AbstractsBiology & Animal Science

Typescript. Bibliography: leaves [157]-166. xiv, 166 l illus., tables In an effort to interpret the trends of specialization within the genus Peperomia, carpel morphology, meiotic chromosome number, meiotic irregularities, mode of leaf arrangement, and leaf and stem anatomy of 26 Hawaiian species of Peperomia have been .studied . Based on the available data, the following trends of specialization may have occurred in the genus: 1. There has been a reduction in the number of carpels composing the gynoecium. A tricarpellary gynoecium has given rise to a bicarpellary, and finally to a monocarpellary gynoecium. Such a trend is demonstrated by a reduction of the number of stigmas, as well as by a reduction in number of dorsal carpellary bundles in the ovary wall. 2. The basic chromosome number of the Hawaiian species of Peperomia is n =22, and one species has a variation of n =24. Polyploidy has been observed, and numbers of n = 44 and n = 48 have been recorded. The presence of meiotic irregularities and polyploidy suggest the possible roles of hybridization and polyploidy in speciation within the genus. The possible role of alteration of chromosome number in somatic cells in the speciation of the Hawaiian species is discussed. 3. Whorled leaf arrangement in the genus Peperomia has been derived from a spiral phyllotaxy. It is suggested that the whorled arrangement was brought about by three factors, Le., the failure of internodes to elongate, the lateral fusion of leaf primordia, and the fusion of the neighboring leaf traces. The failure of internodes to elongate is due to reduction of both cell division and cell elongation. 4. In this genus, vascular bundles are scattered in the pith resembling those of monocotyledons. Secondary growth has been greatly reduced through the elimination of cambial activity. The loss of cambial activity, and the reduction of the development of pericycle and endodermis, as well as the absence of xylem fibers are interpreted here as degrees of advancement toward simplification from the related genus Piper. The results obtained from studies of the number s of carpels and chromosomes do not support Yuncker's grouping of the species into subgenera.