On the Origin of Species by Means of Natural Selection, Or, The Preservation of Favoured Races in the Struggle for LifeAppleton, 1898 |
Dentro del libro
Resultados 1-5 de 52
Página 6
... occur in a case of its natural fecun- dation . " So that here we have perfect or even more than commonly perfect fertility , in a first cross between two distinct species . This case of the Crinum leads me to refer to a singular fact ...
... occur in a case of its natural fecun- dation . " So that here we have perfect or even more than commonly perfect fertility , in a first cross between two distinct species . This case of the Crinum leads me to refer to a singular fact ...
Página 13
... occur . The fertility , both of first crosses and of hybrids , is more easily affected by unfavourable conditions , than is that of pure species . But the fertility of first crosses is likewise innately variable ; for it is not always ...
... occur . The fertility , both of first crosses and of hybrids , is more easily affected by unfavourable conditions , than is that of pure species . But the fertility of first crosses is likewise innately variable ; for it is not always ...
Página 19
... occurs in grafting ; for Thouin found that three species of Robinia , which seeded freely on their own roots , and which could be grafted with no great difficulty on a fourth species , when thus grafted were rendered barren . On the ...
... occurs in grafting ; for Thouin found that three species of Robinia , which seeded freely on their own roots , and which could be grafted with no great difficulty on a fourth species , when thus grafted were rendered barren . On the ...
Página 22
... occurred with many species , for a multitude are mutually quite barren . With sterile neuter insects we have reason to believe that modifica- tions in their structure and fertility have been slowly accumulated by natural selection ...
... occurred with many species , for a multitude are mutually quite barren . With sterile neuter insects we have reason to believe that modifica- tions in their structure and fertility have been slowly accumulated by natural selection ...
Página 25
... occurs in various degrees ; in both , the male element is the most liable to be affected ; but some- times the female more than the male . In both , the tendency goes to a certain extent with systematic affin- ity , for whole groups of ...
... occurs in various degrees ; in both , the male element is the most liable to be affected ; but some- times the female more than the male . In both , the tendency goes to a certain extent with systematic affin- ity , for whole groups of ...
Otras ediciones - Ver todas
Términos y frases comunes
admit affinity allied species ancient animals appear Archipelago arctic areas become believe birds Cambrian changes characters cies classification climate closely allied common progenitor continent crustaceans degree deposited difficulty distant distinct species domestic doubt embryo eral Europe existing extinct fact faunas fertilised fertility flowers formations formerly forms fossil fresh-water Fritz Müller Gärtner genera genus geological period geological record Glacial period groups of species habits hybrids hybrids produced important individuals inhabitants inherited insects instance intermediate intervals land larvæ less living mammals manner marine Marsupials migration modified descendants mongrels mountains natural selection naturalists nearly occur oceanic islands offspring organisation parent parent-form peculiar perfect pistil plants pollen present probably produced quadrupeds reciprocal crosses regions remains remarked reproductive resemblance rocks rudimentary organs sediment seeds Silurian South America stage stamens sterility structure successive suppose terrestrial tertiary theory tion variations varieties whilst widely different wings