Predicting the abundance of hollow-bearing trees in montane forests of southeastern Australia

Poisson regression analyses were used to relate the number of hollow-bearing trees on 523 sites in the montane ash forests of the Central Highlands of Victoria to a range of environmental variables. Region, logging history, the dominant species of eucalypt, slope angle, topographic position and the age of the stand influenced significantly the number of hollow-bearing trees. A simple predictive model containing these factors has possible application in geographic information systems and may assist in the assessment of wildlife habitat. The number of multi-aged stands and living trees with fire scars indicates that some individuals of ‘fire-sensitive’ montane ash eucalypts appear to survive intense wildfire.     

Water Pathways in Higher Plants: I. FREE SPACE IN WHEAT LEAVES

A technique has been developed for the study of pathways ofwater movement in the xylem and free space of wheat leaves.Plants were treated with Lead-EDTA chelate through either theroots or the leaves; after treatment the lead was precipitatedin situ as lead sulphide with hydrogen sulphide gas and itslocation determined by light and electron microscopy. Bulk water movement was in the lumen of the xylem, where therewas always a heavy deposit of lead sulphide after root treatments.Outside the xylem the deposits were confined to the cell wallsand were most dense in the middle lamella. Deposits were notfound in the cells themselves. The main zones of water loss,marked by heavy deposits of lead sulphide, were associated withthe stomata, the junctions of the periclinal walls of the epidermalcells, and the cuticle, leaf hairs, and specialized epidermalcells with pitted walls associated with the vascular bundles. Entry of lead chelate into the leaves was adequately describedby a diffusion model. The free space seemed to be located mainlyin the water of hydration of the pectin middle lamella and wasesmated to occupy 3 to 5 per cent of the volume of the tissue.     

Water Pathways in Higher Plants: II. WATER PATHWAYS IN BOOTS

The technique for studying the pathways of water movement described,in the first paper of this series has been applied to the transpirationstream in the roots of higher plants. Free space is confinedto the cell walls except in flooded tissue where intercellularspaces are also included. Errors involved in free-space estimatesare discussed and free-space volumes of 5.4 per cent have beenobtained for wheat root cortex and 4.1 per cent for carrot xylemparenchyma. The main water-absorbing regions of roots beginimmediately behind the elongating zone, where the first xylemelements are fully differentiated, and end when the endodermisundergoes secondary wall development. In the cortex the transpirationstream is located mainly in the cell wall. Calculations indicatethat the symplastic pathway is of only minor importance in transpiringplants. At the endodermis the free-space pathway is blockedby the Casparian strip and all water and solute entering thestele must pass through the lumen of the endodermal cells. Thepermeability of individual endodermal cells varies considerablyboth between cells of the same species and between those ofdifferent species. Once inside the endodermis, the transpirationstream returns to the cell-wall pathway until it reaches thexylem vessels where it enters the lumen of the mature xylemelements.     

Water Pathways in Higher Plants: III. THE TRANSPIRATION STREAM WITHIN LEAVES

Water in the transpiration stream is distributed throughoutthe leaves in the vascular bundles. In wheat, water appearsto be confined to the main veins by the mestome sheath and toenter the mesophyll through the walls of the smaller veins.Within the mesophyll the water in the transpiration stream movesin the free space of the cell walls to the evaporating surfacesof the leaf. The lead chelate, which is used to trace the transpirationstream, accumulates at the final points of evaporation at themargin of the leaf. Lead chelate accumulates beneath and onthe surface of the cuticle, being partly associated with theanticlinal walls of the epidermal cells, the walls of the stomatalguard cells and specialized epidermal cells. Chelate does notaccumulate at the base of substomatal cavities, indicating thatthe cuticle of the epidermis is the main evaporating surfaceof the leaf. The behaviour in broad bean, laurel, and plantainis essentially the same. The rate of peristomatal and cuticulartranspiration is closely related to the size of the stomatalaperture. Conditions which control stomatal aperture also causechanges in the dimensions of the epidermal cells.