The Origin of Species by Means of Natural Selection; Or, the Preservation of Favored Races in the Struggle for Life ...A.L. Burt, 1890 - 538페이지 |
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60 페이지
... produced only two seeds - and there is no plant so unpro- ductive as this - and their seedlings next year produced two , and so on , then in twenty years there would be a million plants . The elephant is reckoned the slowest breeder of ...
... produced only two seeds - and there is no plant so unpro- ductive as this - and their seedlings next year produced two , and so on , then in twenty years there would be a million plants . The elephant is reckoned the slowest breeder of ...
62 페이지
... produced , and yet the average stock be fully kept up ; but if many eggs or young are destroyed , many must be produced or the species will become extinct . It would suffice to keep up the full number of a tree , which lived on an ...
... produced , and yet the average stock be fully kept up ; but if many eggs or young are destroyed , many must be produced or the species will become extinct . It would suffice to keep up the full number of a tree , which lived on an ...
285 페이지
... produce any offspring , are generally very sterile ; but the parallelism between the difficulty of making a first cross , and the sterility of the hybrids thus produced - two classes of facts which are generally confounded together - is ...
... produce any offspring , are generally very sterile ; but the parallelism between the difficulty of making a first cross , and the sterility of the hybrids thus produced - two classes of facts which are generally confounded together - is ...
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adapted admit affinities allied species America ancient appear Asa Gray beak become bees believe belonging birds breeds cause cells characters climate closely allied color continued crossed crustaceans degree developed difficulty distinct species divergence domestic doubt effects eggs embryo existing extinct extremely facts favorable fertility flowers formation forms fossil Fritz Müller genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hybrids hybrids produced important individuals inhabitants inherited insects instance instincts intercrossing intermediate intervals kind lamellæ larvæ less living male mammals manner marsupials migration modified descendants natural selection naturalists nearly nest occasionally oceanic islands offspring organs parent peculiar perfect pigeons pistil pollen present principle probably produced quadrupeds ranked remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive suppose tend theory tion variability variations varieties vary whole widely different wings young