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Tsuga canadensis, which may be a reflection of .the stronger apical dominance in the former species. The pipe model would have to be modified to account for the above data, such that each unit pipe system had many more but smaller tracheids near the top than the bottom of the tree, and such that the trunk component of a unit pipe had more and wider tracheids than the lateral branch component. A more useful morphogenetic model involves hormonal gradients that control tracheid size and number in the plant. Hydraulically the ar- chitecture of these species favors the trunk over lateral branches and may thus help the upper leaves on the tree to compete with lower leaves for water and minerals. FAGERBERG, WAYNE, R. Dept. of Biology, Southern Methodist University, Dallas, TX 75275.- A morphometric analysis of the homogeneity of palisade cell structure in leaves of Helianthus annuus. L. Leaves were divided into four quadrants and random samples taken from each quadrant. The ratio descriptors, Vv and Sv were cal- culated to describe the relationship between organelle compartment and cell size for the chloroplast, mitochondria, vacuole, micro- body, oil, starch, and mitochondrial - chloroplast membrane compartments. Since ratio values do not often reflect changes in mean cell volume, cell volumes and actual compartment sizes were also determined. In mature fully expanded leaves statistically significant variations were found between quadrants in Vv ratio of the chloroplast, vacuolar and starch compartments and in the Sv ratios of the granal membranes. The granal membrane compartment was the most variable, between sampled quadrants. The starch compartment was significantly smaller in the bottom 1/2 of the leaf suggesting that starch may be more rapidly mobilized from the lower half of the leaf. This study suggests that palisade cells are not homo- genous throughout the whole leaf due to variation in organelle compartments involved with photosynthesis. These results will be compared to similar data derived from developing leaves. FIORES, EUGENIA M. Escuela de Biologia, Univer- sidad de Costa Rica, San Josg, Costa Rica, Amgrica Central. - Cauline glands of Gunnera insignis. Cauline glands of Gunnera insignis were studied with light and scanning electron microscopy. Two types are recognized: (1) stellate glandular trichomes secreting mucous material and (2) whitish lobulated bodies covered by stomata which release water. The glandular trichomes develop around the leaf primordia and between the numerous squamules. These organs, as well as the shoot apex, are immersed in the mucous secretion. Many filaments of Nostoc and other organisms (algae, fungi, nematodes, insect larvae) are observed living in the mucilage. Nostoc is also recognized inside the trichomes and cauline tissues. Eventually, these trichormes degenerate and form brownish spots associated with Nostoc. The structures wich release water develop later and occupy the spaces left by the glandular trichomes. They cease functioning, turn green and extend longitudinally when the leaf~ which they surround Developmental and Structural Section 21 reaches maturity. The interaction Gunnera - Nostoc represents the only known symbiosis between an angiosperm and a nitrogen-fixing bluegreen alga. This relationship is still not well known. Apparently in Gunnera the alga Nostoc penetrates through the glandular trichomes. It seems pertinent to study the role of these glands in relation with Nostoc penetration and the nitrogen fixing mechanism. FOLSOM, MICHAEL W. Dept of Botany, Univ. of Alberta, Edmonton, Alberta, CANADA T6G 2E9. -Structural aspects of the central cell gf Soybean. Glycine max (L) Merr. with respect to fixation technique. Ultrastructure of the eight nucleate embryo sac of soybean Glycine max (L.) Merr. demonstrates an unusual sequence of events in the central cell. Metabolites enter the embryo sac, are polymerized into starch grains, and are degraded mostly disdppearing from the central cell before fertilization. These starch grains are organized into groups that have been referred to as "packets" by previous workers. Unlike starch grains reported in most plant cells these packets do not appear to be membrane bound. The absence of a membrane is most likely not caused by fixation problems since other membrane bound organelles of the central cell exhibit normal membranes. The addition of Alcian Blue 8GX (AB) to the fixation process shows that rather than being naked or bound by a plastid membrane, these paskets are at least partially enclosed in a layer of amorphous material, a mucopolysaccharide, deposited some time after the starch grains begin to form. Coomassie Brilliant Blue has shown that the material surrounding the starch packets has a protein component. The role of Alcian Blue acting as stabilizing agent for this glycoprotein and the preservation of cellular components by various fixation techniques (e.g. GA/Os04, GA + AB/Os04, GA/OsOi/TA/OsO4, and freeze substitution) will be discussed with respect to the starch packets and associated glycoprotein in the central cell. FREEMAN, THOMAS P., MURRAY E. DUYSEN AND THOMAS J. GULYA. Departments of Botany and Plant Pathology, North Dakota State University and U.S.D.A. Agricultural Research Service, Fargo, N.D. 58105. chloroplasts caused by Pseudomonas syringae pv. ta etis. Severe chlorosis and ultrastructural modifi- cations of chloroplasts occur in sunflowers in response to infections of Pseudomonas syringae pv. tagetis. Chlorosis became apparent within two days after the cotyledons of ten day old sunflower seedlings were inoculated with the bacteria. The first symptoms gererally appeared in the center of leaves at the second node above the cotyledons. During the rext few days the chlorosis progressed to include leaves at several nodes. Despite the fact that some of these leaves lost essentially alL of their pigmentation they remained turgid and continued to expand. The loss of pigmentation is directly related to ultrastructural changes within the chloroplast. Grana thylakoids became dilated and separated from the granal stacks. These thylakoid membranes were not altered as in the cases of chromoplast formation or normal senescence. Both grana and stroms thylakoid membranes coalesced to form a large membrane sheet in the center of the plastid. Starch and plastid ribosomes were lost early in the chlorotic cycle. Other cellular organelles do not appear to be altered by the bacterial i nf ection .
22 Developmental and Structural Section FRENCH, J.C. Department of Biological Sciences, Mississippi State University, Mississippi State, MS 39762-5759. - Preliminary observations on the anatomy and systematic occurrence of secretory structures in Araceae. A preliminary survey was made of the structure and systematic occurrence of extrafloral nectaries, wax glands, resin canals and laticifers in Araceae. Extrafloral nectaries were found in only two subfamilies, Philodendroideae and Lasioideae; extrafloral nectaries from both taxa have a similar anatomical organization. Wax glands were found on the undersides of leaves at the juncture of certain primary veins and the midvein of several species of Alocasia and Xenophya. A wax gland comprises a palisade layer of epidermal cells that excretes a thick outer plaque of wax. Resin canals have been found in roots, stems and leaves of certain genera of Lasioideae and Philodendroideae. Resin canals in roots of Philodendron, Cercestis and Culcasia have a sclerenchyma sheath surrounding the epithelTum. Resin canals in some species of Culcasia lack both an epithelium and intercellular space, and have only sclerenchyma. Laticifers of Colocasioideae were found to contain a variety of particles in their latex, including osmiophilic bodies about 8 vm in length. Two types of these large particles have been found, one typical of latex from Old World genera, e.g. Colocasia, and a second type typical of New World genera, e.g. Syngonium. Laticifers from roots of Colocasioideae examined thus far differ from those in the shoot in lacking the large osmiophilic particles in latex, and in lacking anastomoses. FRENCH, J.C. and P.B. TOMLINSON. Department of Biological Sciences, Mississippi State University, Mississippi State, MS 39762-5759 and Harvard Forest, Petersham, MA 01766. - A summary comparison of vascular bundle organni-zation in Araceae, Cyclanthaceae and Pandanaceae. In previous, separate studies compound vascular bundles have been investigated in three families of monocotyledons: Araceae, Cyclanthaceae and Pandanaceae. These results are brought together in the form of a summary comparison. Compound bundles from different taxa may appear to have a similar construction when comparisons are based on single transverse stem sections. However, when the three-dimensional course of bundles is compared from representatives of Araceae, Cyclanthaceae, and Pandanaceae, distinctly different patterns of construction are found. These results confirm the usefulness of cinematographic methods in comparative studies of the anatomy of monocotyledons. The results also support the view that these families probably have no close phylogenetic affinity. In addition, the concept of the compound vascular bundle has been broadened to include: 1) forms which. intergrade with amphivasal bundles, a common feature of some Araceae, e.g. Dieffenbachia, Philodendron and 2) bipolar or multipolar bundles resul`ting from longdelayed fusion between a leaf trace and axial bundle(s), which is a consistent feature of Cyclanthaceae. FRENCH, J.C. and P.B. TOMLINSON. Department of Biological Sciences, Mississippi State, MS 39762 and Harvard Forest, Petersham, MA 01766. - Cinematic analysis of stem vasculature in Philodendron (Araceae. A survey of stem vasculature in Philodendron has been made using cinematic analysis of series of transverse secti ons . Phil1odendron exhi bi ts the most di verse vascular organiza~tion in the Araceae, with respect to both the arrangement of xylem and phloem in vascular bundles and the three-dimensional course of the bundles. In a few species (P. scandens) simple collateral bundles are present in the central cylinder, and when leaf traces are followed basipetally each trace fuses with an axial bundle. In other species bipolar,or tri- to multipolar bundles predominate in the central cylinder, and exhibit a complex pattern involving unpredictable fusion and/or anastomosis of components in compound bundles. In some species with compound bundles each collateral component is completely surrounded by a sclerenchyma sheath, while in other species little or no sclerenchyma is present, and compound bundles appear to intergrade with amphivasal bundles. In addition to intermediate types, well-defined amphivasal bundles are present in some species, which have a solid core of phloem and a continuous cylinder of xylem. In some species of Philodendron with amphivasal bundles some of the tracheary elements do not develop in a typical fashion. Even in mature stems secondary cell walls of some elements remain thin and unlignified or are absent, and cell diameters are reduced. When this condition occurs, it is typically found in many bundles in a stem, and has been found in 17 species (e.g., P. smithii, imbe, hastatum, longilaminatum) thus far. GRAYBOSCH, ROBERT A.* and PALMER, REID G. Genetics Department, Iowa State University, Ames, IA. 50011. - Cytological studies on a male-sterile mutant (ms2) in soybean (Glycine max). All known male-sterility mutations in soybeans are of the genetic type; to date, six such recessive nuclear mutations have been described. The ms2 mutant was discovered in 1975, but no cytological studies aimed at elucidating exact causes of male sterility have been undertaken. This report presents results of preliminary studies on cytological events associated with the ms2 mutant, accomplished via comparative studies of anther and pollen development in male-sterile and male-fertile plants. Squash preparations reveal that chromosome pairing and segregation is normal in microspore mother cells of developing sterile anthers. Microsporogenesis proceeds normally until tetrad stage, at which time premature abortion usually occurs; on rare occasions separation of microspores from tetrads occurs, but release of microspores from callose was not observed. Abnormalities in the tapetal layer are associated with tetrad degeneration. These are manifested in the form of vacuoles or inclusions, first observed during first meiotic division of microspore mother cells. They progressively enlarge during anther ontogeny. Tapetal development resembles that occurring in plants homozygous for either the ms3 or msp (partial male sterile) mutations. Anther morphology is normal during early developmental stages, but a progressive degeneration of external tissues is noted. GRIMSON, MARK J.* and HOWARD J. ARNOTT, Department of Biology, The University of Texas at Arlington, Arlington, TX 76019-0498. - Electron microscopy of druse crystals in the abscission zone of Phyllanthus niruri L. Abscission plays an important role in the development and survival of plants. In Phyllanthus niruri L (Euph-orbiaceae), masses of druse crystals are found proxi- mal to the abscission zone of the leaf and flower as well as
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