科研之友
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摘要
this work has aimed to verify the existence of a pattern of the post-seminal development in poaceae. thus, olyra humilis nees (bambusoideae); axonopus aureus p. beauv. e paspalum polyphyllum nees ex trin. (panicoideae); chloris elata nees e eragrostis solida desv. (chloridoideae) have been studied. besides, it was compared the structures of poaceae seedlings with those of other monocotyledons. all are perennial, rhizomatous, and cespitous species whose caryopses differ in size. they all present albuminous seeds, lateral and differentiated embryos, with endogenous embryonic (adventitious) root, cotyledons divided into hyperphyll (scutellum), reduced sheath and hypophyll (coleoptile); coleorhiza (reduced primary root); and mesocotyl (axis between the scutellum and the coleoptile). the presence of epiblasts (embryonic leaves) was noticed in olyra humilis, chloris elata and eragrostis solida. since the post-seminal developmental of all the studied species is similar, it represents a pattern in poeaceae. the coleorhiza, which shows positive geotropism, grows first, followed by the coleoptile and the plumule, in the opposite direction, which form from the mesocotyl development. in all species, the first leaves are similar to the definitive ones (metaphyll) except olyra humilis, where they are converted into a cataphyll - probably interpreted as a basal character in bambusoideae. the reduced primary root (coleorhiza) and the hypophyll, which is modified into a coleoptile, are considered derived features in poaceae, when compared with the other monocotyledons.
