Seite - 224 - in The Origin of Species
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Text der Seite - 224 -
224 ORIGIN OF SPECIES
special function
; but they are nowknown to be of the highest
importance for the fertilisation of the species through the
aid of insects, and have probably been gained through natural
selection. No one until lately would have imagined that in
dimorphic and trimorphic plants the different lengths of the
stamens and pistils, and their arrangement, could have been
of any service, but now we know this to be the case.
In certain whole groups of plants the ovules stand erect,
and in others they are suspended; and within the same
ovarium of some few plants, one ovule holds the former and
a second ovule the latter position. These positions seem at
first purely morphological, or of no physiological significa-
tion; but Dr. Hooker informs me that within the same
ovarium, the upper ovules alone in some cases, and in other
cases the lower ones alone are fertilised
; and he suggests that
this probably depends on the direction in which the pollen-
tubes enter the ovarium. If so, the position of the ovules,
even when one is erect and the other suspended within the
same ovarium, would follow from the selection of any slight
deviations in position which favoured their fertihsation, and
the production of seed.
Several plants belonging to distinct orders habitually pro-
duce flowers of two kinds,—the one open of the ordinary
structure, the other closed and imperfect. These two kinds
of flowers sometimes differ wonderfully in structure, yet may
be seen to graduate into each other on the same plant. The
ordinary and open flowers can be intercrossed
; and the bene-
fits which certainly are derived from this process are thus
secured. The closed and imperfect flowers are, however,
manifestly of high importance, as they yield with the utmost
safety a large stock of seed, with the expenditure of won-
derfully little pollen. The two kinds of flowers often differ
much, as just stated, in structure. The petals in the imperfect
flowers almost always consist of mere rudiments, and the
pollen-grains are reduced in diameter. In Ononis columnse
five of the alternate stamens are rudimentary; and in some
species of Viola three stamens are in this state, two retaining
their proper function, but being of very small size. In six
out of thirty of the closed flowers in an Indian violet (name
unknown, for the plants have never produced with me per^
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Buch The Origin of Species"
The Origin of Species
- Titel
- The Origin of Species
- Autor
- Charles Darwin
- Verlag
- P. F. Collier & Son
- Ort
- New York
- Datum
- 1909
- Sprache
- englisch
- Lizenz
- PD
- Abmessungen
- 10.5 x 16.4 cm
- Seiten
- 568
- Schlagwörter
- Evolutionstheorie, Evolution, Theory of Evolution, Naturwissenschaft, Natural Sciences
- Kategorien
- International
- Naturwissenschaften Biologie
Inhaltsverzeichnis
- EDITOR'S INTRODUCTION 5
- AN HISTORICAL SKETCH of the Progress of Opinion on the Origin of Species 9
- INTRODUCTION 21
- Variation under Domestication 25
- Variation under Nature 58
- Struggle for Existence 76
- Natural Selection; or the Survival of the Fittest 93
- Laws of Variation 145
- Difficulties of the Theory 178
- Miscellaneous Objections to the Theory of Natural Selection 219
- Instinct 262
- Hybridism 298
- On the Imperfection of the Geological Record 333
- On the Geological Succession of Organic Beinss 364
- Geographical Distribution 395
- Geographical Distribution - continued 427
- Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs 450
- Recapitulation and Conclusion 499
- GLOSSARY 531
- INDEX 541