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  • Author or Editor: E.L. McWilliams x
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Abstract

Violet silverleaf (Leucophyllum candidum I.M. Johnst.) is found in Mexico (1) but is native in Texas only in southern Brewster County in the Trans-Pecos (1, 9, 10, 11) where it usually is found growing on gravely hills. It has an affinity to soils of limestone origin and is prevalent especially on caliche hillsides.

Open Access

Abstract

Salvia regla Cav. is native in Texas only in the Chisos Mountains, Big Bend National Park, located in Brewster County (1, 5, 6). It is found in Mexico from Coahuila and Durango to Oaxaca with the type from Regia in the state of Hidalgo (5). In the Chisos, it is found in Oak Creek Canyon, Lost Mine Trail, and Green Gulch; it is especially prevalent around the western slopes of Mount Emory at altitudes of generally over 1610 m (1 mile). It is called the Queen of the Chisos Mountains and is considered by many the most beautiful of all the autumn-flowering shrubs (6). Mountain sage is found in dappled shade and is quite spectacular when in bloom from June to October. It is a favorite of many species of hummingbirds and is browsed by deer. It becomes a prime attractant to hummingbirds on their return migration to the tropics in September-October when planted out of its natural environment.

Open Access

Abstract

Seeds of Coreopsis tinctoria Nutt., Ipomopsis rubra (L.) Wherry, Linum perenne L., and Asclepias tuberosa L. were germinated under constant light at 155 ± 10 μEm−2sec−1 on a thermogradient plate to determine optimum temperatures for germination. Optimum temperatures were 30°C for C. tinctoria, 25° for L. perenne and 30° for A. tuberosa. I. rubra exhibited poor germination at all temperatures in light. C. tinctoria, L. perenne and A. tuberosa germinated within temperature ranges of 15° to 35°, 15° to 25°, and 25° to 35°, respectively. A. tuberosa was the slowest germinating of the 3 species.

Open Access

Abstract

Whole plant net CO2 exchange, light compensation points, and acclimatization were determined for Philodendron scandens Subsp. oxycardium (Schott) Bunt, Epipremnum aureum (Linden & Andre) Bunt (Pothos), Brassaia actinophylla Endl. and Dracaena sanderana Sander before and after 4 and 15 week acclimatization periods at 27 μE m−2 sec−1 (400-700 nm), for 12 hr/day. Philodendron scandens Subsp. oxycardium, E. aureum, B. actinophylla and D. Sanderana exhibited CO2 uptake rates of 0.53, 1.16, 1.18 and 0.50 mg CO2 dm−2hr−1, respectively, at 57 μE m−2 sec−l (3400 lx) after 15 weeks of acclimatization. Each species showed a significant increase in net CO2 uptake during the study period. Dark respiration decreased 63% in P. scandens Subsp. oxycardium, 71% in E. aureum, 53% in B. actinophylla and 64% in D. sanderana during the acclimatization period.

The regression correlation coefficient of CO2 uptake with light intensity increased for each species during the study. At 15 weeks, P. scandens Subsp. oxycardium, E. aureum, B. actinophylla and D. sanderana exhibited r values of .95, .98, .96, and .91, respectively. Light compensation points decreased between week 1 and week 15 as follows: 33 to 7 μE m−2 sec−1 in P. scandens Subsp. oxycardium, 38 to 6 μE m−2 sec−1 in E. aureum, 14 to 4 μE m−2 sec−1 in B. actinophylla and 119 to 15 μE m−2 sec−1 in D. sanderana.

As a result of acclimatization, all species exhibited increases in net CO2 uptake and decreases in dark CO2 evolution concomitantly indicating a reduction in dark respiration. Leaf area increase was negatively correlated with light compensation point. B. actinophylla had the highest leaf area increase with 2.16 dm2, E. aureum and P. scandens Subsp. oxycardium were intermediate with 1.08 and 0.96 dm2, respectively, while D. sanderana, the species with the highest light compensation point exhibited the lowest leaf area increase (0.44 dm2). Philodendron scandens Subsp. oxycardium, E. aureum, B. actinophylla, exhibited similarly rapid rates of acclimatization, while D. sanderana acclimatized much more slowly and had a significantly higher light compensation point.

Open Access

Abstract

Stem cuttings taken from rooted propagules of a 2-year old South Texas live oak, Quercus virginiana Mill., and maintained for 2 years in a greenhouse rooted in greater numbers than did cuttings taken directly from the original tree 2 years later. Rooting of cuttings from trees 5-8 years decreased with tree age.

Open Access

The effects of three light levels (1403, 806, and 462 μmol·s-1·m-2 on the severity of damping-off caused by Pythium myriotylum Drechsler in Amaranthus hybridus L. `Quelite' were tested. The observed mortality (33%, 69%, and 81%, respectively) decreased as light intensity increased. The reduction in plant growth and maturity in a shaded location is related to the observed increase in suspectibility to damping-off in such an environment.

Free access

Abstract

Texas silverleaf, cenizo, or purple sage [Leucophyllum frutescens (Berl.) l.M. Johnst.] is native to Texas in the Rio Grande Plains, southern Trans-Pecos and sparingly in the Edwards Plateau (1, 5, 7, 8). It is not a true sage (Salvia) but is in the same family (Scrophulariaceae) as penstemon, snapdragon, and Indian paintbrush. It is found in plant hardiness zones 10a, 9a, 9b, 8b, and 8a (6) as far north as London in Kimble County where it is most prevalent on south-facing slopes of caliche hills.

Open Access

One-node explants and one-node stem cuttings of Asian jasmine [Trachelospermum asiaticum (Siebold & Zucc.) Nakai] were rooted, respectively, in vitro [tissue culture (TC)] or by conventional macropropagation (MACRO). The TC and MACRO stem bases were then analyzed for differences in the time-course sequence of 1) root primordia initiation and development and 2) adventitious root xylem development and root-to-shoot xylem connections. Early root primordia were observed at Day 3, and, by Day 7, root-to-shoot xylem connections were equally developed in TC and MACRO systems. Continued development and emergence of adventitious roots were observed at Days 8 to 10. At Days 13 and 18, when viewed using scanning electron microscopy, TC root hairs were morphologically thicker and one-third to one-half the length of MACRO root hairs. There was no apparent difference in root-hair density. Inferior TC root-hair length may be a factor in the acclimation of TC-generated plantlets.

Free access

In vitro tissue-cultured (TC) and macropropagated (MACRO) 18-day old adventitious roots of Asian jasmine [Trachelospermum asiaticum (Siebold & Zucc.) Nakai] were compared for their ability to absorb and translocate radiolabelled P from a nutrient solution. Samples were taken at 1, 2, 4, 8, 12, and 24 hours after the initial dosage of the nutrient solution with 7.4 × 10-2 MBq KH 32 2PO4/liter. TC roots were capable of absorbing P, but at significantly lower levels than MACRO roots. Greater P absorption occurred in MACRO roots within the first hour and continued for the duration of the experiment. However, there was no significant difference in the rate of P translocation from roots to shoots between treatments. Root systems formed in vitro survived acclimation and had developed into well-branched root systems after 13 weeks. Reduced P absorption by TC roots did not limit either P translocation or survivability during and after acclimation.

Free access

Abstract

The CO2 exchange rates of Peperomia obtusifolia A. Dietr. plants (tops and roots) were measured for 12-hour light and 12-hour dark cycles during 5 weeks of acclimatization at 30 µEs-1m-2. A carbon balance analysis of the data indicated that the growth conversion efficiency (Yg) remained constant (0.73 ± 0.1 and 0.77 ± 0.04 before and after acclimatization, respectively). The daily rate of substrate production from photosynthesis (ΔS/Δt) remained constant at 18 ± 2 mg C plant-1 24 hr-1, at the acclimatization photosynthetic photon flux density (PPFD), but the daily rate of synthesis of carbon into new material (ΔW/Δt) increased by 55% within the first week. The maintenance coefficient (m) decreased from 13.0 ± 0.9 to 7.4 ± 0.4 mg g-1 24 hr-1, and change in m may be a criterion for selection of plants that can be adapted for use at low PPFD. The light compensation point (LCP) was reduced during acclimatization, but its use underestimated the PPFD required for 24-hour plant maintenance because of failure to account for night-time respiratory losses. It is suggested that the PPFD at which ΔW/Δt is zero or slightly above is more reliable than the light compensation point for determining PPFD required for plant maintenance.

Open Access