LE3 .A278 2005

2005

Evans, Rodger

Acadia University

Bachelor of Science

Honours

Biology

Biology

Cornus canadensis is a member of the Dogwood family, Cornaceae. Two species, C. canadensis and C. suecica, share a character not found in any other Cornus species, and found in relatively few plants in general - explosive pollination. Explosive pollination occurs when the petals explode open when touched by a passing insect, and the stamens burst from within the flower releasing pollen over the body of the insect. As a means to understand how this process works, we undertook a comparative floral development study of explosive (C. canadensis) and non-explosive (C. racemosa) species. Flowers of both species were collected throughout the growing season and embedded in either paraffin wax or Spurr's resin for sectioning to observe internal anatomy and cellular structure. Flowers were also dissected and dehydrated for observation with a Scanning Electron Microscope. Initial results point to the development of a "trigger" on the abaxial surface of one or more petals in each C. canadensis flower. The margins of the four petals of C. canadensis are also highly interdigitated, and thus held tightly closed, compared with the petals of C. racemosa which are simply appressed to one another. Stamen morphology also differs between the two species as cells midway up the filament of C. canadensis become elongated approximately one third of the way through development and the filament narrowed. The anthers of C. canadensis appear to remain closed within the mature bud, opening simultaneously with the petals. It is hypothesized that the interdigitated cells hold the petals together and the filaments are flexible and push on the petal, thus causing pressure to build; the pressure would be released once the trigger was touched by an insect, pulling the petals apart and allowing the stamens to "explode" outward.

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