The relationship between hydraulic specific conductivity (k) and vulnerability to cavitation (VC) with size and number of vessels has been studied in many angiosperms. However, few of the studies link other cell types (vasicentric tracheids (VT), fibre-tracheids, parenchyma) with these hydraulic functions. Eucalyptus is one of the most important genera in forestry worldwide. It exhibits a complex wood anatomy, with solitary vessels surrounded by VT and parenchyma, which could serve as a good model to investigate the functional role of the different cell types in xylem functioning. Wood anatomy (several traits of vessels, VT, fibres and parenchyma) in conjunction with maximum k and VC was studied in adult trees of commercial species with medium-to-high wood density (Eucalyptus globulus Labill., Eucalyptus viminalis Labill. and Eucalyptus camaldulensis Dehnh.). Traits of cells accompanying vessels presented correlations with functional variables suggesting that they contribute to both increasing connectivity between adjacent vessels-and, therefore, to xylem conduction efficiency-and decreasing the probability of embolism propagation into the tissue, i.e., xylem safety. All three species presented moderate-to-high resistance to cavitation (mean P values = -2.4 to -4.2 MPa) with no general trade-off between efficiency and safety at the interspecific level. The results in these species do not support some well-established hypotheses of the functional meaning of wood anatomy.

Approximate expressions for correlation functions in binary inhomogeneous mixtures are derived in a framework of the mesoscopic theory [Ciach A., Mol. Phys., 2011, 109, 1101. Fluctuation contribution is taken into account in a Brazovskii-type approximation. Explicit results are obtained for two model systems. In the two models, the diameters of the hard cores of particles are equal, and the interactions favour a periodic arrangement of alternating species A and B. However, the optimal distance between the species A and B is much different in the two models. Theoretical results for different temperature and volume fractions of the two components are compared with the results of Monte Carlo simulations, and the structure is illustrated by simulation snapshots. Despite different interaction potentials and different length scale of the local ordering, properties of the correlation functions in the two models are very similar.

A theoretical treatment of some of the factors influencing air seeding at the pit membranes of xylem vessels is given. Pit membrane structure, viewed as a three-dimensional mesh of intercrossing fibrils, and vulnerability to water-stress-induced air seeding are examined in the context of the Young-Laplace equation. Simple geometrical considerations of the porous membrane show that the vapor-liquid interface curvature radius is a function of fiber-fiber distance, fiber radius, wetting angle and position of the wetting line. Air seeding (maximum pressure) occurs at the minimum curvature radius, therefore air seeding is not simply determined by the fiber-fiber distance but is a function of the geometry of the pit membrane and of physicochemical quantities like surface tension and wetting angle. As a consequence of considering a wetting angle different from zero, the minimum curvature radius becomes larger than half the fiber-fiber distance. The present model considers that, for a given pressure difference at the pit membrane, all local interface curvatures are the same. In this sense, pit membranes work as variable capillary valves that allow or prevent air seeding by adjusting local curvatures and interface positions relative to the pore-forming fibers, following the pressure differences across the membranes. The theoretical prediction for the air seeding threshold is consistent with recent experimental data for angiosperm trees.