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We have surveyed the distribution of plants in the northeastern United States that contain cyanogenic compounds. Approximately 200 species of plants from 45 families are known to contain compounds capable of liberating hydrogen cyanide upon hydrolysis. These are primarily found in the Gramineae, Ranunculaceae and the Rosaceae. The chemical structures compounds of the cyanogens have been studied in only a small number of the species included, and investigation of the biology and chemistry of these plants should prove especially profitable.  相似文献   

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Phytophthora infestans, the causal agent of late blight disease, has been reported in North America since the mid-nineteenth century. In the United States the lack of or very limited sexual reproduction has resulted in largely clonal populations of P. infestans. In 2010 and 2011, but not in 2012 or 2013, 20 rare and diverse genotypes of P. infestans were detected in a region that centered around central New York State. The ratio of A1 to A2 mating types among these genotypes was close to the 50∶50 ratio expected for sexual recombination. These genotypes were diverse at the glucose-6-phosphate isomerase locus, differed in their microsatellite profiles, showed different banding patterns in a restriction fragment length polymorphism assay using a moderately repetitive and highly polymorphic probe (RG57), were polymorphic for four different nuclear genes and differed in their sensitivity to the systemic fungicide mefenoxam. The null hypothesis of linkage equilibrium was not rejected, which suggests the population could be sexual. These new genotypes were monomorphic in their mitochondrial haplotype that was the same as US-22. Through parentage exclusion testing using microsatellite data and sequences of four nuclear genes, recent dominant lineages US-8, US-11, US-23, and US-24 were excluded as possible parents for these genotypes. Further analyses indicated that US-22 could not be eliminated as a possible parent for 14 of the 20 genotypes. We conclude that US-22 could be a parent of some, but not all, of the new genotypes found in 2010 and 2011. There were at least two other parents for this population and the genotypic characteristics of the other parents were identified.  相似文献   

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Indigenous populations in New World nations share the common experience of culture contact with outsiders and a prolonged history of prejudice and discrimination. This historical reality continues to have profound effects on their well-being, as demonstrated by their relative disadvantages in socioeconomic status on the one hand, and in their delayed demographic and epidemiological transitions on the other. In this study one aspect of aboriginals' epidemiological situation is examined: their mortality experience between the early 1980s and early 1990s. The groups studied are the Canadian Indians, the American Indians and the New Zealand Maori (data for Australian Aboriginals could not be obtained). Cause-specific death rates of these three minority groups are compared with those of their respective non-indigenous populations using multivariate log-linear competing risks models. The empirical results are consistent with the proposition that the contemporary mortality conditions of these three minorities reflect, in varying degrees, problems associated with poverty, marginalization and social disorganization. Of the three minority groups, the Canadian Indians appear to suffer more from these types of conditions, and the Maori the least.  相似文献   

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Maps of physiognomic classes of vegetation in the northeastern UnitedStates before European human impact and for the late 20th century, based onpollen data, closely resemble each other, indicating a robust pattern in theface of the novel and extensive disturbances of the last 500 years. On the otherhand, species abundances have changed considerably, with today's vegetationhaving less Fagus L. and TsugaCarrière and more Betula L.,Picea A. Dietr., and Abies Miller.Picea and Castanea Miller increasedfrom 1700 to 1900, but have decreased in this century. The difference betweenthe main physiognomic classes has remained strong, however, with continuouslymore Picea, Abies andBetula in the north and more QuercusL. and Carya Nutt. in the south, indicating the dominanceof climate in regulating the relative abundances of these genera. Thevegetational patterning within these broad classes has changed in some placesand remained stable in others, suggesting differences in local factors thatdetermine relative species abundances. The influence of slight altitudinalgradients, for example, may influence forest composition only after severalgenerations of trees, while substrate differences may be apparent in the firstforest that regenerates after agricultural abandonment or logging. Forests oftoday, therefore, reflect complex interactions of disturbance and environment,and may be in equilibrium with some but not all features of their currentenvironments.  相似文献   

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During the second half of the twentieth century interest in the development of integrated ocean governance has continued to grow, within individual states and on the international level as well. In the United States the work of the Stratton Commission led to the creation of the National Oceanic and Atmospheric Administration (NOAA) and the passage of the Coastal Zone Management Act. These developments were but the start of what has become ongoing concern with establishing coherent and comprehensive approaches to the management of ocean and coastal space. Globally, interest in more systemic approaches to ocean management increased with the negotiations for the 1982 United Nations Law of the Sea Convention and was further sparked by the issues raised at the 1972 Stockholm Conference on the Human Environment and the 1992 United Nations Conference on Environment and Development held in Rio de Janeiro. Several states have recently undertaken new initiatives to further the development of integrated ocean policies that reflect recognition of the need for ecosystem-based management. The purpose of this contribution is to examine developments in three states, the United States, Canada, and Australia, that have given this subject substantial attention and to assess the efforts being made and the nature of the problems that are being encountered.  相似文献   

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The issue of the status of the Northwest Passage has ebbed and flowed in U.S.-Canada relations for decades, but the effect of global warming in the Arctic has moved this issue from the largely academic and legalistic realms to the forefront of bilateral (and international) relations. Intimately linked to Canadian nationalism, U.S. adherence to the doctrine of freedom of the seas, and to politics in both nations, the opposing positions held by the two states can no longer afford to be implacably held. Rather, it is time to put pride and politics aside and return to the “special relationship” between Canada and the United States in order to effect meaningful and mutually beneficial continental security.  相似文献   

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