Experiments were conducted in a growth chamber to determine the effects of planting depth on the developmental sequence of velvetleaf seedlings and the effect of cyanazine placement relative to velvetleaf planting depth on cyanazine toxicity. Velvetleaf seedling emergence was delayed when seeds were planted 6 cm deep compared to the 2- and 4-cm planting depths. Lateral roots did not appear until after the cotyledons had emerged and expanded. This was followed by secondary root emergence from the primary root which occurred before adventitious roots appeared from the hypocotyl for the 2- and 4-cm planting depths. The first true leaf did not unfold until after the secondary root system was well developed. The quantity of adventitious roots on the hypocotyl increased with increasing planting depth. Velvetleaf adventitious roots appeared to be involved in cyanazine toxicity when cyanazine was placed above the seed. Increasing planting depth increased the proportion of seedling absorptive tissue above compared to below the seed. This resulted in increased cyanazine exposure for the deeper planted velvetleaf seeds when herbicide was placed above the seed.

Controlled-environment experiments were conducted to determine the effects of soil temperatures of 5 to 20 C, seed depths of 0 to 6 cm, and above- or below-seed cyanazine placement on germination and seedling development of giant foxtail and velvetleaf. Giant foxtail did not germinate at 5 C and failed to emerge from 6 cm deep within 21 days at 10 C. Increasing soil temperature above 10 C increased giant foxtail germination and emergence. Velvetleaf germinated at 5 C but did not emerge within 21 days. Velvetleaf emerged within 21 days from soil depths of 2 to 6 cm at soil temperatures of 10, 15, and 20 C. Giant foxtail and velvetleaf seed germinated on a soil surface kept moist by mulch or frequent watering. Giant foxtail seedling survival was 100% after germination on the soil surface. Velvetleaf often failed to become established; only 28% of the velvetleaf that germinated at 20 C survived. Injury to giant foxtail by cyanazine increased with increasing soil temperatures and decreasing seed depths. Cyanazine placement above or below the seed did not have a consistent effect on giant foxtail injury. Cyanazine placed above the seed was more injurious to velvetleaf than placement below at 15 and 20 C. Differential responses of giant foxtail and velvetleaf seed germination and seedling survivability to initial seed depth appears to be a major factor in weed population shifts when tillage is reduced or eliminated.

Performance of seedlings of seven rain forest, canopy dominant Shorea species was studied in a transplant experiment in forest sites at three different elevations (low, mid and high) within the humid zone of southwest Sri Lanka. Five species generally inhabit low- to mid-elevations, one at mid- and lower montane elevations, and one exclusively at lower montane elevations. Temperature, rainfall and cloudiness varied with elevation. For each site seedlings were grown in pots under partial shade conditions using similar soils and evermoist conditions. All growth measures showed differences among elevation sites, among species and in the interaction between species and elevation sites. Performances of species collectively showed (i) decline in height and leaf number with increase in elevation, (ii) higher dry mass at low- and mid-elevation sites compared to that at high-elevation and (iii) a higher mass of single leaves at the mid-elevation site than at the high-elevation site. Rank order of species changed across elevations for both height and dry mass. Dry mass declined with elevation in four of the seven species studied. S. gardneri, the only exclusively lower montane species, increased dry mass with elevation. Height declined with elevation for six of the species with only S. gardneri showing no change. Changes with elevation in the rank order of species for total leaf number and mass of single leaves were small. However, total leaf number and masses of single leaves differed among species and among elevations. S. megistophylla and S. disticha had a few leaves with high individual masses, while S. gardneri, S. affinis and S. trapezifolia had many leaves with less mass per individual leaf. One group of species showed relatively little change in leaf number per seedling and large changes in mass of single leaves. The other group varied more in leaf number but mass of individual leaves remained constant. Growth allocation to leaf production versus individual leaf size appears related to the successional division of Shorea section Doona. Also all species grew better at the low-elevation site irrespective of their natural ranges except S. gardneri, whose natural range is restricted to high elevations, and exhibits markedly lower growth responsiveness than the other wide ranging species.