Resting buds from five locations on long shoots in each of six crown positions were compared for 30 Larix laricina (Du Roi) K. Koch saplings. At each locus, bud sizes, numbers of bud scales and preformed leaf primordia (basal and axial for long-shoot buds), and apical widths were positively related to parent-shoot length. Along individual shoots, (i) terminal and lateral long-shoot buds contained fewer basal-leaf primordia than the more proximal short-shoot buds; (ii) terminal buds contained the most bud scales and axial-leaf primordia; and (iii) numbers of bud scales increased, while numbers of axial-leaf primordia generally decreased, basipetally among lateral buds. Comparison of bud leaf content with leaves on elongated shoots by regression showed that numbers of preformed and neoformed leaves increased with shoot length, but numbers of neoformed leaves did so to a greater degree. Internode lengths, numbers of leaves per lateral bud produced, and leaf lengths were greater on neoformed than on preformed shoot segments. Because of their capacity for neoformed growth following preformed growth and because of increases in internode lengths among all axial leaves, shoots from subjacent lateral buds replaced experimentally decapitated tree leaders (terminal buds) in one season, with little or no loss of height growth.
To maximize the in vitro seed germination of three Cypripedium species, C. candidum Muhl. ex Willd., C. reginae Walt., and C. calceolus var. parviflorum Salisb. Fern., the optimum time of seed collection and the suitability of various media were studied. A cold treatment was investigated for C. candidum. Seed pods were collected at regular intervals after pollination, ranging from green pods at 5 weeks to dry undehisced pods at 12 weeks. Seed was inoculated onto three media, Harvais, Van Waes and Debergh, and a modified Norstog and germination was assessed at 4-week intervals for 20 weeks. Cypripedium reginae germinated better than the other two species. Except for C. candidum in 1989 when germination peaked for seed collected at 6 weeks after pollination, seed collected at 8 weeks after pollination had the highest germination. After 8 weeks, germination decreased sharply in all species, dropping below 1% for C. candidum. There were differences among media but the effects on germination were not consistent and depended on the year, the date of collection, and the species. Subsequent development of protocorms was superior in all cases on the modified Norstog medium. The effect of cold treatment on germination of C. candidum was variable and therefore its importance is questionable. Key words: in vitro, germination, Cypripedium, lady's slippers, seed maturity.
This paper presents a mathematical model of Fraxinus pennsylvanica (green ash) shoots, which yields realistic computer graphics images of shoot geometry, and makes it possible to visualize shoot expansion using computer animation. The model is based on the mathematical formalism of Lindenmayer systems (L-systems). The paper emphasizes the process of model construction, with the aim of making the methodology applicable to other plant species. The central issue is the identification of field data necessary to build a comprehensive developmental model of plant architecture. Key words: Fraxinus pennsylvanica, plant architecture, shoot expansion, modeling, L-system, computer graphics.
Summary. Shoot preformation was investigated in buds of four clones of Fraxinus pennsylvanica var. subintegerrima (Vahl) Fern. at two sites in Manitoba in the second (1988) and third (1989) growing seasons after grafting. More preformed primordia were produced in terminal buds in 1989 compared to 1988 at each site. Both terminal and lateral buds at Morden contained significantly more primordia than those at Winnipeg. The numbers of preformed primordia were significantly different among clones. Clone 3 produced the most and clone 1 the fewest primordia in terminal buds. Despite quantitative variation, the pattern was similar among clones for terminal buds at each site and in each year. A similar pattern was evident for lateral buds at the Winnipeg site in 1989 but at Morden, clones 4 and 1 had the largest number of preformed primordia. Data from 1989 revealed that numbers of primordia were correlated with bud dimensions, parent shoot length, diameter and number of leaves, and location of the bud on the parent. Shoot dry weight was also related to these variables and revealed a non-linear increase in dry weight with shoot length. Multiple regression, with parent shoot length and location of buds along the parent axis as independent variables provided a reliable indicator of preformation in the crown. Although there is a genotypic component to preformation, variation between sites, years and crown locations suggests plasticity in bud development.
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