Thesis (M.S.)--Oregon State University, 2004. / Printout. Includes bibliographical references. Also available via the World Wide Web.

Call number: LD2668 .T4 1934 T51

8 pp.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Thesis (Ph. D.)--Virginia Commonwealth University, 2009. / Prepared for: Dept. of Biology. Title from title-page of electronic thesis. Bibliography: leaves 135-141.

Growing on dry saline soils throughout the Intermountain Region of the United States is a group of herbaceous, perennial species of Atriplex, including A. corrugata, A. cuneata, A. cuneata ssp. Introgressa, A. falcata, A. gardneri, A. tridentata, and A. welshii, designated as the Atriplex gardneri complex. Highly adaptive and competitive in the arid salt deserts, these species are valuable as forage for livestock and wildlife. Because of extensive variation present within this complex, considerable taxonomic confusion has resulted. To clarify taxonomic and phylogenetic relationships, selected populations and plants were analyzed morphologically, cytologically, ecologically, phenologically, and genetically. Polyploidy is common within most of the major taxons. The polyploid species show little morphological variation from that of their diploid ancestors. Diploids occupy well drained soils relatively low in salt and grow in isolated pockets; polyploid derivatives are more widely distributed, growing in the lower valley floors characterized by heavy soils of high sodium content.

Because of the greatly increased supply of genetic variation which it provides, introgression is of great importance in determining both the rate and the direction of evolution. Hybridization between the genera Cowania and Purshia provides an excellent model for demonstrating the various products which might be expected from introgression. The present study is an attempt to further investigate phylogenetic relationships of Cowania mexicana and Purshia tridentata by use of cytological and biochemical techniques.

Previous research has shown that polyembryony occurs in many species of the Ulmaceae. The purpose of this study was to determine the method of multiple embryo formation in netleaf hackberry, Celtis reticulata Torr. Collections of specimens were made throughout a two-year period. Collections were begun in early spring while the trees were still in the bud state. Collections were continued regularly throughout the growing season. The collections were preserved in FAA solution and were prepared for microscopic examination as follows: (1) The tertiary butyl paraffin method was used for dehydrating and embedding. (2) Sectioning was done on a rotary microtome at 7-20 microns. (3) Staining of the slides was accomplished by Conant's Quadruple. Examination of the slides reveals at least two, and possibly four, ways by which polyembryony may occur in C. reticulata. The most frequent method of multiple embryo development appears to be the development of an extra egg-like cell--probably a synergid--in the embryo, sac. Some slides show the egg-like cell after it has begun to develop into an embryo. The splitting of the zygotic embryo was observed on the slides and supported by germination studies in which double epicotyls were found on a single hypocotyl. Suspensor budding appears to be a means of multiple embryo formation, but the possibility of faulty interpreation of the sections, due to the plane in which they were cut, could discount this theory. Nucellar budding is also a possible means of multiple embryo development. However, here again the possibility exists that faulty sectioning of the material occurred. While the slides appear to show embryos being formed along the nucellar layer, these embryos could be of synergid origin. If nucellar budding does actually occur, it would have great genetic and evolutionary significance. Seed germination studies reveal a high percentage (20%) of multiple seedlings. It is also noted that frequently a seed will abort a few weeks after pollination. The reason for this abortion is unknown, but the author speculates that this is due to embryo degeneration. The possibility of a growth-stimulating substance being injected into the plant by the Psyllid which parasitizes C. reticulata is, the author believes, a plausible theory worthy of further study.

Natural environments are often limiting to plant growth in more than one resource due to the simultaneous fluctuations in resource supply and demand. The mechanisms a species uses to acclimate to simultaneous resource variation may not be uniform among species of the same growth form. Four evergreen ericaceous shrubs responded individualistically to fluctuations in light and water in an experimental garden study. <i>Rhododendron maximum</i> and <i>Kalmia latifolia</i> were able to acclimate photosynthetically to high and low irradiance under both high and low water availability. <i>Rhododendron catawbiense</i> and <i>R. minus</i> showed significantly higher acclimation to high light in high water treatments. All four species were able to reduce their osmotic potential and water deficit at the turgor loss point seasonally, especially in low water treatments. Low soil water availability also reduced midday conductance and water potential in all four species. Rhododendron maximum and <i>R. catawbiense</i> were very conservative in their water use patterns. <i>Rhododendron minus</i> and <i>K. latifolia</i> exercised less stomatal control over water loss but did not appear to experience water stress under these treatment conditions. Rhododendron catawbiense was the most sensitive to low water availability and had the lowest turgor pressure of the four species. Daily carbon dioxide assimilation was highest in high light, high water. treatments and lowest in low light, low water treatments for all four species. During the two years of this study, these species did not show any consistent pattern of increased growth in the high light, high water treatments where carbon dioxide assimilation was highest. Since these species are native to low resource habitats, their abilities to significantly increase growth during periods of high resource availability may be less than that of plants adapted to high resource availability. The results of these experiments indicate that these four species of the same growth form respond differently to simultaneous fluctuations in light and water resources. / Ph. D.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.