The Origin of Species by Means of Natural Selection: Or, The Preservation of Favored Races in the Struggle for Life, Том 2D. Appleton, 1897 |
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Стр. 3
... seeds , in order to show that there is any degree of sterility . He always compares the maximum number of seeds produced by two species when first crossed , and the maximum produced by their hybrid offspring , with the average number ...
... seeds , in order to show that there is any degree of sterility . He always compares the maximum number of seeds produced by two species when first crossed , and the maximum produced by their hybrid offspring , with the average number ...
Стр. 7
... seed , which vegetated freely . " Mr. Herbert tried similar experi- ments during many years , and always with the same result . These cases serve to show on what slight and mystericus causes the lesser or greater fertility of a species ...
... seed , which vegetated freely . " Mr. Herbert tried similar experi- ments during many years , and always with the same result . These cases serve to show on what slight and mystericus causes the lesser or greater fertility of a species ...
Стр. 8
... seeds . as freely as it is possible to imagine . " Had hybrids when fairly treated , always gone on decreasing in fertility in each successive generation , as Gärtner believed to be the case , the fact would have been notorious to ...
... seeds . as freely as it is possible to imagine . " Had hybrids when fairly treated , always gone on decreasing in fertility in each successive generation , as Gärtner believed to be the case , the fact would have been notorious to ...
Стр. 12
... seeds produced , up to nearly complete or even quite complete fertility ; and , as we have seen , in certain abnormal cases , even to an excess of fertility , beyond that which the plant's own pollen produces . So in hybrids themselves ...
... seeds produced , up to nearly complete or even quite complete fertility ; and , as we have seen , in certain abnormal cases , even to an excess of fertility , beyond that which the plant's own pollen produces . So in hybrids themselves ...
Стр. 13
... seed out of the same capsule and exposed to the same conditions . By the term systematic affinity is meant , the general resemblance between species in structure and constitu- tion . Now the fertility of first crosses , and of the ...
... seed out of the same capsule and exposed to the same conditions . By the term systematic affinity is meant , the general resemblance between species in structure and constitu- tion . Now the fertility of first crosses , and of the ...
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The Origin of Species by Means of Natural Selection: Or the Preservation of ... Charles Darwin Ограниченный просмотр - 1982 |
The Origin of Species by Means of Natural Selection: Or, The Preservation of ... Charles Darwin Просмотр фрагмента - 1982 |
The Origin of Species by Means of Natural Selection: Or, the Preservation of ... Charles Darwin Недоступно для просмотра - 2014 |
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accumulated adapted admit affinity allied species ancient animals appear Archipelago arctic areas become beds believe birds breeds Cambrian changes characters classification climate closely allied continent crustaceans degree deposited difficulty distant distinct species domestic doubt embryo Europe existing extinct fact faunas fertilised fertility flowers formations formerly forms fossil fresh-water Fritz Müller Gärtner genera genus geological record Glacial period groups of species habits hybrids hybrids produced important individuals inhabitants inherited insects instance intermediate intervals land larvæ less living mammæ mammals manner marine Marsupials migration modified descendants mongrels mountains natural selection naturalists nearly occur oceanic islands offspring organisation paleozoic parent parent-form peculiar perfect pistil plants pollen present probably produced quadrupeds reciprocal crosses regions remains remarked reproductive resemblance rocks rudimentary organs seeds Silurian slight South America species belonging stage stamens sterility structure successive suppose terrestrial tertiary tion variable variations varieties whilst widely different wings