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Rolston St. Hilaire

A World Wide Web course tool (WebCT) developed by the Univ. of British Columbia was used as an aid in teaching landscape plant identification and landscape construction at New Mexico State Univ. WebCT is a set of educational tools that are easily incorporated into the teaching of classes. Course assignments, slides of plant materials, and course grades were posted on the Web. A chat tool provided real-time communication among students and the electronic mail facility allowed personal communication with a student or communication to all course participants. Access to WebCT is controlled by username and password, so course material is restricted to course participants. Student progress through materials posted on the Web site can be monitored because WebCT maintains records about student access to web pages. Course statistics, such as the total number of hits per page, time spent on each Web page, and the date and time when student first accessed or last accessed the Web site, are kept by WebCT. Students were able to review highly visual material such as slides of landscape plants at their own pace. Also, students had quick access to their grades.

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Rolston St. Hilaire

Indigenous stands of Taxodium mucronatum Ten. are found in North and Central America, but relatively little is known about the propagation of the species. Progeny from one tree in the Mesilla Valley near Las Cruces, N.M., and from two trees in the Gila National Forest, New Mexico, were observed to be relatively cold-hardy. I initiated this research to find the best conditions for asexual and sexual propagation of those three trees. Terminal softwood cuttings were collected on 16 Oct. 1998 from a half-sibling of the Mesilla Valley tree, and from two half-siblings from the trees in the Gila National Forest. Cuttings were treated with two concentrations of IBA and rooted under intermittent mist in the greenhouse for 13 weeks. Cuttings taken from the Mesilla Valley source and from one of the half-siblings from the Gila did not root. The other half-sibling plant from the Gila showed 82% rooting when cuttings were treated with 8 g IBA/kg. Fifty percent of cuttings rooted when they were treated with 3 g IBA/kg. Root number and root length were greatest for cuttings treated with 8 g IBA/kg. Replication over time will determine whether stock plant environment and the time of taking cuttings affect rooting. Strategies that optimize seed germination and seedling development of asexually and sexually propagated material are being evaluated.

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Rolston St. Hilaire

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Emad Bsoul* and Rolston St. Hilaire

Although valued for its fall foliage color, bigtooth maple (Acer grandidentatum Nutt.) is not widely used in managed landscapes. Furthermore, information on the tolerance of bigtooth maples to drought is scant. We studied water relations, plant development, and carbon isotope composition of bigtooth maples indigenous to New Mexico, Texas, and Utah. Plants were field grown in New Mexico using a pot-in-pot nursery production system. Plants were maintained as well-irrigated controls or irrigated after the weight of pots decreased by 35% due to evapotranspiration. Drought treatment lasted 71 days. Among the drought-stressed plants, plants native to Logan Canyon in Utah (designated UW2), had the greatest root: shoot dry weight ratio (3.0), while plants with the lowest root: shoot dry weight ratio (0.9) were half siblings from a tree native to the Lost Maples State Park in Texas (designated LMP5). Among the five sources we tested, LMP5 had the greatest (1242 cm2) leaf area, while UW2 plants had the smallest (216 cm2). Regardless of the treatment, plants from LMP5 had the highest shoot dry weight (25.7 g). Plants showed no differences neither among sources nor between treatments in relative water content, specific leaf weight, xylem diameter, root dry weight, plant dry weight, relative growth rate, and carbon isotope discrimination, which averaged - 26.53%. The lack of differences in these parameters might be due to selection of these sources from provenances we deemed to be the most drought tolerant. Our selection was based on the results of a previous greenhouse study of 15 bigtooth maple sources. We conclude that these sources, and in particular, plants from LMP5 in Texas, might hold promise for use in areas prone to drought.

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Cathleen Feser, Rolston St. Hilaire and Dawn VanLeeuwen

Mexican elder (Sambucus mexicana Presl.) is used in arid landscapes of the Southwest, but the plant is known for its unpredictable performance in those landscapes. We studied drought responses of mexican elder plants grown in an arid environment using an in-ground nursery production system. Plants were maintained as well-irrigated controls or exposed to cyclic drought and irrigated based on evapotranspiration. Drought treatment lasted 165 days. Plants exposed to drought had more negative predawn and midday water potentials than well-watered plants. The ratio of variable to maximal fluorescence (Fv/Fm) for the drought group (0.76), was near the optimum value of 0.8, suggesting that chloroplasts of drought-stressed plants maintained high levels of activity. Drought cycle, but not drought treatment affected stomatal conductance. Drought-stressed plants had lower transpiration rates than controls except at drought cycle five when transpiration rates were similar between irrigation treatments. Relative water content was higher in controls (76%) than plants exposed to drought (66%). Leaf area of well-irrigated plants was over four times higher than that of plants exposed to drought. Leaf area to root dry weight ratio of drought-stressed plants was 79% lower than control plants. Severely reduced leaf area of drought-stressed plants might be one reason why landscape personnel conclude that mexican elder plants perform poorly in arid landscapes.

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Rolston St. Hilaire and James M. Thompson

Strong linkages among 2-year community colleges and 4-year universities are likely to foster the transition of more students into higher education and enhance student diversity. Two New Mexico educational institutions, Doña Ana Branch Community College (a 2-year community college) and New Mexico State University (a 4-year university), offered a landscape construction class as a joint course offering for students at both institutions. The objective of this educational approach was to develop a system that facilitates the seamless integration of compatible curricula from a community college and a university. Course evaluations showed that 63% of students enrolled in the combined class rated the combining of a university and community college class as an above average or excellent model of education. When asked to rate whether classroom materials and laboratory activities supported learning, 94% of the class rated those materials as excellent. Eighty-eight percent of students rated the presentation of subject matter as above average or excellent when asked if the subject matter was presented in an interesting manner. Students valued the experiential learning projects and would highly recommend the course to their peers. In this redesigned course, women and minorities constituted 63% of the class, suggesting that this educational approach has the potential to retain a large number of underrepresented groups in landscape horticulture. We conclude that this collaborative approach for teaching landscape horticulture is likely to enhance horticultural education and foster a seamless educational experience for students who transition from a community college to a university. Also, this educational approach could serve as a model for curricula that combine practical knowledge with advances in science and technology.

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Rolston St. Hilaire and James M. Thompson

Strong linkages among 2-year community colleges and 4-year universities are likely to foster the transition of more students into higher education and enhance student diversity. Two New Mexico educational institutions, Doña Ana Branch Community College (a 2-year community college) and New Mexico State University (a 4-year university), offered a landscape construction class as a joint course offering for students at both institutions. The objective of this educational approach was to develop a system that facilitates the seamless integration of compatible curricula from a community college and a university. Course evaluations showed that 63% of students enrolled in the combined class rated the combining of a university and community college class as an above average or excellent model of education. When asked to rate whether classroom materials and laboratory activities supported learning, 94% of the class rated those materials as excellent. Eighty-eight percent of students rated the presentation of subject matter as above average or excellent when asked if the subject matter was presented in an interesting manner. Students valued the experiential learning projects and would highly recommend the course to their peers. In this redesigned course, women and minorities constituted 63% of the class, suggesting that this educational approach has the potential to retain a large number of underrepresented groups in landscape horticulture. We conclude that this collaborative approach for teaching landscape horticulture is likely to enhance horticultural education and foster a seamless educational experience for students who transition from a community college to a university. Also, this educational approach could serve as a model for curricula that combine practical knowledge with advances in science and technology.

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Rolston St. Hilaire and Carlos A. Fierro Berwart

The effects of 1H-indole-3-butyric acid (IBA), cutting position on stock plants, the date of propagation, the type of rooting substrate and temperature on rooting of mussaenda (Mussaenda erythrophylla Schumach. & Thonn. `Ashanti Blood' and `Rosea', and Mussaenda philippica A. Rich `Aurorae') stem cuttings were determined. Cuttings of `Ashanti Blood' produced the largest number of roots when treated with 15 mmol (3000 ppm) IBA and rooted in perlite at 29 °C (84 °F). Cutting position on stock plants did not affect rooting in any of the three cultivars. Propagation date and temperature of the rooting medium affected root numbers in `Aurorae'. With `Rosea', only the type of rooting substrate affected root number. Rooting percentage was 22%, 48%, and 39% in `Ashanti Blood', `Aurorae', and `Rosea' respectively. After 30 days of propagation average root length was 4, 12, and 4 mm (0.2, 0.5, and 0.2 inch) in `Ashanti Blood', `Aurorae', and `Rosea' respectively. Growers must determine precise rooting conditions for each cultivar to obtain consistent rooting of cuttings. This process may not be economically feasible on a commercial basis because rooting percentages are relatively low. We conclude that other methods of clonal propagation need to be evaluated before uniform rooted stem cuttings of mussaenda can be produced economically.

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Coye A. Balok and Rolston St. Hilaire

Plant development, leaf morphology, leaf cuticular wax content, and leaf water relations were determined for seven tree species exposed to consecutive cycles of drought. The objective of the experiment was to identify plant taxa suitable for landscapes prone to drought. On the day drought treatments began, plant development traits and leaf morphology varied among species. Leaf cuticular wax content was different among species and ranged from 0.053 mg·cm–2 in California white oak (Quercus lobata Née), to 0.200 mg·cm–2 in Texas red oak (Quercus buckleyi Buckl.). Was content in Bur oak (Quercus macrocarpa Michx.) and Shumard oak (Quercus shumardii Buckl.) averaged 0.105 and 0.11 mg·cm–2, respectively. At harvest, Texas red oak plants treated with drought had the highest root-to-shoot dry weight ratio which averaged 3.1. In contrast, plants of Arizona ash (Fraxinus velutina Torr.) and California white oak that were frequently irrigated had the lowest root-to-shoot dry weight ratio. Drought did not affect stem elongation, total lamina area, leaf dry weight, and specific leaf weight. Abaxial leaf surfaces of Arizona ash were the most pubescent and averaged1836 trichomes/cm2. Drought-stressed plants of golden rain tree (Koelreuteria paniculata Laxm.) had the most negative midday leaf water potential, which averaged –2.5 MPa. Plants of Chinkapin oak (Quercus muehlenbergii Engelm.) that were irrigated frequently had the least negative predawn leaf water potentials. Predawn leaf water potentials tended to be more negative for Arizona ash and golden rain tree than for the oak species. These results suggest that some species of oak might perform well in landscapes prone to drought.

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Rolston St. Hilaire and William R. Graves

Its more westerly native range and apparent xeromorphic foliar traits have led to speculation that black maple (Acer nigrum Michx.f.) is more drought resistant than sugar maple (Acer saccharum Marsh.). We examined differences in morphology and anatomy of leaves of trees of these species indigenous near the 43°N latitude in the midwestern and eastern United States. Leaves were collected during July, Aug., and Sept. 1995, from 10 trees in each of 24 sites at longitudes of 71°W in Maine to 94°W in Iowa. Density of trichomes on abaxial surfaces and lamina surface area showed quadratic relationships with longitude and were greatest for leaves from westerly sites in Iowa. The percentage of total lamina surface area partitioned in the two most basipetal lobes increased linearly with longitude. Abaxial surfaces had 6 to 960 trichomes/cm2, lamina surface area was 28 to 176 cm2, and surface area partitioned in basipetal lobes was 5% to 9%. A quadratic regression function related increases in trichome density to decreasing mean annual rainfall at collection sites. Specific leaf mass ranged from 3.5 to 7.6 mg·cm–2 and did not relate to longitude. Scanning electron microscopy showed leaves throughout the range had similar trichome morphology, and light microscopy is being used to examine variation in leaf anatomy and stomatal traits.