The Origin of Species by Means of Natural Selection,: Or the Preservation of Favoured Races in the Struggle for LifeJohn Murray, Albemarle Street., 1891 - 432페이지 |
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19개의 결과 중 1 - 5개
68 페이지
... pistils placed , in relation to the size and habits of the particular insect which visited them , so as to favour in ... pistil , and four stamens with shrivelled anthers , in which not a grain of pollen can be detected . Having found a ...
... pistils placed , in relation to the size and habits of the particular insect which visited them , so as to favour in ... pistil , and four stamens with shrivelled anthers , in which not a grain of pollen can be detected . Having found a ...
69 페이지
... pistils alone in another flower or on another plant . In plants under culture and placed under new conditions of life , sometimes the male organs and sometimes the female organs become more or less impotent ; now if we suppose this to ...
... pistils alone in another flower or on another plant . In plants under culture and placed under new conditions of life , sometimes the male organs and sometimes the female organs become more or less impotent ; now if we suppose this to ...
71 페이지
... pistil stand so near each other as almost to insure self - fertilisation , the fullest freedom for the entrance of pollen from another individual will explain the above state of exposure of the organs . Many flowers , on the other hand ...
... pistil stand so near each other as almost to insure self - fertilisation , the fullest freedom for the entrance of pollen from another individual will explain the above state of exposure of the organs . Many flowers , on the other hand ...
72 페이지
... pistil , or slowly move one after the other towards it , the con- trivance seems adapted solely to ensure self - fertilisation ; and no doubt it is useful for this end : but the agency of insects is often required to cause the stamens ...
... pistil , or slowly move one after the other towards it , the con- trivance seems adapted solely to ensure self - fertilisation ; and no doubt it is useful for this end : but the agency of insects is often required to cause the stamens ...
73 페이지
... pistil of each cabbage - flower is surrounded not only by its own six stamens but by those of the many other flowers on the same plant ; and the pollen of each flower readily gets on its own stigma without insect agency ; for I have ...
... pistil of each cabbage - flower is surrounded not only by its own six stamens but by those of the many other flowers on the same plant ; and the pollen of each flower readily gets on its own stigma without insect agency ; for I have ...
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accumulated adapted admit affinities allied species America analogous ancient appear beak become bees believe belonging birds breeds cause cells characters climate closely allied colour continued crossed crustaceans degree developed difficulty distinct species domestic animals doubt effects eggs embryo existing extinct extremely facts favourable female fertilised fertility flowers formation formerly forms fossil Fritz Müller genera genus geological geological period Glacial period gradations greater number habits Hence hybrids important increase individuals inhabitants inherited insects instance instincts intercrossing intermediate kind lamellæ larvæ less living male mammals manner Marsupials migration modified descendants natural selection naturalists nearly nest occasionally occur oceanic islands offspring organisation organs parent peculiar perfect pigeon pistil pollen present preserved principle probably produced quadrupeds ranked reciprocal crosses remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive supposed tend theory tion variability variations varieties vary whilst whole wings young