Interaction of the Stigma With the Pollinium in Dendrobium speciosum

Abstract

Pollination of D. speciosum is effected by the deposit of the pollinia from one flower into the stigmatic cup of a flower on another plant. The pollinia are submerged into the viscous liquid of the stigmatic cup. This liquid contains the detached stigmatic cells and mucilage.

Post-pollination phenomena within this species include a more intense perianth colour and the closure of the perianth. This is followed by the swelling of the column and ovary and, after 4 days, cell division in the ovary.

Following pollination the pollinia break apart as the tetrads dissociate from each other. The pollen grains progressively hydrate and germinate from the outside of a pollinium to the inside. The changes in the pollen grains associated with hydration and germination are described. The stigmatic mucilage is considered essential in the hydration and germination of the pollen. The detached cells of the stigma located near the entrance to the stylar canal are seen to lose the starch from the amyloplasts after the pollen tubes have passed.

The structure of this stigmatic type is discussed in relation to its functions with the large pollen aggregate.