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Date of Award

Spring 2005

Document Type

Restricted Thesis: Campus only access

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Dr. W John Hayden

Abstract

Acalypha deamii, a plant species of river flood plains in Virginia and the mid-west, has three different flower types: staminate, ordinary pistillate, and allomorphic pistillate. Whereas most species of Acalypha have 3-carpellate pistillate flowers, in A. deamii, the ordinary pistillate flowers are 2-carpellate and the allomorphic flowers are 1-carpellate. Because allomorphic flowers are poorly understood, this study was undertaken to document their early developmental stages. Specimens were collected from populations along the James River, preserved in formalin-acetic acid-alcohol, dehydrated in tertbutanol, embedded in paraffin, and sectioned on a rotary microtome. Slides were stained in a combination of iron-alum hematoxylin and safranin and studied via light microscopy. From the earliest stages, allomorphic flowers can be recognized by the numerous multicellular pointed protuberances covering the exterior. Internally, at the level of cells and tissues involved in reproduction, allomorphic and ordinary pistillate flowers are similar. To date, reproductively significant structures documented in allomorphic flowers of A. deamii include: an obturator, nucellar beak, hypostase, pollen tubes, the egg apparatus, polar nuclei, antipodal cells, early embryos, and endosperm. These reproductive structures are consistent with sexual processes of development and reproduction in normal pistillate flowers. Mature embryo sac structure is also consistent with Landes' prediction of Penaea-type. The distinguishing features of allomorphic flowers and fruits (indehiscence, bristly surface) appear to be adaptations for biotic seed dispersal.

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