Shirley C. Tucker

ORIGIN OF SYMMETRY IN FLOWERS

Phylogenetically significant floral features include number, order of initiation and position of appendages, symmetry, aestivation, degree of fusion, and loss of parts. These features can be studied ontogenetically, and the ontogenies compared among related taxa to yield information on the relative time during ontogeny when the feature is determined or manifested. The family Leguminosae has three subfamilies which differ in floral symmetry, aestivation, and in location and degree of fusion of organs. It is proposed that these kinds of features arise early in ontogeny (during organogeny) and that as a consequence they are considerably more stable than those features which arise at mid-stage (during form change and enlargement) or at late stages of ontogeny (those which involve differentiation of tissues and cells). The mid-stage-determined features include many which separate related genera, while those determined late in ontogeny tend to characterize and separate related species. For any one feature, advanced taxa tend to express the feature precociously. For example, zygomorphy can be expressed even before organ initiation as an oval rather than circular shape of the floral apex. In other flowers, zygomorphy may be expressed first at sepal, petal, or stamen initiation, or it may be delayed until enlargement of petals or stamens. The order of organ initiation also is an expression of symmetry; in many legumes, members of each whorl are initiated sequentially from one side of the floral apex to the opposite side rather than simultaneously or helically. Elucidation of developmental differences between similar or related taxa can provide a basis for understanding how subfamilial and tribal differences could have evolved in the Leguminosae.

Thiocarbohydrazide binding for botanical specimens for scanning electron microscopy: a modification

The ligand osmium binding technique utilizing thiocarbohydrazide has been a successful alternative to evaporation or sputter coating of botanical specimens. A modification to this technique is presented which we have found successful in our laboratory for the preparation of a variety of specimens. This technique permits an overall reduction in the quantity of osmium necessary to provide conductivity. Further, dehydration time and specimen handling is reduced by the complete chemical dehydration of the tissue utilizing 2‐2‐dimethoxypropane.

Floral ontogeny, pattern formation, and evolution in Hibbertia and Adrastaea (Dilleniaceae)

Floral development was compared with scanning electron microscopy in 12 Australian species of Hibbertia representing most of its morphological variation, and in the related Adrastaea (Dilleniaceae). Calyx and corolla arise in quincuncial helices in radially symmetrical species, while the petals initiate unidirectionally from one side in zygomorphic species. Stamen number (3-200+) proliferates by centrifugal addition of individual primordia or by innovations of common primordia and ring meristems. Common primordia arise in single-stamen positions alternately with petals, and each produces one to several stamens centrifugally that remain attached to a shared base and form a stamen fascicle. A ring meristem in Adrastaea initiates a whorl of five stamens, alternate with the first stamens but outside their whorl. In radially symmetrical species of Hibbertia, a first ring of stamens is supplemented centrifugally by additional stamens on a meristem ring. The first stamens in zygomorphic species of Hibbertia initiate as a terminal ridge on the floral apex, with subsequent stamens added centrifugally on one side and two carpels initiated on the opposite side. The carpels arise as a simultaneous ring in radially symmetrical flowers, or as a simultaneous pair in zygomorphic species. Staminodial presence is viewed as of minor significance. Four pollinator syndromes are proposed for Hibbertia, related to differing floral architecture.

Ontogeny of staminate and carpellate flowers of Schisandra glabra ( Schisandra )

Schisandra glabra (Schisandraceae) is a rare monoecious liana in forests of the southeastern United States. Both types of flowers are solitary in leaf axils and radially symmetrical, with eight to 13 greenish yellow to red tepals in the flower. Each male flower has five (four to seven) spirally arranged stamens forming a red pentagonal synandrous shield. Transitions between tepals and stamens occur occasionally. Each carpellate flower contains 25–30 free, spirally arranged carpels on a conical receptacle. Histological study shows that the floral apical meristem is more highly convex than the vegetative apex; both have tunica-corpus configurations. All primordia, starting with tepals, are initiated acropetally, in a continuous 2/5 phyllotaxis. Apical diameter increases greatly after tepal initiation, more so in carpellate than in staminate flowers. The apical residuum in staminate flowers expands to form the center of the staminal shield, with the stamen primordia projecting as flattened marginal extensions. The connective region of each stamen broadens markedly, resulting in wide separation of the sporangial pairs of each stamen. Just before anthesis, each connective arches outward so that the sporangia appear lateral. In carpellate flowers, the carpel primordia are initiated helically; the apical residuum forms a narrow, spinelike structure. Floral development in Schisandra is compared with that of other primitive angiosperms such as Illicium and Myristica.

Dedifferentiated Guard Cells in Magnoliaceous Leaves

Evidence has been obtained that guard cells and other epidermal cells as well as mesophyll cells undergo division during wound repair of mature leaves in 26 magnoliaceous taxa in the genera Kmeria, Elmerrillia, Magnolia, Manglietia, Michelia, Paramichelia, and Talauma. Division of epidermal cells is believed to be rare in mature leaves, and division of guard cells is particularly unusual in most species previously studied.

Preference for Some Other Pollens Shown by Lines of Honeybees Selected for High and Low Alfalfa Pollen Collection

SummaryThe collection of pollen by high and low alfalfa pollen collecting lines of honeybees was studied at Baton Rouge, Louisiana, where no alfalfa (Medicago sativa) is grown. The high line collected significantly more pollen than the low line from Trifolium repens, Cornus drummondii, Ampelopsis arborea, Polygonum spp., Lippia lanceolata and Geranium carolinianum. The low line collected significantly more than the high line from Tradescantia bracteata, Rhus radicans, Ambrosia spp. and Solidago spp. Twenty-four pollen sources were studied.