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Notes: The total resistances to CO2 uptake by Sticta latifrons Rich, and Pseudocyphellaria amphisticta Kremp. were separated into transport and carboxylation components by calculation after transformation of net photosynthesis rate against CO2 concentration curves into a linear form. The use of this technique circumvented the problem of measuring the internal CO2 concentration of the lichen thalli. Both species exhibited an increase in transport resistance at high thallus water contents and an increase in both transport and carboxylation resistances at low water contents. At low and intermediate water contents internal transport resistances were larger than carboxylation resistances when measured at limiting CO2 concentrations. However, at ambient CO2 concentrations carboxylation processes were the dominant factors limiting photosynthesis at all, except the high, water contents.

Notes: The gaseous exchange pathways of Sticla latifrons Rich. and Pseudocyphellaria amphisticta Kremp. were examined using both light and scanning electron microscopes. The size and frequency of the pores in the gas exchange structures (cyphellae and pseudocyphellae) and in the medulla were measured and from these CO2 diffusion resistances were calculated. Pseudocyphellae were found to be smaller and more widely spaced than cyphellae, consequently the resistance of the pseudocyphellae, was much greater than that of the cyphellae. Medulla resistances were low in both lichens and are probably unimportant, even at high water contents. No evidence of hyphal swelling was found. Gas exchange structure resistances were more than five fold greater than medulla resistances. It is suggested that this arrangement of resistances may simultaneously encourage refixation of respired CO2 and maintain a non desiccating environment for the lichen algae. The internal transport resistances calculated in this work approximate experimentally obtained values.

Notes: Abstract Standard infra-red gas analysis techniques were used to compare the photosynthesis of the liverworts Marchantia foliacea Mitt. and Monoclea forsteri Hook. Parameters measured include net photosynthetic rates, light response curves, quantum efficiencies, diffusive resistances to CO2 and water, apparent photorespiration and chlorophyll content. A series of morphological measurements were also made to determine resistance of pores and the ‘mesophyll’ to dorsal surface ratio, A mes/A. Marchantia has a cuticularised thallus with the photosynthetic tissues arranged in air chambers giving an A mes/A of 9 whilst Monoclea has a solid thallus, A mes/A of 1. Both species are shade adapted and it was found that whilst the air chambers were advantageous for water relations they increased maximum photosynthesis only slightly. Calculations showed that the solid thallus would be photosynthetically superior in very moist environments. The results are discussed with reference to existing ideas on the evolution of the structure of land plants.

Notes: Summary Detailed statistical analysis of data obtained from five species of New Zealand native trees was used to develop an empirical model of pressure-volume curves. The model combines an exponential turgor function with a hyperbolic osmotic function and provides a very good fit to all data sets. The resultant function permits precise calculation of the bulk modulus of elasticity and turgor loss point from simple manipulation of the coefficients as well as providing the usual estimates of osmotic potential and free water content. The use of several water relations parameters, rather than one or two, each expressing different ecological aspects has permitted a better insight into the adaptability of the species. The data was obtained as part of an investigation into the causes of forest mortality to examine the tissue water relations of the principal species and to assess their ecological status. For all parameters highly significant differences were found between species. Silver beech (Nothofagus menziesii) and quintinia (Quintinia acutifolia) or tawari (Ixerba brexioides) are well separated and are consistently placed in opposing groups by the parameters. Osmotic potential proved to be of limited value for differentiating sites possibly because of the greater amplitude of diurnal variation compared with the site differences and also because of large within site variation. However variations in the pressure potential at the turgor loss point, which was closely correlated with osmotic potential, discriminated the levels of effective precipitation at the study sites, and the drought tolerance of the species. For one species, tawari, it proved possible to classify the sites on the basis of water content at the turgor loss point and osmotic potential using discriminant analysis. Variation in the water potential at the turgor loss point, which was closely correlated with osmotic potential, can be used to rank the species in order of drought adaptability and this was found to coincide with their order of permanence on the site. The bulk modulus of elasticity and the coefficient of elasticity are closely linked but their value in the ecological comparisons was limited by higher variability than found for other parameters. Ranking of the species using the variability of the parameters indicates the presence of to two distinct survival strategies; stress avoidance and stress tolerance. The two canopy species utilise opposing strategies and may be less at risk than the seral plants which combine both strategies. The data provides evidence for current stress on the unhealthy site which most stongly affects the seral species.