The structure and leaf development of the shoot apical meristem in embryos and seedlings of Thuja orientalis L. were observed by using SEM, and the area of the shoot apical meristem was studied by an image analyzer. The shoot apex of embryos was of a round tip cone shape with flat sides; it was transformed into an inverted boat shape. In seedlings, the shoot apical meristem was of a convex-rectangular shape during the early stages of development of two decussatelst leaf primordia; but in the later stage of the development, it turned into a flat square shape. The shoot apical meristem was of a convex diamond shape during the early development of whorled four 2nd leaf primordia; but it turned into a flat diamond shape in the later stage of this process. In the early development of the 3rd leaf primordia, it was transformed into a convex square shape. Both the minimal and maximal areas of the shoot apical meristem gradually decreased as the plant developed from an embryo into a seedling. In seedlings, the 1st leaves showed a decussate phyllotaxis, while the 2nd leaves and later leaves all showed a four-leaf whorl phyllotaxis. All the leaves developed into needles.

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Arabidopsis thaliana(L.)Heynh. is an excellent model for studies of developmental genetics in plants. We have focused on the developmental genetics of leaf morphogenesis of Arabidopsis and several important processes in leaf morphogenesis have discovered from analyses of mutants in leaf morphology. This review summarizes our current understanding of the genetic mechanisms that regulate the expansion of leaf cells in Arabidopsis.

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Recent phylogenetic studies of the colonial Volvocales are reviewed. They are based on morphological data of vegetativ eultrastructure and life cycle or nucleotide sequence data. Comaparative morphological studies of the sexual reproduction of the colonial Volvocales suggested that the four-celled species Gonium sociale is placed in a phylogenetic position separated from other members of the colonial Volvocales(Nozaki 1986). A cladistic analysis based on morphological data also indicated the peculiar phylogentic position of G. sociale(thus transferred to another genus Tetrabaena)and suggested that the evolution from isogamy to anisogamy had occurred once within the colonial Volvocales(Nozaki & Itoh 1994). However, molecular phylogeny based on rRNA sequence data resolved multiple evolution of anisogamy as well as reverse evolution from anisogamy to isogamy within such organisms(Larson et al. 1992). More recent molecular phylogenetic research based on rbcL sequence data of the colonial Volvocales(Nozaki et al. 1995)supports the morphological study(Nozaki & Itoh 1994), with regard to the evolution of isogamy/anisogamy.

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真菌の二形性とは、一つの菌株が環境条件によって二つの異なる栄養増殖形態を示すことである。そのうち、単細胞性の酵母と、細胞の連なった菌糸との間で可逆的におこる二形性についての研究では、パン酵母やカンジダ酵母での分子遺伝学的諸法を適用した報告がなされるようになり、遺伝的制御を受けていることが分かってきた。形態形成や分化のモデルとして、最近の知見について総説する。

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Two convenient methods for observation of cells at the surface of plant organs, are introduced. The first method is negative staining of organ surface with water-insoluble dye, which is followed by observation with binocular dissecting microscope. In this method boundaries between the cells are visualized by the accumulation of pigment of waterproof felt-tip pens or orcein dissolved in propylene glycol α-monomethyl ether. The second method is the replica-SEM method, in which replicas of plant organs made of epoxy resin are observed by a scanning electron microscope: the molds for the replicas are prepared using dental impression polymer. These methods have been originally developed in USA and Australia and some adaptations for Japanese users are described.

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