The genus Sonneratia and its fossil allies

Abstract

The development, morphology and structure of the flower, embryo, fruit and seeds in two species of Sonneratia, S. acida L. and S. apetala Ham. Are given; and they are compared with the structure of the flower of Sahnianthus Shukla and with that of the fruit and seed of Enigmocarpon parijai Sahni, considered to be the fruit of Sahnianthus. The flowers of Sonneratia closely resemble in many gross features those of Sahnianthus and possess in addition bracts and a loose tissue of floral nectary around the base of the ovary. The fruit wall in S. acida and Enigmocarpon parijai also possesses arenchyma and nests of sclereids.

The fruit of S. acida dehisces irregularly as in Enigmocarpon and has no persistent calyx as in the fruit of S. apetala. The general structure of the fruit, placentation and vascular supply in the two are also more or less similar. The seeds of Enigmocarpon parijai, however, are said to possess both hypostase and epistase. There is a clear hypostase in Sonneratia, but no real epistase in it, like that in the Malpighiaceae. The inner wall of the inner integument in Sonneratia is very thin. When detached, it looks like a compressed hood in the micropyle in matured seeds. There is a conical nucellar beak on top of embryo sac in both the species of Sonneratia and is pushed up a little in the micropyle. The net result of compression during the further development of seeds is that the inner integument with its thin inner wall comes to lie over the nucellar beak, like the frayed end of a whip and gives an appearance of an epistase lying in the micropyle. There is, however, no organic continuity between the two, and, therefore, it is not a true epistase as in Malpighiaceae. In the seed of Enigmocarpon parijai also, there is no continuity between the basal conical part of the so-called epistase and the frayed whip-like end lying in the micropyle. It is, therefore, suggested that it may also have been formed of two distinct components, the nucellar beak on the top of the embryo sac and the thin integumental part lying above it in the micropyle. It was further observed that there is hypostase in several members of the Lythraceae such as Ammania, Woodfordia and Cuphea. They do not have a real epistase but only a nucellar beak.