Embryological studies in compositae - IV. A contribution to the life-history ofSpilanthes acmilla, Murr. (S. calva, Wt. Ic.)
Morphology and embryology ofSpilanthes acmilla, Murr. has been investigated and its systematic position in the tribe Heliantheae is discussed. Floral parts arise in acropetalous succession. Stamens are four to five in number with bisporangiate anthers. Tapetum is of the plasmodial type. Pollen grains have an echinate exine and are shed at the three celled stage. Endothecium exhibits fibrillar thickenings at the time of anther dehiscence. Ovules are anatropous, unitegmic and tenuinucellate. Embryosac development conforms to the Polygonum type. In a great majority of cases organised embryosac is six celled with only two antipodals. Occasionally the number of antipodals may be three or four. There is a great variety in the nuclear behaviour in the micropylar antipodal in having a secondary multiplication and subsequent fusion resulting in the formation of a polyploid nucleus. Very rarely aposporic uninucleate embryosac-like structures are noticed at the chalazal end of the ovule. These however do not show any influence on the sexual behaviour of the gametophytes.
Fertilisation is porogamous, endosperm isab initio cellular and embryogeny conforms to thesenecio variation of the Asterad type.
In the mature fruit, the wall is five layered with the innermost layer infested with tannin. Endosperm persists as a thin layer adhering to the integument which itself is three layered.