科研之友
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摘要
this paper deals with the morphological features of the tracheary elements of the vegetative organs in four portulaca species (portulaca hirsutissima camb., p. halimoides l., p. wedermannii poelln. and p. mucronata link.) occurring in southeast and northeast brazil. the vessel elements are small (%26lt; 25 米m) and with simple perforation plate. the pattern of wall thickening varied from bordered pitting (in roots) to scalariform and helicoidal (stem and leaves). statistical methods show variation in vessel-element diameter in different vegetative organs; wider elements were observed in roots. tracheids occurring in leaves of p. hirsutissima and p.wedermannii, have morphological features that are similar to terminal tracheids or tracheoid idiolasts frequently associated with xerophytes. the paedomorphic features (juvenlism) observed here may be related, in part, to aspects of water transport and storage as described in cactaceae.
