The reduction of cytochrome c by cytochrome b5 was studied over a wide range of ionic strengths in four different buffer systems. The reaction rate decreased linearly as the I1/2 was increased, suggesting that electrostatic interactions are important in the interaction. The ionic strength dependence of the reaction rate was in quantitative agreement with the theory of Wherland & Gray [Wherland, S., & Gray, H.B. (1976) Proc. Natl. Acad. Sci U.S.A. 73, 2950] only if the effective radius of the interaction was 2 A. This indicates that the interaction between the two proteins is best described as the sum of n complementary charge interactions, each involving a specific lysine on cytochrome c and a specific carboxyl group on cytochrome b5. The number of complementary charge interactions, n, was calculated to be five to seven, in agreement with the results of our specific modification studies. Ultracentrifugation and gel permeation techniques were used to demonstrate that cytochrome b5 and cytochrome c formed a stable complex at low ionic strength.

The genus Davidsonia (Cunoniaceae) is revised on the basis of available herbarium collections, field studies over its geographic range, fresh and preserved materials and previous accounts. Formerly considered a monotypic genus, Davidsonia is found to comprise three species; D. pruriens F. Muell., the type species, from northeastern Queensland; D. jerseyana (F. Muell. ex F.M. Bailey) G. Harden & J.B. Williams, a known variety from northeastern New South Wales here elevated to specific rank; and D. johnsonii J.B. Williams & G. Harden, a well-known but hitherto undescribed species from northeastern New South Wales and southeast Queensland. Each species is fully described and illustrated, and the lectotypification of D. pruriens is clarified.

A population of Prostanthera staurophylla was recently rediscovered in the Mt Mackenzie area near Tenterfield on the Northern Tablelands of New South Wales. A detailed morphological comparison of these plants with the previously known population occurring in the Torrington area revealed that the populations were morphologically sufficiently distinct from each other to be recognised as separate species. Prostanthera teretifolia is reinstated as a distinct species, separate from P. staurophylla. The former species occurs near Torrington, whereas, P. staurophylla is restricted to the Mt Mackenzie area near Tenterfield. Descriptions, botanical illustrations and comments on the conservation status of each species are provided. IntroductionThe staff of the Northern Tablelands Region of the New South Wales National Parks and Wildlife Service (Department of Environment and Conservation) have been conducting floristic and vegetation inventories of the reserves within their care since 1997. These surveys have resulted in extensions of ranges for a number of highly restricted species and the discovery of many new taxa (Hunter et al. 1996;Hunter 1997;Hunter 1998;Hunter & Copeland 2001). During a flora survey of Mt Mackenzie Nature Reserve (by one of us -JTH), specimens were collected of a Prostanthera growing amongst heath plants within crevices of a single granite outcrop. Although this plant was tentatively identified as Prostanthera staurophylla (sensu lato -as circumscribed by Conn 1992), an initial comparison of the morphological features of these plants, with those that occur in the Torrington area, suggested that they were distinct. † Deceased 31 July 2005

Boronia boliviensis J.B.Williams & J.T.Hunter, a new rare granite outcrop restricted species from the Bolivia Hill area of the Northern Tablelands of New South Wales is described and notes are provided on its distribution, ecology and conservation status.

Trochocarpa montana J.B