FRUIT AND SEED STRUCTURE OF THRYPTOMENE-CALYCINA (MYRTACEAE)

At anthesis the receptacle of flowers of T. calycina (Lindl.) Stapf is enclosed by a layer of small cells with a thick cuticle. The hypoderm is consists mostly of large oil-containing cells interspersed with muc h smaller cells. The tissue surrounding the ovary consists mostly of s pongy parenchyma. The micropyle of the ovule is formed only by the inn er integument which is double-layered. The embryo sac at anthesis is t ypical of the Myrtaceae, and appears to follow the monosporic polygonu m type, with considerable nucellar tissue surrounding it. In a mature fruit the parenchyma is compressed into a thin band surrounding the se ed. The integuments form a two-layered seed coat within the fruit. The aborted ovule is displaced below and to one side of the developing se ed. In fruit weathered for several years there is an accumulation of p henolic material giving the fruit a black appearance. The two layers o f the seed coat within freshly shed fruit lie closely together and sta in strongly with the lipid stain auramine O. In fruit weathered for at least 2 years the two layers of the seed coat become separated for at least part of their length and staining from auramine O is less inten se. The breakdown in seed dormancy in weathered fruits is probably due to a less complete barrier to water uptake provided by the separation of the two layers. This would increase lateral and radial movement of water. The observed reduction in the hydrophobic lipid content of the testa layers probably also aids water entry into the seed in a weathe red fruit.