The early growth of two hybrid Populus × euramericana (Dode) Guinier clones and a species clone each of P. deltoides Bartr. ex Marsh, and P. nigra L. in controlled environments was studied in terms of growth of organs, partitioning of dry weight among parts, and growth analysis parameters. The hybrid clones grew more vigorously compared with the species clones with regard to most of the parameters measured. From 7 weeks after planting onward, the hybrid clones had greater plant dry weight, leaf dry weight, leaf area, and root dry weight than did the species clones. The hybrids developed a larger root system and greater leaf area per unit weight earlier than did the species clones. The greater leaf area was associated with lower specific leaf area. At all times the hybrid clones had significantly greater relative growth rates which were associated with early differences in unit leaf rate and later differences in leaf area ratio among the clones.

-J. 2010. The Biology of Canadian weeds. 144. Pastinaca sativa L. Can. J. Plant Sci. 90: 217Á240. The parsnip, Pastinaca sativa, was introduced to North America shortly after European settlement as an important root-crop. It subsequently escaped cultivation and naturalized as a less palatable ''wild'' form. Cultivation of parsnip has diminished in Canada to the point where it is now only a minor crop, but the wild form has increased as a troublesome weed, particularly in eastern regions.Wild parsnip is most prevalent in eastern Canada and the northeastern United States, but occurs across the continent except in the far north and extreme southeast. As a monocarpic biennial with a large tap root, it reproduces entirely by seed. A wide variety of habitats and soil types are tolerated. It is considered a noxious weed because of its toxic properties (primarily photo-activated dermatitis) to both humans and livestock. It invades disturbed sites, rights-of-way, pastures, perennial crops, and reduced-tillage fields where it effectively out-competes shorter vegetation.In arable fields, wild parsnip is normally controlled by tillage. Manual removal, cutting, and mowing can be effective in reducing seed production, but direct contact with plants or sap is hazardous. Various herbicides have been reported to be useful in the control of wild parsnip (e.g., glyphosate, 2,4-D, triclopyr, etc.), but little quantitative information is available on application rates and levels of control. Le panais, Pastinaca sativa, a e´te´introduit en Ame´rique du Nord peu apre`s la colonisation Europe´ene pour sa culture. C'e´tait un le´gume racine important. Par la suite, l'espe`ce s'est e´chappe´e pour donner une varie´te´« sauvage » moins comestible. Au Canada, la culture du panais a diminue´e pour n'eˆtre pre´sentement qu'une culture marginale. Toutefois la varie´te´sauvage s'est tellement re´pandue qu'elle est devenue une mauvaise herbe proble´matique, surtout dans les re´gions de l'Est. Le panais sauvage est surtout pre´valent dans l'est du Canada et le nord-est des É tats-Unis, mais on le retrouve un peu partout sur le continent, sauf dans les re´gions tre`s nordiques et celles le plus au sud-est. Cette bisannuelle monocarpique dote´e d'une grosse racine pivotante se multiplie uniquement par les semences. Elle tole`re de nombreux habitats et types de sol. On la conside`re comme une mauvaise herbe nuisible en raison de sa toxicite´(elle provoque essentiellement une dermatite active´e par la lumie`re) pour l'eˆtre humain et le be´tail. Le panais sauvage envahit les sites perturbe´s, emprises des chemins, les paˆturages, les champs de vivaces et champs ou le travail du sol est re´duit, en surpassant la ve´getation plus courte. Sur les terres arables, le labour permet de maıˆtriser son e´tablissement. Le sarclage manuel, la coupe et la tonte peuvent s'ave´rer efficaces pour re´duire la production de semences, mais il est risque´d'entrer en contact direct avec la plante ou sa se`ve. On rapporte que plusieurs herbicides permettent de lutter co...

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