1990. Structural aspects of the leaves of seven species of Portulaca growing in Hawaii. Can. J. Bot. 68: 1803-181 1.Seven species of Portulaca growing in Hawaii can be divided into two groups based on the morphology, anatomy, and ultrastructure of their leaves. Portulaca oleracea, P. molokiniensis, P. lutea, forming group A, have spatulate to obovate leaves, paradermal minor veins, and mesophyll cells that completely encircle the minor veins. The chloroplasts in their bundle sheath cells are larger than those in the mesophyll cells and have well-developed grana and reduced peripheral reticulum. Bundle sheath mitochondria are larger and more numerous than those in the mesophyll, and chloroplasts in the mesophyll cells have well-developed grana and peripheral reticulum. Portulaca pilosa, P. villosa, P. sclerocarpa, and P. "ulupalakua," forming group B, have lanceolate to oblong-oblanceolate leaves, peripheral minor veins, and incomplete wreaths of mesophyll cells. The choroplasts in their bundle sheath cells are about the same size as those in the mesophyll and have reduced grana and well-developed peripheral reticulum. ' The bundle sheath mitochondria are about the same in size and number as those in the mesophyll, and the mesophyll chloroplasts have well-developed grana and reduced peripheral reticulum. Groups A and B may be equivalent, respectively, to types ii and i of R. C. Carolin, S. W. L. Jacobs, and M. Vesk (Aust. J. Bot. 26: 683-698, 1978) and to coronary subtypes B and A of E. V. Voznesenskaya and Y. V. Gamalei (Bot. Zh. Leningrad, 71 : 1291-1306, 1986), which constitute groupings of Portulaca species studied by those authors. KIM, I., et FISHER, D. G. 1990. Structural aspects of the leaves of seven species of Portulaca growing in Hawaii. Can. J. Bot. 68 : 1803-1811. Sept espbces de Portulaca prksentes a Hawaii peuvent Ctre rtparties en deux groupes d'aprbs la morphologie, l'anatomie et I'ultrastructure de leurs feuilles. Les Portulaca oleracea, P. molokiniensis et P. lutea, qui constituent le group A, ont des feuilles spatulks a obovCes, des nervures mineures paradermiques et des cellules de mCsophylle encerclant complbtement les nervures mineures. Les chloroplastes des cellules des gaines pCrifasciculaires sont plus gros que ceux des cellules de mCsophylle et ont des granums bien differenciks et un kticulum pCriphCrique rkduit. Les mitochondries de la gaine pCrifasciculaire sont plus grosses et plus nombreuses que celles du mtsophylle et les chloroplastes des cellules du mCsophylle ont des granums et du reticulum pCriphCrique bien diffCrenciCs. Les Portulaca pilosa, P. villosa, P. sclerocarpa et P. cculupalakua., qui constituent le groupe B, ont des feuilles IanceolCes oblongues-oblancColCes, des nervures mineures pCriphCriques et des couronnes incompletes de cellules de mesophylle. Les chloroplastes des cellules de leur gaines ptrifasciculaires sont B peu prbs de la mCme grosseur que ceux du mCsophylle et ont des granums rCduits et un rCticulum ptriphCrique bien diffCrenciC. Les mitochondries de la ga...

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Plants maintained in high soil salinity generally develop particular structures to either tolerate or survive such adverse environments. Excretion of excess ions by special salt glands or other similar structures is a wellknown phenomenon for regulating the mineral content of many halophytes. However, the three chenopod halophytes of Suaeda inhabit high saline soils, yet they exhibit no signs of salt excretion structures. The current study has been undertaken to assess the structural attributes of these halophytes to reveal their cellular characteristics during growth in salt tolerance. Transmission and scanning electron microscopy, as well as ion chromatography, have been employed for the study. One of the most noticeable features uncovered was the epidermal cutinization shown to be heavy on the outer epidermis and characterized externally by thick wax plates. Numerous vesicles and membranous invagination in the vacuoles were common features within the mesophyll cytoplasm. Invaginations of the vacuolar and/or plasma membrane frequently formed secondary vacuoles which later became distinct, membranebound compartments. Significant accumulation of solid sodium chloride salts was well demonstrated in the vacuoles of air-dried epidermis. Finally, salt tolerance mechanisms in these Suaeda have been discussed with respect to other halophyte modifications that improve salt tolerance in various ways.

Structural differentiation of the connective stalk in giant duckweed, Spirodela polyrhiza, was examined to reveal the anatomical and ultrastructural characteristics within reduced shoot. The study focuses primarily on structural features of the connective stalk (CT), which connect offspring to their mother fronds. Photoautotrophic offspring fronds remained connected by stalks to mother fronds in the reproductive pockets until separation. The CT originated from the meristematic region of the abaxial frond and joined the fronds laterally with two abscission layers. The most notable features of the CT were polymorphic mitochondria, random occurrences of fi brillar structures in intercellular spaces, and great variability in cell wall thickness. Vascular tissues in CTs were highly reduced, demonstrating only a central vascular strand. Grana with 2 to 4 thylakoids and starch grains were found in the chloroplasts. A chlorophyll assay indicated high chlorophyll concentrations in daughter fronds and low concentrations in CTs. The frond and CT, while physically connected to each other, functioned independently. Despite great reduction in S. polyrhiza, the CT has proven to be very effi cient for separating offspring from the mother frond, which lends to its capacity for rapid vegetative reproduction. The ultrastructural aspects of CTs in S. polyrhiza were characterized for the fi rst time in this study.