SUMMARY The influence of season, and certain agronomic treatments (irrigation, nitrogen fertiliser, density of planting and sowing date) on leaf number were analysed in a series of sugar‐beet crops grown during the five seasons 1978‐82. Leaf appearance was a linear function of thermal time (accumulated temperature above 1°C) and could be described by four variables: a) the thermal duration of the seedling establishment phase, d′s; b) the thermal time interval between appearance of each of the early leaves, θe; c) the thermal duration of the early phase of leaf appearance, d'a, and d) the thermal time interval between the appearance of each of the later leaves, θ1. The progression of leaf death could also be described by a thermal time interval, θd. There were only small differences in the number of leaves produced by the eleven crops grown during the five seasons. Such differences as appeared, were largely attributable to changes in d'a and θ1, which were interpreted as responses to increasing competition for mineral nutrients and assimilate at the shoot apex. θe was similar in all crops; 30°Cdays were needed between the appearance of each of the early leaves. Only the early leaves died. Each one was retained by the plant longer than its predecessor. Increasing soil moisture deficit under an unirrigated crop shortened θd and depriving crops of nitrogen lengthened it. It is concluded that small differences in the rates of leaf appearance did not greatly influence the rates at which leaf canopies expanded early in the season, but that the rates of leaf death influenced both the time at which the canopies reached their maximum sizes and the rates at which leaf areas subsequently declined.

SUMMARYThe relationships between the amounts of nitrogen fertilizer applied and taken up by sugarbeet crops and the concentrations of sugar and α-amino-N in the storage root were examined using data obtained from fertilizer-response trials on different soils in the UK and Belgium between 1974 and 1985. On unmanured mineral soils, crop uptakes of N without fertilizer ranged from 65 to 190 kg/ha and increased linearly with the amount of fertilizer N applied. On organic soils or mineral soils that had received large applications of organic manure, crop uptakes of N were very large (295–383 kg/ha) and were not increased by applications of fertilizer N.The amino-N contents of harvested beet increased with crop N uptake. The distributions of crop N to the storage root and of storage-root N to amino-N differed, especially in manured, diseased and drought-affected crops. Greater proportions of crop N were present in the storage roots of manured crops than in conventionally fertilized crops, and more of the storage-root N was present as amino-N in crops affected by virus yellows or drought than in healthy, unstressed crops.The fresh weight concentrations of sugar in the storage root also differed between sites and years but were not consistently reduced by applications of fertilizer N at individual sites. However, when compared across sites, concentrations were negatively correlated with crop N uptakes and the amounts of N in storage roots. This was because particular crops grown on mineral soils with large applications of manure or on organic soils had large N uptakes and exceptionally low concentrations of sugar.The physiological implications of these relationships between N uptake and amino-N and sugar accumulation are discussed.

The influence of season, and certain agronomic treatments (irrigation, nitrogen fertiliser, density of planting and sowing date) on leaf number were analysed in a series of sugar-beet crops grown during the five seasons 1978-82. Leaf appearance was a linear function of thermal time (accumulated temperature above 1 "C) and could be described by four variables: a) the thermal duration of the seedling establishment phase, d's; b) the thermal time interval between appearance of each of the early leaves, Be; c) the thermal duration of the early phase of leaf appearance, d'a, and d) the thermal time interval between the appearance of each of the later leaves, 81. The progression of leaf death could also be described by a thermal time interval, Bd.There were only small differences in the number of leaves produced by the eleven crops grown during the five seasons. Such differences as appeared, were largely attributable to changes in d'a and 81, which were interpreted as responses to increasing competition for mineral nutrients and assimilate at the shoot apex. Be was similar in all crops; 30"Cdays were needed between the appearance of each of the early leaves. Only the early leaves died. Each one was retained by the plant longer than its predecessor. Increasing soil moisture deficit under an unirrigated crop shortened Bd and depriving crops of nitrogen lengthened it. It is concluded that small differences in the rates of leaf appearance did not greatly influence the rates at which leaf canopies expanded early in the season, but that the rates of leaf death influenced both the time at which the canopies reached their maximum sizes and the rates at which leaf areas subsequently declined.

Small, E., Pocock, T. and Cavers, P. B. 2003. The biology of Canadian weeds. 119. Cannabis sativa L. Can. J. Plant Sci. 83: 217-237. Cannabis sativa has been cultivated for millennia in Eurasia and for centuries in North America, as a source of a textile fibre, oilseed, and intoxicating drugs such as marijuana. Considerable literature is available on the agricultural and biological properties of these basic three cultigens, but relatively little is published on wild-growing plants of the species. Most weedy C. sativa differ from the cultigens in a number of ecological properties, particularly with regard to reproductive biology. The species is the classical example of a "camp follower" that is exceptionally adapted to the habitat conditions around settlements: rich, highly manured, moist soils, and open areas resulting from recent removal or disturbance of the vegetation. In Canada, spontaneous populations have been found in all provinces, but forms that have re-evolved wild adaptations are concentrated along the St. Lawrence and lower Great Lakes. The ruderal plants pose a minor weed problem to agriculture but a major problem to law enforcement, and decades of eradi-cation have exterminated many of the naturalized populations in Canada. With the recent re-authorization of hemp cultivation in Canada, it is inevitable that there will be additional escapes and a reinvigoration of the ruderal phase of the species. Mechanical erad-ication for 2 or 3 yr is effective at destroying populations, and young plants are easily eliminated by herbicide applications. Small, E., Pocock, T. et Cavers, P. B. 2003. Biologie des mauvaises herbes au Canada. 119. Cannabis sativa L. Can. J. Plant Sci. 83: 217-237. On cultive Cannabis sativa L. depuis des millénaires en Eurasie et depuis des siècles en Amérique du Nord pour ses fibres textiles, son huile et la production de drogues comme la marijuana. On a beaucoup écrit sur la biologie et les paramètres agricoles des trois principaux cultigènes, mais relativement peu sur les variétés sauvages de cette plante. La plupart des variétés envahissantes de C. sativa se distinguent des cultigènes par plusieurs propriétés écologiques, surtout au niveau de la reproduction. L'espèce constitue en soi un exemple classique de la « plante colonisatrice », car elle est exceptionnellement bien adap-tée aux conditions souvent associées aux endroits habités : les sols humides et riches en fumure ainsi que les espaces dégagés résultant de l'enlèvement ou de la perturbation de la végétation. Au Canada, on recense des peuplements spontanés dans toutes les provinces, mais aussi des formes sauvages modifiées le long du Saint-Laurent et en bordure des Grands Lacs. Les plantes rudérales ne posent pas énormément de problèmes comme adventices aux agriculteurs, mais sont une véritable source d'ennui pour les forces policières qui ont passé des décennies à lutter contre les peuplements naturels au Canada. La culture du chanvre ayant été de nou-veau autorisée au pays depuis peu, l'espèce s'échappera inévitablement ...

SummaryData from 11 sugar-beet crops grown at different sites, in different years and with some variations in husbandry have been used to re-examine the process of dry-matter partitioning. Two-phase linear models did not describe adequately the distribution of dry matter. There was no evidence of a discontinuity in the partitioning between root and shoot at any point in crop development. It is suggested that, contrary to a recent view, events in the shoot, rather than the storage root, largely determine how dry matter is allocated between growth and sugar storage.