considerable overlap in the distribution of these parameters between specimens. Warts in C. endlicheri were more likely to be bent-over near their tops than those in C. glaucophylla, and the angle bending of warts was greater in C. endlicheri. Quantification of these parameters produced complete separation of multiple specimens of the two species, and could potentially be used to help determine whether premature failure of C. glaucophylla heartwood in ground contact is the result of its substitution by C. endlicheri. More generally it can be concluded that the morphology of large warts may have taxonomic value in identifying coniferous wood species beyond the generic level.

Features of the secondary xylem that facilitate branch abscission in juvenile Wollemia Nobili

Wollemi pine (Wollemia nobilis) does not shed individual leaves but instead cleanly self-prunes the whole first-order branch with all the leaves still attached. A zone of stranded xylem at the branch base, the site of branch abscission, is described here in relation to the profusion of bordered pits and ray parenchyma cells that occur in this region. We propose that the much higher occurrence frequencies of these two features, compared to those in the stem and in the outer regions of the branch, results in a zone of radially-orientated weakness which facilitates branch abscission. We also suggest that since the stranded xylem region has a smaller cross-sectional area than the outer regions of the branch, the prevalence of bordered pits promotes water flow, and thus may alleviate the effects of this region on water supply to the foliage. Our observations represent, to the best of our knowledge, the first report of the involvement of bordered pits and ray parenchyma in branch abscission.

Identification of yellow stringybark (Eucalyptus muelleriana) and silvertop ash (E. sieberi) wood is improved by canonical variate analysis of ray anatomy

Summary The woods of yellow stringybark (Eucalyptus muelleriana) and silvertop ash (E. sieberi) are both used for the manufacture of flooring, but yellow stringybark is the preferred species because it contains fewer natural defects and dries faster and with less degrade than silvertop ash. Sometimes companies manufacturing flooring from yellow stringybark find that the wood they process contains higher levels of natural defects than expected, possibly due to the presence of silvertop ash in the wood that they receive from sawmills. It is difficult to prove this, however, because timber from both species looks similar in the rough-sawn condition and is similar anatomically. Hence, a reliable method of identifying the two species is needed. This study used canonical variate analysis to analyse linear combinations of quantitative indicators of ray anatomy in an attempt to clearly separate the wood of the two species. Canonical variate analysis scores derived from the analysis of ray height and cell number, frequency of biseriate rays and frequency of rays per square millimetre were able to completely separate 13 authentic samples of each species. This approach to separating the two species was validated using a further 16 reference specimens provided by industry (eight of each species) and 16 unknown specimens. Analysis of the reference specimens identified one specimen labelled silvertop ash that was clearly yellow stringybark, and one sample of yellow stringybark was identified as silvertop ash. Overall, however, canonical variate analysis of linear combinations of ray features produced fewer misclassifications of the two species than the use of ray parameters on their own. Canonical variate analysis shows promise as a means of more clearly separating yellow stringybark from silvertop ash and may also prove useful in separating those eucalypt wood species whose final identification in taxonomic keys depends on their ray anatomy.