An anatomical assessment of branch abscission and branch-base hydraulic architecture in the endangered Wollemia nobilis.

BACKGROUND AND AIMS: The branch-base xylem structure of the endangered Wollemia nobilis was anatomically investigated. Wollemia nobilis is probably the only extant tree species that produces only first-order branches and where all branches are cleanly abscised. An investigation was carried out to see if these unusual features might influence branch-base xylem structure and water supply to the foliage. METHODS: The xylem was sectioned at various distances along the branch bases of 6-year-old saplings. Huber values and relative theoretical hydraulic conductivities were calculated for various regions of the branch base. KEY RESULTS: The most proximal branch base featured a pronounced xylem constriction. The constriction had only 14-31 % (average 21 %) of the cross-sectional area and 20-42 % (average 28 %) of the theoretical hydraulic conductivity of the more distal branch xylem. Wollemia nobilis had extremely low Huber values for a conifer. CONCLUSIONS: The branch-base xylem constriction would appear to facilitate branch abscission, while the associated Huber values show that W. nobilis supplies a relatively large leaf area through a relatively small diameter 'pipe'. It is tempting to suggest that the pronounced decline of W. nobilis in the Tertiary is related to its unusual branch-base structure but physiological studies of whole plant conductance are still needed.

Axillary meristems and the development of epicormic buds in wollemi pine (Wollemia nobilis).

Intact trees of Wollemia nobilis Jones, Hill and Allen (Araucariaceae) routinely develop multiple coppice shoots as well as orthotropic epicormic shoots that become replacement or additional leaders. As these are unusual architectural features for the Araucariaceae, an investigation was made of the axillary meristems of the main stem and their role in the production of epicormic and possibly coppice shoots. Leaf axils, excised from the apex to the base of 2-m-high W. nobilis plants (seedling origin, ex situ grown), were examined anatomically. Small, endogenous, undifferentiated (no leaf primordia, no vascular or provascular connections) meristems were found in the axils from near the shoot apex. In the more proximal positions about half the meristems sampled did not differentiate further, but became tangentially elongated to compensate for increases in stem diameter. In the remaining axils the meristems slowly developed into bud primordia, although these buds usually developed few leaf primordia and their apical 'domes' were wide and flat. Associated vascular development was generally restricted to provascular dedifferentiation of the cortical parenchyma, with the procambium usually forming a 'closed loop' that did not extend back to the secondary vascular tissues. Development of the meristems was very uneven with adjacent axils often at widely differing stages of development into buds. The study shows that, unlike most conifers, W. nobilis possesses long-lived meristematic potential in most, if not all, leaf axils. Unlike other araucarias that have been investigated, many of the meristems in the orthotropic main stem will slowly develop into bud primordia beneath the bark in intact plants. It appears likely that this slow but continued development provides a ready source of additional or replacement leaders and thus new branches and leaves.

An audit of hypertensive care in general practice.

This mainly urban based study of hypertensive care in general practice consisted of 5,400 patients of these 287 individuals were diagnosed as being hypertensive, a practice prevalence of 5.31%. Among those between 30-80 years (2456 patients) there were 265 hypertensives, a prevalence of 10.8%. The overall male: female ration was 1:1.8. Hospitals were involved in the management of 53.9% of the hypertensives. The use of WHO criteria to make the diagnosis had increased from 38.6% to 59% over the past five years. The completence of history taking and relevant investigations was suboptimal, 78.9% of the hypertensives had their BP checked in the previous year. Management of hypertension is similar to other practices who have performed audits. There is room for improving standards in all clinical activities relating to hypertension.