Abstract
Ultrastructural analysis of Pennsylvanian lycopod megaspores reveals that wall ultrastructure type can be correlated with dispersal strategy. Megaspores of Mazocarpon possess a unique wall structure comprised of interconnected tubules, which correlates with a unique dispersal strategy. Valvisisporites and Lagenoisporites probably dispersed like modern Selaginella megaspores and, consequently, display a comparable wall organization. It is possible to elaborate a general sequence of wall development stages within these Pennsylvanian megaspores in response to spore enlargement. These proposed stages are: (1) changes in disposition of wall units, (2) loss of excess space between units and (3) loss of all or nearly all space centrifugally.
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