Influence of Date of Flushing on Flowering in Pinus banksiana
NUMEROUS attempts have been made to relate the year-to-year variability in flowering of forest trees to seasonal fluctuations in weather conditions which, in turn, are believed to influence the internal physiological processes regulating flower initiation1. The pronounced effect of photoperiod on flowering, noted in many herbaceous species, appears to be lacking in forest trees, and observations indicate that most trees are photoperiodically day-neutral2,3. However, until more definitive experiments have been undertaken, photoperiod cannot be ruled out as a factor influencing flower formation.
Regulation of Ontogeny in Temperate Conifers
Through their life stages, long-lived forest trees must adapt to challenges resulting from vast changes in size and external environment. Trees accomplish this by producing new tissues and growth habits adapted to specific life stages by pluripotent meristems. The morphology and physiology of these new tissues are determined by complex interactions of the external and internal environments of the tree, and gene expression both within meristems and during differentiation of cells produced by meristems. The trajectories of various age-related changes are both inter-related and independent at various scales, and, for the majority of species, are not purely physio-mechanical responses to increased tree height. Understanding the relationships between tree developmental state, tree size and its environment requires both a whole-tree approach integrated through time to encompass life stage strategies, and a molecular approach to understand the cues, transduction pathways and epigenetic mechanisms that regulate whole-life ontogeny.
D'une application pratique des indices bio-météorologiques
Abstract The purpose of the author is to determine statistically in what part of Switzerland maize could be cultivated with certain chance of rentability. The author gives first the method he used for determining the biometeorological index of four species of maize which were selected by the Swiss agronomical research stations. He has considered two possibilities for the growing period: ( a ) raising-ripening (l'approche globale); ( b ) raising-flowering, flowering-ripening (l'approche fractionee). From the biometeorological index, he calculated retrospectively the ripening time of these four species in the years 1901–1965. Assuming a priori that maize should be harvested before October 15th at the latest, he calculated, for a number of meteorological stations, the relative number of years when such conditions were fulfilled. Dividing the country in regions of similar mesoclimates and sorting these stations per region, it is possible to average the maximum altitude where maize can ripen at least 7, 8, 9 and 10 times within 10 years. Finally, taking into account the exposure and ground slope, he draws maps of the theoretically possible extension area, which maps are more reliable and detailed than the ones derived from actual means.