AN EMBRYOLOGICAL STUDY OF KAVA, PIPER METHYSTICUM

An embryological study of Piper methysticum Forster f. (Piperaceae), u ndertaken to identify the probable cause for the absence of fruits in cultivated varieties, has revealed that the majority of plants in all the cultivars examined bore only male flowers. The anthers are tetrasp orangiate and the anther wall comprises a well-developed endothecium w ith fibrous thickenings, two middle layers and a glandular tapetum. Me iosis is normal and simultaneous cytokinesis leads to tetrahedral micr ospore tetrads. Pollen degeneration was observed but was of very rare occurrence. The pollen grains are released when they are 2-celled and appear to be healthy and capable of germination. The unilocular ovary contains a single basal ovule which is orthotropous, bitegmic, and cra ssinucellar. Both integuments contribute to the formation of the micro pyle. The development of the female gametophyte conforms to the tetras poric Fritillaria-type. No abnormalities were noticed either in meiosi s of the megaspore mother cell or in subsequent development leading to the formation of the mature embryo sac. Occasional parthenocarpy was observed but without viable seeds being present inside. It is suggeste d that, although the lack of fruit formation in this species is not be cause of any deficiencies in its embryological development, it may be due to a simple self-incompatibility mechanism.