Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item The State of Water and Cell Morphology In Deep Frozen Populus(1985) Hirsh, Allen Gene; Solomos, Theophanes; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md)By using differential scanning calorimetry, electron microscopy, light microscopy, and freezing survival experiments, it is shown that superhardy Populus balsamifera v. Virginiana (Sarg.) is capable of withstanding liquid nitrogen (LN 2) temperatures because of the formation during cooling, at a temperature of about -30°C and cooling rates less than 30°C/hr, of aqueous glasses in the intracellular solutions. In more detail, the major findings concerning the state of intracellular water are: (1) the bulk of the intracellular contents go through an equilibrium glass transition at about -28°C during slow (<5°C/hr) cooling; (2) smaller additional amounts of intracellular material go through equilibrium glass transitions at about -47°C and -70°C; (3) as a result of the resistance to homogeneous nucleation of these glass forming intracellular solutions when they are in equilibrium with extracellular ice at<.-20°c, cooling/warming at any combination of rates from 3°C/hr to 1200°C/min between -20°c and -196°C is non-injurious to fully hardened wood; (4) death associated with quench cooling in LN2 from -15°C is correlated with the devitrification, (cold crystallization) near -90°C upon warming of the very low temperature glass forming component, followed by further devitrification of the higher temperature components, especially between -30°c and -20°c; and (5) the vacuolar compartment appears least resistant to devitrification and capable of thereby causing death even when the cytoplasm resists devitrification. In addition, it was found that when fully superhardy wood is cooled slowly (3°C/hr) after being imbibed with water (doubling total water content) massive intracellular freezing occurs. Despite the fact that total tissue water of tender Populus (summer wood) is 2x that of the artifically water loaded hardy wood on a gram H20/gram dry weight basis, tender wood cooled at 3°C/hr to -50°c does not display intracellular freezing. It is killed by -2°C. It is shown that in both tender and hardy wood <10% of water is extracellular. Thus a significant excess of extracellular water appears to cause intracellular freezing and this may be a major reason for the large water loss seen in the fall 'hardening off' of most temperature zone woody plants. It is also shown that during slow cooling, the plasma membranes of both hardy and tender Populus cells stick to and collapse the cell wall, but that these membranes stay smooth in the case of superhardy cells and wrinkle markedly in the case of tender cells. Membrane-associated particles appeared to clump in the membranes of slowly cooled tender cells but not in the slowly cooled hardy cells.Item A REVISION OF THE GENUS ODONTONEMA (ACANTHACEAE)(1982) Baum, Vicki M.; Reveal, James L.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Odontonema Nees (Acanthaceae, Acanthoideae, Acanthatae, Odontonemeae) is a New World tropical or subtropical genus of 26 species and two varieties. Members of the genus are distributed from coastal central Mexico southward throughout Latin America into northern South America, with one species located on the southeastern coast of Brasil (a second species from Brasil is from an unknown location). Odontonema also is found on the Caribbean Islands. The genus consists of four major groups which, at this time, are not given formal taxonomic recognition: 1) red-purple (rarely white) flowered species (O. callistachyum and its relatives); 2) red flowered species with typically a bottle-shaped corolla (O. schornburgkianum and its relatives); 3) white-purple flowered species with a more strongly bilabiate corolla (O. nitidum and its relatives); and 4) yellow flowered species (O. hondurense and its relatives). Although a few members of Odontonema may be seen in cultivation, the present revision is based on an examination of herbarium material found in both New and Old World herbaria, a numerical analysis of macromorphological features, and an examination of pollen morphology. The four groups within Odontonema defined above were established after the numerical analysis, and all species save one (O. cuspidaturn) were found to have 3-colporate pollen characteristic of sect. Odontonemeae. Descriptions were prepared of each species based on available herbarium specimens...Item Insect-Nematode-Red Pine Association in Western Maryland with Major Emphasis on Bursaphelenchus xylophilus and Monochamus spp.(1985) Harman, Amy Susan Litten; Krusberg, Lorin R.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Western Maryland red pines, Pinus resinosa Ait. Were examined over three years, 1982-1984, to determine the distribution of Bursaphelenchus xylophilus, the pinewood nematode. Ca. 47-year-old (older) and ca. 25-year-old (younger) trees were subdivided into the following categories: (1) trees with mostly green needles; (2) trees with mostly reddish-brown needles; (3) trees with no needles but with bark intact; (4) trees with no bark; and (5) trees with chlorotic, bleached-green needles. The pinewood. nematode infected 76.5% of older red pines and 68% of younger red pines. The nematode was not evenly distributed in trees in any tree decadence category or by tree age. Bursaphelenchus xylophilus infected 15.1% of the samples from trunk, primary and secondary branches in older red pines and 18.5% in younger red pines. By tree decadence category older trees had the highest infection (25.2%) in green needled trees (category 1) whereas younger trees had the highest infection (28.7%) in bleached-green needled trees (category 5). Trees collected in late May-early June 1982 lacked Monochamus rearings and belonged to categories 1, 2, 3 and 4. Trees from these categories had emergences of Ips spp., Tetropium schwarzianum Casey, Pissodes approximatus Hopkins and Otiorhynchus spp. in summer 1982. From bleached-green needled red pines (category 5) collected in late July-early August 1983 two Monochamus species emerged in 1984, M. carolinensis (Olivier) and M. scutellatus (Say), as well as other insects including Neacanthocinus pusillus (Kirby) and Amniscus collaris Haldemann. Chrysobothris scabripennis Cast. and Gory emerged from trees cut in 1983, but which remained uncaged in the field until 1984. Bursaphelenchus xylophilus was present in 94% of tracheal systems of both M. scutellatus and M. carolinensis. Pinewood nematode was found infesting 4.2% of N. pusillus specimens. One specimen each off. approximatus, Ips spp. and C. scabripennis were positive for B. xylophilus. Dolichomitus tuberculatue tuberculatus (Geoff.), an ichneumonid parasite, was reared from Monochamus spp. larvae. Two deutonymph mites, Dendrolaelap isodentatus (Hurlbutt) and Trichouropoda hirsuta Hirschmann, were located externally on Monochamus spp. beetles.