The Various Contrivances by which Orchids are Fertilised by Insects

by Charles Darwin

THE

VARIOUS CONTRIVANCES

BY WHICH

ORCHIDS ARE FERTILISED BY INSECTS.

 

By CHARLES DARWIN, M.A., F.R.S., &c,

 

SECOND. EDITION, REVISED.

 

WITH ILLUSTRATIONS.

 

NEW YORK:

D. APPLETON AND COMPANY,

549 AND 551 BROADWAY.

1877.

CONTENTS.

Preface to the Second Edition  Pages v–vi

List of Papers and Books bearing on the Fertilisation of the Orchideæ &c.  vii–x

Introduction  1–5

CHAPTER I.

OPHREÆ.

Structure of the flower of Orchis mascula—Power of movement of the pollinia—Perfect adaptation of the parts in Orchis pyramidalis—Other species of Orchis and of some closely allied genera—On the insects which visit the several species, and on the frequency of their visits—On the fertility and sterility of various Orchids—On the secretion of nectar, and on insects being purposely delayed in obtaining it 6–44

CHAPTER II.

OPHREÆ—continued.

Fly and Spider Ophrys—Bee Ophrys, apparently adapted for perpetual self-fertilisation, but with paradoxical contrivances for intercrossing—Herminium monorchis, attachment of the pollinia to the front legs of insects—Peristylus viridis, fertilisation indirectly effected by nectar secreted from three parts of the labellum—Gymnadenia conopsea, and other species—Habenaria or Platanthera chlorantha and bifolia, their pollinia attached to the eyes of Lepidoptera—Other species of Habenaria—Bonatea—Disa—Summary on the powers of movement in the pollinia 45–79

 

CHAPTER III.

ARETHUSEÆ.

Cephalanthera grandiflora; rostellum aborted; early penetration of the pollen-tubes; case of imperfect self-fertilisation; cross-fertilisation effected by insects which gnaw the labellum—Cephalanthera ensifolia—Pogonia—Pterostylis and other Australian orchids with the labellum sensitive to a touch—Vanilla—Sobralia 80–92

CHAPTER IV.

NEOTTEÆ.

Epipactis palustris; curious shape of the labellum and its importance in the fructification of the flower—other species of Epipactis—Epipogium—Goodyera repens—Spiranthes autumnalis; perfect adaptation by which the pollen of a younger flower is carried to the stigma of an older flower on another plant—Listera ovata; sensitiveness of the rostellum; explosion of viscid matter; action of insects; perfect adaptation of the several organs—Listera cordata—Neottia nidus-avis; its fertilisation effected in the same manner as in Listera—Thelymitra, self-fertile 93–127

CHAPTER V.

MALAXEÆ AND EPIDENDREÆ.

Malaxis paludosa—Masdevallia, curious closed flowers—Bolbophyllum, labellum kept in constant movement by every breath of air—Dendrobium, contrivance for self-fertilisation—Cattleya, simple manner of fertilisation—Epidendrum—Self-fertile Epidendreæ 128–148

 

CHAPTER VI.

VANDEÆ.

Structure of the column and pollinia—Importance of the elasticity of the pedicel; its power of movement—Elasticity and strength of the caudicles—Calanthe with lateral stigmas, manner of fertilisation—Angræcum sesquipedale, wonderful length of nectary—Species with the entrance into the stigmatic chamber much contracted, so that the pollen-masses can hardly be inserted—Coryanthes, extraordinary manner of fertilisation 149–177

CHAPTER VII.

VANDEÆ continued.—CATASETIDÆ.

Catasetidæ, the most remarkable of all Orchids—The mechanism by which the pollinia of Catasetum are ejected to a distance and are transported by insects—Sensitiveness of the horns of the rostellum—Extraordinary difference in the male, female, and hermaphrodite forms of Catasetum tridentatum—Mormodes ignea, curious structure of the flowers; ejection of the pollinia—Mormodes luxata—Cycnoches ventricosum, manner of fertilisation 178–225

CHAPTER VIII.

CYPRIPEDEÆ—HOMOLOGIES OF THE FLOWERS OF ORCHIDS.

Cypripedium, differs much from all other Orchids—Labellum in the form of a slipper with two small orifices by which insects can escape—Manner of fertilisation by small bees of the genus Andrena—Homological nature of the several parts of the flowers of the Orchideæ—Wonderful amount of modification which they have undergone 226–246

 

CHAPTER IX.

GRADATION OF ORGANS, &C.—CONCLUDING REMARKS.

Gradation of organs, of the rostellum, of the pollen-masses—Formation of the caudicle—Genealogical affinities—Secretion of nectar—Mechanism of the movement of the pollinia—Uses of the petals—Production of seed—Importance of trifling details of structure—Cause of the great diversity of structure in the flowers of Orchids—Cause of the perfection of the contrivances—Summary on insect-agency—Nature abhors perpetual self-fertilisation 247–293

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Index 294

LIST OF WOODCUTS.

PAGE

1.

Orchis mascula ....................................................................................................................................................................................................................................................

8

2.

Orchis„ mascula„ pollinia of ....................................................................................................................................................................................................................................................

12

3.

Orchis pyramidalis ....................................................................................................................................................................................................................................................

18

4.

Moth's head and pboboscis, with attached pollinia ....................................................................................................................................................................................................................................................

31

5.

Ophrys muscifera ....................................................................................................................................................................................................................................................

46

6.

Ophrys„ aranifera ....................................................................................................................................................................................................................................................

50

7.

Ophrys„ arachnites ....................................................................................................................................................................................................................................................

51

8.

Ophrys„ apifera ....................................................................................................................................................................................................................................................

53

9.

Peristylus viridis ....................................................................................................................................................................................................................................................

62

10.

Gymnadenia conopsea ....................................................................................................................................................................................................................................................

65

11.

Habenaria chlorantha ....................................................................................................................................................................................................................................................

69

12.

Pollinia of habanaria chlorantha and bifolia ....................................................................................................................................................................................................................................................

74

13.

Cephalanthera grandiflora ....................................................................................................................................................................................................................................................

81

14.

Pterostylis longifolia ....................................................................................................................................................................................................................................................

87

15.

Epipactis palustris ....................................................................................................................................................................................................................................................

94

16.

Epipactis„ latifolia ....................................................................................................................................................................................................................................................

101

17.

Spiranthes autumnalis ....................................................................................................................................................................................................................................................

107

18.

Listera ovata ....................................................................................................................................................................................................................................................

116

19.

Malaxis paludosa ....................................................................................................................................................................................................................................................

130

20.

Masdevallia fenestrata ....................................................................................................................................................................................................................................................

136

21.

Dendrobium chrysanthum ....................................................................................................................................................................................................................................................

139

22.

Cattleya ....................................................................................................................................................................................................................................................

144

23.

Diagram illustrative of the structure of the Vandeæ ....................................................................................................................................................................................................................................................

150

24.

Pollinia of Vandeæ ....................................................................................................................................................................................................................................................

154

25.

Pollinium of Ornithocephalus ....................................................................................................................................................................................................................................................

160

26.

Calanthe masuca ....................................................................................................................................................................................................................................................

161

27.

Coryanthes speciosa ....................................................................................................................................................................................................................................................

174

28.

Catasetum saccatum ....................................................................................................................................................................................................................................................

182

29.

Catasetum„ saccatum„ ....................................................................................................................................................................................................................................................

183

30.

Catasetum tridentatum ....................................................................................................................................................................................................................................................

194

31.

Monachanthus and Myanthus ....................................................................................................................................................................................................................................................

199

32.

Mormodes ignea ....................................................................................................................................................................................................................................................

209

33.

Cycnoches ventricosum ....................................................................................................................................................................................................................................................

222

34.

Cycnoches„ ventricosum„ section through bud ....................................................................................................................................................................................................................................................

223

35.

Cypripedium ....................................................................................................................................................................................................................................................

227

36.

Transverse section of flower of an Orchid ....................................................................................................................................................................................................................................................

236

37.

Rostellum of Catasetum ....................................................................................................................................................................................................................................................

256

38.

Disc of Gymnadenia conopsea ....................................................................................................................................................................................................................................................

272

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P.S.—I am much indebted to Mr. Q. B. Sowerby for the pains which he has taken in making the Diagrams as intelligible as possible.