Contributions to the embryology of the Menispermaceae I. Cocculus villosus DC.

Abstract

The structure and development of the gynœcium, ovule and embryosac ofCocculus villosus DC. has been studied. There are generally three fertile carpels in a flower, but a fourth one is frequently present. The extra carpel is generally abortive. The carpels are arranged in a spiral manner on the floral axis. In the beginning two ovules develop in each carpel. Later the lower one of these is suppressed. These observations show that the few-carpellary gynoecium ofCoccufnts villosus has been derived by reduction from a multicarpellary structure and the uni-ovular carpel from a bi-ovular type. The functional ovule is amphitropous up to the development of the embryo-sac, but becomes campylotropous during the formation of the endosperm. There are two integuments, which remain free from each other and the nueellus up to the mature embryo-sac stage. The micropyle is formed only by the inner integument. The nueellus is characterised by the development of a small epidermal cap. The primary archesporium is restricted to a single cell. A primary wall cellos cut off. The megaspore mother cell gives rise to a linear tetrad of megaspores. The chalazal megaspore alone is functional. The development of the embryo-sac corresponds to the normal type. The polar nuclei fuse at an early stage. The synergids possess small hooks and show a clear filiform apparatus in the later stages. The antipodal cells develop large vacuoles.