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INVESTIGATIONS OF NORTH AMERICAN CYCADEOIDS: EARLY OVULE ONTOGENY
Author(s) -
Crepet W. L.,
Delevoryas T.
Publication year - 1972
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1972.tb10083.x
Subject(s) - ovule , megaspore , biology , extant taxon , ontogeny , cretaceous , genus , botany , evolutionary biology , pollen , paleontology , genetics
Ovules on cones of the genus Cycadeoidea from the Cretaceous were found preserved at the pregametophytic stage of nucellar development. At this stage, the ovules are distinct from those of extant gymnosperms in that there is a greater degree of differentiation in both the integuments and the nucellus in Cycadeoidea . Linear clusters of three or four cells, which consistently occur in the middle of the nucellus, are interpreted to be the remains of linear tetrads of megaspores. This example of exceptional preservation allows, for the first time, a comparison of early ontogenetic events in a fossil seed with those of extant seeds.