Abstract
Lemmas, paleas, ventral lodicules and carpels of Stipa tortilis and Oryzopsis miliacea are leaflike in mode of initiation and early growth. The stamens are stemlike, and the ovule develops directly from the floret apical meristem and seems best interpreted as being stem borne Both the dorsal lodicules and the calluses are unique in initiation and growth and are best interpreted as organs sui generis. The major developmental differences between the two taxa are seen in the awn, lemma, callus, and gynoecium Features seen in S tortilis, which are lacking in O miliacea are (1) many cell divisions in the protoderm and ground meristem in the awn and lemma-apex, (2) periclinal divisions giving ridges in the frontal plane of the lemma-apex, (3) early differentiation of sclerenchyma mother cells in the awn, (4) a tremendous amount of cell enlargement in the ground meristem of the callus, and (5) more rapid development of the gynoecium It is possible to divide the developmental differences between taxa into qualitative (due to a specific developmental phenomenon occurring in one taxon but not in a comparable morphological position in another taxon) and quantitative (due to different amounts of a specific developmental phenomenon occurring in comparable morphological positions in different taxa) It is speculated that qualitative differences are the result of the activity of different batteries of genes There are flowers, other than in grasses, with stemlike stamens and caulinary ovules or placentae This indicates that there is more than one basic type of flower or that the flower has evolved more than once This is not totally unexpected, since many other functional plant features have evolved more than once It is possible to have more than one type of flower and yet have the Angiospermae remain as an intact, natural taxon Because plants are developmentally very simple, it is not surprising to see some similarities among different plant organs However, these similarities have no great "morphological significance"
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