Observations of flower buds of Dendrobi1w1 Tomie 'Tokyo.· D . Indonesia. and seedlings of a Dendrobiwn hybrid flowering for the first time showed that all flower buds were borne with the labellum uppermost. Just before or during opening. the buds turned, positioning the lip below all other floral segments in a process known as resupination. The degree of turning depended on the orientation of the inflorescence relative to the ground and position of the pedicel. Individual flowers, at successive nodes along the inflorescence, alternated in turning clockwise and counterclockwise. Our results indicate that (1 ) only buds. flowers in the process of opening, and newly opened blossoms can undergo rcsupination; (2) mature flowers cannot reorient themselves if the angle of the inflorescence is changed: and (3 ) bending and twisting of the pedicel contribute to the final position of the flower.
Removal of noral segments from Dendrobium (Orchidaceae) nowers indica1es 1ha1 resupination may be regulated or is at least affected by pollinia and/or stigmas. Olher noral segments do n?l appear 10 have a direct effecl. However. excision of the perianth may resuh in senescence and death, which could be caused by desicca1ion and/or ethylene evolution.
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