Fruit and Seed Structure of Thryptomene calycina (Myrtaceae)

Abstract

At anthesis the receptacle of flowers of T. calycina (Lindl.) Stapf is enclosed by a layer of small cells with a thick cuticle. The hypodermis consists mostly of large oil-containing cells interspersed with much smaller cells. The tissue surrounding the ovary consists mostly of spongy parenchyma. The micropyle of the ovule is formed only by the inner integument which is double-layered. The embryo sac at anthesis is typical of the Myrtaceae, and appears to follow the monosporic polygonum type, with considerable nucellar tissue surrounding it. In a mature fruit the parenchyma is compressed into a thin band surrounding the seed. The integuments form a two-layered seed coat within the fruit. The aborted ovule is displaced below and to one side of the developing seed. In fruit weathered for several years there is an accumulation of phenolic material giving the fruit a black appearance. The two layers of the seed coat within freshly shed fruit lie closely together and stain 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 intense. 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 weathered fruit.