On the stomata ofSalvinia herzogii (Salviniaceae,Pteridophyta)

The structure of the stomata of the floating leaves ofSalvinia herzogii has been analyzed with light and scanning electron microscopy. Peculiar extensions (cuticle?) of the outer and inner tangential sides of the walls of the guard-cells are described. Both extensions, partially joined at their ends, are encircling a pore. This structure is used to propose an alternative explanation for the risk of the occlusion of the ostioles, different from that given byHaberlandt. The conductivity of these stomata was checked with a porometer and the ostioles proved to be permanently open. Their type of stomatogenesis is discussed. The stomata ofSalvinia are considered to be vestigial structures and their sunken position is taken as evidence in support of a xeric hypothetic ancestor of the genus.