Abstract: An anatomical study on the stems of Vanilla planifolia and V.siamensis was made recently and the result showed that the arrangement and structure of stem tissues of these two species were different.In the cross section of the stem of V.planifolia,there is an annular sclerenchyma composed of some particular cells which are small and with sepcialized and thick walls between cortex and vascular tissue region.But in the stem of V.siamensis,this not only the important anatomical character to distinguish the two species,but also has potential value in the study of hybridization and breeding between the two species.

Key words: Vanilla, Stem, Anatomical characters