The plumules of newly-excised wampee embryos, which are more sensitive to dehydration than the roots, became more resistant to water loss when axes were allowed to sprout on woody plant medium [WPM; McCown and Lloyd (1981) Hortscience16, 453] before being dried. Pre-treatment of sprouting axes (seedlings) with sucrose incorporated in the WPM enhanced survival. Although the roots withered following further dehydration of seedlings cultured on WPM containing 60% sucrose, excised plumules were capable of generating adventitious roots when a combination of 10 mM α-napthaleneacetic acid and 10 mM indole-3-butyric acid was used during subsequent in vitro incubation.

The aim of the present study was to examine the micromorphology of the cork-oak (Quercus suber) acorn and to evaluate the efficiency of the pericarp as a barrier to water loss. When the desiccation curve obtained at 25 ± 1°C and 62% RH for physiologically mature acorns collected from the tree was compared with that corresponding to fully ripe acorns which had been shed, the latter showed a slightly lower rate of water loss. A marked reduction in the mean rate of water loss was recorded for intact acorns compared with those from which the pericarp had been removed. The external surface and transverse sections of the pericarp from both mature and fully ripe acorns were examined by scanning electron microscopy. Two zones presenting morphological and micromorphological differences were identified: an area including the point of attachment to the cupule and an apical zone covering the embryo. The microstructure of the pericarp showed an external thick cuticle and a single external palisade layer of closely packed cells with no intercellular spaces. Underlying this layer, there was a further parenchymatous layer of poorly differentiated, roughly isodiametric cells. The pericarp in the cupular zone consisted of only this undifferentiated layer between the two epidermal cell layers and contained vascular bundles with many xylem elements.