Abstract
To aid in understanding of the early events in seed development, surface topography observations with the scanning electron microscope can be coupled with new methods of clearing tissues for light microscopy study. These techniques reveal that two to four ovules begin development along the placental ridge as conduplication of the carpel proceeds in Trifolium repens L. A multicellular archesporium may develop giving rise to several sporogenous cells and ultimately to more than one megasporocyte. However, meiosis is completed in only one megasporocyte to give rise to a single linear tetrad of megaspores. The chalazal megaspore functions in megagametogenesis. Megasporogenesis and megagametogenesis progress as ovule ontogeny proceeds. The outer integument develops more rapidly than the inner and contributes to the final form of the campylotropous ovule. The most dramatic change in ovule form occurs as the tetrad develops and the functional spore enlarges and divides mitotically to produce the two‐nucleate megagametophyte. It can be demonstrated that this early gametophyte develops faster than it is allowed to expand in the nucellar mass. This may in part explain why there is gametophyte failure and reduced seed set in clovers.
Published Version
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