FILAMENT HISTOLOGY AND ANTHER DEHISCENCE

Several distinctive histological features of the stamen, especially of filament, were described, some for the 1st time. These included commonness of (a) mesarch xylem maturation, amphicribral bundles or collateral strands with phloem considerably enveloping the xylem, and clustering of sieve elements of a bundle and their spatial separation from tracheary elements, (b) exclusively helical wall thickenings of tracheary elements and absence of sclerenchyma, (c) open stomata, a weakly developed cuticle, a prominent intercellular-space system, xylem lacunae, and (d) tannins and crystals. Some of the features in category (a) were related to the nutritional needs of developing pollen grains in the anther. Features in category (b) were directly related to the usual expansion of the stamen, in particular the filament, before and at anthesis. Features in category (c), and possibly (d), probably promoted a rapid loss of water or a disruption of the water supply to the anther, and possibly facilitated anther dehiscence. These features operated in isolation or in unison. Tannins, crystals and secretory structures were implicated in the protection of pollen against predators.