96 resultados para relative survival
Resumo:
The embryological features of three species of Swertia (s.l.) - S. erythrosticta, S. franchetiana, and S. tetraptera were characterized, and the observations were used, together with previously gathered data on other species, to evaluate a recently proposed polyphyly, based on molecular data, of Swertia s.l. Comparisons of species within the genus showed that they have diversified embryologically, and there are significant between-species differences. Notable features that vary between species include the number of cell layers that form the anther locule wall, the construction of the wall of the mature anther, tapetum origin, the cell number in mature pollen grains, the structure of the fused margins of the two carpels, the ovule numbers in placental cross-sections, the shape of the mature embryo sac, the degree of ovule curvature, antipodal variation and the presence of a hypostase, and seed appendages. They share characters that are widely distributed in the tribe Gentianeae, such as a dicotyledonous type of anther wall formation, a glandular tapetum with uninucleate cells, simultaneous cytokinesis following the meiosis of the microsporocytes, tetrahedral microspore tetrads, superior, bicarpellary and unilocular ovaries, unitegmic and tenuinucellar ovules, Polygonum-type megagametophytes, progamous fertilization, nuclear endosperm, and Solanad-type embryogeny. The presence of variation in embryological characters amongst the species of Swertia s.l. strongly supports the view that Swertia s.l. is not a monophyletic group. Frasera is better separated from Swertia s.l. as an independent genus, and is only distantly related to Swertia s. s. judging from the numerous differences in embryology. Swertia tetraptera is very closely related to Halenia, as they show identical embryology. (C) 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 383-400.
Resumo:
In this paper, We analyzed the geological and geographical settings of dinosaurs extinction at the end of Cretaceous, especially the effect of the change of the elements contents on dinosaurs extinction. We studied basis on the two typical sections-Cretaceous-Paleocene boundary (Baishantou section (in Jiayin, Heilongjiang province of China) and Arkhara-Boguchan Coal Mine section (in Far East of Russian)) and Longgushan section (in Jiayin, Heilongjiang province of China) mainly. This work provided some evidences for forecasting the effects of global environmental change on bio-circle. The followings are the primary gains: According to the paleo-climate indexes (CaO/MgO,Sr/Ba) and the results of Factor Analysis, we found that there were similar climate in Baishantou section and Arkhara-Boguchan Coal Mine section near the K/E boundary, and both of them took on the trend of temperature declining and precipitation heightening after transitory high-temperature and drought. There are similar change and evlution rule of the elements contents near the boundary in the both sections (Baishantou section and Arkhara-Boguchan Coal Mine section). Both iron group elements and chalcophile elements appeared obvious abnormity. There are not visible correlation between the change of elements contents and climate indexes. This shows that the elements abnormity maybe came from the factors excluding climate or the factors were too many to conceal the influence of climate. --The result of cluster analysis showed that the boundary between BST3-8 and BST3-9 may be the K/E boundary of Baishantou section, and the top of twofold coal were the K/E boundary of Arkhara-Boguchan Coal Mine section which was consistent with accepted conclusion formerly. By contrast of elements contents in dinosaur bones and general organism, in surrounding rock and general sand stone, the regulation of the change of elements contents in dinosaur bones and surrounding rock, we confirmed that dinosaur extinction in Jiayin were relative with the high abnormities of Sr, Ba, Pb, Cr and the low abnormity of Zn, at least, it was them which speeded up dinosaurs extinction. After a series of analysis, we concluded that dinosaurs extinction of this areas tied up with the relative high background values of geo-chemical elements , paleo-climate and disaster incidents. First of all, high background values provided the necessary condition for the accumulation of the elements. Secondly, the drought climate adverse to the survival of dinosaurs, and led them to extinct gradually. finally, disaster incidents, the eruption of volcano or the collision of aerolites, made them exit this planet.
Resumo:
Grain is one of the primary material conditions of the human survival and the grain production concerns the stability and development of the society directly. The regional patterns influence greatly on the grain production and the rational production distribution the regional comparative advantages and promotes grain production. This thesis starts with summarizing of the characteristics of changes and the overall trend of regional pattern of grain production of our country since 1949. Then it carries on network analyses to the factors, which influences the evolvement of regional grain production patterns of our country. And finally it gives some proposals to the grain production distribution in the future. The main content includes: Firstly, Reviewing the regional evolvement of grain production in our country, and analyzing the changes of the regional pattern of grain production of our country on the provincial scale and county scale separately, since 1949, especially since the reform and opening up policy. The main grain production areas are acting an important position in ensuring the national grain security, so this thesis analyses the main matter of the main grain production areas, forecasts the grain production situation in the future, and selects the Northeastern main grain production areas as the typical area to carry on the positive research. Secondly, this thesis analyzes the origin causes from two respects of natural and social economy of the regional evolvement pattern of grain production in China. Thirdly, based on the summarizing to the status of the regional pattern of the grain production, this thesis proposes the precept of the grain production distribution in the future in our country. Therefore, the areas of three major cereal crops, rice, wheat and corn, are confirmed on the basis of the comparative advantages. Finally, this thesis puts forward the security system of guaranteeing the grain production progressing steady in China. According to the above analysis, some conclusions have been achieved as follows: (1) The grain gross production gets on extricating itself from awkward position frequently while fluctuating greatly annually since 1949 in China. (2) Since the reform, its traditional regional pattern of grain production, the most of which was concentrated in the south area, has changed rapidly. China's center of gravity of grain production has shifted from the south to the north, and on the belts of latitude, the grain production has represented a trend of focusing to the middle area in China. (3) The main grain production areas play a very important role in ensuring China's food security. With their relative severe situation of the problems of agriculture, rural area and peasant, China has carried out a series of measures, which aim at improving the food-producing conditions of the main grain production areas, and enhancing the grain yields there. Under this condition, a forecast of the producing amount of the main grain production areas under the nation's self-supplying rate of over 95% shows that the increasing provision production in these areas can meet the demand of the country. (4) The natural and social economic factors influence together on the changes of the grain production regional pattern. Along with the state system transition and progress of agricultural science and technology, the regional pattern of grain production is affected heavier by the agricultural policy and technological elements. (5) The grain production will be concentrated to the middle province in the future, which economic development level being medium-sized; According to crop allocation, although the rice superiority production area located in the South, its comparative advantage index is little in some degree. Meanwhile, the wheat and corn superiority production areas are in the North mainly and its scale superiority and production level advantage are all comparatively obviously.