FLORAL DEVELOPMENT IN CAESALPINIA (LEGUMINOSAE)

Utilizing scanning electron microscopy, we studied the early floral ontogeny of three species of Caesalpinia (Leguminosae: Caesalpinioideae): C. cassioides, C. pulcherrima, and C. vesicaria. Interspecific differences among the three are minor at early and middle stages of floral development. Members of the calyx, corolla, first stamen whorl, and second stamen whorl appear in acropetal order, except that the carpel is present before appearance of the last three inner stamens. Sepals are formed in generally unidirectional succession, beginning with one on the abaxial side next to the subtending bracts, followed by the two lateral sepals and adaxial sepal, then lastly the other adaxial sepal. In one flower of C. vesicaria, sepals were helically initiated. In the calyx, the first-initiated sepal maintains a size advantage over the other four sepals and eventually becomes cucullate, enveloping the remaining parts of the flower. The cucullate abaxial sepal is found in the majority of species of the genus Caesalpinia. Petals, outer stamens, and inner stamens are formed unidirectionally in each whorl from the abaxial to the adaxial sides of the flower. Abaxial stamens are present before the last petals are visible as mounds on the adaxial side, so that the floral apex is engaged in initiation of different categories of floral organs at the same time.     

DICHOTOMOUS BRANCHING IN MAMMILLARIA (CACTACEAE)

Cruciate dichotomous branching is a regular phenomenon in at least two species of cacti: Mammillaria perbella and M. parkinsonii, and there is exomorphic evidence that it occurs in other species of this genus. The specimens examined showed no obvious changes in the phyllotaxy of the two shanks derived by dichotomy. In the ecologically and morphologically specialized Cactaceae, it is quite unlikely that dichotomous branching represents the retention of a primitive character. It is furthermore improbable that it is of taxonomic value above the species level.     

SCIENCE IN CHINA (SCIENTIA SINICA)

Science in China is a comprehensive academic journal of natural scienes sponsored by the Chinese Academy of Sciences.The primary purpose is to provide regular,rapid and authoritative reviews of currcnt important developments in scientific research in China for scientific workers in China and other countries.The contents are selected by an extensive editorial committee which is composed of the most highly esteemed scientists in China today.     

HETEROSTYLY IN LITHOSPERMUM COBRENSE (BORAGINACEAE)

Lithospermum cobrense Greene exhibits the floral dimorphisms and strong self-incompatibility system typical of most distylous plants. Flowers of the long styled (pin) form produce smaller pollen grains but more pollen per flower than flowers of the short styled (thrum) form. Corollas of pins and thrums are equal in size. The breeding system of L. cobrense is less specialized than, and probably ancestral to, that of L. caroliniense.     

GROWTH OF ULVA FENESTRATA (CHLOROPHYTA) IN MICROCOSMS RICH IN ZOSTERA MARINA (ANTHOPHYTA) DETRITUS1,2

In laboratory experiments discs cut from thalli of Ulva fenestrata Postels & Ruprecht grew in diameter and biomass (dry weight and ash-free dry weight) more when dead leaves of Zostera marina L. were present than when absent. A maximum increase in dry weight of 500% in 14 days occurred with Zostera present compared with only a 200% increase with no detritus. When NO^?₃ and PO^3-₄ were added the weight of an Ulva disc increased by over 800% when Zostera was present but by only 400% in controls. In general penicillin G (475 units/ml) caused a reduction in algal growth in cultures containing detritus. It is concluded that bacteria on the detritus may compete with algae for nutrients but by releasing unknown substances the bacteria promote the growth of Ulva.     

MICROSPOROGENESIS IN PEANUT (ARACHIS HYPOGAEA)

The stage of pollen development at the time of anther culture is an important factor in the production of haploids. The objectives of the current study were to develop a staining procedure for peanut (Arachis hypogaea L., ssp. hypogaea) microspores, to describe and document the stages of microsporogenesis in peanut, and to confirm a previous report concerning correlations of peanut floral bud shape with stage of microspore development. A staining procedure using propionic carmine provided adequate staining of pollen mother cells, microspores, and pollen. Pollen mother cells and microspores could easily be differentiated by their size and cell wall structure. Plants grown in a controlled environment were found to have highly synchronized microspore development, both within an anther and among anthers contained in the same bud. In addition, floral bud shape was confirmed as a reliable indicator of anther stage in peanuts.     

生物多样性的几个问题（续）

从生物多样性的现状、存在的问题及应采取的措施等三个方面比较全面地叙述了我国生物多样性的情况。“生物安全”是《生物多样性公约《签订后每次缔约国会议都要讨论的中心议题之一。为之本文也用一定的篇幅作了较详细的介绍。     

AUTOPOLYPLOIDY IN TOLMIEA MENZIESII (SAXIFRAGACEAE)

Tolmiea menziesii comprises diploid (2n = 14) and tetraploid (2n = 28) cytotypes that differ in geographic distribution. Chromosome counts now available indicate that the diploid and tetraploid cytotypes occupy the southern and northern portions, respectively, of the range of Tolmiea. Available data strongly suggest that Tolmiea represents an example of autopolyploidy. The genus is monotypic and very distinct in both floral and vegetative morphology among genera of tribe Saxifrageae. Infraspecific taxa have not been recognized in T. menziesii, and the two cytotypes appear to be indistinguishable morphologically. Karyotypic, flavonoid chemical, and preliminary allozymic data are all in agreement with the contention that the tetraploid cytotype is of autopolyploidal origin.     

CHROMOSOME NUMBERS IN CENCHRUS (GRAMINEAE)

Gametic chromosome numbers are reported for 22 populations representing 6 taxa in the genus Cenchrus. Numbers of n = 17 were obtained for C. incertus M. A. Curtis, C. longispinus (Hack.) Fern., and for the previously unreported C. mitis Anderss. Populations of C. echinatus L. have the number n = 34, and C. myosuroides H.B.K. n = 35. Irregular meiosis was observed in 2 chromosomal races of C. ciliaris L. having numbers of n = 18 and n = ca. 16, respectively.     

HETEROPHYLLIC DEVELOPMENT IN MUEHLENBECKIA (POLYGONACEAE)

Flowering shoots of Muehlenbeckia platyclados Meisn. bear only reduced scale leaves which resemble the membranous sheath portion (ochrea) of leaves of other members of the Polygonaceae. Shoots propagated from cuttings bear enlarged foliage leaves with distinct lamina, petiole, and ochrea zones. The developmental basis for this heterophylly is explored in order to determine whether scale leaves resemble foliage leaves in their pattern of ontogeny or are developmentally unique. SEM and histological analyses have shown that scale leaves and foliage leaves are distinctive from inception. The scale leaf arises as a collarlike growth and extends over the shoot apex as a hooded sheath without evidence of blade initiation. By contrast, the first stage of foliage-leaf ontogeny is the differentiation of the distal lamina from the future leaf base. As the foliage-leaf ochrea encircles the stem axis, the lamina grows erect and projects from the abaxial surface of the sheath. Lamina reduction coupled with ochrea elaboration in intermediate leaf types indicate a homology between the entire scale leaf and foliage-leaf ochrea. Despite this homology, the production of the bladeless scale leaf does not involve a mere suppression of the foliage-leaf lamina. Erect growth of the saccate ochrea of the foliage leaf contrasts with the hooded expansion of the scale. Early histological differences, including contrasting rates of cell differentiation, also distinguish the two organs. This disparity in modes of growth and differentiation from inception results from separate, predetermined courses of ontogeny. Unlike other plants studied, leaf size and degree of leaf elaboration decrease with shoot meristem enlargement in Muehlenbeckia. Leaf packing does increase with shoot development and may contribute to variations in leaf morphology. It is concluded that the peculiarities of the heterophyllic leaf sequence in Muehlenbeckia are a property of the shoot system as a whole.