-^ T J?
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f LNTERNATIONAL SCIENTIFIC SERIES
THE ORIGIN OF
FLORAL STRUCTURES
THROUGH INSECT AND OTHEE AGENCIES
BY THE
REV. GEOEGE HENSLOW, M. A., F. L. S., F. G. S.
PROFESSOR OF BOTANY, QUEEN'S COLLEGE, AND
LECTURER TO ST. BARTHOLOMEW'S HOSPITAL MEDICAL SCHOOL, LONDON
AUTHOR OF "evolution AND RELIGION," "CHRISTIAN BELIEFS RECONSIDERED,'
"botany FOR CHILDREN," "FLORAL DISSECTIONS," ETC.
WITH EIGHTY-EIGHT ILLUSTRATIONS
NEW YORK
D. AP PL ETON AND COMPANY
1888
OO^
PREFACE
The belief that we must look mainly to the environment
as furnishing the influences which induce plants to vary
in response to them — whereby adaptive morphological
(including anatomical) structures are brought into exist-
ence— appears to be reviving. To illustrate the progress
of this belief, I will give a few cases.
In 1795, GeofFroy Saint Hilaire " seems to have
relied chiefly on the conditions of life, or the ' monde
ambiant,' as the cause of change." *
In 1801, Lamarck "attributed something to the direct
action of the physical conditions of life " as the means
of modification, "something to the crossing of already
existing forms, and much to use and disuse."
In 1831, Mr. Patrick Matthew (who, like Dr. W. C.
Wells in 1818, anticipated Mr. Darwin in the theory of
" natural selection ") " seems to have attributed much
influence to the direct action of the conditions of life."
* I quote from Mr, Darwin's " Historical Sketch " in his Origin of
Species, 6th ed., 1878.
VI PREFACE.
In 1844, the " Vestiges of Creation " appeared. The
author suggests that " impulses " were imparted to the
forms of life, on the one hand advancing them, and on
the other hand tending to modify organic structures in
accordance with external circumstances ; the effects thus
produced by the conditions of life being gradual.
In 1852, Mr. Herbert Spencer " attributed the modifi-
cations [of species] to the change of circumstances."
In 1859, " The Origin of Species " appeared. Mr.
Darwin did not at first seem to lay so much stress as
his predecessors upon the action of the environment as
a cause, for he says : " It is curious how largely my
grandfather. Dr. Erasmus Darwin, anticipated the views
and erroneous grounds of opinion of Lamarck." Again,
in speaking of the constancy of some varieties, he says,
" Such considerations incline me to lay less weight on
the direct action of the surrounding conditions, than on
a tendency to vary, due to causes of which we are quite
ignorant."* He had, however, previously said, " Changed
conditions of life are of the highest importance in
causing variability. ... It is not probable that vari-
ability is an inherent and necessary contingent under
all circumstances." f
With regard to my own opinion, having been eariy
and greatly interested in Paley's "Natural Theology,"
as well as the "Vestiges" when Mr. Darwin's work
* Or. of Sp., p. 107. t Ibid., p. 31. See also Desc. of Man, ii., p. 388.
PREFACE. Vll
appeared, the great difficulties I felt in accepting
natural selection as any real origin of species lay,
first, in the seeming impossibility of the histological
minutiae of the organs in adaptation having been selected
together; and, secondly, in the idea that all those
wonderful and "purposeful" structures which Paley
thought could only have been " designed," could be the
ultimate result of any number of accidental and appa-
rently at first "purposeless" variations. In a broad
sense natural selection seemed obviously true ; for
Geology had revealed the fact that the world had been
peopled over and over again by old forms dying out and
new forms coming in ; so that although it might account
for the extinction of the former, it did not seem to me
capable to account for the origin of the latter. I, there-
fore, still looked to the environment as affording a better
clue to the source of variations.*
In 1869, when watching a large humble-bee hanging
on to the dependent stamens of EpUohiu'ni angusti-
folium, the idea first occurred to me that insects them-
selves might be the real cause of many peculiarities in
the structure of flowers. The thought passed through
my mind that the way the stamens hung down might
perhaps have become an hereditary efiect from the
repeatedly applied weight of the bees.
In 1877, I advanced this idea as a speculation
* See Letter to Nafu7-e, vol. v., p. 123.
• • •
Till PREFACE.
when suggesting the origin of nectaries and irregu-
larities of flowers in my paper on " Self-fertilisation of
Flowers." *
In 1880, Mr. A. E,. Wallace reviewed Dr. Aug. Weis-
mann's " Studies in the Theory of Descent." f In this
work the author says : " According to my view, trans-
mutation by purely internal causes is not to be enter-
tained. . . . The action of external incitincj causes is
alone able to produce modifications." Mr. Wallace adds
that he had "arrived at almost exactly similar con-
clusions."
In 1881, when reviewing Paul Janet's work on
" Final Causes," :|: I took occasion to remark that " I
regarded the environment as by far the most important
"cause" of variations, in that it influences the organ-
ism, which, by its inherent but latent power to vary,
responds to the external stimulus, and then varies
accordingly."
In 1881, appeared the first really systematic treatise
that I know of, by Dr. C. Semper,§ which dealt with the
origin of variations in animals as beino; referable to the
environment.
In 1884, Dr. A. de Bary's "Comparative Anatomy of
the Vegetative Organs of the Phanerogams and Ferns,"
* Trans. Lin. Soc, 2nd ser., Bot., vol. i., p. 317.
f Nature, xxii., p. 141. J Modern Revieiv, 1881, p. 53.
§ The Natural Conditions of Existence as they affect Animals," Intern.
Sci. Ser., vol. xxxi.
PREFACE. IX
was published in English. In the Introduction, the
author writes as if it were a perfectly well understood
thing that species have arisen by adaptations to the
influences of the environment.*
In 1886, Mr. Herbert Spencer contributed two articles
on " The Factors of Organic Evolution " to the Nineteenth
Century. \ In these he showed, from many passages in
Mr. Darwin's works, especially "Animals and Plants
under Domestication " and in his later volumes, that he
became much more favourably inclined to the belief that
the effects of the environment were accumulative, and
that in the course of some generations the variations set
up tended to cease and become fixed. Mr. Spencer par-
ticularly notes the change of view, as illustrated by the
expression " little doubt " being replaced by " no doubt "
in the following sentence : " I think there can be no
doubt that use in our domestic animals has strengthened
and enlarged certain parts, and disuse diminished them ;
and that such modifications are inherited." + It may
be added that in " The Cross and Self Fertilisation of
Flowers" (1876), and in "Forms of Flowers" (1877),
Mr. Darwin makes many observations upon the efiects
of the external conditions upon plants as influencing and
modifying them in various ways. It is curious to note
that the three influences upon which Lamarck laid
* See, e.g., p. 25. t See p. 570 and p. 749.
X "Use" and "disuse" in animals corresponds to what I have
called "hypertrophy " and "atrophy" in plants, in this work.
X PREFACE.
emphasis are just those which Mr. Darwin himself
latterly, though often indirectly perhaps, laid stress upon
in his experiments, viz. crossing, use and disuse, and the
physical conditions of life.
In 1886, also appeared an article in Nature, entitled,
" Plants considered in Relation to their Environment."
It was not signed, but the author alludes to the external
conditions as bringing about all sorts of changes in the
vegetative system. He stops short of discussing floral
structures.
In 1886, Dr. Vines' " Physiology of Plants " appeared.
After discussing various views and theories of reproduc-
tion, he observes, that " variability was first induced as
the response of the organism to changes in the conditions
of life." * . . . We conclude, then, that the production of
varieties is the result of the influence of the conditions
of life, t
In the last page of his work. Dr. Vines calls attention
to Naegeli's view as follows : " Naegeli suoftrests, and his
suggestion is worthy of serious consideration, that there
is an inherent tendency to a higher organisation, so that
each succeeding generation represents an advance, ... as
in cases of what is termed saltatory evolution." Thus,
* Page 676. Dr. Vines here uses almost identically the same words
as myself in 1881. I have just found that Mr. St. G. Mivart said much
the same in 1870, Genesis of Species, p. 269. See also 0. Schmidt's
Doctnne of Descent and Darwinism, p. 175.
t Page 679.
PEEFACE. XI
while Mr. Darwin seems at last to have tacitly accepted
Lamarck's ideas, at least to a considerable extent, we
have here a return in 1887 to the views of the author of
the " Vestiges " of 1884
1888. I have attempted in the present work to return
to 1795, and to revive the " Monde ambiant" of Geoffi-oy
Saint Hilaire, as the primal cause of change. My object
is to endeavour to refer every part of the structures of
flowers to some one or more definite causes arising from
the environment taken in its widest sense. To some
extent the attempt must be regarded as speculative ;
and, therefore, any deductive or a priori reasonings met
with must be considered by the reader as being suggestive
only.
CONTENTS
CHAPTER /^ PAGE
Geneual Principles ... ... ... ... 1
II. The Pkincxple of Ncmbeb ... ... ... 7
ni. The Principle of Number — Continued ... ... 25
IV. The Principle of Arrangement ... ... 39
Y. The Principle of Cohesion ... ... ... 48
VI. The Principle of Cohesion— Con^mwed ... 54
VII. The Principle of Cohesion —Coji^iwwed ... ... 62
VIII. The Principle of Adhesion ... ... ... 78
IX. The Cause of Unions ... ... ... ... 84
X. The Receptacular Tube ... ... ... 89
XL The Forms of Floral Organs ... ... ... 101
XII. The Origin of " Zygomorphism " ... ... 116
Xm. The Effects of Strains on Structures ... ... 123
XIV. Acquired Eegularity and "Peloria" ... 128
XV. The Origin of Floral Appendages ... ... 133
XVI. Secretive Tissues ... ... ... ... 140
XVII. Sensitiveness and Irritability of Plant Organs ... 151
XVIII. Origin of Conducting Tissues ... ... 164
XIV CONTENTS.
AFTER PAGE
XIX. Colours of Flowers ... ... ... ... 174
XX. The Emergence of the Floral Whorls ... 184
XXI. The Development of the Floral "Whorls ... 191
XXII. Heterogamy and Actogamt ... ... ... 198
XXIII. Heterostylism ... ... ... ... ... 208
XXIV. Partial Diclinism ... ... ... ... 220
XXV. Sexuality and the Environment... ... ... 230
XXVI. Degeneracy of Flowers ... ... ... 2.51
XXVII. Degeneracy of FLoyf ess— Cuntinued ... ... 273
XXVIII. Progressive Metamorphoses ... ... ... 285
XXIX. Ketrogressive Metamorphoses ... ... ... 295
XXX. Phyllody of the Floral "Whorls ... ... 301
XXXI. The Varieties of Fertilisation ... ... ... 311
XXXII. Fertilisation and the Origin of Species ... 329
LIST OF ILLUSTRATIONS.
FIGURE PAGE
1. Diagram of a typical flower composed of six whorls ... 3
2. Diagram of the positions of opposite leaves, illustrating the
method of passage to alternate arrangements ... ... 11
3. Diagrams of floral aestivations, showing the passage from the
two-fifth or quincuncial, to the contorted ... ... ... 15
4. Diagram of flower of Garidella, with stamens superposed to
petals ... ... ... ... ... ... ... ... 21
5. Diagram of flower of Hellehorus niger with stamens super-
posed to twenty-one nectaries ... ... ... ... 22
6. Diagrams illustrating the anatomy of the floral receptacle of
a "Wallflower, showing the origin of the floral members ... 32
7. Diagram of the leaf-traces in the stem of Arahis albida ... 39
8. Vertical and transverse sections of the wall of the inferior
ovary of Campanula medium, showing how the sepaline
cords originate those of the rest of the floral organs (see
fig. 15, p. 71) 43
9. Flower of Phyteuma, showing cohesion by contact and con-
genital, in the corolla ... ... ... ... ... ... 50
10. Flower of 3fimu?Ms undergoing " dialysis " ... ... ... 51
11. Stamens of Centaurea, showing syngenesions anthers j method
of fertilisation by "piston-action" (b), nectary and direc-
tion of insect-proboscis, etc. ... ... ... ... ... 60
12. Anatomy of the floral receptacle of Hellebore, showing the
changes in orientation of the cords ... ... ... ... 64
13. Anatomy of the floral receptacle of Pelargonium, showing
changes in the orientation, in the separation and in the
imion of the cords ... ... ... ... ... ... 65
XVi LIST OF ILLUSTRATIONS.
FIGURE PAGE
14. Anatomy of the floral receptacle of Ivy, showing the multi-
plication and differentiation of the cords, etc. ... ... 68
15. Anatomy of the floral receptacle of Campanula medium,
showing the distribution of the cords, etc. (see fig. 8, p. 43) 71
16. Origin and development of the ovule in Beta ... ... ... 73
17. Carpels of Acer, showing the thickened bases, preparatory for
ovules 75
18. A separate carpel of Primula sinensis, with marginal ovules
and a " heel-like " process, the origin of the free central
placenta ... ... ... ... ... ... ... ... 76
19. Anatomy of the floral receptacles of Lysimachia and Primula,
showing the cords of five carpels ... ... ... ... 77
20. Echium, showing declinate stamens and protandrous condition 82
21. Ovary, stamens, and stigmas of J.nsfoZoc/iia ... ... ... 83
22. Vertical sections of buds of Pyrus and Cotoneaster, showing
degrees of adhesion or undifferentiated condition between
the ovary and receptacular tube ... ... ... ... 90
23. Orchis Morio (?), with arrest of pistil, the receptacular tube
represented by a rod-like pedicel. Two anthers are deve-
loped instead of one (a) ... ... ... ... ... 92
24. Eeceptacular tube of Eose, bearing a leaf and a stipular sepal 93
25. Vertical section of the receptacular tube of Hawthorn, with
supernumerary carpels arising from the summit ... ... 93
26. Leaves of Pear with hypertrophied and sub-fasciate petioles 94
27. Fuchsia with foliaceous sepals, partly detached from the ovary 94
28. Anatomy of the receptacular tube of Prunus, showing the
origio of the petaline and staminal cords ... ... ... 95
29. Part of the receptacular tube of Cherry, showing the distri-
bution of cords in the sepaline lobes ... ... ... ... 97
30. Anatomy of inferior ovary of Alstrcemeria, showing the junc-
tion between the ovary and the tube ... ... ... 97
31. Flower of Duverjioia, showing its adaptability for intercrossing 107
32. Flower of Calceolaria, showing thickened ridges, etc., and
adaptability for intercrossing .. . ... ... ... ... 109
33. Flower of Dictamnus, showing declinate stamens and displace-
ment of petals ... ... ... ... ... 110
34. Flower of Epilohium an gusti folium, showing dependent sta-
mens and displacement of petals ... ... ... ... Ill
LIST OF ILLUSTRATIONS. xvii
FIGDRE p^OE
35. Flower of Veronica Chamcedrys, showing method of fertilisa-
tion by insects, and degeneracy of anterior petal Ill
36. Flower of Teucrium, to show effect of weight of insect with
exposure of stamens ... .., ... ... ... * ... 117
37. Diagrams of Narcissus cernuus, to show instability in the
heterostylism and lengths of stamens ... ... ... 121
38. Basal end of a Pear, to show cause of thickening in response
to forces ... ... ... ... ... ... ... ... 124
39. Diagram of a declinate bough, showing distribution of forces 125
40 a. A diagram of declinate stamens, to show distribution of forces 126
406. Flower of Lamiww aZ&Mm, to show distribution of forces ... 126
41. Base of flower of Amaryllis, showing the honey -protector ... 134
42. Adhesive epidermal cells of roots of Orchids ... ... ... 137
43. Stipules of Imjiafiejis, showing nectariferous tissue ... ... 140
44. Petals passing into nectariferous stamens of .4<ra(/eT!e ... 141
45. Cells of hair of Tradescantia, showing the state of protoplasm
before and after excitation by electricity ... ... ... 152
46. Climbing peduncle of Uncaria, thickened after irritation by
the support ... ... ... ... ... ... ... 156
47. Flower of Genista tinctoria, before and after mechanical
irritation ; the claws of the keel and wing petals being
in unstable equi'librium ... ... ... ... ... 160
48. Flowers of Lopezia in three stages, showing movements of the
staminode and stamen ... ... ... ... ... 161
49. Flower of Medicago sativa, before and after mechanical irrita-
tion, the staminal tube being in unstable equilibrium . . . 162
50. Transverse sections of conducting tissues of Fumaria, Ruhus,
and of a Crucifer ... ... ... ... ... ... 164
51. Diagram of emergence of the petaline stamens of Peganmn
outside the sepaline ... ... ... ... ... ... 189
52. Flower-bad, and same opened, of Sfellaria media, showing
conditions of degeneracy and adaptations for self-fertili-
sation ... ... ... ... ... ... ... .,. 255
53. Flower-bud, and essential organs of Epilobium montanum,
showing positions for self -fertilisation ... ... ... 255
54. Styles and stigmas of the two forms of Pansy, showing the
conditions which (a) prevent and (6) secure self-ferti-
lisation, respectively ... ... ... ... ... ... 255
XVlll LIST OF ILLUSTRATIONS.
FIGURE PAGE
55. Styles and stigmas of self -fertilising forms of Pansy ... ... 257
56. Details of structure of cleistogamous Violets ... ... ... 258
57. Details of structure of cleistogamous Oxalis Acetosella ... 260
58. FloWer-bud and stamens of cleistogamous Impa^ieris ... ... 261
59. Flower-bud and section of cleistogamous Lamium amplexi-
caule ... ... ... ... ... ... ... ■•• 261
60. Corolla, stamens, and style of Salvia clandestina, showing
adaptations for self -fertilisation ... ... ... ... 262
61. Transitional forms between bracts and leaves of Hellehorus
viridis ... ..• ... ... ... ... ... .■• 286
62. Inflorescence of CorwwsyJorida, showing floral mimicry ... 287
63. Inflorescence of Dariumia, showing floral mimicry ... ... 287
64. Involucral bract of Wtf/eZZa, bearing an anther ... ... 288
65. Glumes of Lolium, both antheriferous and stigmatiferous ... 288
66. BranuncuZws with a foliaceous sepal ... ... ... ... 289
67. Foliaceous calyx of Tri folium repens with stipulate leaves,
borne by the receptacular tube ... ... ... ... 289
68. Flower and leaf of JIussfe?ida 290
69. Linaria with one sepal petaloid ... ... ... ... ... 291
70. Calyx of Garden Pea with carpellary lobes ... ... ... 292
71. Ovuliferous sepal of Violet ... ... ... ... ... 292
72. Corolla of Foxglove with filamentous processes, some being
antheriferous ... ... ... ... ... ... ... 292
73. .Igitt'Zejfia, the corolla with polleniferous spurs ... ... 293
74. Ovuliferous petals, etc., of £e^07i!a ... ... ... ... 293
75. Ovuliferous anthers of Sempervivum ... ... ... ... 294
76. Stigmatiferous and ovuliferous stamens of Begonia ... ... 294
77. Carpels and ovules originating from a placenta of Carnation,
the carpels again ovuliferous (a) ... ... ... ... 295
78. Stameniferous carpels of Willow and Ranwnculus auricomus 296
79. Petaliferous placentas of Cardamine pratensis and of Rhodo-
dendron ... ... ... ... ... ... ... ... 296
80. Metamorphosed sub-petaloid carpel of Polyanthus ... ... 297
81. Foliaceous connective of Petunia .. ... ... ... 298
82. Petalody, or " hose-in-hose " form, of connective in a double
Co]\imhine (Aquilegia) ,,. ... ... ... ... ... 298
83. Foliaceous stamen and petal of the Alpine Strawberry and
stamen of the Green Rose 302
LIST OF ILLUSTEATIONS. xix
FIGURE PAGE
84. Stamen of Jatropha Pohliana, with foliaceous membranes to
the anther-cells ... ... ... ... ... ... ... 302
85. Metamorphosed and foliaceous ovules of Mignonette ... ... 305
86. Metamorphosed and foliaceous ovules of Sisymbrium Alliaria 306
87. Tubular excrescence on the labellum of Cattleya, homologous
with an ovule ... ... ... ... ... ... ... 306
88. Multifold carpels, with ovuliferous margins, from a malformed
Primrose 308
THE
OEIGIN or FLOKAL STRUCTUEES
THEOUGH INSECT AND OTHER AGENCIES.
CHAPTER I.
GENERAL PKIXCIPLES.
Introductory. — Much has been -written on the structure of
flowers, and it might seem almost superfluous to attempt to
say anything more on the subject ; but it is only within the
last few years that a new literature has sprung up, in which
the authors have described their observations and given
their interpretations of the uses of floral mechanisms, more
especially in connection with the processes of fei'tilisation.
Moreover, there is a considerable amount of scattered
literature on special points which seems never to have been
collated, so as to show the relative significance of the dif-
ferent classes of observations to which the authors have
devoted themselves respectively. The consequence is, that,
good as each in itself may be, it often requires the help of
other classes of facts to enable one to fully elucidate any
question to be discussed.
Now, the primary object of the first really scientific study
of plants was their classification, and no longer with the
sole view of ascertaining the real or imaginary medicinal
uses of herbs ; as had been the case in Gerarde's time, when
a botanist and a herbalist were one and the sarce.
3
2 THE STRUCTURE OF FLOWERS,
Systematic botanists, however, have hitherto invariably
contented themselves with observing differences of structure
only; and paid little or no attention to the "why" and the
" wherefore " of the differences they seized upon as being
more or less important for the purpose of distinguishing
species. When, however, the desirability of a more thorough
knowledge of the origin of parts of plants as interpreting mor-
phological characters was felt, developmental history began
to be studied ; a method strongly insisted upon by Schleiden,
for example ; and the most elaborate result of this method of
investigation is undoubtedly Payer's Traite d' Organogenie Com-
faree de la Fleur, published in 1857: but if it be thought
sufficient to limit the study of J3owers to tracing their mor-
phological development alone, one soon begins to see that it
is far from being so, and, taken by itself, it may lead one into
false interpretations, so that to the study of development
must be added that of anatomy, To Ph. van Tieghem we
are indebted for an elaborate treatise, entitled Recherches snr
la Structure du Pistil et stir VAnatomee Comparee de la Fleur
(1871), dealing with the more minute details of floral struc-
tures. This treatise, however, still leaves much to be
desired. I
Besides these methods, analogy and especially teratology
furnish assistance of no mean value. Here we are especially
indebted to Dr. M. T. Masters for his standard work on
Ternfology*
Now, any one of these methods taken alone would be
insufficient, and in many cases would be far from thoroughly
accounting for particular points under consideration.
Hence to arrive at a complete interpretation of the origin
of every sort of structure to be found in flowers, it can only
* A Gpiman edition, FJlanzen Teratologic, ed. TaiEmer, 1886, Las
numerous additions.
GENERAL PKINCIPLES.
be done by calling in the aid of each and all these methods
to the very utmost extent possible.
Lastly, to attempt any theoretical exposition of tlie evo-
lutionary history of flowers, considerable caution is required ;
for the causes of variation ai-e generally so obscure, the
chances of seeing them in activity so small, and experimental
methods of verification well-nigh impossible, that specula-
tions on this subject cannot altogether escape the bounds of
hypothesis so as to become demonstrable facts. Hence
observations which I shall make later on, with reference to
the origin of existing floral structures, will not profess to be
an3'thing more than theoretical, and at most only a "work-
ing hypothesis " for future investigations.
The Structure of a Typical Flower. — Before consider-
ing how the innumerable forms
of flowers dev^iate from one
another, it is advisable to assume
some typical form or plan as a
preliminary basis to start from,
or to which all flowers, if pos-
sible, may be referred as a
standard. It would be qaite
possible to adopt some kind of
flower as it exists in nature,
but as this would be arbitrarv,
it may be better to take an ideal
type, and the diagram (Fig. 1) will answer the purpose,
in which the outermost circle is supposed to represent a
cross section of the five Sepals constituting the Calyx. The
second circle is that of the five Petals of the Corolla. The
third stands for the Anthers of the five Stamens superposed
to the sepals; the fourth being those of five Stamens super-
posed to the petals. These two whorls of stamens together
Fig. 1. -Diagram of a tj-pical Bower.
4 THE STRUCTURE OF FLOWERS.
constitute tlie Anclroecium. Lastly, there are represented
two * whorls of Carpels forming the Gynoeciura f or Pistil.
The outermost whorl of carpels is superposed to the sepals,
the innermost to the petals.
There may be additional structures in flowers, such as
disks, honey-glands, etc. ; but as these, when they occur on
the floral-receptacle, are merely cellular protuberances and
form no part of the floral whorls proper — not being foliar in
their origin— they may be omitted, especially as their posi-
tion is by no means constantly the same in all flowers.J
The Principles of Vakiation. — Having thus assumed an
ideal type, we may at once consider the " Principles of
Variation," as I propose to call them, in accordance with
which the different members of flowers can be altered; so
that by means of various combinations of these principles all
the flowers in the Vegetable Kingdom can be brought under
this one fundamental plan.
There are five principles which require special considera-
tion. They are usually designated by the terms Number,
Arrangement, Cohesion, Adhesion, and Form.
"Number" refers to the number of whorls and the
number of pai-ts in each whorl. If two or more whorls
contain the same number of parts or be multiples of one
another, they are said to be " symmetrical " or " isomerous."
If they differ in the number of parts they are " unsym-
meti-ical " or " anisomerous."
"Arrangement" refers to the relative positions of the
* Why I assume two whorls for the pistil, instead of one only, as is
generally done, will be understood hereafter. I have since found that
Robert Brown carae to the same conclusion (Col. WorJcs, i. 293).
t I adopt the spelling ayncecium for the sake of uniformity ; it may
be regarded as a shortened form of Gyncecoecium.
J I do not here allude to certain glandular structures, which may
be the homologucs of arrested organs.
GENERAL TRINCIPLES. 5
different wliorls, as well as of those of the individual members
of the whorls with regard to each other.
" Cohesion " signifies the union of parts of any, but of the
same whorl. The original or ancestral condition of the
parts composing every whorl is presumed, on the principles
of evolution, to have been one of entire freedom ; so that
the members were as completely separate or free as, for
example, they are in a Buttercup. Reversions to this con-
dition of freedom may occur, and then the process is called
" dialysis , " as in the case of a polypetalous Camimnula
occasionally cultivated as a garden plant.
" Adhesion " signifies the union of parts of different
whorls ; as well as that between the ovary and the recepta-
cular tube, constituting the so-called inferior ovary. I regard
adhesion as representing a more advanced or a more highly
differentiated state than that of cohesion. Reversions may
occur by " solution," which brings about a freedom of parts
normally united, as in the abnormal cases of Apples, double
Saxifrage, members of the JJmhelUfenv, etc., which have all
their parts perfectly free, though with inferior ovaries under
ordinary circumstances.
" Form " refers to the shape of the organs ; such as those
of sepals and petals upon which generic characters are so often
founded, the length of the filaments, and other peculiarities.
If all the parts of any whorl be exactly alike, it is said to
be " regular ; " if not, the whorl will be " irregular."
The above five principles constitute the most important
in accordance with which N'ature has brought about the
infinite diversity which exists in the Floral world. There are
minor distinctions, hereafter to be considered, such as colours,
scents, etc. ; but they are of less importance in investigating
the causes at work which have evolved specific and generic
differences amongst flowering plants.
6 THE STRUCTURE OF FLOWERS.
There is another point which may be here noticed. That
a flower-bnd is a metamorphosed leaf-bud is now an accepted
fact ; but an obvious difference between thera consists in the
arrested state of the axis of tbe former, constituting the floral
receptacle ; and the question arises, how has this arrest been
brought about ? Like all other peculiarities of structure
to be described, I would attribute the arrest primarily to the
altered nature of the foliar organs on becoming members
of flowers. Thus, a Fir-cone and a Buttercup are arrested
branches ; but when the parts of a flower are reduced ia
number, and instead of being in a continuous spiral are
grouped in " compressed cycles," * I would then (hypo^
thetically) attribute this further reduction of the axis, as
well as other features hereafter to be described, to the
irritation of insects in probing for juices, and causing
nectaries to be formed, f It is the commonest thing for leaf-
buds to be arrested, and sometimes metamorphosed as well,
by insects puncturing and depositing their eggs in them.
Such may be seen on the terminal shoots of Yews, Thyme,
and in certain kinds of Oak-galls, etc. In all such cases the
immediate effect is the total arrest of the axis, though the
leaves may be but slightly altered, as in the Yew. How
the various metamorphoses of leaves into petals, etc., has
followed will be discussed later on.
It must not be forgotten, however, that the tendency to
shorten the axis is primarily, in some cases, due to the
altered structure of the foliar organs, as in Gymnosperms ;
whereby they undertake the reproductive functions. At
the same time, I think insects have had a good deal to do
with it, in many other phanerogams, Avhich have but few
pai'ts to their Avhoi-ls.
Each of the above principles must now be considered in
detail.
* See pp. 41, 42. t See p. 140, seqq.
CHAPTER II.
THE PRINCIPLE OF NUMBER.
Number — General Observations— The first principle of
Vai-iation to be considered is that of the number of parts
composing the different whorls of flowers. There are good
reasons for considering that six whorls, consisting of five,
four, three, or two parts each, as the case may be, should be
regarded as the theoretically complete number of verticils
of any flower.
Anatomical investigations prove that the rule is for the
pedicel to contain — at least, immediately below the flower, —
if the latter be pentamerous, ten more or less distinct fibro-
vascular cords, five of which belong to the sepals and five to
the petals ; if it be hexamerous, there will be six cords, three
for each whorl of the perianth. Each of these cords can
give rise by branching, first, to a whorl of stamens and
subsequently to a whorl of carpels, furnishing at least two
marginal and one dorsal cord for each of the latter.
In many flowers both whorls of stamens are present, and
the androecium is then isomei-ous with the entire perianth.
More often one whorl is arrested, and then it may be either
one ; but most usually it is the petaline. On the other
hand, the calycine may not be developed as in Primroses,
Eliavmus, etc.
The absence of the petaline stamens is possibly attribu-
8 THE STRUCTURE OF FLOWERS.
table to the law of compensation, in consequence of tlie
enhanced growth of the corolla, the petals thereby abstract-
ing the nourishment that would be required by the stamens
superposed to them.
That the number of staminal whorls should be two in
verticillate flowers, i.e., equal to the perianth, is apparent
from the fact that two whorls prevail in Monocotyledons and
are not at all uncommon in Dicotyledons ; and when the
petaline whorl alone exists, as in PrimulacecB and Myrsinece,
calycine staminodia are sometimes present which tend to
restore the complete number, as in the genus Samolus in the
former and in the tribe Theophmstece of the latter order.
The reduction of the number of carpels is very generally
carried to a greater extent than that of the stamens. Assum-
ing two complete whorls of carpels as the primitive number,
not only are both rarely to be found in the same flower, as
in Bidomus, but a portion only of one whorl is commoner
than even a single entire whorl. Thus, two are characteristic
of Cruciferce, Polygalece, and of most of the gamopetalous
orders ; while one carpel only prevails in Leguminosce and
elsewhere.
That the absence of parts of, as well as of entire whorls
of flowers as they now exist does not represent primitive
conditions, is testified to by the frequent occurrence of
various kinds of degradations, such as were alluded to above in
the case of the staminodia of Samolus, etc. Thus, with regard
to the calyx, it is a noticeable fact that when the inflorescence
consists of a large number of flowers, especially if small and
closely compacted, there is a strong tendency for the sepals
to become partially arrested and remain rudimentary, or even
not to be developed at all. This, is particularly observable
in some epigynous orders as JJmbelliferce, Araliacece, Capri-
foliacece, Rubiacece, Composite, etc.
THE PEINCIPLE OF NUMBER. 9
The degradation of the corolla is likewise very common.
As its enhancement has been due to insect agency, so,
conversely, its reduction in size, colour, etc., is presumably
often the result of the neglect of insects. Consequently
inconspicuousness becomes a characteristic feature of self-
fertilising flowers. By increased degradation the corolla may
disappear entirely, as in Sagina apefala, some cleistogaraous
flowers, and in the IncompletcB generally. Sach degradation
is also characteristic of wind-fertilised flowers.
As both calyx and corolla may be degraded and disappear,
so may the stamens and carpels, unisexual and neuter flowers
being the result.
Further observations, however, wnll be made upon this
subject when treating of the several whorls respectively, and
especially when discussing the phenomenon of degeneracy.
The Origin of Different Numbers. The number of parts
constituting the floral whorls is, without doubt, primarily
due to phyllotaxis ; and therefore, to understand why certain
numbers, such as fives, fours, and threes prevail, it is needful
to give some prelimiuary remarks on the principles of leaf
arrangement. It has long been observed that these are
referable to two kinds — one in which two or more leaves are
situated on the same node, when they are decussate,* that
is to say, each pair or whorl of three or more leaves alternates
in position with the whorl immediately above and below it.
The second system is when only one leaf occurs at a node ;
the leaves are then said to be alternate. The leaves are then
arranged on a continuous spiral line, and can be represented
by the fractions of the well-known series ^, J , |, |, ^%, -^^^ etc.
Of these fractions the denominator represents the number of
* Rare exceptions occur in species of Potamogeton, in which alternate
intemodes between the distichously arranged leaves are suppressed, so
that they become opposite, but are all in the same plane.
10 THE STRUCTURE OF FLOWERS.
leaves in a "cycle," and tlie numerator the number of times
a spiral line, passing through the position of the leaves, coils
round the stem in forming a cycle ; thus, with the f arrange-
ment, any leaf being taken as number 1, the sixth leaf will
be first that falls in the same vertical line Avith number l,the*
leaves 1 to 5 constituting the cycle. The portion of the
spiral line which passes through the leaves 1 to 6 coils twice
round the stem, and if projected on a plane forms two circles.
The ano-ular distance, measured from the centre of the stem
or circles, between any t\v'o successive leaves is always found
by multiplying 360° by the fraction : thus f X 360° = 144°.
The interpretation, therefore, of the prevailing numbers
3 and 5 in floral whorls is that they are, in most cases, cycles
of the ^- or f types respectively; while 4 is primarily due
to the union of two pairs of opposite and decussate parts.
6, 8, 10 are merely the doubles of the preceding, and mostly
represent two pairs of whorls or cycles blended together,
thus forming one whorl, or so closely appi'oxiraated as
scarcely recognizable as two ; though the rare number 8, in
some cases, such as Nigella, and Helleborus fcetidus, may repre-
sent a cycle of the f type. Similai'ly, the still rarer numbers
7, 9, and 11 in flowers correspond to the absence of these
numbers as denominatois of any fractions of the above
prevailing series.
With the exception of dimerous and tetramerous whorls,
all the rest are presumably due to alternate arrangements.
Now, opposite leaves present a more primitive type than
alternate ; that this is so, is not only reasonable from the
primordial condition of the cotyledons of Dicotyledons, but
the transition from an opposite to an alternate condition
may be often witnessed on rapidly growing stems, such as
of the Jerusalem Ai'tichoke. Whenever this plant bears
opposite leaves below, and alternate leaves above, it will be
THE PRINCIPLE OF NUMBER. 11
found that the aiTarigement of the latter is almost invariably
represented by the f type. It is secured by developing inter-
nodes between the two opposite leaves of each pair, and by
shifting their positions so as to acquire ultimately an angular
divero-ence of 144°.*
The feature to be especially observed in the transitions
from opposite to alternate arrangements is the order in which
the opposite leaves separate so as to assume successive
positions on the continuous spiral line passing through their
insertions, when they have become alternate. This will be
understood from the accompanying diagram, in which the
numbers represent the order which the leaves will ultimately
assume on the | type ; tliough they ai-e placed tis if still
opposite and decussate. The numbers 1 and 2, .3 and 4, 5
and 6, etc., represent the successive pairs of opposite leaves,
the arrows showing the direction of the spiral.
It will be at once ob- ^ 2
served that the numbers G, 5
9, 14, and 22 are in the 10
13
same row, and correspond to -.o a
the divergences |, |, ^V, 21
/y. Ko. 17 falls into the 3 8 11 IG 19 20 15 12 7 4
series f , and completes the 22
second cycle of that type v l/(=--Xo-j-l)
from ISTo. 1. n
It may be observed 6
here, as occasion will arise 1 >
for a fuller allusion to the Fig. 2.-Oi>posite leaves passing into alternate.
significance of the fact, that, with the so^e exception of the
* I have fully explained this in my paper, On the Variations of the
Angular Divergences of the Leaves of Heliauthns Tuberosus, Trans. Lin.
Soc, vol. xxvi., p. 647. See also On the Origin of the Prevailing Sijstems
of Phyllotaxis, I.e., 2nd series, vol. i. p. 37.
12 THE STRUCTURE OF FLOWERS;
distichous or ^ type, every other arrangement always has
three leaves in every projected circle.
It may be noticed that No. 4 not only does not occur in
the row 1, 6, 9, etc., — a fact which corresponds with the i^arity
of a ternary arrangement occurring amongst flowers of
Dicotyledons,— but in order to fall over No. 1 it would have
to pass through 270°, that is from right to left, practically
an impossibility ; so that when "threes" are met with in
Dicotyledons we must look for .some other interpretation
than to refer them to the J type.
The numbers 7 and 11, as stated, are extremely rare in
flowers, and this is in accordance with the fact that they
belong to another series, viz. ^, \, |, j\, y\, etc , which is rarely
represented in nature. E.xamples, however, will be found in
the leaves of Sedum reflexum, on some branches of Araucaria
imhricata, and sometimes in the Jerusalem Artichoke. In
the last case, it will be discovered that the heptastichous or
f type arises out of verticils of threes, in precisely the same
way as the pentastichous or | type does from an opposite and
decussate arrangement ; and as there are always four leaves
in every projected circle, for every type of this series, except-
ing the first or -J, it can only occur where the leaves are
narrow or are short, or do not occupy too much space so as
to overshadow one another.
Variations in the Floral Symmetry. — Besides the fact
that certain numbers are often characteristic of certain
species, genera, or even orders, great variations in the sym-
metry exist, not only in different genera of the same order,
but in different species of the same genus.*
Now, with reference to this latter fact, it must be borne
in mind that flowers are so highly differentiated from the
* See note by tlio author, On the Causeft of the Numerical Increase of
Parts of Plants, Journ. Lin. See. Bot., xvi. p. 1.
THE PRINCIPLE OF NUMBER. 13
leaf type, that thej have undergone such wonderful transfor-
mations and adaptations to insect and other agencies and to
their environing conditions, so that the simple and original
laws governing the arrangement of the leaves, here pro-
pounded for the origin of what may be called the " primitive
symmetry " of the floral organs, have become in many cases
masked or interfered with. Hence, to deduce those orio-inal
laws from the present structure of flowei's, it is not only neces-
sary to consider the floral symmetry of an immense number
of genera, and so ascertain what are the relative proportions
of certain numbers when associated with alternate and oppo-
site leaves respectively, but to discover what may have been
the interfering causes which have modified what would
have been the immediate effects of the fundamental laws of
phyllotaxis.
Thus, it will be found that the numbers of the parts
of whorls are liable to vary on their own account, while
the arrangement of the foliage varies independently at the
same time ; so that where the floral symmetry of a plant
does not tally with the leaf arrangement, the discrepancy
may be due either to subsequent changes occurring in the
flowers or in the leaves, or perhaps in both.
For example, a qnaternary floral type may be, and often
is, associated with alternate leaves ; where there is reason
to suspect that the former was established from a primitive
opposition in the leaf organs, but that the foliage has subse-
quently differentiated into a spiral arrangement, leaving the
original 4-merous symmetry of the flowers unaffected, as in
many of the Onagracece ; Epilobium., indeed, often furnishing
ocular demonstration, as, while the lower leaves may be
opposite, the upper are often alternate.
On the other hand a quinary arrangement is often
associated with what may be called a persistent opposition
4
14 THE STRUCTURE OF FLOWERS,
in the leaves, as in Carijophyllece and Labiafce. This may-
be due eithei' to an abrupt change from opposite leaves or
bracts to a spii-al one in the flower, or by a reversion
from an alternate to an opposite position of the leaves, the
floral organs retaining the arrangements due to their spiral
origin.
The symmetry is based on Calyx, Corolla, and in many
cases the Androecium also ; but the carpels are not generally
regarded, for it does not usually extend to the gynoecium,
though it is very frequently retained in the androecinm,
vv^hich is often some multiple of that of the perianth
whorls.
In presenting the reader with what may be regarded as
ostensible grounds for the interpretation proposed, attention
will be first directed to the more obvious correlations be-
tween floral symmetry and leaf arrangements, as appear
from certain numerical proportions ; and, in the next chapter,
to significant facts observable in the symmetry of particular
plants.
Commencing with genera possessing alternate leaves and
a quinary floral type, the prominent fact becomes at once
apparent that this correlation far exceeds in numerical
proportion any other. Thus, of above eighty Dicotyledo-
nous orders* examined in all, no less than 1285 genera
have quinary flowers associated with alternate leaves, and
this is exactly what one would expect according to the
theory advanced that 5-merous whorls are cycles of the
f type-
As a corroboration is the fact that such whorls often
have their parts arranged quincuncially in estivation (Fig.
3, a) ; and when they are not so they can be referred to
* I consulted the first volume of the Genera Plantarum for this
purpose, which embraces the Thalamijlorcc and Galyciflorcc.
THE PRINCIPLE OF NUMBER. 15
it, as I have explained elsewhere : * thus Fig. 3 shows how
the varieties of imbricate aestivations are deducible from
the |- type (a), bj shifting the edge of the 2nd member under
the 4th (b, " vexillary "), the 3rd under the Sth (c, " imbricate
proper "), and the 1st under the 3rd (d, " contorted ").
Similarly ternary ortrimerous whorls are almost universal
amongst flowers of Monocotyledons, and the ^ type of phyllo-
taxis is equally common in the foliage. It has been seen
tliat the ^ type cannot be deduced from opposite leaves, and
consequently never occurs, as ft^r as I know, amongst the
foliage of Dicotyledons. The comparatively few genera in
this class with ternary flowers is therefore in accordance
with the views herein expressed ; and where they occur, as
a 6 o
Fig. 3.— Floral iEstivaticns.
in Berberis, there are special features which lead one to
believe they are not due to the ^ type at all, but to the
breaking up of a high continuous spiral into groups of
threes, as will be explained hereafter.
If, however, we take a theoretical departure from a
single cotyledon, as occurs in Monocotyledons, then the next
leaf can be at either of the limiting positions of the angular
distances of 180° or 120°, but not less ; for if it were less
than 120°, there would be four leaves in any projected
circle, and this would immediately introduce a member of
the series ^, ^, f , etc., as shown above. The consequence is
* See my papei-, On the Origin of Floral Estivations, Trans. Lin. Soc,
2ncl series, Botany, vol. i. p. 177.
13 THE STRUCTLTRE OF FLOWERS.
tliat the ^ and ^ types are exceedingly common in the foliage
of ^lonocotjdedons, while the f, as far as I am aware, is
entirely wanting in that class, whether in foliage or flowers.
Of genera having alternate leaves bat associated with a
binary or quatemaiy floral symmetry, there are about 270 in
number of about 30 orders. Now, the co-existence of alternate
leaves with 2- or -l-meroiis flowers appears at first sight to
negative the theory ; but, as mentioned above, these and
other irregularities have been brought about by subsequent
differentiations in the foliage or flowers. On the other hand,
opposite leaves with quaternary flowers are not at all in-
frequent, though not quite so commou as when they are
alternate ; thus, Oleacece and Onagracece are so conditioned.
Again, in liosacece, which is an order characterized by having
alternate leaves and 5-merous flowers, three genera alone
out of seventy have opposite leaves, and these three also are
accompanied by 4-merous flowers ; viz. Elwdofypus, Coleogyne,
and Encryphia. These three genera thus acquire their
importance fi-om being isolated amongst others to which
they are allied, and which are generally otherwise charac-
terized. Many orders have both foliage and floral symmetry
remarkably inconstant, and all four combina'tions, viz. 4-
merous and 5-merous flowers with opposite or alternate
leaves almost indiscriminately, as in the tribes Biosmece and
BorosmecB of Etcfacere ; and it is a noticeable fact that,
associated with this inconstancy of correlation, there is an
inconstancy in the leaf arrangement, opposite and alternate
leaves being often in species of the same genus, and even on
the same individual plant.
The total number of genera noticed as having 4-merous
flowers and opposite leaves was 110 in 25 orders ; whereas 1
noticed 276 genera of 30 orders as having 4-merous flowers
associated with alternate leaves. This, I believe, is due to
THE PRINCIPLE OF NUMBER. 17
subsequent differentiation in the foliage to an alternate
condition, the quaternary condition of the flowers remaining
unaltered.
Similarly with the last condition, I found 212 genera of
30 orders with a quinary arrangement of the flowers corre-
lated to an opposite condition of the leaves, this being an
apparent anomaly of the same kind, but which is, however, to
be interpreted in the same way. Thus the Labiatce are con-
stantly 5-merous in the flowers, but with as constantly
opposite leaves. Now, if we contrast this order with Scro-
phularinece, we find a similar constancy in certain genera
only, as in BMnanthus, etc. ; while other genera have alter-
nate leaves as Linaria, Digitalis, etc.
There is an alternative of interpretations of this fact, for
both can be illustrated in nature. Either all the pentamerous
flowers have been deduced from alternate leaves (as may
have been the case with BMnanthus and Labiatoi), the leaves
having subsequently reverted to the original or ancestral
state of opposition ; or else, the 5-nierous character of the
flowers has arisen by a sudden change (possibly due to the
stimulus of insect agency) from opposition in the leaves or
bi-acts to an alternate arrangement in the parts of the flower.
As an illustration of this latter pi'ocess may be mentioned
the development of the five sepals of Beutzia as compared
with the four of the allied genus Fhiladelphus. In this
latter genus the anterior and posterior sepals appear
together, subsequently the two lateral arise simultaneously.
In Deutzia, however, the two anterior sepals correspond to
ISTos. 1 and 3 ; two sepals are lateral, viz., Nos. 4 and 5 ;
and the posterior sepal is No. 2. Thus the opposite and
decussate pairs of sepals of Philadelphus would be repre-
sented by the figures 1 and 2, 3 and 4. If these were to
break up into a quincuncial spiral and shift their positions.
18 THE STRUCTURE OF FLOWERS.
they would, with the addition of one moi'e sepal, assume
those represented by Beutzia.
o.
5
6
-1
^ 2— >
4
3 5
Philadelphua.
Exactly the same procedure occurs in the change from
opposite to alternate arrangements of leaves in the Jeru-
salem Artichoke, as I have explained in treating of the
varieties of leaf-arrangement in that plant.
Calycantlius is another instance illustrating an abrupt
change from an opposite condition of the leaves to the ^x
type in the bracts enveloping the flowers, and which then
pass insensibly into sepals and petals.
Symmetrical Increase and Decrease in Floral Whorls. — -
As another instance of variability adding further coroplica-
tions, it may be observed that in both kinds of arrangements,
namely, of those plants possessing alternate and those pos-
sessing opposite leaves, there are many genera whose floral
symmetry ranges from one to some higher number in the
different species of the same genus. Thus 4-5-merous flowex's
are especially common. I found it so in more than 100 genera
of 23 orders examined among alternate-leaved plants ; and
58 genera of 19 orders among those with opposite leaves.
Again, some genera have species the whoi'ls of whose
flowers range from 3 to 5 or 6, or from 4 to 6 in the number
of parts ; others from 5 to 7 or 5 to 8, etc. In these
cases it is often quite impossible to explain what has been
the immediate causes producing such variations. The only
interpretation that can be given is that the primary sym-
metry having been originally determined by phyllotaxis, it
THE PRINCIPLE OF NUMBER. lU
changes, whether in the individual or in its descendants,
through the law of " symmetrical increase or decrease." By
this I mean that the number of sepals, petals, and stamens
often vary together from the typical number by the addition
or subtraction of a member. Thus, in a single corymb of
an Elder, 4-, 5-, 6-merous flowers may be often found ; simi-
larly, while early blossoming Fuchsias may bear 3-merous
flowers, they are replaced later by the regularly 4-merous
ones. Although these changes frequently occur in tJie same
plant, they usually are not permanent. Yet they occasionally
appear to have become so, as in the terminal flowers of Adoxa
and Monotropa. On the other hand, the constant occurrence
and, therefore, specific character of 4-merous flowers in
Potentilla Tormenfilla, and 3-merous in Tillcea vmscosa, 1
should be inclined to attribute to the fixation of a symmo-
ti'ical reduction which has taken place from the permanent
5-merous type so characteristic of Potentilla, and many
genera of the Crassulacece. Not infrequently the difference
of number is pronounced by systeraatists as generic; thiis,
while Bnhia has 5-merous flowers, Galium has 4-mcrous. A
simitar ditference lies between Rata and Haploplnjllum*
If a cause be looked for, it would seem to be merely a
question of nutrition. If the symmetry varies in the same
plant, it is obvious that a corolla of four petals could not
have been provided with the same amount of nutritive
material as a 5-merous one. But if it be a specific character,
as in Tormentil (which, it may be observed, affects the more
or less barren soil of heaths), then the change has become
fixed and is now hereditary.
* By running the eye through the artificial keys at the commence-
ment of the Orders in the Genet a Plantarmnoi Bentham and Hooker, it
will be seen how frequently these authors regard the number of parts in
the Calyx and Corolla as a prominent generic character.
20 THE STRUCTURE OF FLOWERS.
Unsymmetrical Decrease in certain Floral Whorls. —
Another modifying cause o£ tlie cliange of symmetry is
the adaptation to insect or other agency for fertilisation.
This I believe to have played a most important part in modi-
fying flowers, as will be explained more fully hereafter, more
especially in affecting the Androecium and Gyncecium, than
the Perianth, as far as " number " is concerned, this latter
organ being altered by their agency, more especially in Form.
Thus, the loss of one or more stamens is very characteristic of
certain groups, as in the Labiates, when the remaining mem-
bers of the andrcecium become altered in length and position
so as to facilitate the intercrossing of distinct flowers.
On the other hand, with inconspicuous and cleistogamous
flowers, there is a strong tendency to reduce the number of
stamens, as in Cbickweed to three, the allied species Siellaria
Solostea having ten. Similarly, in the cleistogamous flowers
of Violets they are sometimes reduced to three or two ; since
a very small amount of pollen is really quite sufficient to
fertilise a considerable number of ovules.
The gynoecium has very frequently a less number of
carpels than the other whorls have parts. Now, the primary
effect of intercrossing is to enhance the size of the corolla
and to give a preponderance to the andrcecium. On the
other hand, one result is to check for a time the growth and
development of the gyncecium of most insect-visited herma-
phrodite flowers, i.e. to render the flower protandrous ; and
I strongly suspect that the generally reduced number of
carpels in highly differentiated flowers — as of the Gamopetalce,
in comparison with the TTialamiflorce and CalycifJorce — is cor-
related to the fact that they have been for many generations
visited by insects. This idea is supported by the fact that
bicarpellary genera sometimes tend to restore the ancestral
number of the five carpels, as is occasionally the case in
Gesneria.
THE PRINCIPLE OF NUMBER.
21
In some cases, nature seems, as it were, to try and com-
pensate for the loss of the carpels by an increase in the
quantity of seeds. Thus, while no Labiate flower has more
than four seeds, it has been ascertained that a Maxillaria
bore 1,700,000 seeds ; and I found by calculation that a single
plant of Foxglove yielded a million and a half apparently
good seeds.
The relative advantages of having many or few seeds
will be discussed later on.
Illustrations from RANUNCULACEiE. — Certain genera of
the Eanunciolacece are particularly instructive in showing
how members of the floral whorls originate in phyllotactical
methods, but are more or less
altered in their positions by the
lateral union of their fibre- vascular
cords ; so that they become ar-
ranged in superposition instead
of being alternate, or vice versa.
Thus, in Garidella (Fig. 4) (with
which. Helleborus foetidus partly
agrees), the sepals and petals are
both arranged, and arise succes-
sively, in quincuncial order; the
petals being (correctly, in accord-
ance with phyllotaxis) superposed to the sepals. The an-
droecium forms a whorl of eight stamens, and represents
a cycle of the f arrangement ; the proper angular divergence
of 135° is, however, not retained, in consequence of the fibro-
vascular cords being intimately connected with those of the
petals. Having thus established the first whorl of eight, the
rest of the staminal series follow on the same radial lines.
By referring to the diagram (Fig. 4) it will be seen how the
stamens of the outermost whorl group themselves in super-
0-'
/
/
I
€3
\
\
\
e3
Fig. 4.— Diagram of Garidella.
99
THE STRUCTUKE OF FLOWERS.
position to the petals and sepals. Similarly, in Nigella
sativa tlie petals are eight in number, and occupy the same
positions as the outermost whoi'l of stamens of Garidella.
They have, then, the eight stamens of the outermost whorl
of the androecium superposed to them.
In Delphinium the stamens and carpels form a continuous
spiral, represented by |, or approximately by f. In some
cases Braun* found 16 stamens, and the first carpel being
the 17th organ, stood superposed to the stamens No. 9 and
No. 1. In another case 18
stamens were developed, so
that the fii'st carpel stood
superposed to stamen No. 11.
Hellehorus niger (Fig. 5)
has five sepals which emerge
and are arranged in quin-
cuncial order. There are
tweuty-one nectariform pe-
tals, i.e. one cycle of the
■^ arrangement, grouped as
in the accompanying dia-
gram. The petals 1 to 8
and 9 to 16 would correspond approximately to two cycles
of the f type. Radial rows of stamens then follow on the
same lines as the petals.
Eranfhis hijcmalis has, as usually regarded, a 5-8-merous
coloured calyx. A pair of staminodes stand superposed to
each member of the outer whorl. Stamens follow along the
radial lines, of which six terminate in carpels.
Aguilegia vulgaris, or the Columbine, has the sepals, as
* Al. Braun on Delphinium (Pringsheim's .Tahrb. f. Wiss. Bot., 1857,
i. 206), referred to by Henfrey, Morpkol. of Balsanmiece, Journ. of Lin.
Soc., iii. 159.
Fig. 5.- Diagram of Sellehorus niger.
'•. )
THE PRINCIPLE OF NUMBER. 23
usurJ, quincuucially arranged. The petals appear simul-
taneoushj, alternating in position to the sepals. The stamens
occur in ten rows, 5 being superposed to the petals and
5 to the sepals ; and, lastly, 5 carpels appear superposed
to the petals. This flower, then, adopts the more usual
character of alternation in the whorls. But it may be noticed
that while the corolla alternates with the calyx, each of
these outer whorls gives rise to a radial series of stamens.
From the preceding illustrations, it will now be seen that
phyllotaxis lies at the foundation of the arrangements of the
members of floral whorls ; that the -| type prevails in the
sepals and petals, with a strict angular divergence of 144°.
The divergences are, however, subsequently modified in the
stamens and carpels. Thus, in Helleborus niger the petals
clearly represent a whorl of 21 parts, i.e. they are pre-
sumably arranged according to the -^^ type. They are, how-
ever, so far modified in position as to become superposed
to the sepals in groups. Similarly the stamens form
series of 21, each being superposed ia radial lines to the
petals.
The interpretation of these displacements from what
would be due to strict, phyllotactical laws is that the
individual cords of the stamens and carpels are not inde-
pendent as they are in the " leaf traces " of an axial cylinder,
where the cord or cords belonging to each leaf are simply
intercalated side by side with those of the leaves most nearly
approaching the same vertical line, and constitute together
the common fibro-vascular cylinder of the stem. In the
pedicel, however, the rule is that this should contain at least
the same number of cords as there are leaves to the perianth,
or sepals and petals together. These, usually six or ten
cords, on reaching the floral receptacle are sent off respec-
tively as the cords of the sepals and petals ; whereas, it is
24 THE STRUCTURE OF FLOWERS.
these latter which by lateral or radial " chorisis " supply the
cords required for the stamens and carpels
The consequence is that the essential organs have their
cords issuing from a common stem with those of the perianth.
Thus they are compelled to stand superposed to them.
Perhaps the word " compelled " requires a woi'd of ex-
planation. The cord of any organ superposed to another
may be given off either by radial, i.e. lateral, or tangential
chorisis from the cord of the latter. Instead, however, of
the new lateral branch giving rise to an organ by the side of .
the former, it results, partly from the close proximity of the
two and partly from the tendency of the remaining cords of
the cylinder to " close up," that the new member finally
takes up a position in front of, i.e. superposed to, the one
whose cord has given rise to it. When a cord is separated
by tangential chorisis, as is so often the case with staminal
cords, then the resulting organ must necessarily be super-
posed to the one, from the cord of which it has been
detached.
CHAPTER III.
THE PRINCIPLE OF NUMBER — Continued.
Illustrations of Special Numbers. — It will now be advisable
to give examples of particular numbers occurring in flowers,
and attempt to account for them.
One-membered Whorls. — Where one part to a whorl is
only found, it may in nearly every case be regarded as a
degradation from some higher number. The only instances
I am aware of in which the calyx seems to consist of a
single member are some species of Aristolochia. In Musscenda
one out of the five sepals is greatly enlarged to become an
attractive organ.*
One petal is occasionally found. Thus, four genera of
VochysiacecB have each only one petal to their flowers ; but
as the sepals ai'e five in each of the seven genera of this
order, and the petals range from one to five in number, the
inference is clear that the solitary petal of these four genera
is due to the arrest of the others.
One stamen occurs more frequently ; as in Hippuris,
Centranthus, Eupliorhia, Gasuarina, Orchis, Canna, Lilcea,
Lemna, etc. As allied genera have more than one, and it is
accompanied by other signs of degradation or metamorphosis,
* If there be one external foliar organ only, it is regarded as a bract,
as in Willows and Aponogeton.
5
2G THE STRUCTURE OF FLOWERS.
tliere is no doubt but tliat similar processes will account for
one stamen as for one petal. Thus Kippuris with one, is
allied to Mijriophyllum •with four; while Centranthus has one,
Fedia has two and Valeriana three.
Casuarina alone seems to raise a doubt of its being
degraded and possibly a primitive foi"m ; but this is solely
because it has no living allies (excepting perhaps Myrica).
The terminal stamen would not be of itself a point of
importance, as it has a parallel in Eupliorhia ; but it is its
isolation without affinities, its peculiar equisetum-like habit,
which seem to indicate great antiquity, so that no inference
can fairly be drawn to interpret its present monandrous
condition.
Amongst Monocotyledons, Ganna is clearly monandrous
by petalody of the other stamens, Orchis by metamorphosis
also. Lastly, Naias, Gaulinia, Zostera, Zannichiella, &Tid Lemna,
are in all probability greatly degraded forms from higher
plants, degradations being the usual effect of an aquatic life,
and not pt^imitive types of Monocotyledons.
One carpel is not at all uncommon, as in the Legtiminosce.
As Affonsea has five, the absence of four in this order is no
doubt due to arrest. In the tribe Berberece, however (if my
interpretation be correct, of the origin of the seven whorls
of three each constituting the flowers of Berheris, as exj)laincd
below), the one carjDel may be the last of an originally
continuous spiral, formed from eleven pairs of opposite leaves,
now broken up into seven ternary whorls, with one over. It
may, however, be the remaining one of three, which possibly
constitutes a ternary gynoecial whorl, which is characteristic
of the tribe Lardizahalece of the same order Berheridece.
Dimerous WnORLS. — A dimerous arrangement is not par-
ticulaidy common, though a quaternary calyx is dimerous in
its development, as the sepals emerge from the axis in sue-
THE PRINCIPLE OF NUMBER. 27
cessive pairs.* The following may be taken as illustrative
instances. The sepals of Faijaver and Fumaria, the outer
stamens of Cruciferce. In Circcea all the whorls are dimerous,
in Oleacece the essential organs alone, as also in Pingtcicula,
Salvia, Veronica, and Salix diandra.
The question arises, is this number two an original one,
or has it arisen by arresting some parts of a more numerous
whorl ? It is obviously so with Salvia and other genera of
the Lahiaice, where rudimentary stamens are present. So
also with Senehiera didyma where the two stamens take the
place of the four larger ones of other genera of the Cruciferce.
It is probably so with the two imbricate sepals of Poppies,
those of P. orientals being often increased to three, which
seems to be a tendency to revert to a more primitive and
higher number.
With such plants, however, as Circcea, the Ash, and Vero-
nica, which have retained opposite leaves, the dimerous
whorls may be a primitive condition. This idea is ostensibly
supported by the fact that the outer whorls of the flower^
are quaternary and not quinary, since, when this is the
case, the sepals always issue in pairs from the axis, and not
simultaneously as do the petals ; but as long as no rudi-
mentary organs exist, there is nothing to disprove the idea
that in these genera the number of stamens may not be due
to degTadation. Indeed, all analogy would lead one to
suppose so in most cases, as of Circoea and Veronica: the
binary whorls of the former genus, and the quaternary outer
and binary inner whorls of the latter, being presumably due
to " symmetrical reduction " from the prevailing quaternary
* Though the antero-posterior sepals of crnciferous flowers are
regarded as the most external, it is really the lateral ones which are
first provided with fibro-vascular cords from the complete oblong
cylinder in the pedicel, just as in Cleome (see Fig. 6, p. 32).
28 - THE STRUCTUEE OF FLOWERS.
type of tlie Onagracece and quinary of ihe'Scrophularinem
resj^ectively.
Trimerous Whorls. — The number three is strongly
characteristic of Monocotyledons, and appears to be in this
class the immediate result of tlae ^ phyllotaxis. In Dicoty-
ledons, however, there are certain orders in which it prevails,
and it will be noticed that the number of parts in those
orders is generally much increased ; as in Mag7ioUacece.*
Anonacece, Berberis, Laurus Camphora, Bumex, etc. In some
the androecium and gyncecium are so increased in number
that they cease to be whorled, but have become spirally
arranged on a more or less elongated receptacle and are
represented by the fractions f'g- or oy-*
It has been demonstrated above that a pentamerous
arrangement is undoubtedly due to the f phyllotaxis, each
whorl constituting a cycle ; but if the fraction be a higher
one, as -j^- or ox, then the number of parts in a cycle are too
great to be compressed into a whorl. I^ature appears then
to adopt another method. Falling back upon the law that
with these arrangements no part of the continuous spiral, of
sufficient length to constitute a complete circle when pro-
jected upon a plane, ever contains more or less than three
leaves (excepting the ^ type), the series is now broken up
into a succession of ternary whorls, the whole forming the
complete flower, and, being taken together, corresponds to
about or exactly one cycle of a high type. Thus Barberry
has 3 bracts, 3 -|- 3 sepals, 3 + 3 petals, 3 -J- 3 stamens
and one carpel ; that is, seven whorls of threes or twenty-one
* In Magnolia an individual complication is introduced, in that the
immense number of stamens and carpels is secured by doubling the
whole number attributable to the -j^j arrangement. Consequently, instead
of there being five and ehjht " secondary spirals," there are ten in one
direction and sixteen in the other.
THE PRINCIPLE OF NUMBER. 29
parts, and one over. If these seven wLorls were broken up
and arranged spirally, they would be represented by ^\ ; and
then there would be eight coils in the cycle. The presence
of seven and not eight whorls is due to the fact that in
rearranging them, so to say, in a verticillate manner, and by
necessarily shifting the position of the parts, a certain por-
tion of the spiral line is lost in forming each whorl, as the
angular divergence between two parts in a whorl is 120°,
but on the spiral it is nearly 123° ; so that by the time the
twenty-first organ is arrived at, only seven circles have been
completed.
Similarly, in Bttmex, if we supply the theoretically lost
corolla, the flower would consist of twenty-one parts exactly.*
Another and somewhat frequent origin of the number
three in Dicotyledons is due to what I have called sym-
metrical reduction : when not only the difterent species of a
genus may have the number of parts of their floral whorls
ranging from 5 to 4 or 3 ; but such variations may occur on
the same plant. Thus Eutacece (following the Gen. Plant.)
has 34 genera with 5-merous flowers ; 18 genera with species
varying from 5 to 4-merous ; 16 are 4-merous ; 3 range from
5 to 3-merous ; 2 from 4 to 3-merous, and 1 is 3-merous.
Tetramerous Whorls. — That a true quaternary arrange-
ment is due to an opposite condition of the foliage seems
borne out by statistics, though quinary flowers are not at all
uncommon as well. Thus of Biitacerp there are 6 genera
with opposite leaves and 4-merous flowers ; 2 only with
5-merous, and 2 with 4-5-merous flowers. On the other
hand, there are 25 genera with alternate leaves and 5-nierous
flowers.
* High spirals can be otherwise treated, as in the case of Chimonan-
thus, where whorls of fives are made oat of a spiral system of jj (see
below, p. 38).
80 THE STRUCTURE OF FLOWERS.
Another correlation witli a quaternary arrangement is a
not unfrequent valvate condition of the sepals at least, or of
the sepals and petals as well. These conditions prevail, for
example, in Oleacece, Onagracece, and, with the exceptional
genus. Clematis, of the Banunculacece. Too much stress
must not be placed upon this coincidence, as, if the petals
be enlarged through insect or other agency, the valvate
aestivation is often lost, and the petals become imbricate, as
in Fuchsia, Godetia, etc., though it is there retained in the
sepals. This valvate condition is foreshadowed in the ver-
nation of the foliage ; m that opposite leaves are almost
invariably valvate, having the two upper surfaces of the
leaves pressed together, as may be seen in Hypericum and
Vinca ; or else with the edges induplicate, as is characteristic
of Gajxrifoliacece, resembling the sepals of Clematis.*
Though the Onagracece have a preponderance of genera
with 4-merous flowers, there is in this order great variation
in the foliage. It is strictly opposite in Fuchsia and othei's,
but 14 genei-a out of a total of 22 have alternate leaves, while
with some, like Epilohium, it varies on the same stem. This,
I think, reveals the fact that the 4-merous condition has been
first established in the flowers, and subsequently the foliage
has varied from an opposite to an alternate condition in
certain genera, just as it does in an individual plant of
Fpilohiiim.
That symmetrical reduction has elsewhere played an
important part in the origin of 4-merous flowers, is a sup-
position fully borne out by facts. In some cases it has
seemingly established itself as a permanent character, so that
systematists recognize it as generic or specific, accordingly,
♦ See a paper by the author, On Vernation and tlie Methods of
Development of Foliage as protective against Radiation, Journ. Lin. Soc.
Bot., voL xxi., p. 624.
THE PRINCIPLE OF NUMBER. 31
as the case may be ; this, Haplophyllum may be compared with
Bitta, Bitbia with Galium, or, again Fotentilla reptans with
P. Tormentilla, etc. On the other hand, I repeat, when one
observes that of the 71 genera of Rosaceca three only are
recorded in the Gen. Plant, as having opposite leaves, and
these three are characterized as having 4-merous flowers, viz.
Rhodotypus, EucrypJna, and CoJeogyne, there appears to be
a significant correlation between quaternary flowers and
opposite leaves.
A quaternary ari'angement is found very exceptionally
in Monocotyledons, as in the order Naiadacecv, e.g. Tetron-
cium and Potamogeton. As the numbers 6 (i.e. 2 X 3), 4,
2, and 1 are found in different genera, the quaternary
as also binary arrangements may, I think, be reasonably
referred to symmetrical reduction.
Perhaps of all orders the quaternary arrangement (at
least in part) of Crucifers has raised more discussion than
any other kind of floral symmetry.*
Without entering here upon any lengthened discussion
I would only add that, as far as investigations into the
anatomical structure of the pedicel is concerned, there is a
decided difference from what occurs in most flowers having
a definite number of parts, and where the whorls are
regularly superposed to one another, in that the members
of the whorls not being for the most pai't on common radial
planes, they have not their cords fused together in the usual
manner in a radial direction.
A section at some distance below the flower reveals four
or five cords forming a circle. These rapidly increase in
number by branching laterally, till between ten and. twenty
are found arranged in an oval just below the flower. Two
* See my paper On the Structure of a Cruciferous Flower, Trans.
Lin. Soc, 2nd series, Botany, vol. i. p. 191.
32
THE STRUCTURE OF FLOWERS.
cords, one at each, end of the long axis, now part company
from the rest, and enter the lateral sepals (Fig. 6 (a) l.s.),
the antero-posterior sepals next receiving their cords (a.s.
and^.s.). The cylinder tends to close up, and four groups
situate at the corners of the oblong cylinder supply cords for
the i^etals, p. The two honey-glands next put in an appear-
ance, G. They are merely cellular expansions of the floral
receptacle, and are entirely devoid of cords, and therefore
not rudiments of appendages. The two lateral stamens next
receive their cords, l.st., while four other cords are given off
from beside the petaline for the taller pairs of stamens, st.
p.s
a
ls\ = ( = i.sl
t\l.s
Anatomy of Wallflower.
Fig. 6 (6) shows how their cords diverge below and spring
from the siae of the petaline cords, while extra cords arise
between them to form the marginal cords of the carpels (m.c).
From this it will be seen that the longer stamens cannot be
formed by " chorisis " of a common intermediate cord ; but,
like those of all other members of the flower, their cords are
sepai-ated from the common fibro-vascular cylinder of the
stem.
The conclusion suggested by this investigation, and by a
comparative study of Gapparidea', is that a cruciferous flower
is not reducible to an originally quaternary type at all, but
to some higher one. In my paper referred to, I suggested a
THE PRINCIPLE OF NUMBER. 33
quinary ; but I am now more inclined to refer it primarily to
an indeBnite spiral series referable to the jg or ^i type,
which has been reduced, perhaps through insect agency, by
symmetrical reduction to the present anomalous condition.
The process of transition from a hypothetical indefinite
number of stamens to the present bexandrous state may be,
perhaps, seen by comparing the three genera of Capparidece
— Capparis, Polanisia and Cleome. The first has many
stamens and six placentas, which are sometimes reduced to
two. Polanisia has eight stamens, or more rarely six. Their
situations correspond exactly with those of the Cruciferce,
except that, when there are eigbt, there are four on the
anterior side instead of two.
Lastly, Cleome brings us to the same structure as in the
Cruciferce with even the tetradynamous condition of the
stamens ; the elongated torus below the pistil being about
the only " capparidaceous " feature left.
It is not at all uncommon to find more than six stamens
in cultivated plants of the Cruciferce, and when this is the
case I should be inclined to regard it as a tendency to a
reversion to a higher ancestral number.
On the other hand, the close proximity of the two taller
ones on each side not infrequently brings about some degree
of cohesion between them, with an occasional arrest of half
an anther. This has led some to suppose that the pair have
resulted from chorisis. Since, however, their cords diverge
downwards to the right and left, and run down beside the
petalline cords (Fig. 6, b), this clearly proves that the union
is a result of close contact, and that the normal separation is
not due to chorisis, but to a primitive freedom, which has
been retained from a multistaminate condition.
Pentamerous Whorls. — These are by far the commonest
amongst Dicotyledons. And as an enormously greater pro-
34) THE STRUCTURE OF FLOWERS.
portion of plants in this class have alternate leaves and
5-raerous flowers, this correlation alone would be almost
sufficient to prove that the latter issued out of the com-
monest or f type of pbyllotaxis. But since the sepals are
sometimes decidedly quincuncial, as are those of Digitalis,
and the petals frequently so, we have undoubted proof that
they represent cycles of this angular divergence.
As with other numbers, fives may arise by symmetrical
increase from fours, or decrease from sixes ; though in by
far the greater number of instances it is a primitive number,
as stated above. As a rare instance of symmetrical decrease
may be mentioned Lythrum Salicaria, which has usually the
central floret of each axillary cyme 6-merous, but the lateral
ones only 5-merous. As an instance of five parts to a whorl
amongst Monocotyledons, may be mentioned the stamens of
Strelitzia regina; but this number is obviously due to the
sup2:)ression of a stamen.
Although whorls of fives are cycles of the f divergence,
and usually follow after an alternate arrangement in the
foliage, yet it is quite possible to change abruptly from
opposite leaves or bracts to whorls of fives in the flower, as
may be seen in Hypericum and Biantlius. This arrangement,
as I have elsewhere shown, is that most easily acquired
when opposite and decussate leaves become alternate by the
development of internodes (see pp. 11 and 18).
Hexamerous Whorls. — A floral whorl of six parts is, in
most cases, as amongst Monocotyledons, the result of the
combination of two whorls of three each — as the androecium
of Berberis, Tulip, or perianth of the Lily of the Valley. It
may, however, arise from symmetrical increase, as, for
example, in the orders Meliacece and Olacinecs. In the
former, there arc 18 genera with alternate leaves and
6-merous flowers ; 9 with 4-5-merous ; 4 with 4-mcrous ;
THE PRINCIPLE OF NUMBER. 85
4 with 5-6-ineroas, and 1 with. 4-6-merous whorls in the
different species. In Olacinere, of 36 genera, 17 have altei'-
nate leaves and 5-merous flowers ; 7 have 4-5-meroiis ; 4,
5-6-merous ; 2, 6-merous, and 1, 4-6-merous.
As six leaves cannot form a cycle of any of the ordinary
kinds of phyllotaxis, this will account for its rarity in
nature ; and indeed it may probably, without exception, be
divisible into two whorls of three members each, except in
the case of symmetrical increase from five.
Heptamerous Whorls. — Like the number 6, 7 is a very
rare one ; and when present appears to be due to its being a
primitive number or to symmeti'ical change. If any whorls
are deducible from decussating verticils of threes, a cycle
may contain seven parts, as the phyllo tactical series arising
from the breaking up of such verticils into a continuous
spiral arrangement is represented by i, i, f , y\, etc. So that
if leaves on a plant were in whorls of threes, as occurs in
some instances, and not opposite, as in the primitive type
amongst Dicotyledons, then a heptamerous arrangement
would occur. If, therefore, there be any existing illustra-
tion, it must, by the very nature of the case, be exceedingly
rare. It sometimes occurs in Trientalls ; and when this is
the case, it may possibly have arisen as here suggested.
According to the description given of this plant in the
Genera Plantarum, the numbers of the three outer whorls
range from 5 to 9, the capsule being 5-valved. The leaves,
on the other hand, are " saepe tot quot petala subverti-
cillata."
A second cause is arrest. This obviously accounts for
the 7 anthers in Felargonium, for the 10 filaments are present.
A third cause is symmetrical change. Lythrum Salicaria
illustrates this as already mentioned. This flower is some-
times described as 6-merous, but it is not always so. The
36 THE STRUCTURE OF FLOWERS.
central floret of the cyme lias often a higher number than that
of the lateral ones ; so that if they be 6-merous, the central
flower -will be 7-merous. Agapanthus, amongst Monocoty-
ledons, is another instance, its flowers ranging from 6 to 8 in
the number of parts in the whorls.
OcTAMEROUS Whorls. — A whorl of eight parts is not
common ; but it appears in Glilora and in the corolla of Dryas
octopetala, in which it may be a cycle of the f phyllotaxis.
In other cases it is a combination of two whorls, which, as a
rule, can be easily distinguished as the stamens in the Oiia-
gracece, or it may be due to symmetrical change.
Enneamerous Whorls. — The number 9, like 6, 7, and 11,
corresponds to no cycle of any one of the usual forms of leaf-
arrangement, and is proportionately rare. It may occur as a
combination of three cycles of three each, and perhaps this
will account for it when it occurs in Trientalis, and the
androecium of Mercurialis. The stamens of Butomus are
also nine in number.
Decamerous Whorls. — The number 10 never occurs
except as the union of two whorls of five in each, as in the
androecium of Leguminosce.
Endecajiergus Whorls. — Like 7, the number 11 might
occur if the series 1-, ^, |, -^, etc., was as frequently repre-
sented as ^, ^, f, f, etc., when "sevens " would be as abun-
dant as " fives " are now. I do not know of a case where it
could reasonably be referred to such an origin. When it
does occur, as in Cupliea, it is clearly due to an arrest of one
stamen through insect agency. Broiunea is said also to have
sometimes 11 stamens ; if so, this would undoubtedly be due
to numerical increase.
Dodecamerous Whorls. — The number 12 closely verges
on the " indefinite," which simply means a more or less
numerous series of cycles of the same kind. Neverthe-
THE PEINCIPLE OF NUMBER, 37
less, it occurs as a " definite " number in several instances.
The 12 stamens of Lythrum are, of course, two series of six
each. Both 12 and 24 are found in the Crassulacece, as in
Semperviviim, in which genus the petals vary from 6 to 20,
and the stamens from 12 to 40. This seems to show that in
the one case they are combinations of cycles of threes, in the
other, of fives ; just as Berheris illustrates the former, CJdmo-
nayitlms the latter instance.
IxDEPiNiTE Whorls. — As soon as we pass from twelve to
some higher number, then flowers cease to be whorled, and
the parts are arranged spirally, and follow more or less
exactly the laws of alternate phyllotaxis ; interferences occur
in consequence of the want of space, some secondary spirals
being often incomplete. Moreover, since the fibrovascular
cords become fused, in other words branch by chorisis, and
are not independent as of ordinary foliage, parts take up
slightly diiferent positions to what they would if they could
strictly follow phyllotactical laws.
I have alluded to what I call " symmetrical increase and
decrease " as causes of variation in the number of parts of
whorls ; and what brings about these variations in number,
is an excess or deficiency of nutriment and vital activity
respectively. There are innumerable examples of all the
above kinds of changes in number. In fact, if any one or
series of whoi-ls of a flower be w-merous, it may become
n ± a;-merous, and will give rise to symmetrical increase or
decrease accordingly ; or again, three whorls of the same
flower may become n ± x, n ± y, n ± ^-merous ; when all
numerical symmetry between them will be destroyed.
Similarly, if the parts be spirally arranged, the number
may vary from the prevailing one by increasing or decreasing
the length of the spiral, both in flowers of the same plant or
in different species of the same genus ; as, for example, may
6
38 THE STRUCTURE OF FLOWERS.
be seen by comparing the number of stamens in a large-
flowered form of Hanunculus arpiatilis, with the small-
flowered R. hederaceus ; or one genus with an allied one, as
Eanunculus with. 3Iyosurus, in yfhich. the stamens are reduced,
often to one whorl of five only.
Lastly, just as high spirals can be broken up into ternary
whorls, so can the arrangement 2t ^^ separated into whorls
of a lower series, as of 13, 8, or 5 parts respectively. Thus,
of the two genera, which, have opposite leaves, comprising
the order Calycanthacece, Calycanthus illustrates an abrupt
change from opposite leaves to the ^\ aiTangement in the
bract-like sepals of the flower ; but no distinction between
bracts, sepals, and petals can really be made. Chimonanthiis,
however, would seem to be a more highly differentiated type,
in that, not only is the calyx distinguishable from the corolla,
but five exterior stamens constitute a distinct whorl by them-
selves, and the indefinite bari'en ones of Calycanthus are here
reduced to five ; so that, omitting the pistil, the flower con-
sists of four distinct pentamerous whorls.
CHAPTER IV.
THE PRINCIPLE OF ARRANGEMENT.
m. ISM n.z2.m9 i(j.si
Superposition and xAlternation of Whorls. — It has been
already observed that leaves are ai-ranged on two methods,
either being on the same plane, i.e. opposite and verticillate ;
or with only one at a node, i.e. alternate. If the fibro-vascular
cords passing from the leaves into
the stem be traced downwards,
those belonging to the leaves ^S
situate in one and the same ver-
tical line always have their lower
extremities inserted laterally and
not actually confluent in that line,
as will be seen in Fig. 7, taken
from Hanstein's researches.*
This fact is trne, not only for
foliage and bracts, but also to
some extent for sepals and petals.
When, however, we trace the
origin of stamens and carpels, we
find that their cords, instead of
being inserted separately into the fibro-vascnlar cylinder,
generally arise by branching, or by the so-called " chorisis "
* De la Connexion qui existe entre la Disposition des Feuilles et la
Structure de la Zone Ligneuse des Dicotyledons, Aun. des. Sci. Nat., 4®
Ber., torn. 8.
2.7. 4. dJ e. 3.8. S.
Diag^-am of the foliar cord^ in
the stem of the Arabis albida (after
Hanstein).
Fig. 1
40 THE STRUCTURE OF FLOWERS.
of the cords belong-Ing to the sepals or petals, or from both ;
and similarly the dorsal cords of the carpels branch off from
the same stem as that of the sepals or petals, very rarely
from both at once. Simultaneously with the dorsal, two
marginal cords pass up directly into the placentas, having
originated in the same way; and, in so doing, the floral re-
ceptacle usually becomes extinct, and takes, as a rule, no
further part in the construction of the central portion of the
pistil.
Startinsr, then, with these two fundamental sources of the
various arrangements of the parts of flowers, we may first
observe that of opposition or superposition and alternation,,
the former, if represented by decussate pairs of appendages,
is the most primitive type. This is seen in many quaternary
flowers in which the sepals emerge in successively decus-
sating pairs. Such opposite leaves being foreshadowed in]
the cotyledons of exogens.
The next, or rather the first stage of differentiation is/
seen in the spiral condition which obtains in many flowers,
mostly represented by the J and | types : thus, e.g., ^ repre-
sents the arrangement prevailing in petaloid Monocotyledons ;J
and all pentamerous calyces issue in a quincuncial manner.
In Sabia, the petals follow continuously with the sepals inl
the same spiral line, so that the first petal is superposed to
the first sepal. These whorls accordingly represent two
cycles of the § type, as seen above in Garidella (p. 21).
By far the commoner condition is to break up the spiral
into cycles, say of five parts each, and then to shift their
positions, so that they become alternate instead of superposed.
Now, such a decussate arrangement is usually described as a
fundamental law, not only governing opposite and verticillate
leaves, but floral whorls as well ; and particular stress is
laid upon the usual presence of the petaline whorl of carpels,
1' i
THE PRINCIPLE OF ARRANGEMENT. 41
iuasniucli as the law of alternation is thus carried out
completely, and which may be represented as follows — the
hyphens indicating tlie parts superposed to one anothei' —
Sepal-stamen ; Petal-carpel.
From what has been stated above, the true order of
arrangement and superposition would be — Sepal-stamen-
carpel ; Petal-stamen-carpel ; and either one of the staminal
and either one of the carpellary whorls may be suppressed.
Thus, for example, Oxalis, ZygopJiyllum, Geranium, and Rtita
have Sepal-stamen ; Petal-stamen-carpel : while Livmanthes,
Coriarea, and Agrostemma have Sepal-stamen-carpel ; Petal-
stamen, As instances where there is but one whorl of sta-
mens, Campanula and Hermannia ha.ve Sepal-carpel; Petal-
stamen ; whereas Linum and Diosma have Sepal-stamen ;
Petal-carpel.
Of these variations, although Sepal-stamen is commoner
than Petal-stamen, and Petal-carpel than Sepal-carpel,*
yet these are, so to say, rather matters of accident than
otherwise, in that it is probably due to certain exigencies of
nutrition, and especially insect agencies, that such variations
of arrangement exist.
The important fact mentioned above, that floral whorls
are projected cycles and not primitive whorls, has, as far as
I know, been entirely overlooked by botanists. Thus, for
example, Pi'ofessor Asa Gray remarks on the presence of
whorls in flowers as follows : " Cycles alternating with each
other are simply that of verticillate phyllotaxy," f to which
he refers the opposite, ternate, quaternate and quiuate verti-
cils.J In the case of leaves, verticils represent usually more
primitive types, such as twos and threes, and, from an
evolutionary point of view, such precede alternate and spiral
arrangements.
* I.e. in Exogens. t Bot. Text-Book, p. 175. % L.c, p. 120.
42 THE STRUCTURE OF FLOWERS.
On the other Land, wliorls of threes, and fives, and others
in flowers are compressed cycles of spiral arrangements. They
are, therefore, attempts at simulating ancestral or the yerti-
cillate conditions, hnt cannot possibly be primitive whorls
themselves. That the petals can thus become decussating
with the sepals is a result of the fact that their cords are not
strictly superposed to and confluent with those of the latter.
The total number of cords in the pedicel being usually limited
to the same number as there are parts in the perianth, i.e.
the calyx and corolla together, there is ample room for them
to arrange themselves at equal angular distances around the
central medulla of the pedicel. Then from the vascular
cylinder thus formed, they pass off into the sepals and petals
respectively.*
The sepals and petals or the two whorls of a perianth
being thus provided for as to their fibre- vascular cords, the
stamens and carpels, as already stated, generally depend upon
these latter for tbeir positions, and various arrangements
arise according as the cords of the perianth-leaves give off new
members or not. Theoretically there should be at least one
whorl of stamens superposed to the sepals, another superposed
to the petals, and two whorls of carpels as well ; but Avhile
many flowers have both staminal whorls {^Caryophyllece,
Leguminosce, Ericacece, etc.), many others, as the Gamopetalce
retain only one, and more generally the first formed or
sepaline, but sometimes it is the petaline, as in Primulacece ;
the probable cause in each case being certain exigencies in
♦ That foliar organs possess this power of reai-ranging themselves
according to requirements is evident from other considerations ; thus,
many plants having freely growing erect shoots — as, for example,
the common Lam-el — have their leaf -arrangements represented by the
fractions | or ^, but when extending horizontally, as in the usual con-
dition, they are distichous. Similar features are seen in the Jerusalem
Artichoke, which often changes its phyllotaxis on the same stem.
THE PRINCIPLE OF AREANGEMENT.
43
St. J>et.
the flower, through which nourishment is withdrawn at
certain places to produce hypertrophy elsewhere. Thus the
sepaline cord, instead of bearing an anther in Priviula, bifur-
cates at the angle, and each branch proceeds up the margin
of a lobe of the corolla, and aids in nourishing the latter.
As a converse instance of the sepaline cord undertaking
a considerable amount of work, may be mentioned Campanula
medmm. In this plant the 5-lobed fibro-vascular cylinder
of the pedicel sends off five cords
intended for the calyx (Fig. 8, sep.} ;
but, befoi'e reaching the base of the
superior sepal, it sends off an inner-
most and lowest cord to become the
dorsal one of the carpel (d. car.),
which, in this flower, is thus super-
posed to a sepal. It also sends off
two, right and left, one for each
petal alternating with it (pet.) ; so
that each jietal receives two cords,
one from each adjacent sepal, — a
most unusual condition of things,
for petals have almost invariably
their own cords issuing' frora the
Jiet.
pedicel. Lastly, the same sepaline Fig. S— Vertical and transverse sec
^ . tions of the wall of the inferior
cord provides that of the stamen ovary of campanula medium
(after Van Tieghem).
{St.) superposed to it. In this
flower, therefore, we can understand why there is no petal-
ine whorl of stamens ; simply because the corolla does not
possess its own proper fibro-vascular cords to give rise to
them.
On the other hand, in the Malvaceoi after the axis has
supplied cords for the sepals, others furnish those of the
corolla; these latter, however, by radial division form two
44 THE STRUCTURE OF FLOWERS.
to each petal, subsequently dividing into several ; for the
same pair by repeated tangential division gives rise to the
series of stamens (which have been thus doubled) superposed
to each petal, both having arisen from a common cord.
With regard to the numerous carpels of Hollyhock, I
find that the axial cylinder which has given rise to the five
sepals continues on, and by radial division again supplies
cords to the carpels, which are grouped into five sets super-
posed to the sepals, as may be easily seen if the pistil be
examined from below. Hence, as the sepaline or petaline
cords in these flowers each undertake to form a large number
of extra parts — many stamens in the one case, and many
carpels in the other — it is presumable that neither sepaline
stamens nor petaline carpels could be formed.
With regard to the presence, and consequently the relative
position, of one whorl rather than the other of the gynoecium,
it is due to the fact that sometimes the sepaline cord will
give rise to the dorsal carpellary, as in Althcea and Campa-
nula; at others, it is the petaline, as in Fuchsia, Sedum, Ivij,
etc. ; so that the carpels become superposed to the sepals or
petals accordingly. As instructive instances of variations in
this respect occuri'ing in the same family, it may be mentioned
that all species of Campanida which have five carpels, as also
WaJilenhergia capensis, Michauxia, Canarina, and Lightfootia
suhulata, have their carpels superposed to the sepals and
stamens. On the other hand, Musschia (Campanula aurea, L.)
Platycodon {G. grandiflora, Jacq.), and Microcodon have the
carpels superposed to the petals.
The fact that either the sepals or the petals can have
the carpels superposed to them respectively, just as they can
each have a whorl of stamens, and that, in some few ordei'S,
the two whorls are actually present, as in Butomece and
Jancagineoi, led me to assume two whorls as the primary
THE PRINCIPLE OF ARRANGEMENT. 45
or ancestral number of carpels in an ideally complete
flower.
Besides the nsual alternation of whorls resulting from a
regular and equal displacement of every part of the whorl,
there may be unequal displacements ; thus, while Gistus has
a pentamerous flower, with strict alternation of its whorls,
Helianthemum has a tendency to be trimerous; first, in the
two outer sepals being reduced in size, and the pistil to three
carpels instead of five. In this flower there are five petals,
but in correlation with the preceding irregularities, it will be
found that two pairs of petals stand superposed to the sepals,
Nos. 3 and 5, while a single petal is over No. 4 ; Nos. 1 and
2, therefore, have none superposed to them. With regard to
the stamens, it may be added that those of Cistus consist,
first, of one whorl of five, the most interior and first developed
superposed to the sepals ; and a second whorl superposed to
the petals, in which the stamens are grouped into five clusters.
The staminal whorls arise centrifugally.
Another cause of a change of order in the whorls results
from substitution of one kind for another. Thus, in the
female flower of ZantJioxylon, the five carpels are superposed
to the five sepals. In the male, five stamens now occupy
exactly the same place as the carpels, the corolla alternating
with the sepals in both kinds.*
The interpretation I would suggest is that the sepals,
being the only whorl of the perianth developed, the calyx is
the only source for supplying the dorsal cords of the carpels
which thus become necessarily superposed to them.
From Avhat has now been said, it will be seen that the
arrangement of the essential organs of a flower is, as a general
* See Figs, in Le Maout and Decaisne's Descriptive and Analytical
Botann, p. 324. The female flower is described as apetalous, bat Payer
discovered rudiments of the petals.
46 THE STKUCTURE OF FLOWEKS.
rule, most intimately connected with the union of their fibro-
vascular cords with those of the perianth ; and as parts of
flowers are often multiplied, as the petals of Camellia,
perianth-leaves of Daffodils, etc., such has given rise to the
idea of chorisis or dedoublement of French authors ; as if
one organ had split into two or more. That vascular cords
can become repeatedly bifurcated is abundantly observable,
whether radially, as in the case of the carpels of the Holly-
hock, or tangentially, as in producing the stamens of the
same flower. The more correct way, therefore, of regarding
tlie process would seem to be, first, to recognize the phyllo-
tactical origin of the perianth as the basis to start from, and
then to regard each fibro-vascular cord as an instrument
for furnishing any number of appendages, whether they be
additional petals, stamens, or carpels, by the process of
chorisis, not of the complete organ, as generally meant, but
of the cord belonging to it.
To summarize these remarks — we find that the cause of the
alternation of the whorls of the perianth, or of the calyx and
corolla, is due to their being made up of cycles of spiral
arrangements, which are projected on to the same plane, and
so form verticils. Their positions are then shifted so that
the parts of each whorl bisect the angles between the parts
of the whorl succeeding or preceding it.
Secondly, having laid this foundation, the stamens and
carpels follow in superposition to one or other or both of
the preceding whorls in consequence of the branching
of the fibro-vascular cords. And this accounts for super-
position.
It may be still further inquired why in some cases the
sepaline, and why in others it is the petaline cords which
give rise to a whorl of stamens or carpels, as the case may
be. The reply at present must be speculative, for there may
THE PRINCIPLE OF ARRANGEMENT. 47
be more than one influence at work to determine what whorl
shall follow each of those of the perianth.
The immediate cause is nutrition ; but the deeper question,
what dii'ects the nutrition to one cord rather than another,
can only be guessed at in most cases : but as the petaline
stamens are generally absent from at least the gamopetalai,
it would seem that the enhancement of the corolla through
the agency of insects has caused the whorl of stamens in
front of it to be atrophied through compensation. Some
special circumstance, however, we know not what, have
interfered to retain that whorl in Primulacece, and some few
other plants.
The reader must be reminded, however, that this method
of branching in order to give rise to stamens and carpels
from the cords of the perianth is not universal. "When they
ai-e many, it is done by the fibro-vascular cylinder of the
pedicel becoming much enlarged, and consisting of a great
number of cords, all arising by lateral chorisis, it is true,
but long before they enter the floral members ; so that by
the time the latter are about to emerge they each receive
their own cords from the general axial cylinder. This is
what happens e.g., in Banunculacece and Cruciferce.
48 THE STRUCTURE OF FLOWERS,
CHAPTER V.
THE PRINCIPLE OF COHESION.
Cohesion. — General Observations. This term signifies tlie
union between parts of the same kind or whorl ; and the
prefix gamo- is used in conjunction with the terminations
-sepalous, -petalons, and -phyllons, — to indicate that the parts
of the calyx, corolla, and perianth respectively cohere. In
the case of the stamens, they ai"e said to be mon-, di-, tri-, or
poly-adelphous, according as the filaments cohere into one,
two, three, or more groups ; while syngenesious is used for
the coherence of anthers, and, lastly, syncarpous denotes that
the carpels of a pistil cohere.
There are two kinds of cohesion, congenital and by con-
tact.* Congenital cohesion I regard as an advance upon
freedom, or a further state of diiierentiation ; for, according
to the principles of Evolution, freedom or separation of parts
must precede their union ; just as, for example, bones are
free in the embryo which become " ankylosed " in the adult ;
or always free in a fish, while their homologues cohere in
higher types of vertebrates.
Congenital cohesion applies to by far the greater number
of cases of union amongst the parts of the different whorls
* We might appropriately distinguish these two kinds of nnion by
the terms connate or " born together," and coherent or " sticking
together."
THE' PRINCIPLE OF COHESION. 49
of flowers, respectively. Cohesion by contact is the cause of
the anthers being syngenesious in the Composike, It applies,
sometimes at least, to the two margins of each carpel when in
contact np the axis of an ovary, as of that of a Lily. The
stigmas of Asclepias are at first free, but later in their deve-
lopment they become coherent by contact.
Congenital cohesion takes place almost from the very
commencement of growth and development of the parts, so
that when full-gi'own there may be no trace of the line of
cohesion. Fibro-vascular cords, indeed, often occur in the
very position of it, not unfrequently branching off in various
ways, as, e.g., at the fork to nourish the adjacent free portions
of the limb. This occurs in the calyx of Stachys and the
corolla of Primula, etc. In Cavipanula rotundifoUa the fibro-
vascular system of the corolla becomes completely altered, and
instead of representing that of distinct leaves in contact by
their edges, the veins ramify and anastomose all over the
general space between the two adjacent dorsal ribs, com-
pletely obliterating all trace of the line of union between
them. In the case of the Primrose, however, the calyx has
the exact appearance of five pinnately nerved leaves being
united by their thin and impoverished edges, where there is
nothing but translucent tissue without any cords at all.
It is important to observe this more or less complete
modification of the fibro-vascular system under congenital
cohesion, as it shows how much more highly differentiated
a condition has been acquired than when the parts are free.
In the latter case they represent more closely the forms and
venation of distinct foliar organs.
As a curious instance of cohesion of both kinds in the
same organ, may be mentioned the corolla of PJiyfeuma ; the
basal portion of which consists of five petals congenitally
united ; but the five portions of the limb cohere by contact
7
50
THE STRUCTURE OF FLOWERS.
at the apex, and so form a tube which collects the pollen
shed into it by the five free anthers, which are included
within this corolla-tube (Fig. 9).
They thus form the " cylinder " for
the " piston " action of the pistil which
continues to grow, and so sweeps out
the pollen beyond the extremity of
the tube, just as it does from the
syngenesious anthers of the Covi-
positce and Lobelia. The five portions
of the corolla thus cohering by con-
tact subsequently become more or less
free.
The rationale of Cohesion lies in
its adaptation to insect agency, and
Fig. 9.—I'hi/teuma (after Miiller). • t j. j r • t
implies a greater degree or specializa-
tion than when the parts of the whorls are free. Thus in
Thalamifone, of such an order as Ranunculacea; with regular
flowers and with all the parts of the perianth whorls free, the
flowers are usually visited by a much greater number and
variety of insects than are those of orders of Corolliflorce. For
example, Miiller records sixty-two species of insects as seen by
him to visit Ranunculus acris ; whereas the humble-bee alone
enters the gamopetalous tube of the Foxglove. This adapta-
tion oi form to insect visitors will be better appreciated w'hen
we come to discuss that principle of Variation, which so
powerfully affects floral structure.
It occasionally happens that parts normally united become
free : the process is called " dialysis," and may be regarded
as a reversion to an ancestral free condition. Fig. 10 repre-
sents a flower of Mimulus in this condition. The rationale
of cohesion in the sepals, petals, and stamens, I regai'd as the
immediate result of hypertrophy set up by insect agency,
THE PRINCIPLE OF COHESION,
51
Fig. 10. — 3fimulus undergoing "Dialysis"
(after Baillon).
aided by the close proximity of the parts ; and. as a resulting
effect, is the ever-increasing adaptation to the requirements
of insects, which are more and
more specialized, for them, so
that, for example, Lepidoptera
are almost solely adapted to
long tubular flowers like the
Honeysuckle.
An analogous process of
congenital cohesion is well seen
in the fasciation of stems which
occurs particularly often in
succulent shoots, as Asparagus, Cabbage, Lettuce, and the
young shoots of the Ash tree. This is most reasonably
referred to hypertrophy coupled with the close proximity
of the buds which ought to have developed into independent
shoots. Again, cohesion between the sepals or petals of
Orchids is not uncommon abnormally under cultivation ; and
would also seem to be due to the stimulating conditions under
which they are artificially cultivated.
Hypertrophy in an organ is due to a special flow of
nutriment to it ; and cohesion may result from the close
proximity of the parts of the whorl to one another ; but the
influence which brings about the determination of sap to a
particular point, I take to be the mechanical strains induced.
by the insect visitors when alighting upon the flower in
search for nectar or pollen.
If this principle be correct, that the tubular structure of
jalyces and corollas, as we see them now, has arisen through
the requirements of those organs to meet strains thrown upon
fchem; I think it will furnish the solution to many a question
that may arise as to the peculiar shapes of corollas, etc.,
besides explaining the very principle of cohesion itself. An
52 THE STRUCTURE OF FLOWERS.
insect alights on one or two petals. In order to support it,
an immense gain is secured if the flower can call in the aid
of the other petals ; and this is obviously obtained by their
cohesion into a tube, just so far as the required strength is
wanted. Nothing would be gained by the portions of the
limb being united, as far as additional strength was required
to bear the bux'den. The tubular structure is the strongest
possible, and when short, as in rotate corollas, little extra
aid is required ; but if it be long and visited by heavy insects
and not by Lepidoptera, which hover in front of the flower
and only insert their long and slender proboscides, then the
tube finds additional support in the calyx being tubular as
well. At other times mutual support is gained by the close
contact of the flowei^s, as in a capitulum of the Compositce,
from which the calyx vanishes.
Of course, every degree conceivable is met with between
short, stout, and strong tubes with no additional aid, and
slender ones supported by a strengthened gamosepalous calyx.
These are adapted to insects which alight upon the corolla
limb ; while for Lepidoptera the tube is more elongated, and,
as no weight is thrown on the anterior petals, no extra
support is required. That this is the true intei'pretation of
the origin of a gamopetalous coi-oUa, appears from such
negative evidence as is seen, for example, in Lonicera Peri-
chjmenum and Asperula taurina* which have greatly elongated
and contracted tubes, deriving no siipport from the arrested
calyx ; and although somewhat two-lipped, the anterior
member is no larger than the others ; the reverse being
always the case when a heavy insect is the regular visitor.
These two species are exclusively fertilised by the Lepidoptera,
such as the Hawk-moth, which only hovers in front of the
orifice, but throws no weight upon the corolla.
* See Miiller's fignres, Fertilisation, etc., pp. 296, 303.
THE PRFNCIPLE OF COHESION. 53
We may see, as it were, Nature's first attempt to form a
tubiilar process in the Crucifene. Here it is obtained by
simple approximation of the slender claws of the petals,
which are siipported by the erect and closely imbricated
sepals. A step further is gained in Dianthus, in which the
sepals cohere but the petals are still free. The third and
last stage is arrived at when both calyx and corolla are
tubular.
Subsequent to this state of cohesion many additional
structures may arise as they are required in the formation
of ribs, etc., as already explained ; while the very form of
the tube may change from a purely straight cylinder to a
curved or expanded funnel, etc., according as special strains
have to be met, which the original form was not well calcu-
lated to sustain.
These changes of Form will be more fully discussed when
I treat of that principle of Variation.
54 THE STEUCTURE OF FLOWERS.
CHAPTER VI.
THE PRINCIPLE OF COHESIOK — Continued.
Cohesion op the Sepals, or Gamosepalous Calyx. — This is
congenital, and may be free, as in the Carnation and Primrose,
or associated with a " receptacular tube," as in Leguminosce
and Bosacece.
As sepals mostly represent the petioles of leaves, the
tubular part of a gamosepalous calyx consists really of the
fusion of the expanded petioles, the teeth of the limb being
all that remains to represent the blades which are usually
suppressed. The main fibro-vascular cords correspond to
the mid-ribs, while the interspaces are either without additional
" marginal " cords, as in the Primrose, or with single or double
cords in the line of junction, as in the Labiatce ; or they may
be covered with anastomozing reticulations without any linear
cord at all, as in Mimulus.
With regard to the presence of linear cords in the line of
suture, if there be five sepals, there will be at least ten ribs
to the calyx ; i.e., if there be only one marginal cord ; but
as there are two margins which cohere, they may have a
separate cord apiece ; and then there may result fifteen cords
in all. Thus Sfachys has five dorsal cords with barely ti-aces
of five marginal ones ; Ballota has ten, and Nepeta fifteen.
The above arrangements may be modified by the separa-
tion of the two marginal cords in certain places but not in
THE PRINCIPLE OF COHESION. 55
otliers, wtile supernumerary cords can be formed, which
appear to have for their function to strengthen the calyx to
meet the strain upon it when an insect alights upon the
flower.
In the calyx of some species of Salvia, which is strongly
bi-Iobed, though retaining its five teeth, three dorsal (d)
are posterior and two are anterior. There
are two single marginal (m) cords between
the three posterior and dorsal, which corre- ^ ,;
spond to the mid-inbs of three sepals. The m m
two lateral and marginal cords are each in m
double ; while a supernumerary cord (s) lies "' *
beneath the lip of the corolla between the ^'* "^
. s
two anterior marginals. The accompanying
diagram of the sepaline cords of 8. Verbenaca will illustrate
the arrangement.
The ai'raugement of the cords (vi and s) shows that the
strain being greater on the anterior side, the calyx has, as
it were, stretched in that direction, the two marginals having
separated so widely in front, as to require an extra cord (s).
The two lateral ones have not separated to so great an extent,
while on the posterior side, where little or no strain is felt,
the marginal cords have remained single.
As the cord (s) shows how Nature can add a fibro-vascular
cord if required, so one or more can be subtracted by atrophy
where no stress occurs. Thus the petals of the Compositce
have no dorsal or median cords, the five sepaline only being
present below, but pass up the margins of the petals. Con-
versely, in the Primrose, the calyx, giving no support to the
corolla, has no marginal cords.
The above diagram will represent the distribution of the
sepaline cords of S. glutinosa and other species, as well as
S. Verhe7iaca, but in S. ])ratensis the strain has apparently
56 THE STllUCTURE OF FLOWERS. fl
been not so great, consequently the supernumerary cord (s)
lias not been developed.
Such slight differences are signiBcant, because they show-
how readily an organ can respond to different degrees of
force brought to bear upon it by different insect visitors ;
and the cords are invariably placed j ust where the strains are
greatest.
The number of ribs to the calyx has been adopted by
systematists as generic characters in some of the Labiatce, as
well as the tubular or campanulate shape of it. Now, it will
be found that the shape corresponds with the requirements
of the corolla ; so that if the tube of the latter be compara-
tively short and slender, the calyx completely encloses it, and
has its surface strengthened bv a variable number of ribs
according to the genus ; though they ai^e not always constant
on the same plant. As examples, may be mentioned, Mentha
and Melittis, which have a broad campanulate calyx, and a
broad tube to the corolla. Stachys has 5-10 ribs surrounding
the cylindrical corolla-tube. Galeopsis versicolor has 10 •
prominent ribs, and 10 others which reach from the base of
the calyx-tube to about half-way up. Melissa has a very
narrow elongated calyx, which fits the slender tube of the
corolla exactly, and has 13 or 14 ribs.* Similarly Nepeta
Cataria and N. Glechoma support the contracted slender basal
part of the corolla-tube, and have 15 ribs to the calyx.
Teucrium Scorodonia has only 5 dorsal ribs and 2 (posterior)
marginal. The calyx is very broad compared with the slender
corolla-tube, and scarcely, if at all, supports it. This flower,
is visited both by bees, and nocturnal Lepidoptera which
suck without throwing any weight upon the flower.
Cohesion of Petals, or Gamopetalous Coeolla. — As
* This difference in the number of ribs depends upon the lateral and
marginal being single or double.
THE PRINCIPLE OF COHESION. 67
already stated, tliis is congenital, and, as with the calyx, so
with the corolla, the line of junction may be marked by a
marginal cord, or the interspace covered with reticulations as
in Campanula roiundifolia.
As in the calyx of many Labiates, so there may be super-
numerary cords in the corolla, until they may be greatly
increased in number, as in Convolvulus Sepium, Digitalis, etc.
The cords being straight in the tube may ramify in the
lobes, adding thereby marginal veins to the latter, as in
Priimila and the Compositre. In this last, the petals are
devoid of median nerves, hence the importance of the mar-
ginal with their branches up the edges of the corolline lobes.
It would be superfluous to multiply examples if the
principle be understood ; and what I particularly wish the
reader to realize is the, so to say, extraordinary plasticity
which resides in these organs of flowers, in that they
evidently have the power of altering their structure to meet
a variety of requirements ; so that if we might compare them
to architectural buildings, we might say that the floral
Architect at one time saw not only a chance of some orna-
mental improvements in a frieze at some particular place,
graceful lines of colour or curvature in another ; or, again,
flutings, depressions, and elevations, etc., all breaking up any
chance of monotony : but cunningly adds elegant buttresses
without, as well as runs up ribs of masonry within the
walls ; which, while intended to meet particular strains, only
add additional charms to the general and harmonious beauty
of the entire fabric.
CoHESiox OF Stamexs — (1) " Adelphous " Filaments. —
This occurs in various degrees, from a comparatively slight
union at the base, as in Linuvi usltatissimum, to a short
distance from the anthers, as in Malvacece and Leguminosce.
It is undoubtedly an adaptation to insect agency.
58 THE STRUCTURE OF FLOWERS.
If tbe stamens be monadelplious, and tlie union be extended,
it may completely enclose the usual honey-secreting surface
chai'actei'istic of allied genera, the result being that it can
secrete none at all. In such cases, insects are deceived in
visiting the flower, as in Genista, and some other mona-
delplious genera of Leguminosce. Otherwise, the honey is
secreted by some other source external to the staminal tube,
as in Linum catharticum ; in which flower five inconspicuous
glands occur on a fleshy ring, just opposite the stamens. In
Malva, the honey is found in five pits between the bases of
the petals, and in Pelargonium in a long tube formed by one
sepal, the insertion of which remains far below that of the
others, which are carried up by the growth of the pedicel.
In Laburnum* as in Orchis, instead of a secretion, the fluid
is only to be secured by piercing succulent tissue which is
found in front of the vexillum in the form of a cellular
cashion.
In diadelphous species of the Leguminosce, the honey may
be secreted by the inner basal portion of the staminal tube,*
or else, and perhaps more usually, by an annular disk which
suiu'ounds the short pedicel of the ovary, as in Pisum. In
this case the honey is easily secured by the proper insects
as the superior stamen is free, and there is also an additional
facility of access by means of an oval space formed by the
widening of the staminal tube just above their base.
In Cercis, the disk is very large, and the 10 stamens stand
in depressions around it. Consequently they are entirely free.
The staminal tube, together with the petals, which are
more or less interlocked together, protect the honey from
being rifled by the wrong insects, f as it can only be secured
* According to Miiller.
t A curious additional protection occurs in Hippocrepis comosa, in
that the claw of the vexillum, which is elevated in a remarkable manner,
I
THE PRINCIPLE OF COHESION, 59
by such as have proboscides of sufficient length to reach it,
corresponding, of course, to each species or genus.
Papilionaceous flowers being irregular, and visited in but
one way, it is only the superior stamen which is free; but the
staminal tube is often imitated in other flowers where there
may be no cohesion at all, as by the tribe Ocimoidece of
Labiates, Collinsiahicolor of the Scrophularinece and Poly gala,
etc. Similarly, in the case of regular flowers, the mona-
delphous condition may be closely mimicked by filaments
which are stout and sufiiciently rigid to form a column.
This occurs in CnicifercB, Viola, Gonvolvuhis, Crocus, etc. In
some cases, as in Cramhe and Deutzia, the filaments are pro-
vided with wing-like structures which render the tube more
complete. In orange flowers, a certain amount of cohesion
is actually obtained between some of the filaments.
(2) Sti^genesious Anthers. — These, as stated, are not
congenitally united, but by simple contact. As with fila-
ments, so with these, it is an adaptation to jnsect fertilisation.
Jasione viontana furnishes a good instance for an incipient
stage where they just unite at their bases only. This cohesion
is completed in the genus Synanthera of the same order
Campamdacece, as well as in the sub-order Lobeliece. In other
cases of true syngenesious anthers there is a complete lateral
fusion, as in Lobelia and Compositce, in Gloxinia and Im-
patiens. In all these cases the cohesion is by lateral con-
tact only, and not congenital ; that is to say, the jjapillge of
the future anthers on emerging from the axis grow to a
somewhat considerable stage of development as incipient
anthers before coming into contact. They then coalesce,
apparently by a slight solution of the surface of the cellular
carries a triangular flap, which exactly covers the orifice leading to the
honey. A somewhat similar flap occurs in the petals of Phaseolus and
Delphinium, which likewise keeps out unwelcome guests.
60
THE STRUCTURE OF FLOWERS.
walls wliicli touch ; so that when they are fully grown the
cohesion is firmly secured. An imitative cohesion is seen
in the anthers of the Heartsease, which arises from the
interlocking of marginal hairs down the sides of the cells.
Anthei'S, when thas closely approximate without actual
cohesion, are usually called " connivent," as in Ericacece,
and the word is perhaps appropriate to those of Solanum
Dulcamara ; but in this plant the union is very close, and
might even be considered as syngenesious.
The rationale of the close approximation of anthers, or of
actual cohesion between them, is the effect of insect agency,
just as for the filaments ; but the method of extraction of the
pollen varies. In Viola, the proboscis is thrust through a small
orifice between the connectival appendages
of the lower pair of stamens, in order to
reach the end of the honey-collecting spur.
In Heaths and some of their allies, the
anther-cells are at first in contact, and so
prevent the pollen from escaping ; but each
anther is provided with two auricles which
extend to the corolla. A bee on entering
first strikes the projecting stigma, but its
proboscis soon turns one of the auricles
aside, which, acting as a lever, dislocates
the rest, and a shower of pollen falls out.
In Compositce and Lobelia there is a true
piston action. The style continuing to elongate drives the
pollen out of the cylinder formed by the anthers, and elevates
it above the flower, thereby rendering it easy to be dispersed
by insects. This is well seen in Centaurea (Fig. 11) ; (a)
represents the stamens with tlie anther-cells closed above by
the connectival appendages. The arrow shows the direction
of the insertion of the proboscis of a bee to reach the annular
Fig. 11. — Stamens of
Centaurea.
THE PKINCIPLE OF COHESION. 61
lioney-disk at the "base of the style ; in 6, the style-arms have
spread after protrusion through the separated connectives.
The brush-like tuft of hairs has swept the pollen oat by
means of the piston-action of the style.
In Campanula, the action is different, for the anthers
though connivent, have not yet become syngenesious, as in
allied genera, e.g. Lobelia. They at first closely surround
the style, which is provided with long collecting hairs upon
which the pollen is caught. The anthers then shrivel and
fall down. Subsequently a bee enters the expanded bell,
grasps the style with her legs, and so transfers the pollen to
the abdomen. This method is identical with that followed
by bees in getting honey from Crocus, though in this
genus the anthers remain erect, and, being extrorse, at once
dischai'ge the pollen upon the insect without the interven-
tion of the style.
62 THE STRUCTURE OF FLOWERS.
CHAPTER VII.
THE PRINCIPLE OF COHESION — Continued. '
Cohesion of Carpels, or Syncarpous Pistil. — The accepted ■
doctrine that the carpels are metamorphosed leaves, will be
considered more fully when teratological modifications
come to be discussed ; and the proof that an ordinary
carpel, such as a legume, is merely a leaf folded npon itself
in a conduplicate manner with the margins coalescing and
then metamorphosed into a new organ, requires no special
evidence now. That a syncarpous pistil consists of two or
more carpellary leaves coalescing is equally admitted ; and
there are two methods of cohesion. Either the carpels may
be ab initio composed of unclosed leaves, which cohere by their
edges * respectively in contact, thus forming a single cavity
provided with parietal placentas, — such a union implying
a more primitive or arrested condition, from an evolutionary
point of view ; f or they may be individually more or less
closed before coalescence takes place, in this case by their
lateral surfaces. The axile placentation is the result. The
* The theory that the placentas are, at least in part, axial, ^Yill be
seen to be erroneous in consequence of the orientation of their vascular
cords (e.g. Fig. 12, c, p. 64; and Fig. 13, a, h, p. 65).
t Thus the parietal placentation of Orobanche is probably a result
of degradation through parasitism, from the axile, of tbe ScrophularinecB.
It may be compared to a " cleft palate " and " hare-lip " in man.
THE PRINCIPLE OF COHESION. 63
margins show every degree of union from a mere contact
withont real cohesion, thence, cohesion by contact, to a
solid central axial structure formed by congenital cohesion.
Lastly, the ovary may be one-chambered, with a free-central
placenta, as in Caryophyllece and Primzdacece ; or with one or
more ovules attached at the base, as in Bumex, Composites,
Graminece, etc. It is these latter kinds especially which
have given rise to mucli discussion as to the real nature of
the placentas, and as to how far the axis enters into tbeir
construction. To ascertain this latter point, a study of the
distribution and structure of the fibro-vascular cords of
the axis and of the carpels would seem to afford the most
promising clue to the interpretation.
It has been already mentioned that the dorsal cords of
carpels generally arise by lateral division from those of the
sepals or petals; and then the carpels will be superposed to
the one or the other of these organs respectively ; * or, a group
may emerge from the axial cylinder in a horse-shoe form, as
seen in section ; the outermost cord becoming the dorsal-
carpellary, and the ends of the curve the marginal. This is
the case, for example, in Cyclamen.
The point, then, at which the carpellary cords branch off
from a common stem in the first case may be regarded as
marking the termination of their axial character ; and in the
latter case, at the separation of parts of the " horse-shoes "
to form groups of threes. With regard to those cords which
become marginal and placentary, it is important to notice
the position of their spiral vessels. f If they are situated on
the side of the cord nearest to the medulla, the cord may
* See pp. 23, 24, and 42, 43, 44.
t The cords are, of course, reduced to vessels and soft bast only, the
former being mostly spiral, but occasionally becoming more or less
reticulated. I shall adopt the usual word Trachea;.
64 THE STRUCTURE OF FLOWERS.
generally be regarded as axial ; if, on tlae other side, i.e.
nearest to the ovary-cell, and if transverse sections exhibit
intermediate positions, in which they are central or scattered
irregularly within the phloem, they are then marginal and
placentary.
They may change their position from one side to the
other of the cord, as far as I have observed, in three different
ways. The whole cord may twist to the right or left, as in
Hellebore (Fig. 12) ; or, secondly, it may divide into two,
and each half turn towards an adjacent half of another cord
and unite with the latter, as in Pelargonium zonale (Fig. 13, h) ;
or, thirdly, the trachejB may traverse the jDhloem and so pass
out at the opposite side at a higher level, as in Ivy (Fig. 14,/,
p. 68). In any case, as soon as the tracheae are so placed as
to effect their object of nourishing the ovules, they may be
pronounced to be unquestionably and strictly carpellary.
I will take Hellebore as illustrating the first case. Fig.
12 represents a section of the floral receptacle taken imme-
I
a b
c
Fig. 1 2.— Hellebore : sections at base of ovary.
diately above the insertion of the innermost stamens. There
are nine cords* oriented as axial, three of which are beg-inninar
to curve outwards to form the dorsal cords of the three
carpels. Sections made a little higher show that the three
pairs of cords have spread out and revolved so as to bring
their spiral vessels into a radial direction (b, c). In this
* The trachetc are indicated by black lines or dots, the phloem being
inclosed within tho thin lines.
THE PRINCIPLE OF COHESION.
65
position tlie traclieae of each pair of cords face each other.
At this point, then, they have quite lost their strictly axial
chax'acter of facing the centre, and the axis is therefore no
longer concerned in the structure. A little higher the
cavities of the ovaries (indicated by the dotted lines) appear
between the dorsal cord and the pair of marginal ones ; and
now the latter turn their spirals completely towards the
ovary cells, having rotated through 90° in all. The object of
this rotation is to enable them to send off cords to the ovules.
The second method is well seen in Geranmm, Pelargonmm
zonale, and Impatiens. A section of the receptacle of the
first two, made between the insertion of the stamens and the
pistil, shows five groups of three cords each, arranged as in
Fig. 13, a. Small portions of the ten staminal cords are
Fig. 13. — Pelargonium : sections at base of ovary (a, 6, after Van Tieghem).
seen on the circumference of the section. The outermost
one of each group of three will form the dorsal cord of the
carpel. The two inner have their vessels already turned
C6 THE STRUCTURE OF FLOWERS.
towards each otlier, as described in Hellebore, and are in part
required for the placentas. They are, therefore, no longer
oriented as in an axis, i.e. with all the vessels arranged on
the inner edge of the cord and facing the central medulla.
A short distance above the base of the pistil, the inner-
most cords divide in a somewhat irregular maianer, but
rearrange themselves symmetrically round the centre of the
ground tissue in ten cords, as soon as the ovary cells have put
in an appearance. The method by which this condition is
arrived at was described by Yan Tieghem in Geranium
longipes, and with slight modifications it will apply to
Pelargonium zonale. Each of the lateral cords divides into
two (Fig. 13, 6), the two interior and adjacent branches
unite to form a single marginal cord with the tracheae
within or on the outer side (Fig. 13, c). The two outermost
branches pass oif to the right and left, and proceed to join
the corresponding halves from the neighbouring systems.
The pairs uniting thus form five cords of double origin,
alternating with the crescent-shaped marginal cords of the
carpels (r-). There are thus formed five in front of the ovary-
cells, and five in front of the septa , " which," Van Tieghem
observes, " one would regard as axial, if one did not pay
attention to the mode of formation of the coi^ds and to their
orientation."
In his' description of Impatiens Boyleana, he says that
the two innermost branches (Fig. 13, &) unite at first end to
end, i.e. like an 8, with the tracheae at the extremities in
contact ; they then form one cord with the spiral vessels
towards the circumference of the section, by rotating through
90°, accompanied by complete fusion.
In Pelargonium zonale, the tracheae become plunged, as it
were, within the phloem-tissue of the cords, as shown in
Fig 13, c, which then fuse together laterally.
THE PRINCIPLE OF COHESION. 67
Above the ovary-cells, at the base and thicker part of the
style, a section (Fig. 13, d) shows five solid circular buttresses,
the tissue of which is continuous with the central paren-
chyma, in the middle of which a lacuna {T) is formed by
rupture. In the depression between the buttresses, a small
portion of the style and conducting tissue forms a bridge,
as in Fig. 13, d, showing a cavity below it.
It is in this homogeneous mass of ground tissue that we
have a complete fusion of the hypertrophied borders of the
carpels which have thus entirely lost their individuality.
The axis proper disappeared as soon as the spiral vessels
became oriented, as in Fig. 13, a.
Hence the dotted lines radiating from the centre (c)
mark the ideal boundary of each carpel, and the line across
the base of the ovary-cell is the place where rupture will
take place when the fruit is mature. The column, or so-
called "carpophore," remaining is therefore entirely carpellary
in its origin.
The third method by which the tracheae pass from one
side to the other of a cord is partly seen in the preceding ;
and 1 suspect that this is the commonest method of all ; for
though, when axial, the cord has its spiral vessels fixed at
the inner angle, as soon as a change of position occui^s or
whenever it has to branch, the fixity of the position of the
trachese becomes relaxed, and they readily become enveloped
in the rest of the tissue of the cord, and so pass from one
side to the other with perfect facility, as will be seen in the
case of the Ivy.
When a syncarpous pistil has its ovary inferior — that is,
imbedded in the receptacular tube — the real state of cohesion
between the several carpels is masked in consequence of
their partially undifferentiated state ; the ovaries of which
then have the appearance of being simply isolated cavities
68
THE STRUCTURE OF FLOWERS.
sunk within a mass of parenchymatous tissue. In fact, they
might often be called " falsely syncarpous," a term applied
to the Pomece, but which is equally applicable to Ivy and
Fuchsia.
In the pedicel of a flower of Ivy, there are, at a distance
of about three-quarters of an inch from the tapering base of
the inferior ovary, four fibro-vascular cords (Fig. 14, a). A
little higher these split
up into an irregular
circle (b), and shortly
above the base of the
receptaculartube there
are fifteen (c), ten
being more towards
the circumference
than the other five.
The outer ten are for
the sepals and petals.
The five inner will
appear superposed to
the sepals (d), having
been already separated
off by radial chorisis
rather low down; these
are for the stamens.
Then from the petal-
ine cords, by a similar
method of chorisis, a
small cord mns up
the dorsal part of the
ovary-cell and another up the axis. This fixes the position
of the five carpels (if so many be present) as superposed to
the petals (d). There are often only four, or even three,
Fig. 14. — Ivy :
sections from pedicel to summit
of ovary.
THE PRINCIPLE OF COHESION. 69
ovary-cells developed. When this is the case, the cords of
the centre become fused into four or three (2 -j- 2 -f 1) (e),
and take up a position alternating with the ovarj-cells.
They become even more welded together higher up ; but they
separate again, to form twice as many as there are ovary-
cells (/). If there be three, then each cord may bifurcate,
though they do not all do so in every instance ; so that out of
12 cords, three ovular cords are given off to nourish the ovules
(/), and the rest run up the styles, though the total number
of cords may be less than 12, as variations seem to take place.
The ground tissue consists of a loose merenchyma, except-
ing three or four layers of cells below the epidermis, which
are more compact ; the ovaiy-cells — seemingly reduced to a
thickened epidermal layer only — are plunged freely into
this tissue (e). The cords run up the centre perfectly
independent of the ovary-cells (e) with their spiral vessels
on the inside, surrounding a central medulla. Were it not
for the presence of the dorsal cord, there is nothing to hinder
one from calling them axial. It is not until they reach the
top of the ovary-cells that these cords bifurcate and send off
one branch each into the pendulous ovules, the other branches
being conveyed upwards into the styles (/).
The above description will give a fair example of the
distribution of the cords for supplying the several members
of the whorls. The reader can estimate how far the central
cylinder should be called axial. The fact is, that the whole
of the tissue of the carpels, excepting the thickened internal
epidermis covering the ovules, is totally lost in the general
spongy mass in which they are imbedded. But since the
petaline cord gives rise to the small dorsal-carpellary and
one axial, theoretically these two belong to the carpellary
leaf ; and on this ground we should feel inclined to regard
the central cords not as axial but marginal and carpellary,
70 THE STKUCTURE OF FLOWERS.
notwithstanding tlie fact that the trachetB are oriented
inwards ; since it is not until they reach the level of the
insertion of the ovules that they pass either to the middle
or opposite side of the cord. The rest of the carpellary
tissues are undifferentiated, as stated above, and it is this very
common condition in the case of inferior ovaries that has led
botanists to regard the lower parts of the carpels as being of
an axial nature and not foliar.
Tub Formation of Septa. — With regard to the union of
the surfaces of the carpels to form the septa, the rule is for
the adjacent epidermides to be altogether wanting ; and, if
the median tissue be thick, the walls of two adjacent ovary-
cells may be very wide asunder, as in the Ivy. On the other
hand, the septa may be reduced to the two epidermal layers
alone, and then they are often scarcely coherent at all, as in
Balsam and Lemon,
In some cases, the epidermides are not in contact through-
out their entire surfaces, and whenever this is the case the
characteristic epidermal cells reappear, as in Liliacece and
Amaryllidacece. Similarly, as soon as the carpels of Hellebore
become free, the epidermides of the margins appear in their
proper character, which now cohere only by contact. It is
the same with the axile placentas of the Lily.
As instances where the axis seems to be more decidedly
prolonged up the centre, are Lychnis and allied members of
the Silenece. Ph. Van Tieghem has also shown how an axial
cylinder ascends up the middle of the flower of Campmiula
inediiim for about two-thirds of the height. Thus Fig. 15, a,
represents a section of the fluted pedicel ; b shows the lobes
isolated, each containing a portion of the fibro-vascular
cylinder. In c, the broken central cylinder has again closed
up, a section showing a complete circle of an axial character.
The triangular basal portions of the ovary-cells have now
it
THE PEINCIPLE OF COHESION.
71
appeared, d represents a section of two-thirds of the height
of the infei-ior ovary; but now the fibro-vascular cylinder
is dissociated, and forms fifteen separate cords — two being
marginal to each placenta and one belonging to each septum.
As the cords have their spiral vessels reversed in position,
i.e. facing outwards and not inwards towards the centre,
their axial character has ceased.*
iij^
a - d
Fig. 15. — Campanula medium (after Van Tieghem).
The rule appears to me to be that as soon as, or even
before tbe level of the insertion of the ovules is reached, the
internal position of the tracheaa is abandoned. This is the
case with Lychnis.
In some cases there is an apparently axial formation,
* I do not find that matters can be really expressed quite so "diagram-
matically " as, e.g., in his figure d; for Van Tieghem does not pay much
attention to the central and scattered positions of the trachea;, which I
take to be quite as significant as their outward orientation ; for as the
ovules are approached they become dispersed, though a medulla remains.
72 THE STRUCTURE OF FLOWERS,
wliich has proved to be misleading. Thus, in Geranium and
allied genera, the beak-like process from which portions of
the carpels separate when ripe is not axial at all, but simply
the coherent placentas of an entirely carpellary origin.*
This will be understood from the description I have given of
Pelargonium (p. G5).
The mericarps of the fruit of an umbellifer are also
supported on a carpophore, which is likewise usually described
as axial ; but anatomical investigations do not warrant the
conclusion. The commissural surfaces are obviously merely
the result of rupture between the two carpels which have
cohered ; and, in consequence of this union, each epidermis
fails to develop its true character, but remains in an arrested
condition, having the cells somewhat smaller than the rest
of the ground tissue. This enables the mericarps to separate
readily on maturity. A double fibro-vascular cord runs up
the centre to supply ovular cords at the summit of the
ovary-cells. If one traces the cords from the pedicel, there
will be found in the latter a complete fibro- vascular cylinder.
This spreads out at the base of the inferior ovary into ten
clearly defined cords which run parallel to each other from
base to apex, to furnish the petals and stamens ; while two
only coalesce and form the axial cord. It is this cord which
constitutes the stylopod when the fruit is ripe. Hence it
is not axial, but simply the combined marginal cords of the
two ovary-cells.
Free Central Placentas. — The position of an ovule or
ovules on a central support, free from the wall of the ovary,
or directly on the base of the chamber, and apparently quite
* Prof. A. Gray (I.e., p. 213) and Henfrey (EL Course of Bof., 4th ed.
p. 100) both speak of it as axial ; though it was quite correctly described
and figured by M. Seringo so long ago as 1838 (Mem. sur la Fruit des
Otraniacies) : " Les bords de chaque carpel placentaires sent testes at
ferment la colonne."
THE PRINCIPLE OF COHESION.
73
central, has given rise to a good deal of discussion. Two
views have been taken, one being that such ovules are, in
some cases at least, axial in their origin, and not carpellarj at
all ; others would refer all ovules, without exception, to a
carpellarj source. Analogy, indeed, would, if taken alone,
seem to justify the latter conclusion, since the numerical
propoi'tion of ovules having a decidedly carpellarj origin is
unmistakably very great; and any doubt upon the matter
seems to me to have arisen from a want of due appreciation
of the arrest of development, or rather failure of a complete
differentiation which has taken place between the ovary and
axis at the place where the ovule or ovules appear.
This an^est is particularly apparent, as already stated, in
the case of inferior
ovaries, as of the Ivy.
Thus, in the Compositre,
the ovular papilla seems
to arise at the base of a
cavity in the axis, and
might easily be thought
to be axial ; but a slight
eccentricity may be dis-
cerned at a certain epoch
which is the first indica-
tion of its carpellary
origin. In Beta the
basal ovule arises in a
very similar manner,
but as the ovary becomes
more developed, the
ovule is carried up so
OK
Fig. IG.—Beta (after Payer).
as finally to become pendulous (Fig. 16, a, h, c.) It is
much the same in Tijplia and allied genera. The same
9
74 THE STRUCTURE OF FLOWERS.
gradual elevation of the ovule occurs in Bicinus and other
Euphorbiaceous plants.
Similarly, if we compare the differences in allied genera,
as Ranunculus and Thalictrum ; in the former genus the
ovule arises at the very base of the carpel, close to its point
of attachment to the axis, and remains there. In Clematis
and Thalictrum, the marginal cleft of the carpel appears a
little more decidedly above the base, so that the ovule from
its earliest period is situated somewhat higher up, and by a
further development is carried to a yet higher position, and
so ultimately becomes pendulous. Exactly similar differences
occur between the orders Composites and Dipsaceoe.
Hence, it would seem that basilar ovules owe their
positions to corresponding degrees of arrest of the growth
and development of the carpels, and especially of the basilar
portions of the carpellary margins. I think, therefore, we
may draw the following conclusion, that the particular form
of energy which would cause a carpel to emerge out from
and be developed freely and entirely from an axis, is more
or less potential than actual.* Consequently, it develops
the ovule just where that portion of the carpellary margin
would have appeared had it been formed ; so that the tissue
whence the ovular papilla emerges may be considered to be,
strictly speaking, neither axial nor carpellary, but undif-
ferentiated merenchyma, and potentially carpellary.
From a single ovule we may now pass to plurl-OA'ular
ovaries. Dioncea gives us an instance where many ovules
arise at the base perfectly free from the ovarian wall. In
this flower the pistil consists of five carpels, which emerge
congenitally out of the axis, first as a circular rim, which
* It may be noted that it is more actual in Clematis, etc., in that
several ovular papillae are produced in genera with pendulous ovules,
besides being more elevated in position ; but only one in Ranunculus.
THE PEINCIPLE OF COHESION. 75
then becomes a cup, wliicli finally contracts above to
form tlie style, just as in Primulacece. It is, therefore,
unilocular, while a circle of ovules appears on a thick ring
of tissue within the base of the ovary. Other circles of
ovules appear concentrically and centrifugally. It might be
questioned, therefore, whether the ring which carries them
were axial or not. I think, however, the same interpreta-
tion will apply here as elsewhere ; that is to say, the ovules
arise from the place where the bases of the carpels would
have appeared had they been differentiated out of the axis.
In the allied genus Drosera the placentas are strictly
parietal, and the ovules, commencing to emerge half-way up
the wall, appear successively, both upwards and downwards.
1^0 w, as they are centrifugal in Bioncca (corresponding to
the upivard development in Drosera), it looks as if only a
portion of the upper half of the carpels were really repre-
sented at all.
In this genus there is a barren central space within the
ring of ovules, perhaps representing the termination of the axis.
That the basal portion only of syncarpous pistils should
bear ovules is common enough, and the pla-
centas often swell out there to form bosses
which we may reasonably conceive as coa-
lescing to form the continuous ring character-
istic of Dionoia. Thus^ce?- illustrates how each
of the two carpels gives rise to two globular
protuberances on which the ovules are borne
(Fig. 17). Aneviiopsis, as figured by Payer,
has a confluent protuberance bearing several
basifugal ovules. Similar multiovular bosses Fig. n —Carpels of
occur in Solaneoe and Scroplndarinece, giving
the characteristic dumb-bell shape in a transverse section.
Now, if we imagine these swollen ovuliferous placentas
76 THE STRUCTURE OF FLOWERS.
arising from the basal portions of tlie carpellary leaves to
reach the centre of the ovarian chamber, and be there fused
together into a solid mass, we should obtain the apparently
axial structure of Primulacece, Santalacece, etc., with the few
or numerous ovules hasipetal in order of development, cor-
responding to the centrifugal order in Dioncea and the
ascending order in Drosera.
The probability that this is the correct view is supported
by a case I have met with in which the carpels
of Primula sinensis were dissociated, and more
or less foliaceous with rudimentary ovules, not
only along the margins, but with several borne
on heel-like processes,* which extended towards
the centre of the ovary, as represented in Fig. 18.
Anatomical investigations entirely corrobo-
p. ' rate the carpellary nature of the central placenta
of Primulaceoe. The circle of cords, usually ten
in number, which pass up the column to nourish the ovules
are oinginally separated from the sides of the sepaline by
radial chorisis, and become superposed to the sepals ; the
dorsal cords (about ten) having also parted company from
the five sepaline and five petaline. The latter, however, do
not give rise to any placentary cords ; hence there are really
five carpels superposed to the sepals.
With regard to the position of the spiral vessels, they
are not oriented as if axial, but are completely embedded
in the phloem, and consequently central. Moreover, the
cords in section are circular in form, and not wedge-shaped.
The central (if not external) position of the tracheae and the
circular form of the cords are both eminently characteristic
* Van Tieghera, though once regarding the central placenta as axial
(Recherches sur la Structure clu Pistil, 1868), has more recently arrived
at the same conclusion as myself {Traite'do Bot., 1884).
THE PRINCIPLE OF COHESION.
77
features when tliej first cease to fee axial and become appen-
dicular. The accompanying diagrams (Fig. 19), (a) Lysi-
macliia nemorum and (^h) Primula veris, will illustrate these
a.
Fig. 19. — a, Lysimachia nemorum ; b, Primula veris.
remarks. The sections are taken on planes * where the
pistil is emerging from the receptacle ; s. represents the
sepaline cords ; ah. st. abortive stamina! cords ; jj. the petal-
ine and staminal (combined) ; d.c. dorsal carj^ellarj ; pi. c.
placentary cords.
A free central placenta may result from the destruction
of the septa of an originally axile placenta, as occurs in the
Caryophyllece. Thus, the ten rows of ovules in Lychnis
sufficiently indicated their marginal origin. I may add that
a careful investigation into the origin and distribution of the
cords has convinced me that the axis in flowers of the
CaryopTiyllece early ceases to take any part in the structure
of the pistil.
* Fig. a represents a section taken rather lower down than in Fig. h ,•
as the cords in the latter are still undiiferentiated in Fig. a.
THE STRUCTURE OF FLOWERS.
CHAPTER VIII.
THE PRINCIPLE OP ADHESIOJT.
Adhesion of Organs. — This term is diatinguislied from
cohesion by limiting its application to the union of differeut
whorls. Thus, if the petals or stamens he united to the
calyx, they are called episepalous, a term usually synony-
mous with perigynous ; and if the stamens be adherent to
the perianth or corolla, they are epiphyllous or epipetalous
respectively, sometimes also described as perigynous. On
the other hand, if the stamens and pistil be in close con-
junction, showing an adhesion between the filament and the
style, so that the anther and stigma are brought together,
the term gynandrous is applied to them.
Adhesion may be safely regarded as an advance upon
cohesion; and there is, I think, a gi-eat probability of its
being — perhaps, originally, in most if not all cases — a result
of adaptation to insect agency.
With regard to the perigynous condition which involves
a more or less degree of adhesion of the petals and stamens
to the calyx, this is in many clearly a result of the develop-
ment of the receptacular tube with its honey-disk lining it,
as in Bosacece. This causes the free portions of the petals
and stamens to be carried away from the central axis, and
placed in a ring "around the pistil," i.e. perigynous; while
the more or less amount of adhesion of them to the calyx
THE PRINCIPLE OF ADHESION. 79
has suggested the term ejnsepaloics. In the Rose, however,
which secretes no honey, the sepals are almost, if not
entirely free, and articulate readily ; whereas, in other
rosaceous plants, if the receptacular tube does not itself fall
off, as in Prunus, the calyx remains persistent.
Although it is usual to regard perigynous petals and
stamens as episepalous as well — that is, "upon the sepals"
— when the receptacular tube is well pronounced, it is more
strictly in accordance with anatomical structure to i-egard
the former as brought into close proximity to the calyx,
rather than being really inserted upon it. In many other
cases, as in Lythnim and JDapline, the whole of the tube has
all the appearance of being truly calycine and not recepta-
cular; so that "episepalous" will then best describe their
condition of adhesion.
It is rare to find a gamopetalous corolla adhering to the
calyx, but it is so in Cticurbitacece, as in the genera Cucumis
and Bnjonia, where the two outer whorls are united.
Ph. Van Tieghem observes* that the union may be the
result of the fusion of the respective parenchymas alone,
leaving the cords proper to each organ distinct. I think,
however, that it will be found to be more frequently the
case that when the cords are superposed, they are fused
together below, but separate when the organs become free.
This is well seen in Prunus. The sepaline and petaline
cords branch, by tangential chorisis, about half-way up the
receptacular tube, and thus give rise to ten stamens. Each of
the petaline cords branches on either side again, at a different
level, by radial fission, and gives rise to ten more.t So that if
we retain the term " episepalous " for the stamens, we must
understand that, while the actual stamen is practically free
* Traile Botaniqiie, p. 390.
t This -will be described more fully below (see Fig. 28, p. 95).
80 THE STRUCTURE OF FLOWERS.
from the calyx, yet its cord is common with that of the latter
below.
The epiphy lions or eplpetalous condition of the stamens is
almost invariably associated with a state of cohesion of the
perianth-leaves and petals of the corolla ; as exceptional
instances are Scilla and Lychnis, which have the parts of the
perianth and corolla free, but with the stamens adherent to
them ; while, conversely, CampanulacecB and Ericacece have
gamopetalous corollas, but the stamens not adherent to
them.*
The rationale is primarily, in many, perhaps in every
case, an adaptation to insect agency. In the majority of
gamopetalous corollas, the honey usually lies somewhere
between the insertion of the corolla and pistil, being secreted
by one or more glands or an annular disk round the base of
the ovary. There are two positions in which the anthers
may be placed in regular gamopetalous flowers with reference
to the visits of insects for the honey; either around the tube,
as in the Primrose and Scilla, or close around the style, as
in Convolvulus, Campanula, and Crocus. In the former case,
when an insect passes its head or proboscis down the tube, it
touches the anthers on one side of it and the stigma on the
other ; but as the proboscis may pass on either side of the pistil
in the same and different flowers, that is on the near or
remote side, with reference to the position of the insect, such
flowers have every facility of being crossed. If they be
hcterostyled, as the Primrose, then of course each kind has the
greater chance of being crossed by the other sort.
* The distribution of the coi-ds in the floral receptacle of Azalea,
between the insertion of the corolla and pistil, is ve»"y anomalous, having
no symmetrical arrangement around the centre ; while the cords of the
corolla of Campanula, as described above, are peculiar for other reasons.
This may, perhaps, have something to do with the exceptional freedom
of the stamens from the corolla.
THE PRINCIPLE OF ADHESION. 81
In the case of Crocus^ Convolvidus, and other flowers with
a contracted base to the corolla or perianth, the anthers are
situated close round the stjle. In these flowers, the insect
alights on the stigmas, as already described, grasps the central
column and sucks the honey head downwards, and so gets
dusted on the abdomen, the pollen from which is thus trans-
ferred to the next flower visited.
The adhesion of the stamens to the corolla or perianth
thus seems to give a rigidity and firmness, as well as leverage
in some cases, so that the action of the insects is more
accurately secured, and some one particular spot on their
bodies invariably struck and dusted with pollen ; which
would scarcely be the case if the filaments were free and at
liberty to oscillate or swing about in any direction.
In many flowers with irregular corollas, the stamens are
declinate ; and their adhesion to the tube is then of manifest
advantage, for the basal part of the filaments thus acquires an
additional strength to act as a fulcrum, which enables the
filaments to support the weight of the insect. In Echium, for
example (Fig. 20, p. 82), the corolla is even strengthened by
a rib where the stamen is inserted. This part constitutes the
fulcrum. The line of force from the fulcrum intersects a line
perpendicular to the filaments, corresponding to the weight of
the insect ; while the third and upward force is that exerted
by the filaments to counteract the resultant of the two former.*
The origin of the adhesion between the stamens and the
outer whorls is revealed by anatomical investigations ; for
the rule is, as described in the case of Prunus, that the fibro-
vaseular cords of the stamens arise by division from those of
the outer whorls whenever they are superposed to them.
In other words, when adhesions are seen between the
floral whorls, by being superposed to one another, then a
* See also Figs. 38, 3[), and 40, pp. 124-126, and consult text.
82
THE STRUCTURE OF FLOWERS.
fusion of their respective cords will he found. If the members
arise freelj, as in Eatiunculacece and Cruciferce, then their cords
are inserted into the axis, having arisen by radial division
or lateral chorisis.
In the case of the gynandrons pistil, the stamens have
their fibro-vascular cords more or less imbedded in the recep-
Fig. 20. — Echium ; a, side view ; b, before, and c, after shedding pollen ; showing
protuudry.
tacular tube, or rather the common tissue resulting from the
fusion of the ovary and the tube together ; the anther then
stands on the summit, and if there be a short or no style, but
only the stigmas terminating the ovary, then the anther is in
close contact with it, as in Hippuris, Orchis, etc. When there
is a style, the filament may be prolonged in adhesion with it,
as in most orchids possessing the so-called column. It is not
THE PRINCIPLE OF ADHESION. 83
SO, however, in ArisfolocMa, acaording to Van Tiegtem,
tliouo-h often described as such*
To summarize the above remarks, it seems clear that all
adhesions between the two whorls of the perianth, to be
found mostly in the CalyciflorcB, is an accidental occurrence
due to the hypertrophied condition of the axis in forming a
receptacular tube ; so that the term " perigynous " is more
strictly applicable than " episepalous."
Adhesions between the filaments and corolla, or calyx if
the former be wanting as in Baplme, is an adaptation to insect
fertilisation ; whereby a more rigid position is acquired for
the stamens, coupled with a gain of leverage, etc.
Lastly, adhesions between the stamens and pistil only
occur whei-e there is a receptacular tube, or "disk," as in
Nymphcea ; and the fusion of filaments with the style, or
between anthers and stigm^as, is brought about by the very
close proximity of the organs when in an early and undif-
ferentiated state.
* Duchartre, Elem. de Bot., p. 648; Henfrey, I.e., p. 125 ; Bentli. and
Hooker, Gen. PL, vol. iii., pt. 1, p. 123; Van Tieghem, Traite de Bot., i.,
p. 422.
Van Tieghem's description and figure (Fig. 21) is as follows : —
" The styles and stigmas are abortive, and the six carpels ,,.^,,/,-s, ,-^
are reduced to their ovaries. It is, then, the thickened "^
connectives of the anthers, coherent laterally into a tube
and covered above with stigmatic papillae, which now play
the part of stigmas and of the style."
To judge from Payer's figures (Organogenie, pi. 91 and
pi. 109), the stigmas appear to rise from the inner side of the
very short filaments, and might be interpreted as truly car-
pellary stigmas, but fused to the former. A further investi-
gation of the distribution of the fibro-vascular cords should Fig. 21.— Aris-
be made. Moreover, Asarian does not appear to have any- yau^^neghem)!
thing so abnormal.
84 THE STRUCTURE OF FLOWERS.
CHAPTER IX.
THE CAUSE OF UNIONS.
Haying now noticed the different kinds of unions, we may
ask what has brought them about.
We have seen how progressively complex conditions can
be traced from entire freedom, as in Buttercups, through
forms of Cohesion, such as the gamosepalous, gamopetalous,
monadelphous conditions, etc. •, to cases of Adhesion, as of the
perigynous and epipetalous states ; and, lastly, to the adhesion
of the ovary to the receptacular tube.
As stated above, these conditions are correlated with
greater and progressive differentiations of the floral organs,
which have been brought about by insect agencies. The
above-mentioned and other terms do not, however, explain
how or what the immediate influences are which induce
unions of various kinds amongst the parts of flowers ; but
some researches of Mr. Meehan on the Coniferce * will perhaps
give us a clue. There is a well-known and a very generally
prevailing feature amongst certain genera of Conifers — as of
the Cupressinece, for example — that the foliage can appear
under two forms, the leaves being either f i^ee from their bases,
or more or less adherent to the axis. The two forms of leaves
have been recognized as specific characters in Juniperus,
* On the Leaves of the Conifera, Proc. of tlie American Association
for the Advancement of Science, 1869, p. 317.
THE CALTSE OF UNIONS. 85
Jietinospora, etc. ; but both kinds of foliage not infrequently
appear together on the same plant; and, when this is the
case, the spinescent and free leaves are borne on relatively
less vigorous branches, the adherent foliage being charac-
teristic of the more vigorous and quick-growing terminal
shoots. It has been also noticed by Dr. M. T. Masters that not
only do the broad and free leaves of Juniperus and Betinospora
not occur on the leader shoots, but when the plant is varie-
gated then free leaves (on the stem with arrested growth)
are much more variegated than they are on the quick-grow-
ing leader shoot.* The last-mentioned observer has also
noticed that the free foliage is characteristic of the younger
condition of the plant, the adnate foliage that of the adult
state.
The conclusions arrived at by Mr. Meehan are as follows :
(1) The true leaves of Coniferce are usually adnate with the
branches. (2) Adnation is in proportion to vigour in the
genus, species, or in the individuals of the same species, or
branches of the same individual. (3) Many so-called dis-
tinct species of Coniferce are the same, but with their leaves
in various states of adnation.
Another very common form of adhesion, to which I have
already alluded and which is most probably due to hyper-
trophy through succulency at an early stage, is fasciation.f
Under this condition the fibro- vascular cylinder of at least
two " axes," which would be normally separate, coalesce,
and form an oval cylinder with, it may be, only a slight
* Gard. Chron., 1883, vol. xix., p. 657.
t For remarks on this phenomenon the reader is referred to Dr.
Masters's Teratology. It is particularly common in herbaceous plants, as
Lettuces, Asparagus, etc., and not unfrequent in Ash-trees. I observed
a trailing plant of Cotoneaster growing over a rockery by the side of a
stream in a garden, almost every branch of v?hich was fasciated.
10
86 THE STRUCTURE OF FLOWERS.
constriction indicating the union. The medullas, cortical
and epidermal layers, are also continuous throughout and
common to the whole.
Now, the union of two opposite " appendages " to an axis,
as in the case of connate leaves, may take place. This may
be called foliar fasciation in which the fib ro- vascular cords
of each " leaf " are embedded in a common parenchyma, and
all encased together within a common epidermis.
If we regard the receptacular tube of, say. Fuchsia and
Narcissus in the same light, though adherent to the ovary
like a decurreut leaf of a thistle or Sedum, I see no argument
against the supposition that the tube, in such cases as these,
may be regarded as the fasciated petioles of the sepaline
and perianthial leaves, now adherent to the ovary within
them.
A pear would seem to combine both axis and petioles, as
the base of the ovaries is situated much above the commence-
ment of the expansion of the pedicel (see Fig. 22, p. 90,
and Fig. 26, p. 94, and consult text).
Each case must, however, be interpreted on its own
merits ; and I think there will be little difficulty about this,
if we recognize the fact that both the pedicel and floral
receptacle on the one hand, and the petioles or their floral
equivalents on the other, can alike assume all the features of
the so-called receptacular tube.
Now let us apply these principles of union through
hypertrophy to flowers, and we have an interpretation
according to the theory advanced in this book : that differ-
ences of floral structure depend largely upon different dis-
tributions of nutrition in the several organs ; and that the
irritation set up by insects themselves is one of the most
potent causes of a flow of sap to certain definite places,
which encourages local growths, thereby inducing these
THE CAUSE OF UNIONS, 87
unions to take place between the. parts of any whorl, form-
{n<y "cohesions," and also between different whorls, or
" adhesions."
Other causes may determine them, for hypertrophy may
set. in through a purely vegetative stimulus ; for it is not
unfrequent to see abnormal cohesions and adhesions in cul-
tivated orchids, such as petals or sepals adhering to the
column, etc. Such may, with a good deal of probability,
be referred to the artificially stimulated conditions under
which they are grown. These abnormal cohesions between
members of the perianth, and adhesions to the column, have
been observed both in this country and America.* As a
particular instance of the latter kind, Mr. Meehan had
observed several dozens of flowers of Phaius grandifloms which
had the dorsal sepal united to the column, all being confined
to separate spikes from those which have perfect flowers.
In some cases, of the same plant two of the petals were
united so as to form a hood over the column.
Another peculiarity of Orchids is the tendency to convert
sepals or petals into labella, and to multiply the spurs when
an orchid is characterized by them so as to render them
peloric, a sure sign of hypertrophy. f
All these "monstrosities" seem to point to an excessively
unstable condition of equilibrium in the flowers of Orchids ;
and that they are peculiarly sensitive to the effects of nutri-
tive stimuli, whether brought about by visits of insects or
by artificial cultivation. So that the order Orchidece is
particularly interesting, as furnishing indirect or even direct
* As by Mr. T. Meehan. Proc. Acad. Nat. Soc. Phil., 1873, pp.
205, 276.
t The remarkable influence of the presence of a " plant-biig,"
causing the normally irregular corolla of Clerodendron to become
hypertrophied and peloric, will be described hereafter (p. 130).
88 THE STEUCTURE OF FLOWERS.
proof for my theory — that the forms and structures of flowers
are the direct outcome of the responsive power of protoplasm
to external stimuli.*
* We may, perhaps, see some analogy between these unions amongst
floral organs, which thus occur abnormally in orchids and normally in
so many flowers, and inflammatory adhesions in the human subject.
It is well known that certain, otherwise abnormal, unions may be con-
genital, which usually only occur through inflammation set up by
abnormal excitation, but they are not hereditary.
I have alluded to hypertrophy and atrophy as causes of the struc-
tures of flowers, and shall have more to say about them. I would here
add the following analogous phenomena between the animal and vege-
table kingdoms. Sir James Paget remarks : — " Constant extra-pressure
on a part always appears to produce atrophy and absorption ; occasional
pressure may, and usually does, produce hypertrophy and thickening.
All the thickenings of the cuticle are the consequences of occasional
pressure ; as the pressure of shoes in occasional walking, of tools occa-
sionally used with the hand, and the like : for it seems a necessary con-
dition for hypertrophy, in most parts, that they should enjoy intervals
in which their nutrition may go on actively" {Led. on Surg. Path., i.,
p. 89).
The reader will perceive the significance of this passage when
recalling the fact that insects' visits are intermittent.
Atrophy by pressure and absolution is seen in the growth of embryos ;
while the constant pressure of a ligature arrests all growth at the
constricted place. On the other hand, it would seem to be the persistent
contact which causes a climber to thicken (see p. 156).
CHAPTER X.
THE RECEPTACULAR TUBE.
The Calyx or Recepi-acular Tqbe. — This organ consists of
a cellular sheath of varying degrees of thickness, free from
or adherent to the ovary. Much discussion has arisen as to
the true nature of it, whether it should be regarded as axial
or foliar. The older view generally maintained was that it
consisted of the lower part of the outermost whorl of the
perianth or calyx — in other words, that the basal or petiolar
portions of the sepaline leaves were coherent; and if the
ovary were inferior, then they were supposed to be adherent
to the latter as well.
Schleiden appears to have been the first botanist who
propounded the view that it was axial and not foliar. He
was followed by others ; but this idea took two forms.
According to one, it was thought that everything below the
summit of the inferior ovary — that is to say, the outer wall,
the septa and placentas — was axial, and only the fi-ee portion
of the summit of the ovary, together with the styles and
stigmas, were foliar. According to the other view, it was
maintained that the ovaries, styles, and stigmas were foliar,
and the superficial covering to the ovary alone was axial.
The first view was held by Schleiden, A. de Saint Hilaire,
Trecul, Payer, Prantl, and Sachs ; * the latter by Decaisne,
* E.g. Sachs' TexUBoolc of Botany, Eng. (2nd) ed., p. 566.
90
THE STRUCTURE OF FLOWERS.
T^Taudln, Ph. Van Tieghem, and, I tliink, Englisli botanists in
general.*
There are three methods of investigation, which conjointly
may guide us to the discovery of the real natui-e of the tube.
The first is that of following its development ; the second
is teratological, and the third anatomical.
Morphological Investfgations. — In tracing the morpho-
logical development of flowers of the Eosacece, where the
receptacular tube is a characteristic feature, one notices how
a border, surrounding the domelike ternaination of the axis
which soon produces carpellary papillse, rises upwards and
elevates the sepals and the papillae of the petals and stamens.
This border ultimately forms the tube ; and the question is,
whether it should be regarded as the basal part of the calyx
or a development from the axis.
In the Pomeoi we find the apocarpous condition of the
pistil, characteristic of all the other members of the Bo^acem
still retained at first ; but in consequence of the growth and
close proximity of the tube
Avith the carpels, various
degrees of adhesion are
brought about between
them ; thus, in Fyriis (Fig.
22, a), the bases only of
the carpels are from the
first fused into the axis.
In Gotoneaster (6) the fusion
Flff. 22. — a, Pijrus ; b, Cotoneaster fafter Paj-er). . n . i • i i i
^ . i/ ' . >. 1 J extends to a higher level
on the ovaries. Such " half-inferior " ovai-ies occur in
other genera, as Saxifraga granulata, Gloxinia, etc. From
such we pass to completely inferior states, as in Compositce
* Benthain and Hooker describe the inferior ovary of the Pomece
in the terms, " Calycis tubus ovario adnatus."
THE RECEPTACULAR TUBE. 91
and Umhellife7(T, ■while Onagracece furnish illustrations of
an extension of the receptacular tube to considerable distances
beyond the summit of the ovary, as in Circcea, and probably
Fuchaia and (Enotliera are similar cases. A like prolongation
is seen in some Compositfe with " stipitate " pajipus, as the
Dandelion, Tragopogon, Hypochceris, etc.
In tracing the development of the inferior ovary of the
Coynpositcti, the cavity of the ovary appears to be sunk below
the level of the first emergence of the corolla and stamens ;
and it is this which has suggested the view tha,t the ovary
is part of the axis, and that only the style and upper portion
of the ovary which is exposed is foliar.
On the other hand, since there are abundant cases of
transitional conditions ; as, for example, between species of
Saxifrage, — S. timbrosa having an entirely superior ovary ;
S. gramilata, one that is half-superior, and S. tridactylites,
a completely inferior ovary ; and moreover, if we compare
the Pomeoi with the other tribes of Rosacea'., comparative
morphology does not tend to favour the above view held by
Sachs, but rather inclines one to the impression that the basal
part of the ovary must be carpellary and not axial, though
there may be no visible line of demarcation between the
cauline and foliar structures.*
The existence of the above-mentioned facts, and many
cases of reversion to entire freedom by " solution," supply
good reasons for believing that the development of the
carpels is more or less arrested below, wherever they are in
contact with the receptacular tube ; yet they retain their
power of developing at least one ovule, as is often the case in
* To regard the septa of an inferior ovary " as the prolongations of
the margins of the carpels downwards on the inside of the ovary "
(Sachs' Text-Booh, p. 567), seems to be a very strained interpretation in
order to fit the axial theory.
92
THE STRUCTURE OF FLOWERS.
gamopetalous epigjnous orders. Moreover, the ovule is not
strictly basilar and central, but is really situated laterally.
Anatomical investigations, as we shall see presently, entirely
confirm this view.
Tbratological Investigations. — Teratological evidence of
the axial, or in some cases, perhaps, petiolar nature of the
so-called receptacular tube is tolerably abundant. Thus, in
monstrous forms of flowers normally possessing inferior
ovaries, the pistil is sometimes completely arrested, when the
latter is replaced by a long pedicel which is usually Avanting
or else is very short, as in Honeysuckle, Epilobium^ Orchis,
etc. (Fig. 23).* Pears not unfrequently fmmish similar
instances, as in the case of the so-called "Bishop's
Thumb Pear, which sometimes occurs of an
elongated form', destitute of core and seeds.
These fruits, which are merely swellings of the
flower-stalk, are produced from the second crop
of blossoms, which have not energy enough to
produce carpels (core) Avith ovules or ripe
seeds." f There is little doubt that the recepta-
cular tube is, in these cases, converted into the
ifoi-^o^maTfurmed ^odlike structures in consequence of the total
absence of the carpels from within it. In other
words, it is axial.
There are other indications of the tube being axial in its
nature rather than foliar ; thus, it frequently becomes " pro-
liferous ; " that is to say, flowers, or even branches, may grow
out of it, as is often the case with Roses, Prickly Pear,
Umhelliferce, etc. J Again, certain kinds of Pears, Medlars,
* a is the interior of the flower, consisting of a cnp-like depression
with two anthers.
t Gardener's Chronicle, Oct. 9, 1886, p. 464.
X Teratology, p. 100, seq.
I
THE RECEPTACULAR TUBE.
93
Roses (Fig. 24), etc., occasionally bear foliage on the
external surface of the tube, and when the caljx of the Rose
becomes abnormally folia-
ceous, stipules (Fig. 24, st.)
may appear at the summit
of the tube, indicating that
Fig. 24.— Leaf-bearins recpptacular tube of Rose
(alter .Masters).
Fig. 25.— Hawthorn with puper-
iiu\iierary free carptls (after
Masters).
point to be the base of the sepal. Sometimes supernumerary
carpels are borne freely on the top, as in the Hawthorn
(Fig. 25).
On the other hand, a tendency to hypertrophy is some-
times discovered in the petioles of leaves of Apples * and
Pears (Fig. 2('), p. 94) ; and a not infrequent monstrosity is
seen in Fuchsias, where one or more of the sepals become
foliaceous, and then their petioles are formed but often
remain more or le.ss adherent to the ovary if present, which
seems to imply that the tube in this plant might be formed
* Mr. Meehan describes a similar instance of an Apple-tree winch
never bore flowers but always had an abundance of fruit. The latter, how=
ever, were composed of metamorphosed and fleshy floral whorls. He adds,
however, that cork-cells were formed abundantly on the outside of the
apples ; remarking, " It would seem, therefore, that with the lack of
development in the inner series of whorls necessary to the perfect fruit,
those which remained were liable to take on somewhat the character of
bark structure " (Proc. Acad. Nat. Sc. FhiL, 1873, p. 99).
94
THE STRUCTURE OF FLOWERS.
Tdj, or at least is homologous with, the petiolar portion of
the caljcine leaves (Fig.
27).
Phjllomes, however,
are after all but modified
portions of caulomes, and
petioles are still less de-
partures than are blades
from the nature of an
axis ; so that while in
some cases one is inclined
to regard the tube as
more strictly axial, in
others it seem to be more
homologous with a sort of
fasciation of petioles.
We shall see directly
that the receptacular tube
of Prumis contains the
basal portions of the cords
proper to the calyx and
corolla, so that we might
regard the latter as, on
the one hand, axial cords
preparatory to forming
the perianth ; or, on the
other, periantbial cords
not yet differentiated into
petioles.
Similarly, in the case
of monocotyledonous
flowers, as the Daffodil,
since petioles are less dif-
Fig. 26.— Pear with liypertrophied and sub-fasciate
petiules.
Fig. 27. — Fuchsia with foliaceous sepals and
petals (after Masters).
THE RECEPTACULAR TUBE.
95
ferentiated from blades in this class than in Dicotyledons,
tlie inferior ovary may be due to the combination of the pistil
with the united sheath-like portion of the perianth, which is
prolonged above the summit of the ovary just as it is in
Fuchsia, though it is not so pi'olonged in the Snowdrop.
Anatomy of the Receptacular Tube. — Tracing the course
of the fibro-vascular cords from the pedicel below the flower,
say of Primus Lauro-cerasus, the common laurel, there will be
found to be ten, corresponding to the sepals and petals.
The cortical tissue and epidermis are continuous throughout,
from the pedicel to the summit of the tube. It is well seen
also in the tapering end of a pear, from which the cortex
gradually widens, while the fibro-vascular cords run verti-
cally up the middle. Before the cords arrive at the border
of the free tube of the Laurel, they have given rise to the
staminal cords by chorisis, as shown in Fig. 28, a, b. Fie. a
su ^i^j^n
St/
-St. 2
Fig 28. — Receptacular tube of Prunus (after Van Tieghem).
represents a section near the edge of the tube in which both
the sepaline (s) and the petaline (p) have given rise by tan-
gential chorisis to a whorl of stamens {st. 1) ; but the petaline
by radial chorisis to another whorl (st. 2), i.e. to twenty
stamens in all. Fig. b represents a vertical view of the same.*
* The single carpel is represented in Fig. a to show the position of
its three cords, one being dorsal, and the other two marginal.
96 THE STEUCTURE OF FLOWERS.
As loni? as tlie cords are simple, i.e. up to the horizontal
lines in Fig. b, there is nothing to distinguish them from
cords of an axis, as in the pedicel. If, therefore, we regard
the branches above those levels as belonging to the floral
whorls, then the " axis " would terminate at different
heights up the receptacular tube — which would seem to be
rather too forced a view to be acceptable.
Hence it would seem preferable to regard it entirely as
axial until the portions of the perianth issue freely from the
upper part of it. We might compare these branches of the
fibro-vascular cords embedded in the axis (o those belonging
to ordinary leaves, which traverse the stem for various
distances downwards till they ultimately vanish ; only in
the case of leaves they are not coherent into a common
cord below, but remain free from each other. Moreover,
other members of the Eosacece show that they cannot be
always petiolar ; because in the rose the sepals reveal their
foliaceous character, first by always bearing rudimentary
leaflets, and sometimes stipules as well at the top of the
tube (Fig. 24, p. 93).
Further complications in the distribution of the cords
sometimes arise. Thus, in the tube of the Cherry, I find that
the petaline cords assist in furnishing the calyx-limb with
vascular cords, just as those corresponding to the arrested
stamens o£ the Primrose enter the corolla of that plant.
They either do not branch till they reach the angle between
the sepals, or else from a point lower down. The small
secondary branches are mainly directed outwards towards
the margin, as represented in Fig. 29 ; s being sepaline, and
p the petaline cords.
In examining transverse sections of inferior ovaries,
what one almost invariably observes is an inner epidermis,
on some part or parts of which are placentas with ovules,
THE RECEPTACULAR TUBE.
97
an outer epidermis, and an intermediate ground tissue,
apparently nearly uniform in character, from one epidermis
to the other (as in Fig. 14, a to e, p. 68). A definite number
of fibro-vascular cords penetrates this ground tissue. Theo-
retically, if this structure consist of two parts, viz. the
interior carpels and the exterior "tube," some line of
demarcation might be expected to be traceable ; but in the
majority of cases it would seem that, as neither the inner
epidermis of the tube nor the outer one of the carpels are
required, they are not developed at all ; and so the internal
tissues of the two organs become confluent and uniform, and
this accounts for the fact that the dorsal cords at least are
simply embedded in this common tissue. ISTevertheless, in
some cases there actually is a certain differentiation in the
tissue, as Van Tieghem has shown in the case of Alstroemeria
versicolor (Fig. 30), where a yellow band of cells marks the
Fig. 29. — Receptacular tube and
calyx-limb of Cherry.
Fig. 30. — Alstrcemeria (after Van
Tieghem).
junction or congenital fusion of the two parts (indicated by
the line in the figure).
From the pi'ecediug descriptions, it will be seen, with
regard to the sources of the cords belonsfing- to the inner
whorls, that they arise by division, radial or tangential as
the case may be ; and then the secondai-y cords thus parted
off are generally included within the tissue of the tube.
11
98 THE STRUCTURE OF FLOWERS.
These cords of tlie inner whorls may be given o£F at the
terminal point of the pedicel; that is, at the base of the flower.
In this case they may all run parallel from the base to the
summit of the receptacular tube ; or they may branch at
various heights within the tube itself, as in Prunus, described
above ; or, lastly, they may not arise until the summit of the
ovary is reached, when they pass off and enter their respective
floral organs directly. These variations occur in both free
receptacular tubes as well as when coherent to ovaries.
As an example of the first case may be mentioned AlstrK-
meria versicolor ; of the second, Galanfhus nivalis, or Snowdrop;
and of the third. Narcissus. In Alstrosmeria, all the floral
appendages have their cords distinct and independent, but
invaginated by the tube of parenchyma throughout (Fig. 30).
In the Snowdrop, the carpellary cords are distinct, but the
perianth and androecium are inserted in the pedicel by a single
verticil of cords, which becomes double higher up. Lastly, in
Narcisstis, all the parts of the flower are originally inserted
in the pedicel by six cords, of which three give rise by
successive tangential fission to a radial series composed of
the dorsal cords of the carpels, the stamens opposite to the
sepals, and the sepals themselves. Similarly, the other three
form the petals together with the whorl of stamens opposite
to them.*
In Campanula, and to some extent in Lobelia, the cords
* Ph. Van Tieghem, to whose researches I am indebted for the above,
but which I have also paralleled in other cases, rei^resents them neatly by
the following formulas, wherein ( ) signifies vascular union, and [ ] the
cellular union of the receptacular tube ; while (d) stands for the dorsal
and (?)i) the marginal cords of the carpels. Stp signifies petaline and
St. sepaline stamens.
Alstrcemeria—18 S + 3 P + 3 St, + 3 Stp + 3 CJ.
Galanfhus— 13 (S + St,) + 3 (P + Stp) + 3 CJ.
Narcissus— IS (S + St, + d C.) + 3 (P + Stp) + 3 C^].
THE RECEPTACULAR TUBE. 99
belong! no^ to the petals are given off by radial ch crisis from
the sepaline, either quite from the base of the ovary or from
about midway up the tube; they then diverge right or left at
an acute angle, and, as soon as they have reached the summit
of the ovary, pass up into the corolla.* As a rule, however,
the petaline cords of flowers are quite distinct from the
sepaline ; the six or ten, common to Monocotyledons and
Dicotyledons respectively, foi'ming the fibro-vascular cylinder
in the pedicel.
In all these and other cases the cords running up the
receptacular tube proceed originally from the petiole, and
are, so to say, even there intended for the appendages above.
Normally they retain their axial character, in being arranged
in a circle round the centre ; abnormally an appendicular
character can be revealed, by their becoming free and assum-
ing a foliaceous aspect, as in Roses or Fuchsia, as mentioned
above ; so that as long as the tube is normal, i.e. a cylinder
of cortical parenchyma with cords, it is of the nature of axis,
and can develop extra phyllomes and even buds ; but abnor-
mally, the foliar nature, usually limited to the floral membei'S
at the summit, is extended to a greater distance lower down
and the cords may now be converted into petioles, etc.
Hence it appears undesirable to call it either a calyx tube
or axial ; for these terms would seem to bind one to consider
it permanently and in all cases as being either of one nature
or the other. The term receptacular tube is therefore best,
as it certainly " receives " or supports the whorls of the
flowers ; and Teratology clearly shows that it can be either
foliar (petiolar) or axial according to circumstances.
* This reminds one of the way in which stipular appendages of
Galium, etc., are supplied with cords — not by their intercalation into
the common fibro-vascular cylinder of the stem, but — from a horizontal
circular zone of fibres which connects the cords of the opposite leaves.
100 THE STRUCTURE OF FLOWERS.
Just as the two complete vascular cylinders of two separate
floral peduncles can become fused into one oval cylinder when
the latter are " fasciated," so, too, would it seem that the cords
belonging to the separate parts of a floral whorl, where there
is no receptacular tube, can form a single united cylinder,
which one then designates as the receptacular tube.
In the case of the inferior ovary, 1 would again emphasize
the fact that the diificulty felt as to what is axial and what
carpellary is entirely removed if the undifferentiated con-
dition of the carpels be thoroughly understood. Indeed,
whenever two organs are congenitally in union the epidermis
of each is undeveloped, and the two mesophyls become one ;
so that the dorsal cords of the carpels and those proper
to the axis are alike plunged into a common tissue, which,
regarded as one, is neither wholly axial nor wholly carpellary.
CHAPTER XI.
THE FORMS OF FLORAL ORGANS.
The Form of the Perianth — Gteneral Observations. — It
requires but a most cursory observation of flowers to notice
bow gi-eat is tbe variability in tbe forms of all tbeir organs ;
and tbe questions now before us are, bow tbese morpbological
characters are correlated to tbe one process of pollination in
order to secure tbe fertilisation of tbe flower, and bow this
infinite diversity of form bas arisen.
]\Iost important differences in tbis respect follow from tbe
fact of flowers being regular or irregular, and, wlien adayjted
to insects, according as tbe boney is easily accessible or not.
Regular * flowers wben borne singly are almost always
terminal ; f and wben they are arranged in racemes, etc.,
tbey eitber stand out erect at tbe ends of tbeir pedicels so as
to be readily approacbed at any point of their circumference,
as in tbe Wallflower, or else tbey are pendulous ; under wbicb
conditions, as a rule, no particular part is favoured by tbe
* It is usual to speak of a flower as being regular or irregular ; but
the term should be, strictly speaking, confined to one whorl at a time ;
though when the corolla is irregular, the calyx and stamens are usually
somewhat irregular as well.
t The central and terminal flowers of many plants which elsewhere
bear irregular flowers are often regular, as in Horse-chestnut, Pelargonium,
several of the Scrojphularinece, as Snapdragon, Linaria, Pentstemon, etc.
102 THE STRUCTURE OF FLOWERS.
insect more than another. It is only when the flower is
situated laterally and projects horizontally, or approximately
so, with its limb or border in a vertical plane, and, moreover,
is more or less closely applied to the axis, that an insect is
compelled to alight upon it on one side only, when approach-
ing it directly from the fi-ont. It then throws all its weight
upon the organs on the lower or anterior side of the flower,
as is the case with the keel petals of papilionaceous flowers,
with the lips of Labiates, etc. ; or else its weight is sustained
by the stamens or style, or by both together, as in Ejpilobium
angustifolium, Girccea, Veronica, Larkspur, and Monkshood;
and whenever the stamens are declinate, as in Horse-chestnut,
Dictamnus, Echium, Amaryllis, etc.
Flowers which have irregular corollas mostly show various
degrees of "bilatei-al" form in their different whorls, and,
have been called " zygomorphic." Such flowers, as a rule, do
not receive the visits from so many difEei-ent species of
insects as regular flowers. These latter, not being charac-
terized by the possession of any very definite contrivances for
securing special insect agency, are accordingly visited by a
much greater number and variety than those flowers which
have become markedly adapted, and consequently restricted
to particular visitors.
It must not be forgotten, however, that regular flowers,
if the tube leading to the honey be very contracted and more
or less elongated, may become almost as much exclusive as
very irregular ones ; for such flowers are mainly restricted to
Lepidoptera.
The following examples may suffice to illustrate these facts.
Ranunculus acris, which is perfectly regular and with no
specialized structure, is visited, according to Miiller, by more
than sixty different species of insects ; whei'eas species of
Aconitum and Delphini^im, the two most highly differentiated
THE FORMS OF FLORAL ORGANS. 103
and the only genera with irregular flowers of the same order,
are adapted to, and mainly visited by the larger species of
bees. Similarly of conspicuous and regular flowers of
Bosacece, Pnmus comviimis has twenty-seven visitors ; Spircea
JJlmaria, twenty-two ; Euhus fruticosus, sixty-seven ; Fragaria
vesca, twenty-five ; Cratcegus oxyacantha, fifty-seven. On the
other hand, of irregular flowers, Digitalis jptirjpurea has only
three useful visitors ; Linaria, nine or more species of bees,
and Orchis mascula only eight.
As an instance of a long-tubed regular flower, Lonicera
ccerulea may be mentioned. It is adapted to humble-bees, by
which it is chiefly visited. Similarly, the flower of the
Honeysuckle, the Jobes^of^ which are scai-cely if_ at all
UT^^ual, admits only a few_lepidopterous insects which can
reach the honey. So, too, Asperula taurina, which has a tube
Q'to 11 mm. long, is visited by nocturnal Lepidoptera.
^The Origin of Ikregularity. — With reference to the
theoretical origin of irregular whorls, I assume that they
have all descended from regular ones through external
influences.* "With regard to terminal, regular flowers the flow
of sap is directed equally, radially, and in all directions on
reaching the floral receptacle, and there is no inherent
cause to m.ake a terminal flower zygomorphic, or to induce
one or more parts of any whorl to grow differently from the
rest. Hence the primary cause of irregularity must come
from without, and I regard this cause as issuing from the
insect itself ; namely, the mechanical influence of its weight
and pressures. To this external irritation the protoplasm of
the cells responds, and gives rise to tissues which are thrown
out to withstand the strains due to the extraneous pressures
* The fibro-vascular cords of tlie pedicel are arranged at regular
intervals, and are perfectly symmetrical around the medulla in irregular
flowers, just as they are in the case of regular ones.
104! THE STRUCTURE OF FLOWERS.
of fhe insect, and so the flower prepares itself to maintain an
equilibrium under the tensions imposed upon it, and irregu-
larities are the result. Such, for example, occur in bilobed
calyces, as of Furze and Salvia; in the many forms of " lips,"
or labella,* and enlarged anterior petals ; in dependent
stamens, as of Aconite and Epilobium angusHfoUum, or in the
more usually declinate condition, as of Bidamnus, Amarijllis,
etc. la these latter instances, in which the androecium bears
the burden, the anterior petal is either, as a rule, unaffected,
and shows no increase in size, or else there is a tendency to
atrophy, so that it is reduced in size, as are the keel petals
in Amherstia. It is sometimes even wanting altogether, as
in the Horse-chestnut.f
* If the flower be resupinate, then it is the posterior organ which,
now being in the front, has become enlarged ; as in Viola and Orchis.
t There has been more than one investigation into the causes of
zygomorphism (as by Vochtung, Ber. Deutsch. Bot. GesselL, iii. (1885),
p. 341 ; and Pringsheim's Jahrb. f. Wiss. Bot., xvii. (1886), p. 297 : also,
by Dr. F. Noll, Arbeit. Bot. Inst. Wurzburg, iii. (1887), p. 315). H.
Vochtung distinguishes three different sets of causes as producing
zygomorphism, viz. gravitation only ; gravitation acting on the consti-
tution of the organs ; and the constitution of the organs alone.
An objection to gravitation pure and simple is, that all flowers would
be more or less subject to it, and become more or less zygomorphic
accordingly. It does not account for the infinite diversity in the forms
of zygomorphic organs ; nor for the many correlations for insect
fertilisation which exist between all parts of the flower. If to
gravitation, however, we add the weight of the insect, which simply
intensifies it, and couple ■(■(•ith this the pressures exerted by the insect
in various directions, then we have an adequate theory, which
gravitation alone could not supply. When Vochtung speaks of " consti-
tution alone" as a cause, I presume he means hereditary effect. If so,
I would quite agree with him, as zygomorphic flowers now grow to be
such from purely hereditary influences. When, however, he would
attribute the form of Epilohium ang^^stifolium to geotropism, as the
supposed cause of the lowermost petals bending upwards, and the
stamens and style downwards (see Fig. 34, p. Ill), I do not see how
THE FORMS OF FLORAL ORGANS. 105
Compensating processes tlius come into play, so tbat
while some parts are enlarged others are diminished, the
former always having to bear the strains, while the latter are
free from them. Thus the lip of Lamium consists of one
much-enlarged petal, which forms an excellent landing-place,
but the two lateral jjetals, not being required, are atrophied
to mere points. Similarly, while the two posterior petals
enlarge to form the hood, presumably due to the backward
thrust of the insect's head, the posterior stamen has vanished
altogether. The gamosepalous calyx nosv furnishes its aid
to support the slender tube of the coi'olla, not only by
doubling its number of ribs, but by uniting them all together
by means of a sclerenchymatous cylinder within the mesophyl.
If the tube of the corolla be very strong and well able
alone to support the insect, the adhesion of the filaments
being also a powerful addition to its strength, then the calyx
often remains polysepalous, as occurs in the Foxglove,
Snapdragon, Petunia, etc.
If, instead of the anterior petal forming the landing-
place, the tube of a gamopetalous corolla has enlarged so as
to admit the ingress of an insect which partly or entirely
crawls into it; then it is this tubular part which, moi-e
especially having to bear the strain upon it, bulges outwards,
or becomes more or less inflated in form ; while the lip or
anterior petal, not having to bear the entire burden, is not
particularly enlarged, if it be at all. The Foxglove and
Gloxinia, as well as Petunia to a slight extent, illustrate this
adaptation in irregular flowers, while "campanulate" flowers
afford examples amongst regular ones.
gravitation can act in any otlier way than " downwards." Bat if one
observes how a humble-bee suspends itself on the stamens while its
body, so to say, thrusts the petals aside and upwards, we find a much
more satisfactory interpretation in the theory I have proposed.
106 THE STRUCTURE OF FLOWERS.
If no more than the head of an insect enter the flower,
then the corolla shapes itself to fit it. Thus Snowberry,
ScropJmlaria, and Epipactis only admit the heads of wasps,
which are the regular visitors of these plants.
Other instances in which the limb is not much, if at all,
enlarged occur in flowers especially adapted to Lepidoptera.
Hovering, as they generally do, before the flowers, and in-
serting their long proboscides while on the wing, there is no
tendency to develop larger anterior petals, but the irritation
affects the tube only, which thus elongates and contracts,
resulting in little or no irregularity in the flowers, as in
Oenothera biennis, in which the calyx tube has contracted, or
in Honeysuckle, which has a tubular corolla. If bees or
other insects 'visit the flower as well, then some degree of
obliquity may result, as in Teucrium Scorodonia.
Thus, then, may we get a rationale of the structure and
form of floral organs, and their great diversity corresponds to
a similar diversity in the insect world ; for the flower, if it
be visited by many, will presumably take a form correspond-
ing to the resultant of the forces brought to bear upon it ;
if visited by few, it will shape itself in accordance with the
requirements of its principal visitors ; and thus is it that
while some easily accessible flowers receive many classes of
insects, others are restricted to few, or even one ; and then
the insect and the flower are so closely correlated as to almost
impress upon one the idea that they were mutually created
for each other !
The accomiDanying figures of Buvernoia adhatodoides
may illustrate my meaning. Looking at Fig. 31, a, alone (sup-
posing we know nothing of insect visitors), one might ask,
For what use is this great irregularity ? why and how has it
* From a pajaer by Mrs. Barber, Journ. Lin. Soc. BoL, vol. xi.,
p. 469.
THE FOKMS OF FLOrvAL ORGANS.
107
a 6
Fig. 31. — Duveriioia adhatoduulcs.
come into existence ? And no answer is forthcoming. ITow
turning to Fig. 31, h, we see one use at least. The weight of
the bee must be very
great ; and the curious
shape of the lip, with
its lateral ridges, is evi-
dently not only an ex-
cellent landing-place,
but is so constructed
as to bear that weiarht.
Moreover, the two
walls slope off, and are
gripped by the legs of
the bee, so that it evidently can secure an excellent purchase
and can thus rifle the flower of its treasures at its ease.
Irregular corollas are very numerous, but certain prin-
ciples, traceable to insect action, govern their forms. In the
first place, the side upon which the insect rests, or at least
upon which its weight is thrown, is always enlarged, and
mostly forms the landing-place. It is almost always the
antei'ior petal; if, however, the pedicel or ovary has been
too slender to support it, then it has sometimes become
twisted, and the flower is said to be resupinate, so that the
posterior petal becomes anterior in position, and is now the
larger one, since it supplies the landing-place for insects, as
in Orchis. Fumaria might be called semi-resupinate, as the
corolla has only rotated through 90°. A slight modification
occurs in the "Bee-orchis," Oplirys apifera, which is usually
described as having a twisted ovary like a true Orchis ; but in
this species it has scarcely if any twist at all ; the flower,
however, is bent over to the opposite side of the stem, so that
while the posterior petal is still the labellum, the ovary has
itself remained perfectly straight.
108 THE STRUCTURE OF FLOWERS.
The next point to notice is that when the anterior petal
is enlarged, the posterior one or more often enlarges also,
while a corresponding tendency to atrophy affects the lateral
ones. This is seen in many species of Leguminoso}, Scrophu-
larinece, and Labiatce, and in zygomorphic flowers generally.
It occurs thus in the wing petals of many papilionaceous
flowers, as is particularly well seen in Onobrychis. The
immediate causes, I repeat, I would recognize in the weight
of the insect in front, the local irritations behind, due to the
thrust of the insect's head and probing for nectar, coupled
with the absence of all strains upon the sides. In some
papilionaceous flowers the wing petals form a landing-place,,
as in Indigofera and Phaseolus. Whenever this is the case,
they too are enlarged, as the lateral ones are in Fig. 31, and
undertake the duty impressed upon them.
When, therefoi"e, one finds as an invariable rule how the
fi'ont petals enlarge when flowers are compacted and visited
only from the front, and thus become irregular ; and as
such often occur in orders where flowers are normally regular,
as Iheris, Centaurea, Heracleum, etc. ; and, moreover, when
the same phenomena appear in orders having no affinity
between them, as in Labiatce and Orchidece; and are, indeed,
to be found throughout the length and breadth of the floral
world, one is justified in attributing such irregularities to a
common cause, that being, according to my theory, the
responsive power of protoplasm to the irritations from with-
out, set up by insect and other agencies.
Many other special cases might be described from the
different orders of plants, but the above will suffice to illus-
trate this principle of responsive action with resulting correla-
tions to insect agency. I would here, howevei', call the reader's
attention to the mechanical arrangement of forces as shown
in Lamium and Echium, whei'e it will be seen that the
THE FORMS OF FLORAL ORGANS.
109
adhesions of the stamens to the corolla furnish the fulcra,
the cohesion of the petals into a tube affording a greatly
increased power of resistance ; the weight of the insect on
the labellum or declinate stamens is, of course, vertically
downwards, and the line of the resultant, which the lip
in Lamiuon and the stamens whenever declinate have to
exert, passes through the point of meeting of the first
two, and so sustains the insect while visiting the flower.
Other and analogous instances will be described here-
after.
Good illustrations of the occurrence of great thickenings
just where the strain will be most felt, may be seen in the
slipper-shaped flowers of Calceolaria (Fig. 32), Conjanthes,
and Oypripedium. Thus Calceolaria Pavonii
possesses a thick ridge along the upper-
edges of the curved basal part, which
carries the inflated end upon which the
bee stands, and which it depresses to get
the honey. In this species it may be
noticed the anther-cells are separated (a),
so that they can oscillate as they do in Fig. 32.— calceolaria Pa^
n T . T ^ • T ji T •j'lTT vonii (after Kerner).
balvia. In Cypripedmm the edge is folded
inwards, thus strengthening the same part; while in Corij-
anthes the lower portion is enormously enlarged, thus acting
as a powerful spring which forces the anterior end of the
labellum to be in close contact with the column.
The Origin of Irregularity in the Andrcecium. — As it
is with the perianth, so is it with the androecium : if the
petals are regular the stamens are usually regular also ; but
when iin'egularity occurs in the corolla the staminal whorl
follows suit, and the position and form of the stamens are
equally correlated to the effectual pollinatioa of the flower.
Thus, as hyperti'ophy affects the anterior side of the
12
110
THE STRUCTURE OF FLOWERS.
flowers of Labiatce, the anterior stamens are almost invariably
the larger pair. On the other hand, atrophy has affected the
posterior side of the staminal whorl, causing the total loss of
the fifth stamen, and, to some extent, a reduction in length
of the next pair of filaments.
When the weight of the insect is thrown upon the
stamens, they either hang downwards, and the insect
is suspended upon them, as in Epilohium angustifoUicm, or
else they become declinate and then the anterior petal, being
relieved, does not enlarge, either .remaining of the same size
as the rest, or else diminishes, and may even vanish alto-
gether. Thus Vallota, with its perfectly regular perianth
and spreading stamens, may be compared with Aman His,
which has declinate stamens and a small anterior petal.
The terminal flower of a " thyrse " of the Horse-chestnut, like
the terminal flower of a "truss" of Pelargonium, is often
regular with spreading stamens, whereas the normal flowers
have declinate stamens, and
usually only four petals, the
fifth or anterior one being
altogether suppressed.
In some flowers the sta-
mens are dependent at first,
but their anthers rise up when
dehiscing, and so the fila-
ments become declinate in
the pollinating stage. This
is the case with Delphinium,
Epilohium angustifolium, and
Dictavxnus (Fig. 33). In this
flower the anterior petal is
of much the same size as the others, but is often displaced
(Fig. 33), and not immediately below the stamens, — this
Fig. 33. — Dictamnus (after Tieghem).
THE FORMS OF FLORAL ORGANS.
Ill
lateral displacement of the anterior petal being not always
carried out, as it is in the next flower to be described.
In Epilohmm angustifolium CFig. 34) and Godetia, wliicli
have no anterior petals, the bees cling to the dependent
stamens, while the petals have become permanently displaced,
the two lower being somewhat raised, so that the angular
distances are not the same. In Azalea and Rhododendron
there is no anterior petal, but the posterior one is slightly
enlarged, and this alone possesses extra colouring and the
"path-finder." The stamens, being declinate, carry the
insect without the aid of the corolla, so that the antero-lateral
Fig. oi.—Epilobium angustifolium. Fig. 35. — Veronica Cham(zdrys (after Miiller).
pair of petals, not sharing in the support of the insect, are
not enlarged at all.
In Circcea and Veronica Chamcedrys (Fig. 35), the insect
clings to the two stamens and style ; and the anterior petals
are not enlarged, while in the latter flower it is, as iisually
the case, the smallest, the stamens of Veronica being attached
to the lateral petals have to supply the fulcra for leverage,
and consequently these have now become relatively hyper-
trophied.
In many flowers which have sub-declinate stamens, the
latter lie in a more or less boat-shaped anterior petal, show-
ing that the action of the insect has somewhat affected both
the whorls together, as they have each some share in carry-
112 THE STRUCTURE OF FLOWERS.
ing the insect. Such is the case in the Ocimoidece of Lahiatce,
in GoUinsia bicolor, the " Lemon-scented " Pelargonium, etc.
CoKRELATiON OF GROWTH. — I have Only referred to the
forms of flowers as grouped under the terms "regular" or
" irregular," and alluded to a few instances ; for it is not my
object in this work to merely give illustrations of various
kinds, which are presumably well known to the reader, but
to offer a rationale of the whole, without, however, attempt-
ing to say how each individual shape has actually come into
existence. To do this, it would be impossible in the present
state of our knowledge of the history of flowers; my object
being to suggest a probable cause, namely, the mechanical
influence of insects, without excluding others which we
cannot trace. Nutrition, however, must be always borne in
mind as an important one, hereditary influences as others —
as, for example, in the restoration of an irregular flower to a
condition of regularity, as occurs in Linaria, Lamiifni, Glox-
inia, etc. The point, however, which I would specially
emphasize is the correlation existing between the several
parts of the organs, so that, regarded collectively, they all
conspire to secure one and the same end, that being the
pollination of the flower. Thus, as I have shown above, the
caljx of Salvia has a form and structure correlated to the
tube of the corolla ; the corolla has a form in strict adapta-
tion to the weight and pressures of the insect which rests
upon the lip. The stamens are, again, coi'related to the pres-
sures brought to bear upon them, and have grown in
response, forming the remarkable lever-processes, which are
also found in species of Calceolaria. Lastly, the style and
stigma are correlated to the position of the anthers. Hyper-
trophy in one direction has brought about atrophy in
another, so that the two posterior stamens, are rudimentary,
while the fifth has vanished altogether.
THE FORMS OF FLORAL ORGANS. 113
Now, it might be argued, that when one organ changes
its form others must do so in obedience to the " laws of cor-
relation of growth," as Mr. Darwin showed to be the case
with the feet and bills of pigeons. In plants, however, the
connection between various parts, even in close proximity, is
by no means so intimate as between different organs of the
higher animals; while the theory advanced here gives a
common interpretation for the whole of the so-called correla-
tions found in any flower. That one is justified in saying
that correlated growths are much restricted in plants, is
clear from the experience of horticulturists ; thus, while,
e.g., the varieties of pease are infinite, they having been the
object of selection alone, the flowers which produce them
have virtually remained unchanged.
A single coincidence has little or no scientific weight as
indicating cause and effect. It is only when coincidences
can be mliltiplied that they furnish a probability of a high
order; which, even if they do not admit of a verifiable ex-
periment, still furnish a moral conviction, which, by the rules
of philosophy, is equivalent to a demonstration. Now, this
is exactly the case with irregular flowers. They always
occur in similar positions ; they are always constructed so
that the insect in adaptation to them can gain access to
the honey in the easiest way ; their organs are so situated
that the pollen should be transferred accui'ately to the
stigma, etc. And when we find them distributed every-
where throughout phanerogamous plants, the probability
that the same or analogous causes have brought them about
is of a very high order indeed
Moreover, since we have abundant evidence of the re-
sponsive power of protoplasm to build uj) tissues wherever
they are required, I am not assuming an influence on the
one hand without ample evidence of the probability of the
114 THE STRUCTURE OF FLOWERS.
responsive action on the otber, coupled, of course, with here-
ditary and other influences which iix the variation. Thus,
then, as I believe, all flowers as we have them now, which
are in perfect adaptation to insect agency, are the outcome
of the resultant of all the forces, external and internal, which
the insect has actually brought into play or stimulated into
action by visiting them for their honey or pollen.
The belief that such processes may have grown in
response to mechanical irritations is supported by some
interesting experiments made by Mr. O'Brien, of Harrow,
who has kindly favoured me with the following remarks :
" With reference to impressions conveyed by ' nervous ' force
in Orchid flowers, whereby the expansion of the sepals and
petals signifies to the reproductive organs that the time for
fertilisation has arrived, I have observed that the periods of
maturing and of decay may be^either arrested or hastened in
certain orchids by artificial means. With reference to arrest-
ing decay, I took such flowers as Stanhopea and Coryanthes,
which have large membranous sepals, and which, in the
ordinary course of events, become reflexed soon after the
opening of the flowers, and shoi"tly afterwards wither.
These are then followed by the other parts. By seizing the
opportunity as soon as they expaijd, and by passing a thread
round them, so as to keep them in the condition of the flower
when just on the point of expansion, they may be kept good
for a long time, the flowers evidently, as it were, not
realizing the increased lapse of time, and being unaware that
they had passed the period when they would have been ready
for fertilisation. When so secured, a flower of Coryanthes
speciosa on my table kept fresh three times as long as it
would have done on the plant. The dripping of the water
from the horns above the bucket is also arrested. Finally,
on releasing the ligature, the broad wing-like sepals inime-
THE FORMS OF FLORAL ORGANS, 115
diately became reflexed, and the water commenced to drip.
Shortly afterwards the wings shrivelled up, and the flower
decayed in the same manner as it would have done a week
before if left to itself on the plant.
" I will now give an example of deceiving a flower by
artificial means, by making it believe that its fertilisation
has been accomplished without its having taken place at all.
Miltonia Itusselliana carefully guards the approach to the
column by closing the petals over it ; but on pushing these
petals aside with a pencil, I always found that the labellum
faded, and withdrew upwards very soon afterwards. The
showy portion of the flower, evidently having had it con-
veyed to it that its duty was performed, then followed suit.
On carrying the deception still further to the reproductive
organs, by placing small pieces of grit on the stigma, I
found that the ovaries would swell in many cases, just as
though the flower had been properly fertilised by pollen.
This same result often takes place in Orchid flowers under
cultivation, and seed-vessels are obtained of full size, but, of
course, with no vitality in the grains within."
As an analogous instance, I will add that it is the belief
of M 0. Beccai'i that ants are not only responsible for the
remarkable growths in Myrmecodia and HydtiopJiytum, etc.,
but that they have become indispensable for the healthy
development of such plants. The investigations of M. Treub
on Bischidia, the pitchers of which are frequented by ants,
like the stipules of Acacia sphcerocephala, seem to justify one
in concluding that genus also to be one of these so-called
"Ant-plants " (Ann. du Jard. Bot. de Buitenzorg, in., p. 13).
Dr. Lundstrom also believes that the habit of producing
" domatia " is now hereditary, without the actual presence of
the insects (see Journ. Boy. Micr. Soc. 1888, p. 87.)
11() THE STRUCTURE OF FLOWERS.
CHAPTER XU.
THE ORIGIN OF " ZTGOMORPHISM."
BiLATEEAf. Symmetry. — A feature abundantly illustrated
through the flowering world, in the construction of irregular
flowers which are highly specialized for insect agency, and
of which the Labiatoe and Scrophularinece, for example, fur-
nish many instances, is the h^^pertrophy of the corolla in
the direction of an antero-posterior plane, giving rise to a
bilateral structure.
On the one hand, the lips of various kinds, as also the
keel, and often the wing petals too, where they help to sup-
port the insects in papilionaceous flowers, are accounted for
by the weight of the insects bringing about a responsive action
in the protoplasm, thus determining a flow of nutriment to
the parts demanding it, which now grow into the forms re-
quired. On the other hand, the opposite or posterior side is
often influenced as well, so that, as in Lainium, the lobes of
the two posterior petals have grown into the enlarged hood.
The cause of this I take to be the powerful tlirust which
insects exert against the posterior side while their weight is
expended on the anterior. If a humble-bee be watched, as
represented in Fig. 31 (p. 107), it will be seen how eagerly
and determinedly it forces its way into a corolla-tube if it
expand upwards, as in Duvernoia or Lamium. All the pres-
sure is exerted along the median plane, like an oblong wedge
THE ORIGIN OF " ZYGOMORPHISIVL" 117
thrust into a circular tube. The corolla then " gives," as
it were, and expands along the antero-posterior plane. The
calyx follows suit, and often assumes a bilobed funnel-shaped
tube as well ; while the lateral lobes of the corolla tend to
atrophy, since they do not lie along the line of the pressure
due to the weight of the insect (see Fig. 406, p. 126.)
If the floral organs be imagined to consist of some
plastic, extensible, but not elastic substance, and be subjected
to various pressures, strains, thrusts, etc., in imitation of the
motions of insects, it is readily conceivable how the parts
would yield, stretch, or bulge, and become fixed into shapes
very closely resembling what has actually taken place in
natur§. In reality, of course, the ability to grow in response
to the forces applied is to be substituted for the theoretical
plasticity and extensibility of the imaginary mateinal.
Compensatory degenerations occur in various directions,
as in the atrophy of the lateral petal-lobes of Lamium, the
loss of the fifth posterior stamen, the reduction in length of
the filaments of the posterior pair of stamens. In this latter
respect Nepeta differs from other genera , but as we can
readily conceive bow all sorts of differences may and do exist
in the direction and degree of the forces applied
to flowers, some exceptional ones must have
occurred in that genus which has favoured the
growth of the posterior pair, so that they have
become the longer ones ; for there is no rule
without an exception. As another illustration,
Teucrium may be taken. In this genus the
"hood" is entirely wanting; but here, again, psg 36._.Fiower of
the interpretation is that, no hypertrophy Teucrium (after
^ _ ' J i f J PQt_ Jllag., 1279).
having been applied to them, the two petals
of which it is composed have become reduced in size and
"cleft," as shown in Fig. S6, of T. (Teucris) orientate. Bees,
118 THE STRUCTURE OF FLOWERS.
•when visiting the flowers, hang downwards upon the corolla,
as the lip and adjoining lobes are in one vertical plane, and
give no thrust upon the posterior side. All weight, therefore,
is thrown upon the front, just as it is on the stamens of
Epilobium angusti folium, described above. Their weight has
consequently, so to say, " split " the hood in twain, and the
stamens now stand erect in the cleft.
The peculiar form of the corolla, with the whole of the
limb dependent in a vertical direction, must throw the weight
of the insect so much to the front, that the leverage will be
at a considerable disadvantage — much more so than when
the insect stands more directly over the tube of a corolla;
which latter, in that case, is often strengthened by that of
the calyx. To meet this difficulty the pedicel is curved over
at the top, as may be readily seen in our common Wood-
sage, and forms a spring, while hypertrophy has attacked the
posterior side of the calyx, in that it now carries two extra
1 marginal ribs, one on either side of the pos-
,j^ ,,j terior dorsal one, as shown in the accompany-
d d ing diagram. This is exactly the reverse of
d d what occurs in Salvia, and others which are
much more strengthened on the anterior side, when the
insect stands more directly over the centre of the flower.
Additional aid is also gained by the tube of the corolla of
Teucrium being resilient ; the anterior pair of stamens form
two thick ridges, much aiding it in this respect ; the posterior
pair, however, are, so to say, " sunk " into the tissue of the
corolla as to be invisible in a transverse section.
Transitional Forms. — We may sometimes, as it were,
catch the formation of irregular and zygomorphic flowers in
the process of formation ; for it not infrequently happens
that one genus will be irregular amongst its allied regular
ones. Thus Verbascum and Petunia are transitional genera,
THE ORIGIN OF " ZYGOMORPHISM." 119
and stand intermediate between Solanaceoe and Scrophula-
rinece. The former genus has a less zygomorphic corolla than
many of the latter order, and also retains the fifth stamen
in varying degrees of utility. We might regard both these
genera as Solanaceous, and on the road to acquiring zygo-
morphism, but to which neither has yet fully attained.
" The short-tube [of Yerhascum nigrum'] widens out into
a flat, five-lobed limb, which takes up an almost vertical
position ; tlie inferior lobe is the longest, and the two
superior are shorter than the lateral lobes, so that an insect
settles most conveniently upon the inferior. The stamens
project almost horizontally, but curve slightly upwards from
the tube, and diverge slightly from one another ; they
alternate with the petals, and again the superior is the
shortest, and the two inferior longer than the lateral ones.
. . . The style is shorter than the inferior stamens, and
bent down slightly below them "
From this description, taken from Miiller's work,* which,
with slight modifications, would describe Petunia as well,
the reader will see how these flowers fulfil the requirements
of self-adaptation to insect agency ; and in every point of
detail are they responding to the forces impinged upon
them. The weight of the insect being w^ell to the front,
hypertrophy is commencing on the anterior side, while
atrophy follows on the others, there being no special thrust
as yet on the posterior side of the flowers
There are many other genera and species which stand in
intermediate positions between others, and it has always
been a matter of doubt to systematists as to which they
should be referred. The interpretation of their existence I
take to be as here described, namely, that they are in an
actual transitional state, brought about by insect agency, if
♦ Fertilisation, etc., p. 429.
120 THE STRUCTUKE OF FLOWERS.
they be flowers visited; or by fluctuating conditions of nutri-
tion, if not ; and then, arrested in that state.
A further remark on a significant point may be added on
Fetunia. In this flower, as in Verbascum, the limb of the
corolla stands in a vertical plane, the anterior lobe is a
trifle larger than the others, the five stamens have a slight
tendency to be atrophied on the posterior side, while the
stio-ma has become just so much displaced as to hinder self-
fertilisation. This property is, however, by no means yet
lost. Florists are aware of it, and find it necessary to self-
fertilise, but not to cross, these flowers artificially to secure
plenty of seed ; Mr. Darwin corroborates this (Cross and Self,
etc., p. 193).
We have, then, here a case, but by no means an isolated
one, in which the forms of the floral organs are undergoing
a change, but the physiological chai-acters of the essential
organs have not yet been influenced by the external stimulus,
so as to become more or less inert upon one another, as is
sometimes the case in highly differentiated flowers.
Indeed, it would seem to be a universal rule that morpho-
logical changes are more readily acquired than physiological
barrenness ; as by far the great majority of plants have
retained their self-fertilising powers ; and, when they have
lost it, it is easily and rapidly reacquired when the necessary
conditions are supplied.
Eclmim is another instance of almost a single genus
amongst others of the same order characterized by great and
persistent regularity. Rhododendron and Azalea may be
compared with other genera of Ericacece, and the reader will
I'eadily suggest others.
Sometimes the irregularity is confined to the stamens or
style, or both, which may have a tendency to become decli-
nate, as in Calluna, in some Liliaceous and Amaryllidaceous
THE ORIGIN OF " ZYGOMORPHISM."
121
plants, as Narcissus Corbularia. In Anagallis arvensis and
Lyclum harhariim tliez^e is nothing but an obliquity in the
style observable.
In all the flowers which tend to show irregularities the
rule is that the corolla-limb stands in a vertical plane, so
that the flowers are visited from the front. This I take, as
mentioned above, to he generally a primary necessity for
bringing about irregularities of all kinds. There are some
campanulate and pendulous flowers where irregularity occurs
in the lengths of the filaments or the size of the anthers.
Thus, I have observed great fluctuations in the stamens of
Narcissus cermms : some of these I have illustrated in Fig. 37.
I noticed that a peduncle always
bore the same form in every
flower of its umbel. There
were mostly three flo"wers in
each, as of a, 6, and d; one
specimen of a and one of e had
only a single flower; and one
of c had two flowers. In a, b,
c, d, the three short stamens,
as well as the three long ones,
were all of the same height, respectively ; but in e one of the
shorter set was taller than the rest.
Similar fluctuations are not at all uncommon in cultivated
heterostyled plants, as Primroses ; as will be alluded to again
in discussing the conditions of heterostylism.
In Fritillaria Meleagris, though no irregularity occurs in
the perianth leaves, it often appears in the androecium, and
is more especially observable in the lengths of the anthers.
This would seem, therefore, to be another instance of
incipient change.
Calluna vulgaris is likewise just commencing to be
13
Fig. 37. — Xarcissus cernuus.
122 THE STRUCTURE OF FLOWERS.
irregular. The flowers are almost horizontal, closely com-
pacted against the axis, and consequently not readily visited
on any side except from the front. The style and stamens
curve upwards, so that " the smaller bees and flies thrust
the head or proboscis from the front into the flower, and the
upward curvature of the style and stamens causes the insect
to enter by the lower half of the flower, and so to get dusted
with pollen from above." *
Miiller also notices, about this flower, that " the style,
which even in the bud overtops the stamens, grows very
markedly after the flower opens, as the flower itself does.
As a rule, it attains its full length only after the anthers
have completely shed their pollen, at which time also the
four-lobed stigma reaches its full development."
He gives five figures of Saxifraga Seguieri to show the
progressive stages of development. In the first or female
(protogynous) condition the stigmas only are mature, the
anthers, petals, and sepals being far from having attained
their full size. It is not until half the anthei-s have shed
their pollen, and the others ready to do so, that the flower
attains its complete dimensions f
I refer to these facts, which are equally applicable to
many other flowers, to show that growth normally continues
after insects have commenced to visit flowers ; so that there is
plenty of opportunity for the petals, stamens, etc., to respond
to the insect's action before reaching maturity.
Dr. F. Noll has investigated the various movements of
zygomorphic flowers during growth, resulting in the external
position of the flower; and he finds that the excess of
weight on one side is, when necessary, counterbalanced by
active tensions (see Jl. B. Mic. Soc, 1887, p 612 and reffs.).
* Fertilisation, etc., p. 379. t Ii>id, p. 244.
CHAPTER XIII.
THE EFFECTS OF STRAINS ON STRUCTrKES.
Vegetative Organs. — In explaining the origin of ii-regnlar
flowers by insect agency, it will not be amiss to fortify the
theory by describing other instances apart from flowers, and
to add further results which I believe to accrue from the
persistent action of insects on the one hand, and a ready
response on the part of the organ on the other.
Researches into the anatomy of stems have proved the
existence of this responsive power. Thus, a tree will develop
wood in a particular direction if it be compelled to meet
special strains imposed upon it ; for Andrew Knight found
that when trees were allowed freedom in one direction only,
and were thus made to oscillate in definite directions, either
east and west or north and south, the stem became elliptical
in section, the long axis corresponding to the direction of
oscillation. Mr, Hei^bert Spencer has also described how
Cactuses, if submitted to particular strains, develop wood to
meet them.
The various kinds of the supporting tissues of pedicels,
such as collenchyma, sclerenchyma, the so-called liber-fibres
as well as true woody fibre, are all so many contrivances of
the stems to support the weight of the flowers and fruits, and
to overcome gravity So, again, in the case of apples and
peai^s, if they hang vertically downwards they grow as
124
THE STRUCTURE OF FLOWERS,
sjmmetricallj round the insertion of the stalk as an orange ;
but if the pedicel projects obliquely from tlie branch, they
then thicken along the upper side, forming a sort of buttress
running down into the stalk, which also itself tends to
thicken. This enlargement, which gives the peculiar " lop-
sidedness " to several kinds of pears especially, and in a
lesser degree to some sorts of apples, is simply due to the
fact that the force required to counteract the resultant of
the two forces, gravity and tension — which act vertically
downwards and along the stalk, respectively — must be
increased in proportion as the direction of the stalk ap-
proaches the horizontal one. The accompanying diagram
(Fig. 38) represents the basal end of a Dr. Jules Guyot pear
- and in the position in which it -hangs
upon the tree. The letter ty (weight)
is in the line of gravity, t (tension)
acts along the stalk, while r coun-
teracts the resultant, which tends to
tear the pear fi-ora the stalk at the
upper side. This strain must be
met, and the increased thickness
along this upper side enables the pear
to resist it, and thus prevents the
fruit, especially if it be a large and heavy kind, from being
wrenched from the stalk.
A somewhat similar development often occurs with j^lums
and lemons ; only, as there is no receptacular tube in either
case, the weight of the fruit causes them to produce a thick
fold in the carpel on the under side, together with some
degree of hypertrophy on the tipper^ where the tension occurs.
It is not uninteresting to notice how branches of trees
similarly sustain the strain produced by their o^vn weight.
This is done by growing at an acute angle (originally caused
Fig. 38.— Diagram of tlie end of a
JJr. Jules Guyot pear.
THE EFFECTS OF STRAINS ON STRUCTURES. 125
39)
by arising in the axil of a horizontally inserted leaf), much
more often than in a strictly horizontal direction. The
branch, after growing for a short distance upwards, generally
bends downwards, assuming just the same curvature as of
declinate stamens which have to support the weight of
insects.
If the vertical line in the adjoining diagram (Fig.
represent the trunk, and the curved
line a branch, the insertion at /sup-
plies the fvilcrum, w is the weight of f\
the branch, and acts in a vertical
line, p is the power required to
coxmteract the resultant of these two
forces.
When thp bnno-b brpalcs pUT,p-p Fig. 39.— Diagram of a tree and
Yv lien me oougn oreaKs, enner i^janch, iUubtiating the distii-
through an additional weight of snow bution of furces.
or by its own weight on decay, it snaps off at the point p,
i.e. the place where the force acts, as it can no longer over-
come the resultant of /and to.
Reproductive Organs. — Applying these principles to
floral structures, we have already seen in how many ways
the strain to which parts of flowers are subjected, through
the weights and pressures of insects, are met and overcome.
In a large number of instances the organ becomes curved,
and assumes the character of a spring, yielding on pressure,
but recovering its position when pressure is removed. It is
often so with the claws of the petals of papilionaceous
flowers, the stamens of Dicentra, Corydalis, and Veronica
Chamcedrys. Similar structures are seen in many styles, as
those of Pansy (Fig. 54), and in genera of PolygalacecB.
All declinate stamens partake of it to a more or less
degree. The distribution of the forces brought into play to
support the insect is exactly the same as when a bough
126
THE STRUCTURE OF FLOWERS.
Fig. 40(1. — Diafiram of declinate
stamens, illustrating the distri-
bution of forces.
has to support its own weig'ht, as will be easily understood
from what has been described, and by referring to the
diagi'am (Fig. 40a).
If the tissue does not remain firm
under pressure, then the lever-action
of a spring may fail to be secured,
and the organ will oscillate freely,
as on a pivot. This 1 take to be
another result of a constant, but of
course uncon.scious, eifort of the insect
to push the oi'gan in a certain direc-
tion. It is thus that anthers become
versatile, and oscillate, and may
become even inverted in position, Avhen pollination is being
effected by insects. Consequently anthers normally intror.se
can be made to assume a pseudo-extrorse position. This
happens with some Cruciferce as Cardamine pratensis, Tulips,
etc. A similar cause I would attribute to the formation
of the oscillating anthers of Salvia, and of the species of
Calceolaria^ as C JPavonii, which form the
section Aposecos of that genus, as shown m
Fig. 32, a, p. 109
As an example of an entire flower illus-
trating the distribution of forces, the accom-
panying figure of Lamium album (Fig. 406)
will explain how the forms of the calyx and
corolla are adjusted to bear the weight of
the insect. The bee alights on the lip and
then partially crawls into the expanded
mouth of the corolla, so that its weight
now lies in the direction of to. The fulcrum will be at /,
and the i-esultant of these is in the opposite direction to r.
Tbis is where the strain will be felt ; so that it is just at this
Fig. 406. — Lamium al-
bum, showing distri-
bution of forces.
THE EFFECTS OF STRAINS ON STRUCTURES. 127
point where the backward curvature takes place which gives
strength to the corolla-tube. This latter is also greatly
supported by the tube of the calyx, which, as stated, has a
curiously thickened cylinder within the mesophyl.
Finally, if we may admit the existence of this adaptability
to strains and other external forces, and that the various
structures of flowers will grow in response to them and
develop themselves accordingly, we have a clue to the
interpretation of every one of the most diverse forms which
may be found in flowers adapted to insect agency.
Similarly, with regard to several classes of cell structure
which are now recognized as having a supportive function, such
as collenchyma, sclerenchyma, wood fibres, etc., I would con-
tend that such are not formed originally and anteriorly to the
requirements of the plant; but that strains have been responded
to, and the tissues formed accordingly. Then, subsequently,
hereditary influences have come into play, so that noiv they may
appear even before there is any actual necessity for them.
I find that M. J. Baranetzki's observations * on the thick-
ening of cell-walls tend to corroborate this view ; for he, too,
has arrived at the conclusion that the secondary formations
on the interior of the cell-ivalls are always in adaptation to
protect the cell- wall against the pressures exercised upon it.
In alluding to the above instances of levers and mecha-
nical powei'S in plants, one mentally recalls how abundant
they are in the distribution of the bones and muscles in
vertebrates. These latter are, of course, situated only and
exactly where they are required. I cannot help thinking,
therefore, that the old view was fundamentally correct; that
such have been gradually brought into existence by the
efforts to meet the strains put upon them. If this be true,
then one and the same law has prevailed in the evolution of
organs in both the animal and vegetable kingdoms.
* Ann. des Sci. Nat. (Bat.), iv. (1886) p. 135.
128 THE STRUCTURE OF FLOWERS.
CHAPTER XIV.
ACQUIRED KEGULAEITT AND " PELORIA."
Reversions to Regularity. — Dr. Masters observes that "in
cultivated Pelargoniums, tlie central flower of the umbel or
' truss ' frequently retains its regularity of proportion, so
as closely to approximate to the normal condition in the
allied genus Geranium; this resemblance is rendered greater
by the fact that, under such circumstances, the patches of
darker colour characteristic of the ordinary flower are com-
pletely wanting, the flower being as uniform in colour as in
shape. Even the nectary, which is adherent to the upper
surface of the pedicel in the normal flower, disappears, some-
times completely, at other times partially. The direction of
the stamens and style, and even that of the whole flower,
becomes altered from the inclined to the vertical position.
In addition to these changes, which are those most commonly
met with, the number of the parts of the flower is sometimes
augmented, and a tendency to pass from the vertioillate to
the spiral arrangement manifested." *
All the differentiations in an ordinary ^ateral blossom of
Pelargonium brought about by insect agency are, in the above
instances, reversed in consequence of the terminal position
of the flower. A more complete illustration of the effect of
manner of gjrowth and the distribution of nutrition could not
o
Teratology, p. 221.
ACQUIRED REGULARITY AND "PELORIA." 129
well be given, showing how all the features of irregularity
acquired by the ordinary form must have been induced or
impressed upon the flower when growing laterally and easily
visited, but that they are readily lost as soon as the sap
can be distributed radially and so cause the parts to grow
symmetrically round the now vertical axis.
Besides the occasional appearance of one or more terminal
and regular flowers among a truss of irregular ones, it is the
object of florists to induce all the blossoms of many iiTegular
flowers to become regular. Thus cultivated Pelargoniums,
Gloxinias, Azaleas, Pansies, etc., which are normally irre-
gular, tend to become regular under cultivation, and lose their
chai^acteristic features.
In all these cases I am inclined to recognize negative
evidence in favour of the theory advanced ; in that, presuming
the characteristic iin-egularities to have been brought about
by the agency of insects and through the crossing of distinct
flowers by these creatures, and that the irregularities have
arisen under the various pressures, etc. ; then, under cultiva-
tion, though they may be repeatedly crossed by man — the
process, however, not being effected in the same way as by
insects, and consequently the causes of irregularity being
wanting — the flowers now revert to their ancestral forms ;
while ample supplies of nutriment doubtless play an important
part in the process.
Moreover, though any irregular flower may become regu-
lar, it is a significant fact that normally regular flowers are
never known to suddenly assume any definite irregular form.
That the change from in^egularity to regularity is an
acquired constitutional affection is seen in the fact that,
when the flowers of a di'ooping Gloxinia are fei^tilised Avith
their own pollen, a large number of the seedlings will bear
the erect regular form of flower.
loO THE STEUCTUEE OF FLOWO^.3.
In the preceding cases the regalarity occurrinsr in
normallr irregalar flowers is dae to the non-development
or arrest of the nsaallv characteristic features which srive
rise to the irregnlaritv ; so that the resnlring form is a
reversion to, or a restoration of, the ancestral conditions of
the flower which is assumed to have been perfectly regular.
As insects, by their mechanical actions, are here beKeved
to have bronght abont irregularities in flowers ; so, con-
versely, regnlarity can be reacquired through their agency
in another way. Clerodendron is a plant in the corollas of
which certain members of the family Tingid-je take np their
abode as pnpje. The irritation induced by their presence
brings about a hypertix>phy of the corolla, which now
assumes a regular form, •while the filaments and style are
likewise affected, becoming much thicker than in the normal,
in-egular flower.
Reversions to regularity may. therefore, I think, be safely
referred to nutrition as the immediate agent, though such
exti-a flow of nutriment may be brought about by diverse
causes.
'"Pelop.ia."' — Regnlarity may, however, arise in another
way, by the members of the whorl or whorls normally
irregular being all exactly alike. Instead of there being
any arrest, there is here an excess of development. Thus,
if. instead of the anterior petal of Linaria being the only one
provided with a spur, all the petals become spurred, then the
corolla will become regular ; but there is no other tendency
to revert to the ancestral form. This variety constitutes the
form called " Peloria " by Linnaeus.
There are. then, two factors, which appear either singly
or together, in this process of change. First, a terminal
position, as this tends to produce regularity in consequence
of an equable flow of sap in all directions : just as this also
ACQUIRED REGULARITY AND " PELORIA." 131
determines the persistent regularity of all flowers which are
normally so situated and are visited from all directions.
It will be often found that when Snapdragons have pelo-
rian blossoms they are in three-flowered cymes as in Cal-
ceolarias, instead of a raceme, of which the central one
is regular, while the lateral flowers are irregular. Secondly,
whether terminal or not, the influence which first brought
about the change in the anterior part of the flower spreads
to and effects all the rest. This statement, of course, only
expresses what one sees, without explaining the process ;
but the fact that the energy peculiar to the formation of one
organ can affect others is so common, that we may recognize
the process as a principle of growth ; just as stamens may
become petaloid, on the one hand, or pistiloid on the other ;
showing that " petaline energy " can affect the andrcecium
in the first case, and " pistiline energy " in the latter.
That the true pelorian form is correlated to vegetative
energy is seen in the fact that such a flower obvionsly requires
more material than a normal one, and that petalody of the
stamens frequently accompanies the modification. Moreover,
although of course usually sterile under such cii-cum stances,
yet pelorian Linarias have been reproduced when the seeds
were sown in a rich soil. Mr. Darwin also raised sixteen
seedling plants of a pelorian variety of Antirrhinum artificially
fertilised by its own pollen, all of Avhich were as perfectly
pelorian as the parent plant.
That peloria is due to hypertrophy is also seen in the fact
that it always arises by multiplication of the normally enlarged
organ. Thus, in Linaria and Antirrhinum all the petals are
spurred or pouched ; in pelorian Larkspurs and Aconites it
is the spurred and hooded sepal which is repeated ; and in
papilionaceous flowers it is the standard which is multiplied
five times, etc. An abnormal increase in the number of petals
132 THE STRUCTURE OF FLOWERS.
and stamens often occurs in pelorian Pelargoniums, Horse-
chestnut, etc.
If pelorian forms were equally constant as the one-spurred
condition, botanists would undoubtedly have recognized them
as species, or perhaps genera, as it is the comparatively
sh'ght difference in the length of the spur upon which they
separate Linaria from Antirrhinum. Similarly Cortjdalis has
normally but one spar and one nectary. It, however, bears
occasionally two spurs and has two nectaries, as in Dicentra.
" Peloria, then," as Dr. Masters observes,* " is especially
interesting, physiologically as well as morphologically. It is
also of value in a systematic point of view, as showing how
closely the deviations from the ordinary form of one plant
represent the ordinary conditions of another ; thus the peloric
'sleeve-like' form of Calceolaria resembles the flowers of
Fahiana, and De Candolle, comparing the peloric flowers of
the ScrophnlariacecB with those [the normal ones] of Solanacece,
concluded that the former natural order was only an habitual
alteV-ation from the type of the latter. Peloric flowers of
Papilionaceo} in this way are undistinguishable from those
of Bosacece. In like manner we may trace an analogy between
the normal one-spuiTed Delphinium and the five-spurred
Aquilegia, an analogy strengthened by such a case as that of
the five-spurred flower of Delphinium.''^
* Teratology, p. 236.
CHAPTER XV.
THE ORIGIN OF FLORAL APPENDAGES.
Epidermal Trichomes, etc. — While all conspicuous flowers
invite insects of some sort or another to visit them, which, by
so doing, pollinate their stigmas, it is an important thing to
be able to exclude those which would rifle the flower of its
treasures and yet not transfer the pollen from one flower to
another. Dr. Kerner, in his interesting work entitled Flowers
and their Unbidden Guests, has described and figured a large
number of instances of the forms of flowers in which he
detects various processes, some of which produce sticky
secretions, others occurring as hairy " wheels " and " tangles "
of wool, etc. ; all of which tend to stop the ingress of ants
and other small insects, and thus prevent them from getting
at the honey. The question at once arises. How have these
processes been caused ? Without attempting to account
for all, the theory I offer will, I maintain, be answerable
for a good many, especially for several cases of secretive
processes and for the hairy obstructions. All these 1 would
suggest as the immediate i-esults of the irritations set up by
insects ; so that, as a consequence, they occur just and only
where they are wanted ; so that, while they form no hindrance
to the larger and stronger insects which have presumably
caused them to be developed, they, however, may effectually
prevent the smaller ones from entering.
14
134
THE STRUCTURE OF FLOWERS.
In many cases the capability of the flower to restrict
itself to its proper visitors, and at the same time to exclude
the wrong ones, is a common result of the differentiations
Avhich have taken place. Thus, an elongated tube, as in
Evening Primrose, and in some species of Narcissus, etc., is
a direct result of and adaptation to the long proboscides of
Lepidoptera, and in proportion as the tube is elongated so
does it prevent the ingress of short-tongued insects, or of
those with short proboscides.
Apart, however, from such and other general results of
adaptations, whereby flowers have become, for example,
irregular, and consequently their insect visitors are more
and more restricted in number, there are innumerable out-
growths of various kinds which act as special obstructions
to the entry of small insects which would not be able to
])ollinate the flower. Thus, while many regular flowers, such
as Gentians, have developed horizontal hairs all round the
entrance to the tube of the corolla, Honeysuckle and Veronica
Chamcedrys, which are irregular and approached from one side
only, have developed them in the anterior side alone. In
Amaryllis belladonna Kerner describes
and figures (Fig. 41) a one-sided flap
growing out of the perianth, and so
folded as to furnish a very small orifice
for the entrance of a proboscis. There
is no such groAvth on the anterior side,
but only on that one, the posterior,
which is probed by an insect.
In Gentiana Bavarica there are
Fig. 41. — Base of flower of ^ ma- . .■, t, . .^ „
n/ius siiowins boiiey-protector tooth-tiJce processes at the entrance or
the tube, which remind one of the
appendages to the corolla of some of the Silenece. Monotropa
glabra and Daphne Blagayana agree in having a large circular
THE ORIGIN OF FLORAL APPENDAGES. 135
stir^ma nearly blocking up the tube ; and while in the former
tlie irritation set up by the proboscis of an insect has
(presumably) given rise to a glutinous secretion, in the latter
it has caused a development of hair.*
Did "v\e but know what the insects were, and how they
have poised themselves upon the flower, and in what way
their proboscides and tongues have irritated the different
parts, one might be able to describe more accurately the
whole process ; but that such has been the cause and effect,
as above described, seems to me to be too probable a theory
to be hastily discarded in the absence of a better one.
It is one of those ai'guments of deduction that escape
the opportunity of verification, and can only rest for support
upon the number of coincidences which can be found, and
which collectively furnish a probability of a high order.
When, then, we find that these processes always occur
just Avhere we know the heads, legs, bodies, and proboscides
or tongues of insects habitually are placed and irritate the
flower, we are justified in recognizing, not only a coincidence,
but a cause and effect, though we may not be able to trace
the action in each individual case. Thus, it may be asked,
* The remarkable fact of Heliotrope being the solitary exception
out of the order Apocynacece, with the stigma forming a circular rim
below the summit, may meet with its interpretation from a like cause.
The corolla is so folded round the style that it leaves no space between
it and the latter. Hence it may, perhaps, have been due to a similar
"rubbing," that has transferred the stigmatic surface from the now
abandoned apex to a lower level, just where the style-arms ought to
begin to diverge. The papillae, too, differ from the ordinary form in
being pointed like fine hairs. The relative differences in the distribution
of the jjapillae on the style-arms of the CompoaitcB, I would also suggest
as having been brought about by different insects which irritate them
in various ways. So, too, the diverging stigmas of insect-fertilised
cruciferous flowers may be compared with the small globular form of
Belf-fertilisiug species of the Cruciferce,
136 THE STRUCTURE OF FLOWERS.
Why are the three anterior petals of Tropceolum fringed, but
the two posterior, Avhich stand a long way behind, not so ?
Why are hairs produced on the anterior side of a Honey-
suckle and Veronica, but all round the mouth of the regular
Geniiana ? And many other questions of a like sort might
be raised. If we watch the habits of insects with their
tongues, we may easily see how they irritate the various parts
by licking them, not solely Avhere the honey is secreted, but
the filaments, etc. Thus Miiller often watched Rhingia
rostrata licking the staminal hairs of Verhascuni pliceniceuin,
and in many cases the hairs on the filaments offer a foothold
to the insects while visiting the flowers, as in species of
Mullein ; such hairs, if my theory be true, being the actual
result of the insects clutching the filaments or rubbing them
with their claws. In Centaurea, the epidermal cells of the
filaments have produced projecting processes just where the
proboscis rubs against them when searching for honey in
the little cup (see Fig 11, p 60), from the middle of which
the style issues, as shown by the direction of the arrow.
These filaments also exhibit their extreme irritability by
contracting, and so assisting in the " piston action " by
dragging the anther-cylinder downwards over the style.
While recognizing the coincidence between the localiza-
tion of outgrowths, enations, trichomes, etc., and the position
of the parts of insects in contact with flowers when searching
for honey, one must not forget that a great number occur
where such contacts do not take place. Hence we must look
for other possible causes for their origin as well. One of the
commonest forms of trichomes is glandular hairs, and, as Dr.
Kerner has pointed out, when they occur on sepals, pedicels,
etc., they form admirable barriers to the approach of ants
and other creeping insects, which might rifle the flower and
yet not fertilise it. We must be on our guai'd, howevei', in
THE ORIGIN OF FLORAL APPENDAGES.
137
asserting that natui^e has produced them in order to keep ants
off ; for that line of reasoning is prettj sure to land us in
faulty teleological methods. What causes them is not at
present known in all cases ; though we may perceive that
certain conditions, as growth in water, can bring about their
disappearance, as Dr. Kerner remarked in the case of
Fohjgonum amphihium, which only has them Avhen growing
on land.
If, however, we ask, for example, why the Sweet-briar has
them all over it, and why the Dog-rose has none, I do not
know how to reply to the question as yet. We may notice
certain coincidences, that hairy herbacious plants are com-
moner in dry situations and smooth ones in watery; just as
root-hairs occur in a loose sandy soil and their absence is
noticeable in a heavy one; but we do not know how these
different media actually bring about these changes, though
we may feel assured tliat it is solely due to the environment.
If we, thus, look elsewhere than in flowers for any
analogous processes they are by no meang wanting. For
example, it is simply the mechanical irritation brought about
by contact with a foreign
body, probably aided by
moisture and a lessened de-
gree of light, that causes
the epidermal cells of the
aerial roots of the Ivy and
Orchids (Fig. 42) to elon-
gate into adhesive or clasp-
ing hairs, so as to grasp the -pi^ 42.— Adhesive epidermal cells of roots of
body for support. This is jancztwsid) ^'^""^ ' ''' '"''"'™°"*° <^''""
only a form of the ordinary
I'oot-hairs which are immediately developed when the tip is in
contact with a moist soil, and each hair grips and glues itself
138 THE STRUCTURE OF FLOWERS.
to the particles of soil.* Cbatin noticed the production of
hairs when the roots came in contact with any obstacle ; f
but Dr. M. T. Masters observes that the obstacle alone in
their case is insufficient without moisture, for he found that
the roots of Mustard-seed could penetrate a stiff clay, but did
not develop any root-hairs until they came in contact with
the sides of the pot — "Wherever there was a thin film of
water investing a stone or the sides of a porous flower-pot
or a plate of glass, there the root-hairs abounded."
Besides a nutrient or moist medium, actual growth in
water may enormously increase the length and quantity of
root-hairs ; as may be seen in the dependent roots of floating
plants of Hydrocharis, etc. ; or in the hypertrophied con-
ditions of the roots of grasses when growing in water.
That epidermal trichomes may be due to the irritation of
insects is clearly seen by their appearance within the cavities
of certain galls. J In the case, for example, of a very com-
mon one on willows, the leaf bulges out below and forms
a sort of bag, open or closed above. The tissues become
hypertrophied though the epidermis and palisade cells are
still recognizable lining the cavity. The leaf has scattered
hairs on both sides ; but within the cavity much larger hairs,
rich with protoplasmic or other matters, project from all
sides into the interior. Some are straight, others curved,
club-shaped, or with irregularly swollen ends, not unlike the
forms produced on climbing roots by contact with a foreign
body. Again, the crimson "spangles," so common on the
underside of Oak-leaves, are covered with stellate clusters
* Sachs' Phys. of PI. (Eng. ed.), 1887, fig. 12, p. 19.
t Mem. Soc. Nat. Sci., Cherbourg, 1856, p. 5 ; referred to by Dr.
M. T. Masters in Notes on Root-hairs, etc., Jonra. Roy. flort. Soc, vol. v.,
p. 174.
X Caused by species of Nematus.
THE ORIGIN OF FLOEAL APPENDAGES. 131)
of liairs. Similarly, those of Cecidomyia TJlmaricB on Spiraea
Ulmariavire hairy outside, and papillose within ; while similar
ones of a Phytoptus on the Sycamore are lined with long
blunt-ended hairs, and are clothed without by others, long
and pointed. In all these cases the galls, as well as the
hairs, are the product of irritation set up by the presence of
the egg deposited by the insect.*
As another very common instance of the presence of
epidermal papillis and haii^s, may be mentioned their occur-
rence in the stylar and ovarian cavities. The former, and
the placentas especially, may be clothed with delicate hairs
exactly resembling root-hairs. Such may be well seen in
the Poplar, Tamils, Eichardia ^thiojnca, etc. ; and since M.
Guignard f has discovered that the mechanical and physio-
logical irritation of the pollen-tubes is required to cause
their develojiment on the walls of the ovary in Vanilla,
between the longitudinal bands of conducting tissue, it is,
I think, a by no means improbable theory that the tufts of
hairs over the nectaries, " tangles," " wheels," etc., on the
filaments or corolla-tubes, have been actually caused by the
irritation of insects, since they occur just where such irrita-
tions are made.
One use of certain outgrowths has been regarded as
intended to protect the honey from rain. Why, however,
some flowers should be so favoured while many others, as
of the Umhellifero), have no protection at all, is not stated.
The interpretation I have here offered will, of course, apply
to all such growths, whenever they may really keep off rain
or " unwelcome guests."
* Krasan has lately discnssed the formation of the ■woolliness of
galls, etc., Oesterr. Bot. Zeifschr., xxxvii. (1887), pp. 7, 47, 93, seqq.
t Sur la Pollinisation et ses Effets chez les Orchidees, par M. L.
Guignard, Ann. des Sci. Nat., torn, iv., 1886, p. 202.
140
THE STRUCTURE OF FLOWERS.
CHAPTER XVI.
SECRETIVE TISSUES.
Position of Nectaries.* — These honey-secreting organs
seem capable of being formed anywhere. Of course they
are mainly to be found in flowers, but many plants bear
them elsewhere. Thus, some ferns have them on the rachis ;
the common laurel, as also the almond and peach, have two
at the base of the petiole; beans and vetches, as well as
species of Impatiens, have them on the stipules, as shown in
Pitr. 43. Bees may be often seen as busy about the young
shoots of laurel as
if they were visiting
flowers. Acacia
spha'rocejyhala has a
large one, on
the
Fig. 43. — Stipules of Impatiens : a. section phowing anatomy ;
6, with a drop of honey in the centre (after Kei ner).
upper side of the
petiole, which sup-
plies those ants with
food which take np their abode in the gigantic stipules
peculiar to that genus. f
* Les Nedaircs, Ann. des Sci. Nat., Bot., vol. iii., p. 1, 1879 ; also,
Etudes Anatomiqves et Physiologiques des Nectaires, Compt. rend., torn.
Ixxxviii., p. 662, 1879; also, Cross and Self Fertilisation of Plants, y>. 402;
also, Stadler, Beitr. z. Kenntniss d. Nectarieen u. Biologie d. Bliithen.
t See Belt's Naturalist in Nicaragua ; also a paper by F. Darwin,
in Ti-ans. Lin. Soc, on the same subject.
SECRETIVE TISSUES.
141
A microscopic examination of tbe anatomy of nectaries
sLows tliem to be composed of small cells closely resembling
the merismatic condition of ordinary cellular tissue (see
Fig. 43, a), and similar to tbe arrested parenchyma of the
pulvinus at the base of the petiole of sleeping leaves, which
enables that organ to remain flexible. Or, again, it is very
similar to the conducting tissue of the style, which owes its
origin to the irritating effect of the pollen-tubes (chap, xviii.).
The function of the nectary is to secrete honey, or, to
speak more accurately, either principally glucose, or else cane
sugar, or both, for the proportion varies greatly.*
The position of nectaries in flowers is very various, and any
organs can form them. It will be enough to enumerate a few
localities as follows: The Lime, species of MalpigMa,i and
perhaps Coronilla, furnish instances, which are comparatively
rare, of the sepals of the calyx being
nectariferous. In Buttercups, Hellebore,
and Aconite, nectar is secreted by the
petals or their representatives. In
Violets, Atragene (Fig. 44), Fentstemon,
and Stellaria the filaments undertake
the duty, while in Caltlia, Monotropa,
and Ehododendron it is the carpels or
pistil. In most instances the honey is
secreted by glands, disks, etc., issuing
out of the floral receptacle. If the ovary Fig. 44.— Petals passing into
be inferior, then the secreting structure 1^]!^,%^ SrJ. "
is on its summit, as in the Umhelliferce ;
and in that case it is the base of the styles from which the
nectariferous tissue is developed.
The Origin of Xkctaries.— Limiting one's self to those in
* Bull. Soc. Bot. Fr., viii. (1886), Rev. Blhl., p. 212.
t Nature, vol. xvii., p. 78.
142 THE STRUCTURE OF FLOWERS.
flowers, there are many reasons for inferring their existence
to be due to the direct and irritatinsf action of insects them-
selves when searching for juices as food or otherwise.
That a merely mechanical irritation may cause a flow of
nutrient fluid to the spot, so that the tissues may increase in
size by the development of cells, which would not otherwise
occur, is abundantly evident. It is seen, for example, in the
gi^owth and development of galls ; of the so-called " Ant-
plants " on Myrmecodia (p. 115), Acacia sphcerocephala, etc.;
in the thickening of all climbing- organs as soon as the irrita-
tion of the foreign body has commenced ; hence the inference
that hypertrophy may occur wherever an insect's pi'oboscis can
irritate the floral organs, is by no means without foundation.
Why the cell-contents of nectaries should especially give rise
to sugar, is a question at present beyond answering. Those
of conducting tissues appear to do the same. In the case of
nectaries it may, perhaps, have originated as a pathological
phenomenon which has become fixed and hereditary ; for
pathological conditions often determine a flow of gum, as in
Cherry-trees, resins in the Coniferce, watery and sugary dis-
charges from wounds, etc. ; and it is impossible to draw any
hard-and-fast line betv/een a pathological and varietal state :
as, for example, in closing the scar after the fall of the leaf
the fibro- vascular bundles are sometimes stopped by gum —
a process which, in this ease, might be regarded as normal,
and not pathological as in the former.
If a particular locality be perpetually inntated, so to say,
for generations, all analogy shows that the effect may become
permanent and hereditary ; at least, as long as the irritation
is persistently renewed year after year. And, on the con-
trary, the theory is equally supported by the negative evi-
dence of the disappearance of the honey-glands Avhenever the
whole flower degenerates and becomes regularly self- fertilising
SECRETIVE TISSUES. 143
or else anemophilotis. In these cases, in unison with the
desrradation in size and colour of the corolla, or else its entire
loss, the nectaries tend to and generally vanish entirely ; as
may be seen in Polygonum aviculare as compared with P.
Fagopyrum and P. Bistorta.
The simple origin of nectaries, then, according to my
theory, is that insects, having been attracted to the juicy
tissues of flowers, by perpetually withdrawing fluids have
thereby kept up a flow of the secretion which has become
hereditary, while the irritated spot has developed into a
glandular seci'eting organ.* These spots occur wherever the
prevailing insect found it most convenient to search ; hence it
is sometimes at one place, sometimes at another, even in
closely allied plants. Thus, in Buttercups the stamens and
carpels form a compact globe, especially the latter, and defy
the penetration of a proboscis. The corolla, however, admits of
an entrance of its base. In Atragene alpina the basal portion
of the filament forms a nectary (Fig. 4i). Comparing these
with Caltha, the large carpels of this plant admit the passage
of a proboscis between them ; and the nectaries are now
developed on the sides of the ovaries, exactly where they
would be irritated.
In Ranunculus cortuscpfolius, of 'the Canary Islands, which
has a corolla more than two inches in diameter, the petals
are entirely without honey-glands. On the other hand, the
carpels are very large and flat, with plenty of space between
them. Although I could detect no honey in plants grown at
Floore, Weedon, the tissue over the centre of the ovary was
modified, and exactly resembled the ordinary tissue of a
honey-gland. If I am justified in assuming the carpels as
* It is closely analogous to the action of the pollen-tube, which
causes a flow of nutriment to the conducting tissue, only there is a
physiological as well as mechanical irritation in that case.
144 THE STRUCTURE OF FLOWERS.
nectariferous, this would bear out the above remarks, for it
"would be as easily accessible as in the case of Caltha.
The merely occasional puncture and lesion caused by an
insect -which then flies away and does not keep up the irrita-
tion— unless it be renewed by other insects — would not of
itself be hereditary.* Thus, for example, Anemone nemorosa
appears to be honeyless, but supplies pollen to bees; yet
Miiller noticed them frequently probing between the sepals
and stamens, apparently to obtain juices wherewith to
moisten the pollen. This process may have been the actual
origin of nectaries, the result of a wound constantly repeated
and kept up, being a flow of a sweet secretion, which has thus
attracted insects and induced them to repeat the process.
Analogous Cases. — A somewhat analogous illustration is
that of galls, but in them the presence of the egg, and sub-
sequently the grub, keeps up the irritation. These remark-
able structures do not form spontaneously as nectaries now
do, without a puncture ; still, even in this case, there may
be, for all we know, a predisposition to form them ; perhaps
seen in the readiness with which the Oak forms so many
kinds, and they may be now, perhaps, much larger than they
were when insects of any particular species first punctured
the ancestral oak upon which so many kinds have now been
evolved. t The apex of a shoot of Yew attacked by Cccidomj-ia
taxi is transformed into a fleshy ring curiously resembling
the honey-disk of many flowers.
It is well known that in the human subject there may be
a predisposition for tumorous or cancerous growths Avhich
is hereditary ; and there would seem to be a very close
* Injuries, especially to the nerves, naay be hereditary in man ] see
Nature, xxiv., p. 257.
t M. E. Heckel thinks that the female "gall-flowers" of the Fig,
with an abortive ovary, in which the Cynips blastophaga lays its egg, is
now an hereditary form (Bull. Soc. Bot. de Fr., 1886, p. 41).
SECRETIVE TISSUES. 145
resemblance between tumours and galls, thougli oi-igiuating
from different sources, both being liypertrophied conditions
of certain normal tissues. For'^example, Sir B. C. Brodie
thus describes a fatty tumour : " There is no distinct
boundary to it, and you cannot say where the natural adipose
structure ends and the morbid growth begins." It is pi-e-
cisely similar with galls, which are due to cell-division
setting in at certain points of the epidermis and subjacent
tissues.
Although lesions and mutilations will not as a rule prove
to have any hereditary effects, yet the tendency to respond to
an irritation becomes permanent, and the form and structure
of the resulting organ may actually appear long before the
irritation is applied. This is conspicuously the case in the
tendrils of Ampelopsis Veitchii, in which the adhesive "pads"
are in preparation before any contact with a wall has taken
place. This is not the case with A. hederacea. Similarly the
aerial and climbing roots of Ivy are regularly produced
only on the shaded side. They can, however, be readily
made to form on the opposite side, if that be artificially
shaded ; and where, indeed, they may be not infrequently
found in nature, where they can be of no use. Such cases
prove that the tendency to produce them is an hereditary
affection which is present before the irritation is brought into
play. Again, with regard to the tendrils of the Cucurhitaceoi,
thouo-h the coiling does not take place till the irritating effect
induced by contact with a foreign body has brought it about,
yet the tendency is seemingly so strongly hereditary that,
in several cases, the tendrils are coiled while undeveloped in
the bud, and have to straighten themselves before again
coiling on contact, as may be seen in the common Bryony.
In the case, however, of a mutilation, when it has been
once made, the place heals over, and there is an end of all
15
146 THE STRUCTURE OF FLOWERS.
special vital action at the place. If, however, the same
place be induced to secrete by constantly repeated irritations,
as the same flower is repeatedly visited over and over again
before it fades, and the flowers of its offspring have to un-
dergo the same process, year after year, generation after
generation, I think it is at least a reasonable surmise that
there will at last ensue a permanent flow of fluid to the place,
with a corresponding modification of structure, and so the
nectary becomes established. If, however, from any cause
the flowers become neglected, then the nectaries degenerate
and ultimately disappear.
Apart from some general theory of the kind proposed, it
is impossible to assign a reason for glands appearing at all
sorts of places in flowers. A theory to be worthy of accep-
tance must meet all cases, if possible, and I maintain that
the one I propose is compatible with every observation that
has been made in flowers.*
* I would suggest a similar origin for the insectivorous pitchers of
Nepenthes. They originate, as Sir J. D. Hooker has sho^ra, from water-
glands. The effort to dispose of water brought up by the fibro-vascular
cord keeps the tissue of water-glands at the extremity of a cord in a
state of plethora, thereby somewhat arresting any change of form and
retaining the cells in the very characteristic merismatic stage. And if
it now meet with an external irritation from insects attracted by the
escape of fluids a further response to their influence begins, and the
wonderful structures we are familiar with iu the pitchers of Nepenthes
are the final result.
I see no greater difficulty in conceiving of such an origin than in
any other complex structure, such as the human eye. If the latter could
originate from an epidermal cell sensitive to light only, and by succes-
sive increments, traceable more or less distinctly through the various
strata of animal life, finally reach the highest and most complex form
of that of man, there is nothing inconceivable in the growth and
differentiation of a pitcher in response to an external stimulus.
What I cannot conceive of is, that any organ has ever originated
without a definite stimulating cause acting persistently in one and the
SECRETIVE TISSUES. 14<7
Witli reference to tlie continuous flow of nectar, I would
draw some analogy from animal secretions. Mr. Darwin, in
speaking of the cow, observes*": "We may attribute the
excellence of our cows and of certain goats, partly to the
continued selection of the best milking animals, and partly
to the inherited effect of the increased action, through mans art,
of the secreting glands." This fact, recorded in the last
sentence, which I have italicized, is only one example of the
geoeral principle of increase of growth by use, which I take
to be strictly analogous to what takes place in the vegetable
kingdom. And we may notice, in its special application to
the formation of glands and other structures by mechanical
irritation, that it is none other than a mechanical irritation
which keeps up the secretion of milk for prolonged periods.
The common or physical basis of vegetable life, namely
protoplasm, is very nearly t indistinguishable in its properties
from that of animals. Their behaviour is every day being
proved to be not only similar but identical in the two
kingdoms. The effects, under mechanical irritations and
strains, of nutritive matters of the same kind, of poisonous
substances, of electricity, etc., all show that the bond which
unites the animal and vegetable kingdoms together is of one
and the same nature, and that the links of the chain are
forged out of this common basis of life.
It is not to be wondered at, then, but rather to be antici-
same direction. In the case of the eye, I take that canse to be light.
In the case of an irregular corolla or the pitcher of Nepenthes, I assume
it to be insects {Tr. Lin. Soc, xxii., p. 415; Ann. Sci. Nat., 4 ser., xii.,
p. 222).
Conversely, in the absence of light the eye vanishes ; in the absence
of insects, corolla, honey, etc., go; so that negative evidence tends to
support the positive in all cases alike ; see Or. of 8p., 6th ed., p. 110.
* Anim. and PI. under Dom., ii., p. 300.
t See Journ. Boy. Micr. Soc. 1887, 771.
148 THE STRUCTURE OF FLOWERS.
pated, that tissues will behave alike in both kingdoms ; that
organs will grow with use and degenerate with disuse ; that
they will develop processes to meet strains put upon them,
as the limbs of animals have done and as stems * will do by
forming special tissues; and, on the other hand, that they
will atrophy if not called upon to display their powers, as
parasitic organisms abundantly show in both kingdoms ; and
as plants degenerate in water, which saves them the trouble
of supporting themselves.
All this is exactly what one finds to be the case in every
department of the animal and vegetable kingdoms alike,
whenever we search diligently into the anatomy and meaning
of the histological details of all parts of organisms.
Correlations of Floral Nectaries with Pollination. —
There is yet another point observable in glands. As the
position of a gland or nectary is just where it is most easily
accessible to the particular insects which visit the flower —
a fact abundantly illustrated throughout the floral world, —
and since the sole use of it to the plant, as far as we can
see, is that it should attract insects which transfer the pollen
from one flower to another, one naturally looks to see if
the positions of the anthers and stigmas are in any way
correlated to that of the honey-gland. Such is, in fact,
* I would throw out a suggestion that the anomalous stems of
climbers, which often develop supernumerary collateral axes, but all
coherent in one common stem, may be due to a response to the strains
to which these stems are subjected, occurring in various directions, as
they hang dej^endent on other trees. Other peculiar features, as of
innumerable vessels, feeble wood tissues, etc., I take to be due to
degeneracy, through these stems not being self-supporting, so that they
have assumed very much the anatomical characters of subterranean
roots. Again, just as the pericycle plays so important a part in the
structure of many roots, it will be found that this same active layer is
the parent of at least several of the above-mentioned supernumerary
tissues in climbers, as in the tendrils of Cucurbita, Bryonia, etc.
SECRETIVE TISSUES. 149
invariably the case ; so that one cannot but infer that a
common cause has brought about their correlated positions.
This close correlation is, of course, especially observable in
the more highly differentiated flowers. In regular flowers,
accessible on all sides, the glands are placed symmetrically
round the flower — whether on the sepals, as in Lime ; on the
petals, as in a Buttercup; or on the receptacle, as in Geranium
pratense, — or else there is formed a disk, as in so many "disci-
floral " plants. As soon, however, as a flower begins to show
some tendency to irregularity, or the flow^er is visited in one
way only, the honey-secreting organ at once becomes more
restricted in localization; as in the Wallflower, where it forms
two cushions, out of the middle of which the shorter stamens
arise, while the petals form two pseudo-tubes leading down
to those two glands. Again, in the Labiatce, so markedly
zygomorphic, the honey -gland is often restricted to the
anterior side, on which the proboscis is inserted. Similarly
■ in Antirrhinum majus, "the honey is secreted by the smooth
green fleshy base of the ovary, whose upper part is paler in
colour and covered with fine hairs ; ... it remains adherent
to the nectary and to the base of the anterior stamens. The
short wide spur permits the insect's proboscis to reach the
honey from below ; above and in front it is protected by a
thick fringe of stiff knobbed hairs on the angles of the
anterior stamens."*
It is hardly worth while giving other cases to prove the
universal rule, that the position of the honey and its gland is
always where it is most accessible; and the position of the
anthers is, at the same time, just where they will be most
conveniently struck by the insect; while the style and stigma
supply a third correlation, so that the latter organ invariably
hits the insect where the pollen has been previously placed.
* Miiller, Fertilisation, etc., p. 433.
150 THE STRUCTUEE OF FLOWERS,
One more point may he noticed in connection with tlie
above-mentioned correlations, namely, the motility of many
stamens. This is always in reference to fertilisation, and,
if it be an adaptation to intercrossing, then the anther takes
up such a position that the insect strikes it when searching
for honey, as in the Aconite and Tropceolum. If, on the
contrary, the motion is to secure self-fertilisation, then it
is regardless of the honey, and may actually interfere
with the access to it by insects, as in the Bosacece : for in
members of this order, with an indefinite number of stamens,
the further they spread away from the pistil the more readily
is the honey accessible ; but when they curve inwards, and
crowd over the stigmas in the centre, they completely cover
up and conceal the honey-disk.
The position of the anthers in relation to the honey-
secreting organs will, I think, often be found to be the clue
to certain anomalies in flowers. Thus in Geranium pratense
it has been noticed that the petaline stamens stand ulti-
mately externally to the calycine. Now, the position of the
five glands in front of the sepals requires that a tubular space
should exist above them, down which an insect may thrust
its proboscis, as in the Wallflower. Consequently the five
stamens in front of the sepals must be so disposed as not to
interfere wnth this passage. This can only be secured by
their bending well inwards towards the styles below, and
then outwards, above, so as to bring the anthers again on
the same vertical plane as those of the petaline stamens.
The more internal position of the calycine stamens, and
the external position of the petaline ones, are immediately due
to the gland, so to say, forcing the former inwards, while
the buttress-like bases of the carpels thrust the latter out-
wards. This gives rise to the so-called obdiplostemony of
the GeraniacecG.
CHAPTER XYII.
SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS.
General Illustrations — Protoplasmic Irritability. — Having
now stated on what grounds I believe that the cohesions and
adhesions between them, as well as the forms of floral struc-
tures have arisen — namely, in response to the irritations set
up mainly by insect agencies, coupled with the effects of
nutrition, atrophy, hereditary influences, etc., — it will be
desirable to show briefly, not only how remarkably sensitive
almost all parts, both vegetative and reproductive, are to the
action of stimuli, but how they exhibit even visibly respon-
sive effects, both in the protoplasm of the cells and in the
tissues which are composed of them.
The sensitiveness of living protoplasm is one of its most
marked and well-known phenomena. It exhibits changes in
its distribution within the cell as well as motions, which are
the dii-ect result of external stimuli. These may be very
various, such as light, heat, electricity, or a merely mechani-
cal irritation, as well as organic and inorganic solutions.
Of the effects of stimuli upon the protoplasm, some may
be beneficial, and partake of the nature of nutrition, as may
be witnessed in the protoplasmic " aggregation " of insec-
tivorous plants.* Very similar appearances follow electrical
* See Darwin's Insectivorous Plants, fig. 7, p. 40.
152
THE STRUCTURE OF FLOWERS.
or Tneclianical irritations. Thus Fig. 45* shows the effect of
electrical action on the threads of protoplasm ; a represents
a cell of a hair of Tradescantia Virg'i-
niaca ; h the same, after the application
of an electrical current. The followins:
are Dr. Weiss's observations upon this
phenomenon : —
" A constant electrical current is
without influence upon the protoplasmic
excitation ; whereas the alternate shocks f
* From Weiss's Anatomie der Pflanzen, p. 95.
t Pfeffer has noticed that the weight, per se,
^t.wfa1^".'n::;wl ^Z: of the body in contact [if very slight?] is of
ditioii; b, under electrical no consequence to tendrils. Thus cotton-wool
^' weighing '00025 grain produced no effect if
carefully placed on them ; but it did when a gentle impact was caused
by slight currents of air. Tentacles of Drosera have a sensitiveness very
similar to that of tendrils, inasmuch as small splinters of glass only
jn'oduced irritation of the glands when they caused a rubbing as the
result of concussion (see Journ. Boy. Micr. Soc, 1886, p. 285).
Pfeffer concludes that the conduction of sensitiveness is not alto-
gether due to a continuity of protoplasm, as it does not extend to the
epidermis. Since, however, the outer cell-wall of the epidermis can
grow when in contact with a foreign body, it would seem to clearly
indicate that under such circumstances it still retained its pi'otoplasm ;
and that the modern view of the cell-wall being at first a protoplasmic
layer, and not altogether a dead secretion from the protoplasm within
it^is correct ; for otherwise it is difficult to imagine how it could adapt
itself to the surfaces of foreign objects at all.
Heckel, in studying the movements of the stamens in Sparmannia,
Cintus, and Helianthemum, discovered that the epidermis plays an
important part: " L'epiderme, contrairemeut a ce que vonlait Morren
(Ann. des Sci. Nat., t. xix., p. 104), est done dans quelqnes cas I'organe
principal et visible du mouvement. Je rae suis mieux assure du role
qu'il remplit, en enlevant cet epiderme quand les dimensions des filets
mobiles le permettaient sans mutilation profonde (Cistus ladaniferus) :
tout mouvement alors etait suspendu " {Bull, de la Soc. Bot. de Fr., torn,
xxi., 187J-, p. 212). See below, p. 163.
SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS. 153
of an incTuctional apparatus always produce more or less deeply-
extending changes in the form of the plasm, which resumes
its normal character if the power exerted be not too strong.
The protoplasm immediately forms itself under the induc-
tional shocks into lumps or balls ; and, moreover, often sends
club-shaped extensions with great suddenness and energy
into the cell lumen, and immediately brings the circulation to
a standstill. The rotation returns, however, after a period of
rest, the extensions are drawn in, and the former net-shaped
distribution of the protoplasm is restored, even when the
whole mass of the plasm has been changed into a number of
colourless balls and lumj^s. If the current is allowed to go
only through a limited portion of the cell, then the streaming
stops also in this tract only, and that, too, amid the formation
of the lumps and balls.
" A sudden increase and decrease of temperature acts in
the same way ; there ensues a formation of drops, a cessation
of the current, etc. Yet even here a return to the normal
constitution takes place if no real coagulation of the proto-
plasm has occurred. On the contrary, the current often ensues,
after its recommencement, with a greatly heightened speed,
and even boisterously. The grains, etc., found in the cell-sap
outside the protoplasm are, however violently the current
may flow, in no way influenced by it, but remain at rest."
M. E. Heckel has described * the effect of a mechanical
irritation on the protoplasm of the cells of the filaments of
Berheris. He says that the cells of the irritable part are
arranged in a parallel manner, being longer than broad.
Their contents are of a yellow colour, and disseminated
throughout the whole cavity, but especially applied upon
the walls. After receiving the excitation, the same cells,
the surface of which is striated transversely, are massed
* Bull, de la Soc. Bot. de Fr., torn, xxi., 1874, p. 208.
154! THE STRUCTURE OF FLOWERS.
together or aggregated, so as to occupy only two-thirds of
the space they formerly required. The contents, retreating
from different points of the circumference, are condensed in
the centre of the cell, and the transverse stri^ are pro-
nounced in a hiofh desfree. The cells at the back of the fila-
nient are contracted in repose, and extended under irritation,
i.e. in an opposite manner to that of the other side of the
filament. The irritability does not reside in the epidermis.
A I'esult of this aggregation must be a frequent displace-
ment of the nucleus. In Weiss's figure the irritation hap-
pened to be made apparently at one end of the cell, while the
nucleus was at the other ; but in Heckel's description it
appears that the protoplasm is dra^vn from every point ;
so that, supposing the nucleus had been at the lower end
of the cell (Fig. 45, a), it would have been most probably
displaced. The consequence would be, tbat if such a nucleus
formed its cell-plate, the ultimate position of that plate
would be different from Avhat it Avould have been had no
irritation been applied to the organ.
Though one does not look to electricity as a cause in
nature, yet that liglit determines the direction of cell-division
is abundantly proved in the case of leaves, whose tissues alter
according to their position ; the palisade cells, for instance,
bring formed on both sides, if the exposure to light be equal,
or on the under side if that be placed uppermost. Similai'ly
does it influence the formation of stomata.* Again, Stahl has
shown that the direction of the division of the nucleus,
which takes place in the spores of Equisetum depends upon
the direction of the rays of light ; the two daughter-nuclei
lying in the direction of the ray. On the other hand, the
nucleus at the greater distance from the source of light is
that of the root-cell, while the one nearer to the source of
* M. L. Dufour., Ann. Sci. Nat., torn. 50 (1887), p. 33 1. See below, p. 173.
SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS. 153
light is that of the prothalliura cell.* Climbing roots of
Ivy also appear on the dai^ker side of the shoot, etc.
It is impossible to regard the above cases as isolated, but
they are special instances, revealing not only the general
irritability of protoplasm, but the minuter effects upon the
nucleus, which, in its turn, is thus compelled " to respond,"
and sets up cell-division, i.e. the foi-mation of a tissue in the
direction of the external influence, as mentioned above in the
sentence I have italicized.
The next very important point to notice is that cell-divi-
sion can take place in response to, and in the direction of an
external mechanical stimulus, just as well as in that of light.
As the sensitive plant is influenced by, and visibly moves its
foliage under the irritation of a touch or of varying degrees
of light, so do I assume that the peculiar anatomical
structures which permit of those motions are the direct result
of external stimuli. Sparviannia, it may be added, exhibits
three kinds of movement, viz.. Sleep in the calyx and corolla,
ineclianical irritability in the stamens, and an elevation of the
peduncle. (See Heckel, I.e., p. 210.) If this position be
granted we have at least a woi-king hypothesis for the
present theory of the origin of floral structures.
Formation of Tissues due to Irritability. — Apart from
the preceding theoretical supposition, there may be fre-
quently witnessed an actual formation of tissues of various
kinds, through hypertrophy on the one hand, often coupled
with atrophy on the other, and entirely brought about by
physical or mecbanical irritations. Cell-division is thus set
up, a result which would not have occurred had not the
external stimulus been applied.
It is an important fact to notice, that in some cases the
abnormal growth, though immediately following the stimulus,
* See Jl. Roy. Micr. Soc, 1886, p. 287 ; and Bull. Soc. Bot. Fr., 21, p. 65.
156
THE STRUCTURE OF FLOWERS.
and never occurring without it, leaves no hereditary effect as
in the case of galls * and of the thickening of the tissues of
some climbers after they have caught and clung to a foreign
body, such as the petioles of Clematis,^ and the hooked
peduncles of Uncaria (Fig. 46). In other cases the effect
has become hei-editary, and may
then be regarded as a specific
character. These differences are
well seen in the tendrils of Ampe-
lopsis hederacea as compared
with those of A. Veitchii. In
the former there are no traces of
the adhesive " pads " at the ter-
minations of the slender hooked
tips of the branching tendrils.
Fig. 46.— Climbing peduncle of Uncaria, Until Contact with the surface of
thickenej after catching a sunport „ ii i, j /~i ji
(after Treub). ^ vfull nas Occurred. (Jn the
latter species, however, the pads
are in course of development before any contact has taken
place just as the aerial roots of Ivy begin to appear before
contact. It is therefore reasonable to conclude that the
effect of contact has become more or less hereditary in
the latter Japanese species, though not in the American,
These tendrils behave exactly like the clasping roots of
Orchids, Ivy, etc., as well as the so-called " roots " of Lami-
naria, Cutleria, etc. Indeed, the way in which subterra-
nean root-hairs fix themselves to particles of the soil is by
essentially the same method. The irritation caused by con-
tact aided by moisture excites the cell-wall to grow out into
protuberant processes, which enables it to adapt itself to the
* I have examined a considerable number of galls, and can quite
corroborate M. Prillieiix, who has shown how the normal tissues become
hypertrophied {Ann. des Sci. Nat, ser. 6, tom. ii, (1876), p. 113).
t See Climbing Plants, fig. 1, p, 47, and fig. 4, p. 74.
SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS. 157
irregularities of the surface of the particles. An excretion
of mucilage appears to follow, which fixes the organ to the
foreign support. The irritation not only affects the epider-
mal layer, but the subjacent tissues as well, which then assist
the former in grasping the support.*
Another result of growth due to external agencies is seen
in the hypertrophied stipules of Acacia splicerocephala and
the stems of Myrmecodium, etc., in consequence of the irritation
set up by ants. Dr. Beccari f (and M. Treub %) has examined
these " Ant-plants," which occur in Btihiacece, Myristicacece,
Eiophorbiacece, Verhenacece, Melastomacece, and Palmm, and
explains the abnormal structures by variability and heredity.
A small swelling appears on the tigellum of Myrmecodium
serving the purpose of a reservoir of water, but whicb only
grows larger through the agency of ants. These creatures
induce hypertrophy of the cellular tissue. This, then, be-
comes hereditaiy. I would venture to go further, and
attribute the large honey-pits at the base of the leaf-stalk on
Acacia splicerocephala, as well as the terminal " fruit-bodies "
occurring on the tips of the leaflets, to the same cause, viz.
the mechanical irritation of the ants.
There is, in fact, an abundance of evidence to prove that
many organs of a plant, if subjected to irritation, can respond
to it, and not only increase in size by hypertrophy, but
materially alter their anatomical structure and develop new
processes. Secondly, that these altered states, if the irrita-
tion be persisted in, may become hereditary.
* See Fig. 42, a, (p. 137), which represents the inferior side of an
aerial root of Phalasnopsis amahilis in contact with a surface; b is that
of a root which has penetrated the soil (Organisation dorsiventrale dans
les Bacines des Orchidees, par M. E. Janczewski. Ann. des Sci. Nat,
ser. 7, torn, ii., p. 55.
t Malesia, ii. (1884). See Arch. Ital. de Biol., vi. (1885), p. 305.
% Ann. Jard. Bot. Buit, iii., p. 129 (1882).
158 THE STRUCTURE OF FLOWERS.
The influence of the environment upon the anatomical
and morphological structures of plants has been lately and
widely studied from several points of view ; and it has been
shown conclusively, by Constatin and others, how a change of
medium — as, for example, from air to a subtei-ranean one, or,
again, to water — profoundly affects every tissue of the plant,
whether the root, stem, or leaves be submitted to it. So, too,
leaves of many plants have been proved to be very sensitive
to changes of position and to different amounts of light —
which is a most potent and exciting cause in affecting the
mesophyl, palisade, and other tissues, including the epider-
mis, stomata, and even cuticle. It is foreign to my purpose
to describe or discuss these details in the vegetative system
of plants ; my sole object being to draw attention to the fact,
and then to apply it to the sti'ucture of flowers.
Irritability of the Floral Organs. — Perhaps no parts of
plants are more keenly sensitive to stimuli, or show a greater
number and variety of results to excitement than flowers.
A large proportion resemble plants which sleep, i.e. they
exhibit movements ac(!ording to the amount of light and heat
which they receive. So various is this, that LinnoBUS was
able to frame his floral clock. While many thus open their
petals at definite periods and subsequently close them and
die, as Convolvulus ; yet a large number reopen them again
when the due amount of light returns, like Daisies and
other Composites, AnagalKs arvensis, MesemhryantTiemimi, etc.
Others, like Silene nutans, unroll their petals at night, but
roll them up again by day.* Besides these spontaneous
motions of the perianth, the stamens often exhibit move-
ments, apparently without any external stimulus. Thus
Parnassia and Saxifrages slowly move their stamens in suc-
* See Dr. Kerner's description of this flower. Flowers and their
Unbidden Guests, p. 133.
SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS. 159
cession, either towards tlie pistil as in the latter, or away
from it as in the former. Other flowers, like Cratcegtis, Buhus,
and Alisma, have them at first spreading away from, but
afterwards bending over the pistil. These processes facilitate
one or other kind of fertilisation, and are very common.
Slow movements of the filaments after the anthers have
discharged their pollen, so as to place them out of the way
of the pistil, are not at all uncommon in strongly protan-
drous flowers. Echium* and Teucrium Scorodonia'\ will illus-
trate this well-known phenomenon. The "lemon-scented"
or " oak-leaved " species of Pelargonium has small and very
irregular flowers, somewhat papilionaceous in appearance,
with the stamens declinate, lying on the anterior petal ; the
style lies beneath them, with the five stigmas quite undeve-
loped. After the anthers have shed their pollen, they fall
oft", and the filaments bend down outside the flower, while
the stigmas now come to maturity and lie in the very place
Avhere the anthers lay before them.
Similar slow movements are very common in the styles
and stigmas of plants. In the Gompositce and. Campanula,
Lobelia, Qentiana, etc., the style arms with their stigmatic
papillfB curl backwards, and so secure self-fertilisation.
In several of the Scrophnlarinece and Labiakv, the style
gradually bends over, so that the stigma comes in contact
with the pollen. This, however, may be partly due to pro-
longed growth. As examples, may be mentioned Bhinanthus,
Melampyrum,, Oaleopsis, Stachys sylvatica, etc. Treviranus
says the same thing occurs with Gladiolus, the style curving
back towards the anthers. J
* Cf. Figs. 20, h and c, p. 82 : h shows tlie position of the stamens
before pollinatiou ; c, after it.
+ See Miiller's Fertilisation, etc., p. 500, fig. 169.
X Ibid., p. 548.
160
THE STRUCTURE OF FLOWERS.
In addition to slow and seeming-lj spontaneous move-
ments, to which all organs of a flower are liable, there are
many rapid actions, brought about bj the direct means of
external stimuli applied to them. Thus ladigofera and
Genista are two genera in which the claws of the petals are in
a great state of tension when the flower is open, and the
moment they are touched it explodes. The claws, fi^om
having been horizontal, curl down-
wards, and tbe staminal tube with
the included pistil is jerked tip-
wards. Thus Fig. 47, a, represents
a flower of G. tinctoria just expanded.
On passing a pencil point down the
front of the standard, the wings and
keel petals drop vertically, as seen
in Fig. 47, h, looked at from the
front. The staminal tube now lies
against the standard. The keel,
from its extreme tension, splits
where it cnrls at the base, and be-
comes wrinkled in front, as seen in
Fig. 47, c.
There is a plant of the oi'der
Convolvulacece, the corolla of which.
„.,,_.,,.,. , actually closes on receiving a me-
Fig. 41. — Gevista Itnctoria: a, tie- •' o
foro, h after explosion ; c, cUvvs chanical toUch. M. H. Dutl'Ochct,
ol keel. _ '
after observing that the movements
of Mimosa pnJlca and Dionaia muscipula are all in one
direction only, as also of the stamens of Cactus opuntta and
Berheris, adds : '' Mais il est quelques cas oil cette incurvation
oscillatoire s'effectue dans plusieurs sens dilferents, tel est,
par exemple, le phenomene que pi-esente une plante du genre
Yponicea, observee aux Antilles par M. Turpin, plante encore
SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS. IGl
ineclite, qu'il dcsigne sous le nom d'Ypomcea sensitiva. Le
tissu membraneux de la corolle campanulee, de cette plante
est soutenu par des filets ou par des nervures qui, au moindre
attouchement, se plissent ou sHncurvent sinueusement, de
maniere a entrainer le tissu membi'aneax de la corolle,
laquelle, de cette maniere, se ferme completement ; elle
ne tarde point a s'ouvrir de nouveau lorsque la cause qui
avait determine sa plicature a cesse d'agii\" * M. Dutrochet
then observes that this phenomenon is in no way essentially
different from the closing of the corolla of Convolvulus, to
which Ypomasa is nearly allied, when it passes into the sleep-
ing state, as does the calyx or perianth of the Nyctaginece.
Lojoezia coronata exhibits a curious and rapid movement
a i c
Fig. i9.—Lopezia (after Hildebrand). (For description, 6ee text.)
in a staminode. Miiller thus describes it : f "In each flower
there is present one perfect stamen ; a second, standing
immediately below, is reduced to a spathulate leaf, whose
two halves fold upwards, and, in the first stage, projecting
horizontally from the flower, inclose the anther of the perfect
stamen (Fig. 48, a). The stalk of the spathulate leaf has an
elastic tension do^vnwards (6) ; the filament of the stamen
an elastic tension upwards (6), so when an insect alights on
the projecting spoon-shaped blade, as the only convenient
* Recherches Anatomiques et Thy siolngiques sur la Structure Intime
des Animaux et des Ve'getaux et sur leur Motility, 1824, p. 64.
t Fertilisation, etc., p. 265.
162
THE STRUCTURE OF FLOWERS.
spot from whicli to reach two drops of honey that seem to
rest upon a knee-shaped bend in the upper petals (a), the leaf
springs downwards (b), and the stamen is set free and flies
upwards, dusting the low^er surface of the insect with pollen.
When the stamen has thus served its purpose, it gradually
curves upwards out of the flower (c), and the style which was
hitherto undeveloped grows gradually out of the flower in a
horizontal direction, so as to form another alighting place (c)."
Rapid movements in the stamens are not unknown.
I described that of Medicago * many years ago, and now
supply figures. Fig. 49, a repre-
sents the front view of a flower on
expansion ; b, the same after a bee
Las exploded it — the staminal
column has now arisen, curled up-
wards, and abuts against the
standard ; c shows the curved posi-
tion of the stamens, the corolla
being removed. The stamens are
f. inelastic, as they will not return to
Fis.i^.—^fedicagosatim. (For de- a horizonal position without break-
scription, see text.) . .„ , - _
mg across, it pressed downwards.
Many other rapid movements of the filaments are too well
known to need description, such as those of Berheris, Helian-
themum, Sparmannia, Centaurea, and Urtica ; while Orchids
exhibit various movements in the caudicles of their pollinia.
Besides slow movements, the pistil often exhibits rapid
ones on being touched, as are known to occur in Stylidium,
Canna, Maranta and allied plants ; while the flap-like stigmas
of Mimulus,f and of several genera of orders allied to the
Scroplndarinece, close together on being irritated mechanically.
* Joum. Lin. Soc, vol. ix. p. 327.
t Mr. F. W. Oliver has lately investigated the mode of conduction
SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS. 163
There is no need to describe a long series of movements,
my object being simply to emphasize the fact that sensitive-
ness and irritability are pronounced phenomena in flowers,
■which point to a highly irritable" condition of the protoplasm
contained in the cells of all the floral members.* And, although
we cannot now trace the progress of change in the floral
organs under the mechanical and physiological impulses due
to insect agency, the probability that these have been the
actual influences to which the tissues have responded, and
thence evolved the existing floral structures, will now, I trust,
appear to the reader to be of a very high order.
of the irritation in the stigmas of Martynia lutea and il. jprohoscidea, and
of Mimulus lutous and M. canlinalis. He believes it to be due to the
continuity of the protoplasm from cell to cell. The tissue of the stigma
consists of two lamellae. The irritability is confined to several layers
of prismatic cells on the inner side of the lamella, where the continuity
of protoplasm was determined. (Quoted from Journ. Boy. Micr. Soc,
1887, p. 781. Ber. Dentsch. Bot. Gesell., v. (1887), p. 162.)
Mr. Oliver has also lately contributed a valuable paper to the Annals
of Botany (vol. i., p. 237, pi. xii., 1888), on "The Sensitive Labellum of
Masdevallia muscosa." Continuity of the protoplasm occurs in the irritable
"crest" on the labellum, which rapidly rises on being touched; the
mechanism being closely comparable with that of the pulvinus of Mimot<a.
The author corroborates Mr. Gardiner's observation that a large amount
of tannin occurs in the cells with which such irritability is concerned.
References are also given to descriptions of other Orchids remarkable
for having irritable perianths.
* For further information on the effects of light and heat* upon the
opening and closing of flowers, the reader is referred to Sachs'
Physiology of Plants, chap, xxxvi., p. 6-il, whei-e the author gives an
account of Pfeffer's investigations. It is not clear, however, how
temperature acts. A casual discovery may perhaps supply a hint. On
forcing air into the flower-stalk of the white Water-lily, I found that the
petals instantly spread open. May not, therefore, a rise of temperature
cause the air within the tissues to expand, and so at least help to produce
the same eS"ect ?
164
THE STRUCTURE OF FLOWERS.
CHAPTER XVIII.
IRRITATION OF THE POLLEN-TUBE — THE ORIGIN OF CONDUCTING
TISSUES.
The first effect produced by the action of the germination
of the pollen- tube is the formation of the so-called conducting
tissue or layers of specialized cells which nourish the tube
in its downward growth. Like glandular nectaries, this
tissue consists of small merismatic-like cells, highly charged
with nutritive and saccharine substances. In some cases it
is a metamorphosed condition of the epidermis alone, as
Fig. 50. — a, section of (epidermal) conducting tissue of Fumaria ; b, that of Rubus ;
c, section of ovary of Crucifer (after Capes.)
M. Capes has shown in his researches,* as in Fiimaria. Fig.
50, a, represents a section of the stjlar canal, the lining
epidermis having its cells charged with such matters, while
* Ann. dcs Sci. Nat., vii., 1878, p. 209.
ORIGIN OF CONDUCTING TISSUES. 165
three pollen-tubes are seen in section. Fig. 50, h, shows the
fonnation of conducting tissue at the angle of the inflected
carpellarj edges of Ruhus. The epidermal and subjacent
cells form the conducting tissue "in this case. The cells on
the outskirts are charged with sphaeraphids. Fig. 50, c, is a
section of the ova-ry of a Crucifer. The replum or false dissipi-
ment, as in the Papaveracece, forms the machinery for conduct-
ing the tubes. The dotted lines show the original lines of
fusion. Now, it my theoiy be true, that no structure exi.sts
which has not been brought into existence through some
foreign action having been brought to bear upon it — either
directly from without, as insect agency, light, etc., or
indirectly through, nutrition within the plant, — then, the
existence of this specialized tissue would never have arisen
had it not been for the irritating action of the pollen-tubes.
The analogous influence of the mycelium of a parasitic
fungus here gives us the clue. As such causes hypertrophy
to set in, and induces nutritive matters to accumulate upon
which the fungus lives, — just as the irritation of the egg or
pupa of a cynips or other insect causes a similar accumula-
tion of richly nutritive substances to be made within the
tissues of the gall npon which it feeds, — so the germinating
power of the pollen-grain and the growth of the pollen-
tube have actually brought about the formation of these
highly nutritive conducting tissues of the style. The efl^ect
has then become hereditary, so that they are now in course
of formation, at least, during the development of the flower
in pi^eparation for the ingress of the pollen-tubes.
The remarkably stimulating action of the pollen-tube had
been observed moi^ especially in Orchids. Hildebrand
noticed that the influence of the pollen was twofold, in that
it determined the growth of the ovary and the complete
formation of the ovules before the process of fecundation had
166 THE STRUCTURE OF FLOWERS,
taken place.* M. Gnignard has described the effects result-
ing from his experiments. f Thus, in the case of Vanilla
aroniatica, he found the development of the ovary was very
rapid after pollinisation. At the time of flowering, the
placentas have only the rudiments of the papillge which
will develop into ovules, and the conducting tissue formed
by 'the epidermis and subjacent layers on either side of
the placentary projections is still undifferentiated. In
the intervals which separate the bands of conducting tissue,
corresponding to the midribs of the carpels, there is no
appreciable modifications before fecundation ; but as soon
as that has taken place, a layer of elongated papillas, filled
with a granular substance, arises. With regard to the
development of ovules, M. Gruignard remarks : " La pollinisa-
tion et la germination du pollen sont indispensables a leur
formation. L'ovaire d'une fleur non pollinisee ne s'accroit
pas et tombe quelques jours apres I'epanouissement."
As soon, however, as the pollen-tubes are formed, the
ovnles begin to grow, until the twentieth day, when the pri-
mine thickens (much more than in other orchids) and finally
gives to the matured ovule a globular form.
In the mean time the embryo-sac and sexual apparatus
have been forming, and are completed (excepting the fusion
of the two members of each tetrad, which does not take place
to form the secondary embryo-sac nucleus) in little more
than a month after pollinisation- Five weeks after that
period, fecundation commences.
In following the progress of the pollen-tubes, it is not
* Die Fruchthildung der Orchideen, ein Beweis filr dnjypelte Virhung
des Pollen, Bot. Zeit., 1863. Bastardirungsversuche an Orchideen, Bot.
Zeit., 1865.
t Ann. des Sci. Nat., 1886, torn, iv., p. 202; see also Maury,
Observations sur la Pollinisations des 0)-chidSes, comp. rend, de I'Acad.
des Sci., 2 Aout, 1886; and also Guigiiard, do., 19 Juillet, 1886.
ORIGIN OF CONDUCTING TISSUES. 167
till from the twelfth to the fifteenth day that some of them
arrive at the base of the ovary. Before the sexual apparatus
is complete, the extremities of the pollen-tubes separate from
the mass of tubes overlying the" conducting- tissue, twist in
various directions, scrambling over the placentary lobes and
their ramifications, and so approach nearer and nearer to the
ovular fucicles ; but they only penetrate the micropyles,
after the formation of the sexual apparatus. It is supposed
by Strasburger that the synergidte expel a liquid destined
to guide the pollen-tube to the embryo-sac ; others think their
function is to aid in the solution of tissues for nourishment.
In Vanilla, for example, the upper part of the embryo- sac
is absorbed where occupied by the synergidas, and is then
covered by the elongated border of the primine. M. Guignard,
however, adds : — " II est possible qu'il soit attire par un
liquide expulse par les synergides,* comme le pense M. Stras-
burger, ou bien aussi, comme je crois I'avoir constate, par
I'etat special de la coucbe superficielle des membranes cellu-
laires du bord interne du tegument." f
On the action of the pollen-tubes M. Guignard writes as
follows: — "Au contact des faisceaux polliniques, le tissu
conducteur oifre un contenu riche en Sucre reducteur ; I'ami-
don, dans le cas actuel, ne se trouve qu'au voisinage et du
cote externe des faisceaux libero-ligneux des parois ovari-
ennes. Outre le pouvoir d'attaquer la substance amylacee et
d'intervertir la saccharose, comme I'ont montre tout recem-
ment M. Van Tieghem,:J: et M. Strasburger,§ les tubes polli-
niques peuvent aussi, a I'aide des ferments qu'ils contiennent,
* SynergidcB is better, being nearer Simergatai.
t i.e., p. 209.
X Sur rinversion du Sucre de Canne par le Pollen, Bull. Soc. Bot. de
France, 1886.
§ Ueher Fremdartige Bestauhung, Pringsh. Jahrb., vol. xvii.
168 THE STRUCTURE OF FLOWERS.
dissoudre la cellulose, ainsi que le prouvent les soudures avec
fusion que j'ai observees plusieurs fois entre eux dans les
cultures, ou le phenomene est plus facile a voir. D'ailleurs,
la penetration directe des tubes polliniques dans les papilles
du stigmate de plusieurs fleurs, apres dissolution de la
membrane cellulaire, est un fait du meme ordi'e."
I quote this passage in full, that the reader may see how
it comjjletely corroborates my belief that the metamorphosis
of the epidermis and subjacent layers to form the conducting
tissue is entirely owing to the action of the tubes themselves,
as well as the conversion of starch into saccharine, and there-
fore easily absorbable matters.
M. P. Maury has noticed very analogous facts in Ve7-bas-
cum, in that " at the period of pollination the ovules are still
in a rudimentary condition, and altogether unfit for fertilisa-
tion. The nucellus is entirely occupied by the embryo-sac,
in the protoplasmic contents of which there is as yet no
differentiation of oosphere, synergidee, or antipodals. It is
only after the pollen-tube reaches the micropylar canal that
these begin to be formed." *
This observation corroborates what I have said above,
that not only is the pistil delayed in development in insect-
crossing flowers, but that arrest of growth may affect all
parts, and particularly the ovules ; and I strongly suspect if
more instances, of the Gamopetalce especially, were examined
it would be found to be the rule and not an exception. M.
Maury's investigations also agree with M. Guignard's, in
that the action of the pollen-tube is a stimulating one, and
brings about developments which would not, and, indeed,
cannot, otherwise take place.
In Vanda tricolor pallens, experimented upon by M.
* Bull. Soc. Bot. Fr., viii. (1880), p. 529, quoted from notice in
Joum. Roy. Micr. Soc, 1887, p. 433.
ORIGIN OF CONDUCTING TISSUES. 1G9
Guignard, he noticed the not infrequent effect of a rapid
chang-e of colour in the perianth after pollination, although
it did not fade for a week. The swelling began on the
second day in the " gynosteme," and progressed towards the
ovary. From having been four centimetres long on the day
of pollination, December 4th, 1885, by the 15th of ^pril,
1886, it had grown to seven centimetres. The ovules, how-
evei', were not full grow^n, the embiyo-sac having still its
primitive nucleus ; by the 15th of May, the ovules had
attained their complete development. By the 1st of June,
fecundation had taken place in nearly all the ovules. Hence
about six months were required for the process.
In this species the spaces over the mid-ribs were covered
with long hairs, corresponding to the papillge in Vanilla. In
both they appear to have grown after, and as a result of,
pollination.*
In a flower oi Angrrecum superhum which became arrested
the influence of the pollen-tube was remarkably illustrated.
Three weeks after pollination an arrest of development
followed in the ovary ; it had sensibly increased in diameter
in the upper part. On examining the ovarian cavity at the
top, M. Gruignard found only a small number of jjoUentubes,
relatively short in length. f
Another abnormal case was a Vanilla, in which, from
some unknown cause, only two bundles of pollen-tubes were
formed on either side of a placenta. Here the ovary grew
on that side, causing a strong curvature. On the opposite side,
the wall and. the placentas with their ovules were atrophied.
* Max Wichnra found that silky hairs were sometimes the sole
result of his attempts to hybridize willows ; and as analogous instances
are the clothing the interior and exterior surfaces of galls with papillae
or hairs, an indirect result of the irritation set up by the pupae (p. 138).
+ A like interpretation may be given to Vegetable Marrows when
they swell only at their distal end.
17
170 THE STRUCTURE OF FLOWERS.
The exciting effect of tlie tubes is seen when Orchids are
crossed which have no affinity, and are therefore incapable
of fertilisation. Tims, the pollination of Orchis mascula by
Gypripedium pavifloruni even determined the formation of
the sexual apparatus in the former. Similarly, when Orchis
and Listera, as well as Ophrys and Limodorum were crossed,
ovules reaching various degrees of development Avere pro-
duced, but none were impregnated.
Everything indicates (writes M. Guignard) that the
development of the ovules is subordinated to that of the
ovary. In exotic Orchids the thickness of this organ and its
elongation are often very pronounced before the appearance
of the ovules.*
Analogous results have been obtained by Max Wichura's
experiments f in hybi-idizing Willows, who noticed the
following degrees of failure indicating the various amounts
of influence that the pollen-tube had over the sexual ap-
paratus of the plants crossed: (1) the ovaries swell and
ripen, but contain no seed ; (2) the ovaries are quite filled
with silky haii's which clothe the umbilical cord end of the
seed, but contain no embryo; (3) seeds are present, but
small and incapable of germination ; (4) seeds apparently
perfect, but do not germinate ; (5) seeds germinate, but the
seedlings are weak, and soon wither ; (6) seeds few but fertile
and d,ctive; (7) seeds numerous with only a few fertile; (8)
seeds numerous and fertile.
* Gaertner, in his Mdinoire sur les Organes Reprodudeurs des Phaniro.
games, devotes a special chapter to the enlargement of the ovary without
previous pollination, with the result of a pseudo-frait {Versuche u.
Beob. iiber die Befrucht. Organe der Vollk. Gewdchse, 1844).
t Die Bastardhefruchtung in Pflanzenreich, erlauiert an den Bastarden
der Deiden, Von Max Wichura. Mit zwei Tafeln. 4to., Breslau, 1865.
Abstract by Rev. M. J. Berkeley, Journ. Roy. Hort. Soc, New Series,
vol. i., p. 57.
ORIGIN OF CONDUCTING TISSUES. 171
Similar results occur in many cultivated plants without
hybridizing ; as appear in seedless Oranges ; Grapes, such as
" Sultanas ; " Bananas, Cucumbers, etc.
Every other cause capable of acting in the same way will
produce a like result, as in various instances of parasitism,
when the cells become hypertrophied, as do those occupied
by Syncliytrium, or as in the roots invaded by Plasmodiophora.
M. Guignard quotes an interesting case, which fully bears
out the theory advanced in this book, of the results of the
irritation of insects. He says, "A I'appui de cette maniere
du voir je citerai une observation interessante que le hasard
a fournie a M. Treub,* et dont ce savant a bien compris la
signification reelle,"
" Ayaut rencontre des ovaires de Liparis latifolia qui
presentaient un epaississement plus ou moins considerable,
meme dans les fleurs non epanouies, et ou la pollinisation
directe ou indirecte n'avait pu se faire, il trouva a I'interieur
des petites larves qui y avaient penetre de tres bonne heure.
Ces larves ne paraissaient exercer aucune influence nuisible
sur les cellules, et semblaient avoir la faculte de se mouvoir
librement dans la cavite ovarienne, bien qu'on les trouvat au
contact de la parol ou des placentas. Elles se nourrissaient
evidemment des sues de I'organe envahi ; a peine voyait-on
une legere alteration de quelques cellules avec lesquelles elles
etaient en contact. Compares a ceux des fleurs normales
avant la pollinisation, ces ovaires habites par les larves
oif raient des placentas plus grands et plus digites, sur lesquels
s'etaient developpes finalement des ovules revetus de leui-s
deux teguments formes comme sous I'influence de la polli-
nisation. Les dimensions des ovules ne differaient pas de
ceux des graiues mures provenant d'ovaires pollinees, et non
envahis par des larves.
* Notes sur I'Embryon, etc., Ann, du Jard. Bot.de Buit., iii., p. 121, pi. xix.
172 THE STRUCTURE OF FLOWERS.
"II etait done evident que les parasites avaient determine
les memes effets que les tubes polhniques : raccroisement des
ovaires et des placentas et le developpement des ovules."
The reader will here see the importance of this curious
instance as hearing upon my general theory of growth m'
response to irritation ; so that if ovaries, placentas, and ovules
can be stimulated into growth and development, there is
no d priori I'eason why other parts of flowers may not equally
well grow in response to irritations set up by the insect
visitors ; as I have already shown tobe the case in Clerodendron*
and in Mr. O'Brien's experiments. f
Perhaps it will not be amiss to notice here a very similar
action of the suspensor in Orchids, described by M. Ti^eub,
which grows "backwards," escapes from the micropyle, and
then ramifies in various ways, clasping and bui^rowing into
the ovarian walls like a parasite in order to convey nutritive
matters to the rudimentary pro-embryo. J
Finally, M. Guignard remarks upon the degradations in
the essential organs of Orchids as accounting for the well-
known difficulty in raising seed from them : " Malgre le
nombre immense des grains formees dans les conditions'
naturelles comme dans les serres, nombre qui parait etre
d'ailleurs une signe de degradation physiologique dans une
famille ou la differenciation morphologique des organes floraux
est cependant si elevee, I'insuffisance de reserve alimentaire
contenue dans leur embryon microscopique, en necessitant des
conditions speciales pour le developpement, suffit peut-etre a
expliquer les difficultes et les insucces de la reproduction des
orchidees par gTaines, et la parcimonie relative avec laquelle
elles sent distribuees dans la nature."
♦ See p. 130. t See p. 114.
;J; Notes sur VEmbryog^nie de quelques Orchidees, Verhandelingen der
Koninklijke Akadamie van Wetenschappen, 1879.
ORIGIN OF CONDUCTING TISSUES. 173
With regard to tbe difficulty of rearing Orchids, the
reader may be referred to the Report on the Orchids Confer-
ence,* ia which Mr. B. T. Lowne observes : " One of the
difficulties in rearing seedling Orchids arisLS, I believe, from
the fact that the pollen is only developed from the prolifica-
tion of the mother cells, after the pollinia are placed on the
stigma." He also found that, besides the pistil thus stimu-
lating the pollen, "the stimulation due to the presence of
the pollinia gives rise to the development of the capsule,
even whilst the ovules remain unimpregnated." f
The significance of the above details lies in the fact that
external influences, both mechanical and physiological, can
bring about changes in the epidermal X and sub-epidermal
layers, with a determination of a flow of fluids of a specific
character to those specialized tissues. As this is proved to
be true for the conducting tissues, so do I infer it to be
equally so for glands of various kinds.
* Journ. of Roy. Hart. Soc, vol. vii. ; see paper by Mr. H. J. Veitch,
p. 22.
t L.c, p. 48. " Degeneracy " will be discussed in Chaps. XXVI. and
XXVII.
X M. Mer found that stomata were developed in the epidermis of
galls on vine-leaves which normally had none. "Insolation" or
exposure to light has a marked influence on the orm of the epidermal
cells, and in increasing the number of stomata. The walls become
straighter and thicker, and especially the cuticle. M. Mer believes the
production of stomata to be the direct result of the accumulation of
nutrient substances. Comp. Rend, xcv., 1882, p. 395. See also Journ.
Roij. Mia: Soc, 1882, p. 530, and 1883, p. 91. See above, p. 154.
Another important paper on the same subject, fully corroborating
these observations, has lately appeai-ed, by M. L. Dufour, entitled,
Influence de la Lumiere sur la Forme et la Structure des Feuilles,
Ann. des Sci. Nat., 7 ser., torn. 5 (1887), p. 311.
174 THE STRUCTURE OF FLOWERS.
CHAPTER XIX.
COLOURS OF FLOWERS.
The Laws of Colour.— M. de Candolle proposed to divide
the colours of flowers into two series, the Xanthic and Cyanic,
the former containing- yellow-green, yellow, yellow-orange,
orange and orange-red ; the latter, blue-green, blue, blue-
violet, violet, and violet-red ; red being intermediate between
the two series. It Avas thought that flowers were rigidly
bound by these series, and never transgressed them, but that
the tints of a species might vary through each. Thus the
editor of the Gardener s Chronicle, replying to a correspondent
on Feb. 2, 1842 (p. 97), remarks that "a blue Dahlia was
not to be expected. On the other hand, the Hyacinth, being
of the cyanic series, a yellow Hyacinth will not occur."
Yellow Hyacinths are, however, common enough now.
Even in 1856, Dr. Lindley found it necessary to conclude a
leading article on the subject with the words : "At all events
the cyanic and xanthic speculations of philosophers must now
be laid up in the limbo of pleasant dreams."
The many exceptions to this supposed rule met with
between 1845 and 1856 elicited the above remark, and
notably a species of Delphinium, viz. D. Cardinale, containing
" golden yellow in the petals, which are as scarlet as a
soldier's jacket everywhere else, one of the last of Messrs.
COLOURS OF FLOWERS. 175
Veitcli's fine Californian introductions. In this flower there
is no sign of blue. Yet, if there is a genus more pre-
eminently blue than any other cyanic race, it is surely
Delpliinium.^^
It is true that some species have never yet transgressed
their bounds, so that Dahlias still refuse to be bhie now as in
1845 ; and we are still ignorant of the reason.
The effect of nutrition upon the colours of plants is well
known, in that they vary much more in a garden soil than
in the wild state ; and differ in colouring according to the
character and ingredients of the soil. Thus, as described by
a writer in Hovey's Magazine of Horticulture,* striped Dahlias
will be best kept clean by planting them in a poor soil, while
rich soil invariably runs them. E.g. D. var. striata formosis-
sima : No. 1 was planted in a poor gravelly soil, in an open
situation ; all the flowers but two were beautifully mottled.
Ko. 2 was planted upon a rich, cool, sandy loam ; not one-
half of the flowers were mottled. No. 3 consisted of three
plants, very highly enriched ; every bloom but one was self-
coloured. Similar effects follow on the variegated foliage of
Pelargoniums, according as they are grown in a too rich soil
or light one.t
" Alum is said to render the Hydrangea blue ; and some
saline substances, such as phosphate of iron and muriate of
ammonia, appear to brighten the tint of red." | It often
happens, however, that blue and pink corymbs occur on the
same plant of Hydrangea. A cutting taken from a blue
Hydrangea growing at Southampton, and transferred to
Bedfont, changed to the usual colour on blooming there. §
Chloride of lime has been known to make a whole-coloured
* Quoted in the Gard. Chron., 1842, p. 8.
t Gard. Chron., 1876, p. 567. X Ihid., 1813, p. 577.
§ Ibid., 1886, vol. xxvi., p. 118.
17G THE STRUCTURE OF FLOWERS.
Camellia become striped; while ammonia enhances the
colours of Balsams.
Oxidization is believed to have great influence in chang-
ing the colours of plants, just as it affects certain juices when
exposed to the air. Thus, if a leaf of the Socotriae Aloe be
injured, the juice is at first violet in tint, but it soon turns
to brown. If a potato be grated, the pulp rapidlj browns in a
similar way. Many fungi, especially noted for their poison-
ous properties, turn blue on injury, as species of Boletus.
Moreover, they do not do so if exposed to niti'ogen, hydrogen,
or carbonic acid; hence it is presumably the oxygen which
effects the change.
Some flowers change their colours from their first open-
ing to a full expansion: such as Cobcea, from green to violet;
several Boraginaceous plants, from red or even yellow to blue-
purple. Lyciicm harharuvx, the popularly called " Tea-plant,"
is a well-known instance. Others change during the day, as
the " Changeable Hibiscus." This plant has flowers white
in the morning, pink at noon, and bright red by sundown.*
Similarly, a Phlox of a bright pink colour, " in the early morn-
ing, by five o'clock, has its colour of a lightish blue, which
continues to altor as the sun advances, and by nine or ten
o'clock becomes its proper colour ; the clump which catches
the sun's rays first changes first, while the other is still blue."
Though I'efcrring these and other well-known instances to
oxidization. Dr. Lindley, from whose leading article the above
remarks are partly taken, concludes with the observation,
" In fact, we know very little about the cause of changes in
colour, either in plants or animals." Perhaps it remains so
still.
The intensity of the colours of many high Alpine fl.owers
* According to M. Ramon de la Sagra; quoted in Gard. Chron., 1842,
p. .555.
COLOURS OF FLOWERS, 177
has often been noticed ; and when plants growing near Paris
"were transferred to a much higher latitude, the flowers
deepened in colour. This, however, is thought not to be due
to a clearer atmosphere, but to the enhancement of the foliage,
as M. Cb. Flahault showed that the leaves of plants of the
same species are larger in proportion as the latitude is
higher, the comparativelj large dimensions being due to the
din-ation of light of a relatively feeble intensity. Flowers
being dependent upon leaves, great importance must be
attached to th.e power of the latter to store up nutriment for
them. Thus, in the case of Hyacinths both blue and red,
M. Flahault found no difference in the colour of the flowers
when grown in the light or in the dark, the colour being at
the expense of the material stored up in the bulbs. Other
experimenters have found that, while some floW'Crs show no
difference, others do ; thus Askenazy found no difference in
Tulips and Crocuses, though the leaves were etiolated in the
dark. With Hyacinths, however, contrary to Flahault, he
found that light exerted a two-fold influence, an acceleration
of at least a fortnight in flowering and a much more intense
8.nd more diffused colour ; those in darkness being only
tinged where the uncoloured ones where darkest. Pulmonaria
officinalis in darkness changed from red to blue, as usual ;
but in proportion as the buds were in a less advanced stage
when placed in darkness, so were the coloui's fainter. His
conclusion is that some flowers require light to develop tbeir
normal -colours, while othei'S are independent of it.* Mr.
Sorby t agrees with Askenazy ; and concludes that the arrest
of normal development in darkness varies Avith the nature
of the colouring matters, the effect being greater with the
more easily decomposable substances. " Those substances
which when dissolved out from the petals are the most easily
* Bot. Zeit., Jan., April, 1876. t Nature, April 13, 1876.
178 THE STRUCTURE OF FLOWERS.
decolorised by exposui'e to light, are formed in relatively-
greater amount when the flowers are grown iu the dark.
This is easily explained if we assume that a higher vital
power, depending on the presence of light, is necessary to
overcome the more powerful chemical affinities of the less
stable compounds."
The crossing of flowers is well known, and much practised
by florists, to enhance the variety of tints. The interpreta-
tion is that crossing is a stimulating process, and provokes
the petaline energy to a high degree.
From the preceding remarks it will be now gathered
that colours, per se, are a result of nutrition ; and that the
prevalence of brighter colours in conspicuous flowers which
are regularly visited by insects is due to the stimulating
effects which they have produced, thereby causing more
nutritive fluids to pour into the attractive organs.
Besides, however, this general result of brilliant colouring
there are those peculiar and special displays of bright tints
distributed in spots and streaks in certain and definite places
only. These have been called " guides " and " path-finders,"
as they invariably lead to the nectaries. If the theory be
true which I am endeavouring to maintain throughout this
book, all these effects are simply the direct results of the
insects themselves. The guides, like obstructing tangles of
hair and nectaries, are always exactly where the irritation
would be set up ; and I take them to be one result of a more
localized flow of nutriment to the positions in question.
Instead, therefore, of a flower having first painted a petal
Avith a golden streak to invite the insect, and to show it the
right way of entering, the first insect visitoi-s themselves
induced the flower to do it, and so benefited all future
comers.
The Origin op Colouks. — Mr. Grant Allen has written
COLOURS OF FLOWERS. 179
an interesting little book on The Colours of Flowers* in
which he expresses his belief that the first colour on depart-
ing- from the primitive green was yellow. When we remem-
ber that the spore-cases and ^spores of Lycopodium, the
anther-cells of Cupressiis, and the whole anthei^-scale of
Pinas and all the pollens of Gymnosperms are yellow, — again,
when we come to Dicotyledons and find the prevailing tint
of stamens is the same, — we gather probabilities in support
of that view. That Nature next introduced reds, and only
lately, so to say, succeeded in manufacturing blues, seems
probable from the compai'ative rarity of the last colour.
Moreover, when flowers individually change from one colour
to another as they develop from the bud to maturity, it is
always in that order — i.e. from reds to mauves or purples, as
in Ecliium, Puhnonaria, etc., or even from yellows through
reds to purples, as in Myosotis versicolor, so that we still seem
to gather additional support to the theory.
If, however, we ask what has caused these changes, we
are as yet in the dark. A few hints are attainable, and that
is all. Yellows and reds seem to be due to substances allied
to the oxidized products of chlorophyll in autumn leaves.
Again, chlorophyll grains on turning yellow in fruits (Lyciim)
become angular, two or three pointed, and finally granular.
Tn the same way the yellow granules of petals (Cucurhita)
resemble " amyloplasts," or starch-forming corpuscles.f
The general conclusion one arrives at from various
observations is that the original change from the ancestral
green to, probably, yellow is correlated to the change of
function; but why the first colour was yellow, and why it
ever gave place to red or blue, is unknown.
Supposing the yellow-green colour to have spread to the
adjacent parts which then attracted insects, as it does in
* In Nature series. t Sachs' Veg. Phys., p. 320.
180 THE STRUCTURE OF FLOWERS.
some Euplwrhias and Chrysosplenium, for instance, then tlie
visits of insects would bring the required stimulus to advance
the colour to a pronounced yellow ; and so petals, it may be
conceived, came into existence.
Pale and White Varieties. — The paler tints or even a
total absence of colour may seemingly occur as a variety of
any plant. It is often a concomitant of habitual self-
fertilisation in cases where the variety or species is a
degradation from some conspicuous and biightly coloured
insect- visited form. White-flowered individuals often appear
as " sports " amongst seedlings ; the immediate cause of
which it would be difficult to assign, beyond the general
one of the absence of those nutritive conditions which are
requisite for colours, as occurs in Gladioli*
White, however, is useful as a starting-point for florists'
flowers where great variegation is required. Thus M.
Vilmorinf says that "in ten examples of variegation
which were produced under my own observation, the course
was always the same. The original plant, with flowei-s whole-
coloured, gave in the first instance a variety of flowers
entirely white ; afterwards, variegations were produced from
this white variety on its returning towards the coloured type.
. . , This pure white variety usually gives in the first sowing
a greater or less proportion of plants Avith flowers like those
of the coloured type ; but by careful selection through
several generations the pure white type is in most cases
completely fixed. ... It is only among the white varieties not
completely fixed that the variegations make their appear-
ance ; at fii^st they exhibit narrow pencillings, the coloured
portion being only one-tenth, and sometimes only one-
twentieth of the whole surface ; but then in the following
* Garden, 1880, p. 327.
t Flore des Ser. et des Jard. de I'Eur., {Gard. Chron., 1852, p. 500).
COLOURS OF FLOWEES. 181
generation . . . the coloured portions begin to predominate.
... I have never been able to observe a single instance of
variegation coming directly from the coloured original. The
contrary, however, takes place with regard to the dottings ;
these come directly from the coloured tjpe." The variegated
varieties the author had succeeded in fixing were Gomphrena
glohosa ; Antirrliiniin inajus, Convolvulus tricolor, Nertiopliila
insignis, Porfulaca grandiJJora and Delphinium Ajacis..
Other florists have found that by crossing whole-coloured
flowers pure white seedlings may result.
Abutilons have an instructive and, in part, a somewhat
similar history. No hybrids were raised from the old bronze-
red and striped form, which was usually barren, until the
white " Boule de Neige " was introduced. Mr. George
crossed this with " Duke of Malakoff." The white one had
itself previously thrown up every shade of dingy white ; but
whether by being spontaneously crossed or not, does not
appear to be known. Some of the colours of the seedlings
of this cross were pale and dark pink, jjale orange, bright
carmine, salmon, orange-red, etc.*
Somewhat analogous results were obtained by Mr. Veitch
with Rhododendrons imported from Borneo. Thus a cross
between the larger-flowered It. Javanicum, which is orange-
coloured, with the smaller white narrow-lobed R. Jasmini-
fforum, gave rise to the rose-coloured " Princess Royal." A
further cross of the last with the parent R. Jasminiflorum
eliminated the red colour ; the offspring, however, retained
the form and size of the corolla of the " Princess Royal."
It is called " Princess Alexandra."
In the above-mentioned the effect of the white has been
to separate the tints ; so that from the old Bronze- red
Ahutilon Darwinii we get yellows and reds of different
* Gard. Chron., 1878, p. 792.
18
182 THE STRUCTURE OF FLOWERS.
shades. Similarly the orange or buff-yellow BJiododondron
Javanicuvi has been split up into various reds ; the white
having, so to say, eliminated the yellow.
The subsequent effect of crossing with regard to flowers
is variety. With this fact florists and horticultiirists are
familiar : for as soon as crossed or hybrid seedlings are
raised the varieties of colouring become infinite. It has
been observed that the " spots " are more persistent than
the base-colour of the flower. This fact agrees with the
theory advanced that they have, whenever they occur as
guides or path-finders, been determined by the insects and
then become hereditary as much as the shape of the flower
itself ; and as that is maintained much more persistently
than general colouring, so is that specialized colouring which
has been equally due to insect agency.
With i^egard to the correlations which exist between
colours and insect visitors, Miiller especially has observed
several. Thus beetles seem to affect yellows, e.g. Thalicfrum
and Galium verum ; wasps and carrion insects, reddish-
browns, such as of Comarum, Epipactis, etc., while the more
intelligent bees, etc., delight in purples and blues ; and it is
thought that their selective agency has determined the sur-
vival of such special colours as they prefer. This has been
probably the case, but we still want to know what is the
immediate cause which induces one colour to chansfe to
another.
As high colouring or conspicuousness if the flower be
white is due to insects, so pale colouring and inconspicuous-
ness is due to their absence ; but what the nature of the
stimulus is we cannot tell. It enhances the assimilative
powers ; for the crossed plants, as Mr. Darwin abundantly
proved, are usually larger plants. It usually infuses some
of the characters, floral or foHar, of the male parent — but
COLOURS OF FLOWERS. 183
not always : several expe^nmentel•s assert that, after every
precaution, tlie offspring exactly resemble the maternal
parent. But one rule florists always adopt in order to
enhance the colouring is to use the pollen of the better-
coloured plant, the maternal parent being usually the in-
ferior one.
As an illustration of the relative effect, of crossing and
self-fertilisation respectively on the production of colours,
I quote the following passage from Mr. Darwin's work : *
" The flowers produced by self-fertilised plants of the fourth
generation [of Biantlms caryopJiyllus or Carnation] were as
uniform in tint as those of a wild species, being of a pale
pink or rose-colour. Analogous cases [occurred] with
Mimulus and Ipomcea. . . . On the other hand, the flowers
of plants raised from a cross with the fresh stock which bore
dark crimson flowers, varied extremely in colour. . . . The
great majority had their petals longitudinally and variously
striped with two colours."
Uniformity and paleness of tint are thus correlated with
self-fertilisation; and. since, whenever the latter process is
persevered with, an increase of fertility follows, it is not
sui'prising to find that such tints are usually accompanied
by an increased power of seed-bearing. Thus, Mr. Darwin
found that, "the proportional number of seeds per capsule
produced by the plants [of Biantlms'] of crossed origin, to
those by the plants of self -fertilised origin, was as 100 : 125."
Again, of Antirrliinum majus, the relative self-fertility of red.
an^ white varieties was as 98 : 20 ; of Mimulus luteus the
same comparison gave t.he ratio of 100 : 147; while pale-
coloui-ed Pelargoniums are notoriously great seeders. "f
* Cross and Self Fertilisation, etc., p. 139.
t For further illustrations, see my paper on Self-fertilisation, etc.
184 TUE STRUCTURE OF FLOWERS.
CHAPTER XX.
THE EMERGENCE OF THE FLORAL WHORLS,
Theoretically, as already stated, a perfect flower should or
might be composed of six whorls, if its parts be not spirally
disposed, — the perianth, andi"C8cium, and gyncEcium each
consisting of two verticils. The very general rule for their
emergence from the axis is centripetal. The subsequent
rates of development of the several whorls may vary con-
siderably, so that one part which emerged first, or at least
very early, may be late or the last to arrive at maturity.
The calyx or outermost whorl of the perianth when
present is nearly always the first to appear, and to grow
rapidly to a relatively large size, and thus protects the more
rudimentary pat'ts within it ; but if it ultimately remains
rudimentary itself, or, it may be, is not entirely arrested, then
it is the corolla which first emerges, the function of pro-
tecting the essential organs being relegated to it. Such is
the case with the Compositce, Valerianece, etc.
The corolla, with rare exception, emerges before the
stamens, though it is very generally rapidly passed in
development by the latter organs. In Lopezia and Primula,
however, the stamens emerge first ;" and this has led some
botanists* to regard the petals of the last-named plant as
* For references and literature on the stmctnre of Primulacece, see
Masters's paper, On some Points in the Morphology of the Primulaceue,
Trans. Lin. Soc, 2nd series, Botany, vol. i., p. 285.
THE EMERGENCE OF THE FLORAL WHORLS. 185
outgrowtlis from tlie stamens. My own observations tend
to confirm those of Dr. Masters, tLat it is an exceptional fact,
and not constant. It appeared to him " that in Lysimacliia
Nummularia the petals did really sometimes (but not always)
precede the stamens in their development."
The stamens emerge before the pistil, and if there be two
whorls to the androecium, it is the sepaline whorl which
appears first ; though the fully developed stamens sometimes
assume a position, as already explained, within the petaline,
as in Geraniacece. Like the corolla and staminal whorls, the
carpellary appears all at once, and last of all.
With reference to the emergence of the individual parts
of the whorls, it is an almost invariable rule that those of the
outermost whorl of the perianth or calyx, if it consist of three
or five parts, rise centripetally in succession according to the
laws of phyllotaxis. Thus, if the calyx be pentamerous, its
parts invariably emerge in quincuncial order, thus consti-
tuting a cycle of the f type. If it be trimerous, as in Mono-
cotyledons, it is a cycle of the | type. If, however, it be
tetramerous, then the parts emerge in decussating pairs, as
in Tamarix tetrandra, Sparmannia, Fliiladelphns, and the
sepals in the Gruciferce* This clearly shows that a normally
tetramerous calyx is the result of the combination of two
pairs of leaves, corresponding to two nodes, the internode
between the pairs being suppressed.
The parts of the inner whorl of the perianth or petals of
the corolla, as also those of each staminal and carpellary
whorl, almost invariably emerge simultaneously if the whorls
be regular; though pronounced differences may occur in the
case of iiTegular flowers. Similarly, when there is a strong
spiral tendency, as in the Banunculacece, members may arise
* The lateral sepals, thongh overlapped by the other pair, are the
first to receive their vascular cords from the axis.
18G
THE STRUCTURE OF FLOWERS.
successively. If the stamens be very numerous tliey
usually emerge in centripetal order, as in Buttercups ; but
they may form "centrifugal groups," as in Hypericum; the
numerous stamens of Cishis and HeliantheTnum, as well as
of Cactus, Opuntia, and Mesevihryantlieviuvi, and the Loasecp,
are also centrifugal in their development. Lastly, if the
carpels form a whorl, they, too, emerge simultaneously ; but
if they be numerous and spirally arranged they emerge and
develop in succession.
There are some additional points to be observed. The
first is the method of change from tetramerous to pen-
tamerous in the same plant. Thus in Celastrus scandens,
if the flower be tetramerous, the sepals appear in pairs, the
antero-posterior first, then the lateral pair afterwai-ds. If
the flower be pentamerous the sepals arise in succession,
quincuncially, the numbers 1 and 3 being anterior; numbers
4 and 5 are lateral, and number 2 posterior.
Now, by referring to the diagrams above, it will be
seen that this order is in exact agreement with the usual
method of passing from opposite to alternate arrangements
in the foliage. The correct angular distance or divergence
being acquired immediately in the case of the calyx, by
shifting the position of the parts so that the divergence of
144° is obtained. In the case of foliage, this is only secured
after several internodes (see p. 18).
THE EMERGENCE OF THE FLORAL WHORLS. 187
Exactly the same procedure occurs in Sparmannia
and Philadelphus, "wliicli are tetramerous, as compared witli
Tilia and Deutzia respectively, wlucli are pentamerous (see
P-18). _ ]' ^
The next point to be noticed is the alteration in the
order of emergence which takes place in irregular flowers.
The rule seems to be that those parts of the flowers which
assume a greater prominence in the mature state, or have
some special function beyond the rest, emerge and develop
before the others. Thus in Leguminosce and Lahiatce, where
there is a prominent " landing-place " for insects, the petals
issue successively in an antero-posterior order. The carina
of papilionaceous flowers composed of two petals appeal's
first, then the alas together, and finally the vexillum. In
Reseda, the sepals, petals, and stamens issue in a postero-
anterior manner ; but while the sepals finally attain to much,
the same dimensions, the petals remain more or less atrophied
as they emerge towards the anterior side. Then the stamens
appear in the same order upon a cellular ring, which, later
on, grows out into the unilateral disk between the petals and
stamens.
In a few regular flowers the simultaneity is also wanting .
thus in Adoxa the sepals of the tetramerous terminal flower
emerge in pairs, and the four petals simultaneously ; but in
the lateral flowers the posterior sepals issue before the
anterior; and of the five petals the posterior one emerges
first, the two lateral secondly, and the two anterior ones last
of all. These modifications are continued in the order of
flowering. Thus the terminal flower expands first, and "all
at once." Of the lower lateral flowers the two upper
posterior sepals open out first, then the posterior stamens
mature and shed their pollen. The anthers dehisce in suc-
cession from the lateral stamens, and lastly from the anterior
188 THE STRUCTURE OF FLOWERS.
ones. The lower sepals do not separate until after the upper
stamens have shed their pollen.*
Though we are not in a position yet to account for all
such deviations from general rules, yet I think in such cases
as the Leguminosce and Lahiata\ and probably all irregular
flowers, that the rationale may with great probability be
assumed to be the stimulus given from without to meet the
extra strain which, certain petals or stamens or both have to
sustain while supporting the weight of an insect when visiting
them. To meet this demand an extra supply of nutriment is
sent to the parts which thus require it ; and, in fact, I believe
the final result has thus been actually brought about by the
eft'ort of the plant itself, so that it has developed parts in
accordance with its requirements in a manner parallel with
that which has obtained in the animal kingdom.
In the case of Adoxa I would regard the above-mentioned
orders of development as a result of unequal distribution of
nutriment in order of time. Thus the apical flower receives
its nutriment first and develops first ; then the other flowers
which are placed laterally subsequently. And this order of
supply has alfected the parts of the latter flowers in the
same way, so that they develop from above downwards, or
in a postero-anterior manner. It may be compared to a
three-flowered cyme, of which the central flower expands
first, and the two lower ones afterwards.
A feature must here be noticed, though I do not think much,
stress need be laid upon it, which botanists have called " obdi-
plostemony." f If a flower have one whorl of stamens of the
same number as the petals it is isostemonous ; of two, diploste-
monous ; and if the stamens of the older whorl be opposite or
* For a note on Adoxa, see my paper On the Origin of Floral Estiva-
tions, Trans. Lin. Soc, 2nd series, Botant, voL i., p. 194.
t Sachs' Text-Book, 2nd edition, p. 601.
THE EMERGENCE OF THE FLORAL WHORLS. 189
superposed to the petals, and therefore aiitipetalous, then the
above term is used : for the rule is that the calycine whorl
shoald be outermost and emerge first ; then the petaline, which
usually takes a position bigher up on the axil ; and, in at
least most of the genera and orders where obdiplostemony has
been noticed in the completely developed flower, it is simply
due to the petaline whorl of filaments being, so to say, thrust
outside the level of the calycine whorl by the protruding
buttress-like bases of the carpels, as in Geranium pratense.
This is still more the case in Oxalis, where, as in Geranium,
the sepaline stamens become the taller set, the petaline the
shorter; and the position of the former being more internal
than usual, apparently in consequence of the appendages
which grow on the outer side of the filaments,*
Again, the order of emergence may be the same as usual,
namely the sepaline stamens fii'st, then the petaline ; but
the position of the latter, instead of being within as is
the rule, may be apparently on exactly the same plane as
the sepaline, as in Heaths. Since, however,
they do not emerge simultaneously, but one
set is intercalated between the other, or even
outside of it (Fig. 51), this order of appear-
ance is, to my mind, a sufficient proof that
they do not really belong to the calycine pig. 51. _ Diagram
„,] 1 of emergence of
vTiiuii. ppraline stamens
There is no greater difficulty in under- 6*drthe""epa'iine
standing this, than in seeing that a compres- (afier Payer;,
sion of the internodes of opposite and verticillate leaves has
taken place M^hen double the usual number are present in
a whorl. Thus privet has sometimes four leaves at one node,
forming a quaternary whorl, and all on the same plane ; and
* According to Frank, in Oxalidem and Geraniaceo', it is the anti-
petalous stamens which are developed first. See above, p. 150.
190 THE STRUCTURE OF FLOWERS.
this will remind the reader that, since floral whorls. are based
upon pbyllotaxis, ten stamens could not possibly form a
cycle ; and although the eight stamens of a Heath might do
so, there is nothing in the leaf arrangement of that genus to
suggest their being a whorl of the f type.
Since the petaline cords are usually united to the
staminal ones, the fact that the petaline stamens get
sometimes, as it were, " dragged outwards," offers really
no great difficulty ; but is, so to say, a mere accident brought
about by the adaptations of the flower to insect agency.
Indeed, to interpret these irregularities in the emer-
gence, one must look to the final condition to see if there
are any ultimate results in correlation with them. In Oxalis
we get heterostylisra with its corresponding different lengths
of the filaments, and the necessary adjustments of the latter;
since there are at least two sets in each flower, for insects to
readily secure the pollen. In Heaths all the anthers are
arranged in a ring round the style, pressing their cells
against it, and so closely approximated, that when a bee
dislocates one by pushing the lever-like auricle to one side,
she dislocates the whole, and so receives a shower of pollen.
These final arrangements, therefore, are suggestive of the
reason why the points of emergence of the stamens occur just
where they do.
In the case of Hypericum, where the stamens emerge
centrifngaUy, from a definite number of original papillae,
three or five as the case may be, the stigmas extend
outwards ; so that, if they have not been pollinated by
insects, they can come in contact with the latest formed or
the outermost anthei'S.
CHAPTER XXI.
THE DEVELOPMENT OF THE FLORAL WHOKLS.
The order in which the several whorls of flowers emerge
from the axis is, as stated above, almost invariable ; but the
rates of development are very various, and important sexual
and other differences follow as the results. For flowers with
conspicuous corollas or other structures attractive to insects,
the prevailing order of progression subsequent to emergence
is first the calyx, secondly the stamens, and, if tbere be two
series, the whorl superposed to the sepals grows first,
afterwards the whorl superposed to the petals ; then follows
the pistil to a point approaching maturity, when the corolla,
just before expansion, grows very rapidly to its full size ; and
finally the stigmas mature. The anthers have also grown
long before the filaments, which at last elongate very rapidly.
The usual result on maturity is various degrees of jirotandry,
coupled with conspicuousness or attractiveness to insects.
As a few of the examples I have examined may be mentioned
Hanuncnlus acris, Cardamiiie pratensis, Sfellaria Holostea,
Lychnis dioica (male), Malva moschata, Geranium (larger
flowered sp.). Pelargonium, Tropceohim,, Epilohium hirsutum,
(Enotliera biennis, Ipomcea, Veronica Ghamcedrys, etc. In fact,
this order of growth and development prevails generally with
flowers having conspicuous coi'ollas.
The interpretation appears to be as follows. In such
192 THE STRUCTURE OF FLOWERS.
flowers as these, energy is especially directed into the
development of the corolla and andrcEcIum ; the former
being large, and the latter supplied with much and often
highly differentiated pollen. All this means the consumption
of so much more nutriment ; and, as the chief amount of
floral energy is thus directed first into the androecium, then
into the corolla — which often attains a far greater size than the
other organs, — consequently these two whorls tend to diaw
a larsre amount of nourishment to themselves. In conse-
quence of this, the pistil has, temporarily at least, to
suffer ; so that its growth is for a time delayed, and it
does not mature as early as the stamens, which had, moreover,
a considerable start in the race to maturity. Hence the
result is that the stamens are often mature and evea shed all
their pollen long before the stigmas are prepared to receive it.
This, then, accounts for protandry being almost invariably
the rule in the case of relatively conspicuous flowers.*
If flowers have two or more whorls or many series of
stamens, as have many genera of Caryophyllece, Geraniacece,
Jianiinculacece, and Uosacece, then the pistil may arrive at
maturity between the periods of different series, or con-
temporaneously with some of them ; so that, while the flower
is protandrous with regard to the first stamens which mature,
it is bomogamous with others, and thus self-fertilisation can
be readily secured if the flower fail to be crossed.
It may be here observed, though the fact will be dwelt
upon again, that by far the greater majority of flowers,
conspicuous or not, retain this provision for self- fertilisation ;
and that those flowers which normally cannot possibly
fertilise themselves are in a very small minority.
* There are a few protogynons flowers, it is true, which are more
or less conspicuous, but these exceptional cases have their own inter-
pretations, which will be considered later on (see Chap. XXII.).
THE DEVELOPMENT OF THE FLORAL WHORLS. 193
Nearly the same oi'der of development as the above is
maintained with some that have i-ather inconspicuous flowers
in consequence of the corolla being small ; but then it must
be remembered that the other organs are proportionally
small too, and, if they come at all, are visited by small
insects. Such, for example, are Malva crispa, Veronica
serpyllifoUa, V. agrestis, etc. In these flowers, however, the
pistil has a remarkably rapid growth as compared with the
preceding cases. The cause is, that energy is now directed
at once to that organ, instead of being so largely occupied by
the stamens and corolla. The result is that the pistil
matures more rapidly than in the previous cases, and
sometimes even simultaneously with the stamens. The
flower is therefore more nearly homogamous, and self-
fertilisation can with them more easily eusue.
In many cases amongst inconspicuous flowers I could
detect no appreciable difference at all in the rates of
development of the essential organs. I would then describe
the order as Calyx, Stamens + Pistil, Corolla. As examples
are Lepidium campestre, Sisymhrium AlUaria, and S. officinalis.
Nasturtium officinale, Corrigiola littoralis, CEnotliera historta,
etc. These are all, it will be noticed, very small-flowered
plants. They ai-e thus homogamous, and habitually self-
fertilising.
The next order of development to be noticed is Calyx,
Stamens, Corolla, Pistil. As far as my observations go, this
order appears to be mainly confined to gamopetalous flowers,
with a hypogynous corolla, as Linaria minor, L. Cymhalaria,
Veronica spicata, Primula,* Anclmsa officinalis. Borage offici-
* This order of development in Primrose has been observed by
others, and apparently thought to be exceptional ; so that the somewhat
strange suggestion of the corolla being an outgrowth of the andrcecium
was made by Pfeffer ; but it by no means stands alone in this respect.
See Sachs, I.e., p. 609 ; Jahrb. fiir Wissensch., Box., vol. vii., p. 194.
19
194 THE STRUCTURE OF FLOWERS.
nalis, Amsinckia angiistifolia, Statice psilocladia and Plantago
Coronopus, etc.
The remarkable delay in the progress of the development
of the corolla during the emergence and first stages of
development of the stamens is the peculiar feature. It
sometimes allows the stamens to emerge first, as in Primula ;
or if they be nearly simultaneous, then the corolla may be
suddenly checked, as in Veronica. But many differences
occur ; thus they emerge and grow up together in Saviolus,
while in Ancliusa officinalis the corolla rapidly exceeds both
stamens and pistil. In the case of AmsincMa the corolla
and stamens appear to emerge almost together, and then
follows the pistil, which the former quickly exceed in height.
Then the pistil regains the height of the stamens, and they
ultimately mature together. A similar procedure obtains
with Plantago Coronopus : though the petals emerge first,
the anthers quickly outstrip them, and the corolla grows
considerably more than the pistil, which is consequently
delayed ; but when they are nearly developed and the corolla
becomes scarious, then the style elongates with great rapidity,
and the stigmas mature first, so that the flower is ultimately
protogjnous. Exactly the same course is followed by the
floral whorls of Statice psilocladia.
The next order of development is Calyx (if present).
Corolla, Stamens, Pistil ; or even Corolla, Calyx, Stamens,
Pistil. The cause of the corolla developing so soon is the
arrest of the calyx, as in TJrahelliferce, Valerianece, and Com-
positce. The corolla now has to act as a protecting organ, and
always keeps in advance of the essential organs. Indeed, in
the orders with epigynous and garaopetalous corollas, in which
the calyx is usually obsolete or nearly so, the corolla actually
emerges before it.
The last order of development to be mentioned in the case
THE DEVELOPMENT OF THE FLORAL WHORLS. 195
of flowers possessing a corolla is Calyx, Pistil, Stamens,
Corolla. As examples, I find tlie following illustrate this
condition : Ranunculus scelerafus, Cardamine Jiirsuta, Cerastiuin
glomeratwm, Arenaria trinerva, Sagina procuinhens, Spergu-
laria marina, Polycarpon tetrapJiyllum, TrifoUum minus,
Epilobium mojitanum, Gaura parvijiora, etc. This appears to
be the most general condition for very small and incon-
spicuous flowers which are regularly self-fertilised. The
interpretation is the exact converse of the order of develop.
ment first described ; namely, of the whoi-ls of conspicuous
flowers. All the above are inconspicuous, many being rarely
if ever visited by insects ; and as the corolla is minute, no
nourishment is required for the j^etals, the stamens are often
reduced in number and the quantity of pollen diminished.
The pistil at once proceeds to grow, and the result is, if not
homogany, protogyny.
It must be now borne in mind that the above differences
in the order of growth and development must not be regarded
as at all absolute or invariable, but only general rules as to
what takes place ; for the rates of growth of the respective
whorls may vary in the same species according to external
circumstances ; so that a plant may be protandrous at one
time or place, homogamous or even protogynous elsewhere
or in another season, as the case may be. Indeed, Miiller
frequently calls attention to this fact, to which I shall have
occasion to return.
Emergence and Development of the Ovules. — If the
ovules be tolerably numerous, the order in which they appear
is not constant. It may be either from above downwards or
from below upwards on the placenta. Thus, as Payer has
shown by his drawings, in Viola, Reseda, Cistus, Tetrapoma,
Fmnaria, Linum, Buta, Melianthus, Staphylea, Spircea, and
Opuntia the order is basifugal, or from below upwards. On
196 THE STRUCTUEE OF FLOWERS.
the other hand, in Macleya, Dicentra, Epimeduim, Bartonia,
Impatiens, Ly thrum, Dracopliylhim, Malachitim, Cerastium,
Primula, and Samolus the order is basipetal, or from above
downwards.
When the row of oviiles is very numerous, it is the rule
that the point where they first beg'in to emerge is midway,
and the development takes place both upwards and down-
wards simultaneously. It is thus with Helleborus and allied
genera with follicles, Capparis, Epilobimn, Trifolium, Cajo-
pliora, Lafhyrus, Citrus, Passiflora, and the Monocotyledonous
orders, Iridacece and Amaryllidacece. Lythrum and Opuntia,
however, both of which have considerable I'ows of ovules,
develop them, as stated above, in a basipetal and basifugal
manner respectively.
On examining Payer's numerous figures, I find that when
the order of development is fi-om below upwards, the ovnles
have their micropyles upwai-d ; when they develop from
above downwards, the micropyles grow downwards. In
either case, occasionally the middle ones may be somewhat
horizontal, if they are somewhat numerous, as in Bartonia,
Spircea, and Stapliylea. When they are very numerous and
develop both ways from a point midway, then the ovules
may either turn upwards or downwards ; the majority being
downwards in the proportion of nine to five.
As a theoretical interpretation to account for the general
fact of the central ovules developing first when there are
long rows of them, it may be due to the carpel being com-
parable to a lanceolate leaf, where the longest and therefoi^e
the most vigorous nerve-branch of the pinnate nerves is in the
middle. If the rows of ovules emerge from below upAvards,
the carpel may be comparable to a more primitive type, as of
monocotyledons with a palmate foliage. Thus the only
exceptions I can find in Payer's figures of Monocotyledons are
THE DEVELOPMENT OF THE FLORAL WHORLS. 197
tlie Gladiolus and Alsfroemeria, where they are very numerous
and follow the rule of commencing to emerge in the middle,
and then proceed upwards and downwards. Though parietal
placentas seem generally to have their ovules developed from
below upwai-ds, yet, as seen above, it is not uncommon with
an axile placentation. If any intei'pretation be sought, I
should feel inclined to associate it somewhat with a more
primitive state of things, since a parietal placentation presents
a more rudimentary character than an axile. But ivhy they
are developed thus, sometimes upwards, sometimes down-
wards, or both ways at once, is at present as inexplicable as
the fact that leaves develop both basipetally and basif ugally,
either in their entirety, or as to their lobes and notches, which
may be formed on either plan. Perhaps there may prove to
be a common cause for both.
198 THE STRUCTUEE OF FLOWERS,
CHAPTER XXII.
Hetekogamy* and Autogamy.
Pkotandry, Protogyny, Homogamy, and Cleistogamy. — These
conditions prevail in nature in varying degrees of frequency.
The first is common to all conspicuous flowers habitually
visited by insects, and is accompanied by heterogamy. The
fact that anthers mature their pollen before the stigmas of
the same flower are ready to I'eceive it, is due to the extra
stimulus given to the androecium, which mostly effects
simultaneously the enhancement of the corolla or perianth
which attracts the insects (see p. 191). Like everything else
in nature, it is very far from being absolute, and any flower
may be protandrous at one time or place, while it may at
another mature the essential organs together, and then it
becomes homogamous, or it may be even protogynous.
These latter conditions prevail in less conspicuous flowers
and all those which are fluctuating between a condition
* Heterogamy, i.e. union by intercrossing different flowers.
Autogamy, i.e. union by self-fertilising one and the same flower.
Protandry, i.e. stamens maturing the pollen before the stigmas of
one and the same flower are ready to receive it.
Protogyny, i.e. pistil maturing the stigmas before the pollen of one
and the same flower is shed.
Homogamy, i.e. pollen and stigmas of one and the same flower
maturing simultaneously.
Cleistogamy, i.e. autogamous within an unopened perianth.
HETEROGAMY AND AUTOGAMY. 199
requiring insect agency and self-ferfcilisation or autogamy ;
as well as in the majority of flowers which are too incon-
spicuous to invite insects at all, or which never expand. The
series of such flowers tex'minates in perfect and perpetual
cleistogamy.
The first condition, or Protandry, does not now require
special discussion or illustration ; as it is the jDrevailing one
ill most conspicuous flowers : though it must be distinctly
borne in mind tha,t the exceptions are rare in which a flower
cannot fertilise itself at some period or other before it fades ;
even though a large order, as 0)xh{dece, may furnish many
examples.
Protog'yny may arise from several causes. Milller has
mentioned about twenty species of plants iri-espective of the
Grasses which are more or less decidedly protogynoua ; and
what one notices is that many are Alpine species of genera
which have other species dispersed elsewhere that are homo-
gamous or protandrous. Thus Anemone alpina is protogynous,
but A. NarcissifoUa is protandrous. Jxanunculus montaniis, B.
parnassifolius, R. pyrenceus are all protogynous. These may
be compared with the smaller-flowered forms of R. aquatilis
which are homogamous ; but B. flammula, B. acris, B. repens
and B. hulbosus are protandrous with the outermost stamens
only. Thus, this genus supplies a progressive series. Other
protogynous and mountain species are Dnjas octopetala,
species of Saxifrage, as 8. androsacea and 8. muscoides, and
S. 8eguieri: but Miiller found *S^. oppositifolia and 8. tridac-
tylites to be sometimes feebly protandrous, at others proto-
gynous. On the other hand, 8. rotundifoUa, 8. aizoides, etc.
are protandrous. Loiseleuria procumbens, Trientalis Europcea,
Bartsia alpina, Hutchinsia alpina, and Thalictrum alpinum
are all protogynous.
Secondly, a group of plants, the flowers of which have
200 THE STEUCTUllE OF FLOWERS.
the habit of blossoming early, as in the spring or the begin-
ning of the summer, are protogynous ; such are species of
Hellebore, Frunus, and Gratcegus, as well as the Horse-chestnut
and Mandragora vernalis.
Some species are characterized by the habit of living in
shady places, as Geum urhanum and G. rivale, Chrysospleiiium
oppositifolium, Gagea lutea, Paris quadrifolia.
Lastly, others have minute flowers, as Geranium pusillum,
Veronica serpyllifolia, Tojjieldia, and many other species, some
of which I have mentioned when treating of the emergence
and development of the floral whorls, where I have explained
the cause. *
Wind- fertilised or anemophilous flowers are for the most
part protogynous ; for these flowers have been accompanied by
strong degeneracy of the coi'olla and pollen, while all traces
of nectariferous structures are almost invariably and entirely
suppressed.! Hence Thalictrum minus, Polerinm. Sanguisoyba,
Plantago sp., Callitriche, Myriophyllum, Artemisia, Cheno-
podium, Amentiferce, Juncacece, and Graminece are all more
or less characterized by being protogynous while they are
anemophilous as well.
If we are not in a position to trace the actual causes of
protogyny in every instance, we can at least see several
influences which can bring it about. Temperature will be
seen hereafter to be a most potent one ; for a relatively lower
temperature very frequently checks the energy of the corolla
and stamens, without having any necessarily corresponding
effect on the pistil, and several compensating processes then
come into play; so, conversely, the pistil now gains the
ascendancy and can mature first. This, therefore, will
* See Chaps. XX. and XXI,
t Intercrossing by insects may be recovered in anemophilous flowers ;
when honey may be again secreted, as in Salix caprcea and Sanguisorba
officinalis ; see Fertilisation, etc., p. 236, fig. 77.
HETEROGA]MY AND AUTOGAMY. 201
account for some mountain species, as well as those blossoming
early or in shady places, being protogynous.
It must not be regarded as universally true. If flowers so
situated or circumstanced be abundantly visited by insects,
they will respond to their influence ; and the consequence is,
that many Alpine plants are even strongly protandrous, as
well as spring-flowering plants and some which grow in
shady places, as Sanicula Eurojpcea, Odontites serotina, etc. It
is Avhen we compare the protogynous species with others of
the same genus, that the influences of a lower temperature,
shade, etc., more especially suggest themselves as true causes
of protogyny in some species, while others may be homo-
gamous or protandrous.
Many plants normally provided with conspicuous flowers,
but accidentally growing in shady places, may often be found
having them half opened or as quite closed buds, and yet
fully fertile. The same occurs late in the season, when the
flowering period is drawing to a close. Such flowers repre-
sent the preliminary stages leading to a permanently homo-
gamous or protogynous condition, as the case may be, which
are mostly autogamous as well.
Whatever may be the direct cause, and there may be
others besides those I have mentioned, protogyny is easily
brought about temporarily in individuals, or it may become
hereditary and a permanent feature.
It need now hardly be added that, before protogyny is
reached and emphasized, all degrees of passage can be met
with from strong to weak protandry ; then homogamy is
acquired : and, after passing through oscillating conditions,
permanent protogyny can be finally the result.
Many individual plants vary in this respect, being some-
times or in some places in one condition, and at other times
and in other places in another condition. As nothing is
202 THE STRUCTURE OF FLOWERS.
absolute in nature, so in this case, plants respond to the
influences brought to bear upon them, and each individual
may vary accordingly, but if the influence be permanent, then
the variation becomes hereditary, and one or other character is
fixed, and may be regarded as specific or generic as the case
may be. Should the environment change again, what may
have been constant for generations vyill be once more broken
up, and instability ensues.
Miiller records several cases of such oscillations, as in
Pidsatilla vernalis, Dryas odopetala, Bibes petramm, Gentiana
cani/pesfris, Veronica serpyllifolia, V. spicata, Walnut, Hazel,
etc. These vary from protandry through homogamy to
protogyny. He also mentions species which have not yet
arrived at complete protogyny, such as Sihbaldia prociimbens
and Ranunculus alpestris, mountain species which are homo-
gamous ; while R. glacialis is sometimes even slightly pro-
tandrous. Papaver alpinum, Arabis alpina, and Biscuiella
Icevigata are also described as horaogamous.
As the transitions from a conspicuous, protandrous, and
entomophilous or insect-fertilised flower to a homogamous
and autogamous or self-fertilised one, as well as to anerao-
phily, are the effects of degeneracy, they will be considered
more fully when that peculiar condition of floral structure
comes to be discussed.*
* See Chaps. XXVI. aud XXVII.
CHAPTER XXIII.
HETEROSTTLISiM.*
DnroRPHic Flowers. — A large portion of Mr. Darwin's work
on the " Forms of Flowers " deals with the varieties and phe-
nomena of heterostylism, which is specially characteristic of
the PriniulacecB, and Biihlacece, though several instances exist
in other orders as well. He and Mr. J. Scott were mainly-
interested in showing that " illegitimate " or homomorphic
unions were less prolific than " legitimate " or heteromorphic ;
and inferentially took occasion to describe the differential
sexual characters of the forms of the same species. With
regard to this latter fact, when Mr. Darwin experimented
with wild Cowslips, he first thou2:ht that they were tending
towards a dioecious condition, and that the long-styled plants
were more feminine in nature, and would produce more seed :
conversely, that the short-styled plants were more masculine.
Contrary to his anticipation, of plants marked growing
in his garden, in an open field, and in a shady wood, the
short-styled forms gave most seed, the weight of seed being
in the proportion of 41 to 34 ; that is, the short-styled pro-
duced more seed than the long-styled in the proportion of
nearly 4 to 3. Similarly when a number of wild plants were
* Heterostyled, i.e. plants with stamens and styles of different but
corresponding lengths on separate plants.
Homostyled, i.e. when stamens and styles are of the same length.
Hovio-, di., tri-, poly-, and lietero-niorphic, i.e. flowers of the same,
two, three, many, and different forms, respectively.
204
THE STRUCTURE OF FLOWERS.
transferred to his garden, the result was as 430 to 332, the
weight of seed being therefore nearly 4 to 3. Lastly, of
plants covered by a net, six short-styled plants bore about
50 seeds, while 18 long-styled plants bore none at all.
From these results, Mr. Darwin wrote, " we may safely
conclude that the short-styled form is more productive than
the long-styled form. . . . Consequently my anticipation that
the [long-styled form] would prove to be more feminine in
nature, is exactly the reverse of the truth." * We shall
see, however, that his surmise was probably, to some extent,
right, nevertheless.
Mr. Darwin and Mr. Scott have recorded a great number
of experiments in ci'ossiug heterostyled plants, and the
following tables, constructed from details given by those
authors, show to what extent the plants named were benefited
by crossing either way.
LEGITIMATE OR HETEROMORPHIC UNIONS.
LoiiK-
Short-
Differ-
styled.
Styled.
ence.
Primula veris (Wt. of seeds of 100 capsules) •t-G2
is to
44
18
P. elatior (Av. No. of seeds per capsule) 46-5
jj
47-7
1-2
P. vulgaris
■f66-9
)j
65
1-9
„ var. alba [Scott]
19
)>
21
2
P. Sinensis „
50
)j
§64
14
„ [Hildebrand]
41
)j
44
3
P. Auricula [Scott]
73
J)
§98
25
P. Sikkimensis „
35
J)
§42
7
P. cortusoides „
51
)»
§61
10
P. involucrata „
66
j»
69
3
P. farinosa ,,
52
)j
56
4
Hottonia pal. [Muller]
t91-4
ji
66-2
25-2
Pulmonaria off. [Hild.]
1-3
M
1-57
0-27
Mitchella repens
t4-G
J'
41
0-5
Liuum grandiflorum
5-6
J»
4-3
1-3
L. perenne
7
S»
8
1
L. flavum (3 flowers produced capsules)
1
)J
3
2
* Forms, etc, p
1. 20.
HETEROSTYLISM. 205
The fii'st observation is that in twelve cases the sliort-
styled are in excess of the long-styled, and in four cases (f ) this
is reversed. Hence Mr. Darwin's conclusion is not absolute ;
and it is a somewhat remarkable fact that Primula veris (the
Cow\slip) is the identical species from which he deduced the
conclusion that the short-styled was the more feminine of
the two forms. The conclusion now arrived at from this
species would be, that when it is left to itself the short-styled
form sets most seed ; but when artificially crossed it is the
long-styled form which bears best. The cause of the former
result is that some pollen in the short-styled form can fall
upon the stigma and so secure self-fertilisation, which is
impossible in the latter case. The same results occurred with
Mr. Scott.*
Hence Mr. Darwin's first conclusion, that the short-styled
was the more feminine, was drawn from a wrong premise;
as it was not a question of sex so much as of union. When
the results of self-fertilisation are compai'ed, as given in the
table on next page, it appears that the long-styled form of
the Cowslip is the more feminine of the two, in the pro-
portion of 42 to 30.
Of that table, three cases of Primula sp. (f) only show the
short-styled bearing more seed than the long-styled when
illegitimately fertilised ; viz., with Mr. Scott, P. vulgaris, var.
alha, and P. Auricula (i.e. forms more or less modified by
cultivation) ; and with Hildebrand, P. Sinensis, when crossed
* Jovrn. Linn. 8oc. Bot., vol. viii., 1864. This case may be taken to
illustrate one of the disadvantages often accruing through great diiferenti-
ation and adaptation to insect visitors. Though it appears proved that
legitimate crossing sets most seed when carefully and artificially
effected; yet, when the process is left to the capricious visits of insects,
Mr. Darwin's experiments show how nature fails to derive the full
benefit of intercrossine: ; so that the Cowslip has to be contented with the
results of the illegitimate union of the lea?t fertile of the two forms.
20
206
THE STRUCTURE OF FLOWERS.
by distinct plants. The difference, however, being only two
in each ease, is practically inappreciable.
Of the other genera, Linum shows a slight inclination in
favour of short-styled ; but as this genus is exceedingly
barren when illegitimately fertilised, the results here given
of that plant are insufficient for deducing conclusions ; at
all events, these tables show that the long-styled form is
certamly more prolific when illegitimately fertilised, than the
short-styled form when similarly treated.*
ILLEGITIMATE OR HOMOMORPHIC UNIONS.
Primula veris (Wt. of seeds of 100 capsules) 42
P. elatior (Av. No. cf seeds per capsule)
P. vulgaris
)»
,, var. alba [Scott]
»
P. Sinensis „
>)
„ [Hild.] (plants distinct)
j»
„ „ (same flower)
)i
P. Auricula [Scott]
»
P. Sikkimensis „
»
P. cortasoides „
7f
P. involucrata „
ty
P. farinosa „
ai
Hottonia palustris [Miiller]
(plants distinct)
)>
„ „ (same flower)
>»
Pulmonaria off. [Hild.]
>»
Mitchella repens
»
Linum grandiflorura
91
L. pereuno
J>
.ong-
Short-
Differ-
;yleu.
Btyled.
ence.
42
30
12
27-7
121
15-6
52-2
18-8'
3-4
11
tl3
2
35
25
10
18
t20
2
17
8
9
12
tl4
2
14
8
6
41
38
3
38
28
10
30
19
11
77-5
18-7
58-8
15-7
G5
9-2
0
0
0
2-2
2
0-2
2-5
t4-2
1-7
0
t3
3
' "Too low"?
Referring to the column of Differences in the first table,
it will be noticed that two of the four marked (|) of the long-
styled are considerable, namely, P. veris and Hottonia ; but the
* Mr. Darwin noticed that this was the case with the genus Primula
il.c, p. 48).
HETEROSTYLISM. 207
otlier two are practically inappreciable. On the other hand,
considering every difference under 5 as inappreciable, there
are four cases (§) of the short-styled in which it is consider-
able ; and of these it was only 3 in the case of P. Sinensis with
Hildebrand ; consequently one cannot confidently say that the
short-styled is more feminine than the long-styled — at least,
to any well-marked extent.
With the corresponding column in the second table, one
notices nine cases whei'e the difference is great ; while in all
of those marked (f) it is inappreciable. Hence the con-
clusion is much more pronounced in favour of the greater
fertility of the long-styled forms when illegitimately crossed.
Miiller accounts for " the greater productiveness of
illegitimate crossings in the case of the long-styled form
of Sottonia than in short-styled flowers, to the fact that the
former kind of illegitimate crossings occur frequently in
nature ; as these flowers are visited by pollen-seeking flies
which have no need to thriist their heads into the flower
of the short-styled form," which is, therefore, presumably
neglected.*
The table I have here drawn up shows that the greater
fertility of the long-styled form when illegitimately fertilised,
is a general feature of hetei^ostyled plants, and not peculiar
to Hottonia palustris ; hence we must look to a more general
cause.
As another hypothesis, it may perhaps be suggested that,
as the homomorphic condition of sJiort stamens with a short
style seems to have been the primitive form, then in the
* If Miiller's idea be true, Hottonia furnishes another instance of
the disadvantage of great differentiations, and is only one degree better
ofE than the Cowshp. In either case, one is inclined to ask what has
become of the proper insects (whatever they may be) required for the
perfect intercrossing of these flowers.
208 THE STRUCTURE OF FLOWERS.
long-styled form the stamens are unchanged, while the pistil
has elongated ; whereas, in the short-styled form, with now
elevated stamens, these and their pollen have presumably
become differentiated, while the pistil has remained un-
changed. Now the above result appears to indicate the fact
that the long-styled ])istil has not become physiologically
differentiated to so great an extent as the pollen of the long-
stamened form. The result is that it can be fertilised by the
unchanged pollen of the same form more easily than the short-
styled primitive form of pistil by the more highly differentiated
pollen. This is not stated as a proved fact, and must be
only regarded as a hypothetical suggestion. The extreme
limits of differentiation are reached when the flower is
heterostyled in form but dioecious in function. Thus
^giphila ohdurata seemed to Mr. Darwin to be in a dioecious
condition, but derived from heterostylism, in which the
long-styled Avas apparently female, and the short-styled
male.
The species which shows the most marked difference
between the produce of the legitimate fertilisation of the
two forms is P. Auricula (or cultivated vars. of Auricula).
It had been asserted by Prof. Treviranus that the long-styled
unions were absolutely barren.* Mr. Scott shows that this
idea arose from the fact that the plant in question had not
been crossed. His experiments prove that the short-styled
is the most fertile, whether legitimately or illegitimately
crossed, though in the latter the difference is slijjhter : in
the former the ratio being 8 to 6 ; and in the latter, 7 to 6.
Homostyled forms of P. Auricula are not uncommon. Mr.
Scott found that 9 capsules gave 272 seeds, or an average
of 30 seeds per capsule. Compai^ing this with the following
results, its extreme fertility becomes apparent : —
* Scott, I.e., p. 90.
HETEROSTYLISM. 209
Sliort-styled X homostyled gave 8 seeds per capsule.
Short-styled X short-styled „ 14 „ „ „
Long-styled X homostyled „ 5 „ „ „
Long-styled X long-styled -„ 12 „ ,, „
The pollen of the homostyled resembled that of the long-
styled in appearance, though the stamens were situated high
up as in the usual short-styled form. This seems to corrobo-
rate Avhat was said above ; for we have here also a long pistil
fairly fertile with undifferentiated pollen.
Another species of Primula which often bears homo-
morphic flowers is P. Sinensis. Mr. Darwin's attention was
first directed to it by observing a long-styled plant — de-
scended from a self-fertilised long-styled parent — with the
stamens low down but with the pistil of the short-styled
form, though the length of the stylo varied in different
flowers on the same umbel. He fertilised eight flowers with
their own pollen, obtaining five capsules with an average of
forty-three seeds. The examination of the pollen of two
equal-styled plants showed a vast number of small shrivelled
grains. In the case of two white-flowered plants, in which the
pistil was neither properly long-styled nor short-styled, the
size of the grains was in the proportion of 100 to 88 ; whereas,
between perfectly characterized long and short-styled plants
it would have been 100 to 57.
Of the first-mentioned homomorphic plants, four spon-
taneously yielded 180 capsules, with an average of 548
seeds, one containing 72 ; a result higher than could be
expected of either form if self-fertilised. The next genera-
tion proved to he all equal-styled, i.e. the grandchildren of
the four original plants. One of these bore an average of 68
seeds per capsule, with a maximum of 82 and a minimum of
40. Thirteen capsules, spontaneously self-fertilised, yielded
an average of 53"2 seeds, " with the astonishing maximum, in
210 THE STRUCTURE OF FLOWERS.
one, of 97 seeds. In no legitimate union has so high an
average of 68 seeds been observed by me, or nearly so high
a maximum as 82 and 97." *
I give these results of homostyled Auriculas and Chinese
Primroses as illustrating the principle so abundantly proved
amongst other plants — that as soon as they begin to retrace
their steps from a prevailing diffei-entiated condition self-
fertilisation is rapidly resumed, and there follows a resumption
of a vastly increased rate of seed-making. They prove, too,
that however apparently stable these highly differentiated
states may normally be, various conditions of environment
can readily break them down ; thus, with cultivated plants,
usually so much stimulated, starvation is a potent cause.t
Linum perenne, as the above table shows, is particularly
barren when illegitimately fertilised, but a single branch on
a plant has been known to become homomorphic, and then
to set seed abundantly ; this occurred with Mr. Meehan.
Warming found Menyantlies trifoliata to have become com-
pletely homostyled in Greenland.
Trimorphic Flowers. — As a type of heterostylism where
a species adopts three forms, L. Salicaria may be taken.
Briefly summarizing Mr. Darwin's elaborate experiments on
* Forms of Flov;ers, pp. 218-221.
t It is not only true -with heterostyled plants, but the rule applies
generally to highly cultivated flowers, that degeneracy from a floral point
of view is correlated vdth enhanced powers of self-fertilisation. Thus
a professional cultivator of Cyclamens is in the habit of keeping a stock
of " worthless " weedy-looking plants, for the express pui'pose of raising
seedlings, as they are so much more prolific than the true florists' types.
Having obtained them, he then crosses them, and brings them up to the
standard required. Indeed, the fact is well known to all cultivators, that
the poorer the plant may be, from the florists' point of view, the better
seed-bearer is it ; and that continually crossed and " perfect " flowers
are proportionally impotent or tend to become so, when a tendency to
become petaliferous often affects the essential organs.
HETEROSTYLISM. 211
tliis plant, he fonnd that the flowers van'onsly crossed gave
the following results (omitting decimals under .6) : — *
A verage
P.c. of
Formed
Knnil)er
Flosvers.
How crossed.
capsules. (
3f Seeds.
Long-styled
... 38
legit.
with
mid-styled,
>)
.. 51
jj
... 84
J>
>>
short-styled
»>
.. 107
Sliort-stj'led
... 83
))
?»
long-styled
»
.. 81
)>
... 61
rj
»
mid-styled
»
.. 65
Mid-styled
... 92
yy
>7
long-styled
)>
.. 127
»
... 100
^,
>)
short-styled
l>
.. 108
.•5
... t25
illegU
• n
long sta. of m
•d-st.
»
.. 55
t)
... 93
jj
)j
long sta. of short-st.
»
.. 69
»>
... 54
)i
M
short sta. of 1(
3Dg-St.
>J
.. 47
»
... to
J)
)J
short sta. of mid-st.
)>
0
From these results Mr. Darwin concluded that each form
of pistil is as fullj fei'tile as possible, only when it receives
pollen fi'om the stamens of the same length as itself, these
being legitimate unions. It will be seen that the mid-styled
form is the most fertile of the three when legitimately fer-
tilised ; and as all illegitimate unions of the long- and short-
styled forms were too sterile for any averages, the mid-styled
form is also the most fertile when illegitimately crossed, and
is least fertile with its own stamens, as indicated above by
the (t). Hence self-fertilisation in this species is at a very
low ebb.
A few more remarks deduced from Mr. Darwin's observa-
tions t may be added here. From the three forms occurring
in approximately equal numbers in a state of nature, and from
the results of sowing seed naturally produced, there is reason
to belief that each form, when legitimately fertilised, repro-
duces all three forms in about equal numbers.
When they are illegitimately crossed with pollen from
the same fonn, they evince a strong but not exclusive tendency
to reproduce the parent form alone.
* Forms of Floicers, p. 152. f L.c. p. 203.
212 THE STRUCTURE OF FLOWERS.
When the short or niid-stjled forms were illegitimately
crossed by the long-styled, then the two parent forms alone
were reproduced, bat in no case did the third form appear.
When, however, the mid-stjled form was illegitimately
fei'tilised by the longest stamens of the short-styled, the seed-
lings consisted of all three forms. This illegitimate union was
noticed as being singularly fertile, and the seedlings themselves
exhibited no signs of sterility, but grew to the full height.
Finally, of the three forms, the long-stjled evinces some-
what the strongest tendency to reappear amongst the off-
spring, whether both, or one, or neither of the parents are
long-styled.
Although L. Salicaria has not, as far as I know, shown
any signs of variability in the lengths of its filaments and
styles, yet, as is perhaps generally the case with heterostyled
plants, there are one or more species of the same genus which
are normally homostyled. Thus L. hyssopifolium, which is
not social, and is a dwarf form and an annual, bears only six
to nine stamens, the anthers of which surround the stigma,
which is included within the calyx. The three stamens,
which vary in being present or absent, correspond with the
six shorter stamens of L. Salicaria. The stigma and anthers
are upturned as in the last species, and so indicate the fact
that it is a degenerate form from L. Salicaria or some other
intercrossing species, though it has now reacquired its self-
fertilising properties. Oxalis is a genus haviiig trimorphic
species. Many of them are extremely infertile with their
" own form " pollen. Such are the long-styled form of 0.
tetrapliylla, versicolor, Brasiliensis, and cornpressa. On the
other hand, in the long-styled form of 0. incarnata, rosea,
and Piotta', and in the mid-styled form of 0. carnosa, no self-
sterility occurs.*
* According to Hildebrand, Bot Zeitg., xlv., pp. 1, 17, 33.
HETEROSTYLISM, 2l:i
Origin of Heterosttlism. — The question may be now
asked, How has hetevostylism arisen ? We have seen, in the
first place, that in many cases there is a certain instability in
the length of the filaments of tlie stamens and of the styles,
in that they ai'e liable to alter spontaneously, and especially
under cultivation.* In the case of Primula Auricula, the
homomorphic form has the anthers and stigma at the orifice,
while in P. Sinensis they are often both low down ; it is clear
that either might arise in two ways. In the case of the formei",
the stamens, while resembling in position that of the stamens
in the short-styled form, have pollen like that of the long-
styled, the pistil being of that kind. Hence it is reasonable
to assume that the anthers have been uplifted. In the
Chinese Primrose it is the reverse ; so that the pistil
of a long-styled form has been loioered to the level of the
stamens; the stigmas, too, are that of the short-styled.
Eecognizing this instability of the essential organs, it is
reasonable to assume that it may be due to varying degrees
of nutrition which can readily bring about such changes, a
relatively strong vegetative vigour elevating the stamens in
the one case, while a slight tendency to degeneracy with
lessened vital vigour tends to suppress the pistil in the other.
Assuming a homomorphic form to have been the primitive
and ancestral state, we can realize how dimorphism has been
brought about by such varying degrees of stimulus having
been applied to the stamens and pistil. Insect agency
I take to have been this cause, which, at the same time, has
by selection fixed the heights of the stamens and style so
* See the description, given above, of Narcissus cernuus, Fig. 37,
p. 121. Mr. Darwin found Gilia to vary much in this respect. It may
be added that it is a not uncommon feature in flowers which are not
heterostyled, as e.^. cultivated Gladioli and C'roci, Fritillaria Meleagris,
etc.
214 THE STEUCTURE OF FLOWERS.
as to render them permanently dimorphic for legitimate
fertilisation. The predominant insect or insects were (as I
surmise) the direct cause of arresting the fluctuations which
they themselves, as well as accidental soui'ces of nutriment,
had set up in the lengths of the essential organs, thus
compelling them to retain their anthers and stigmas at the
correct height.
If there were from one to three prominent kinds of
insect-visitors the flowers might become adapted to them,
and trimorphism be the result ; if four, tetramorphism ; and
there is no a priori reason why there should not be jDolymor-
phic flowers as well, in the strict sense of the pi'efix of that
term, provided a flower could farnish a sufficiency of stamens.
It is further to be noticed that the rule holds good with
heterostyled plants, as with all other kinds of differentiation,
that in nature, whenever self-fertilisation can be effected,
more seed is borne than by the forms requiring intercrossing.
First, whenever it can be brought about mechanically ; as
has been observed in P. Sinensis, by the corolla, when falling
off, dragging the anthers over the stigma in the long-styled
form, which consequently yields more seed.* In P. veris, it
does not do so ; but as pollen can fall in the short-styled
form, in this species that form is thus the most fertile (see
above, p. 205).
Secondly, when these plants are artificially and legiti-
mately fertilised, and not left to the chance visits of
capricious insects, then the results are as i\\ej should be ;
but if self-fertilisation be artificially and repeatedly practised,
then nature responds to the act ; the anthers and pollen may
in part degenerate, but what is left good is ample to secure
abundant seed, and the self-fertilised form surpasses even the
* Darwin found that, in the absence of insects, the long-styled form
of P. Sinensis was twenty-four times as productive as the short-stjled.
HETEROSTYLISM. • 215
legitimately fertilised heteromorpliic unions in fertility.
Thus, Mr. Darwin observes, " The self -fertility of Primula
veris increased after several generations of illegitimate fertili-
sation, which is a process closely analogous to self-fertilisa-
tion." *
Lastly, if homomorphic forms occur spontaneously, as is
often the case with species of Primula, Mr. Darwin has
shown they are not only " capable of spontaneous legitimate
fertilisation, but are rather more productive than ordinary
flowers legitimately fertilised." f
It was Mr. Scott who suggested that the equal-styled
varieties arose through reversion to a former homostyled
condition of the genus. Mr. Darwin supported this view in
consequence of observing " the remarkable fidelity with which
the equal-styled variation is transmitted after it has once
appeared." |
* Cross and Self Fertilisation, p. 351.
t Forms of Flowers, p. 273; and Cross and Self Fertilisation, p. 352.
X Forms, etc., p. 274; Mr. Darwin was so profoundly impressed witli
the supposed advantages of intercrossing, that he again and again
asserts most positively that self -fertilisation is injurious, often in
diametrical opposition to his own statements and experiments. Thus,
while speaking of heterostyled trimorphic plants, he says, " As I have
elsewhere shown (The Effects of Cross, etc.), most plants, when fertilised!
with their own pollen, or that from the same plant, are in some degree
sterile, and the seedlings raised from such unions are likewise in soma
degree sterile, dwarfed, and feeble." Yet, in the work quoted, he has
not only shown that, when he persevered with self-fertilisation for several
generations, he found it was just the reverse ; as e.g. with " Hero" Ipomcea,
the white Mimulus, etc., and with Primula, as stated above ; but he
more than once draws an opposite conclusion, as when speaking of self-
fertile varieties {I.e., p. 352) : " It is difficult to avoid the suspicion
that self-fertilisation is in some respects advantageous. . . . Should this
suspicion be hereafter verified, it would throw light on the existence [of
cleistogamy]." It is this " suspicion " which I have completely veri-
fied J and, indeed, any idea of " injurionsness " is refuted by the majority
216 . THE STRUCTURE OF FLOWERS.
Besides the more obvious differences in the relative
lengths of the styles and filaments* of heterostjled flowers,
the rule is for the stigmas of the long-styled to be larger or
longer than those of the short-styled,t and to have their
papillae longer and broader..
Thus in the nine species of Primula described by Mr
Darwin, in two only were the stigmas nearly alike in both.
Of three species of Linum, L. fiavum alone had an appre-
ciable difference in the stigmas. In Pulmonaria officinalis
and Polygonum fagopyrum, Forsythia suspensa and ^gipUla
elata, it was not, or scarcely appreciable.
Again, besides those mentioned there were twenty species
in which the stigmas of the long-styled were markedly
superior to those of the short-styled.
of plants in a wild state being constantly self-fertilised, as Miiller,
and, indeed, Mr. Darwin himself has shown to be the case. Thus,
he gives two lists, of forty-nine species in each, (Cross and Self Fert.,
etc., pp. 357 and 365), one of self-sterile, the other of self-fertile plants, and
adds, " I do not, however, believe that if all known plants were tried in
the same manner, half would be found to be sterile within the specified
limits; for many flowers were selected for experiment which presented
some remarkable structure ; and such flowers often require insect aid "
{I.e., p. 270). The proportion of self-sterile plants is, in fact, extremely
small. Miiller remarks, e.g., of the highly differentiated order Scrophu.
larinem, that " in default of insect-visitors, self-fertilisation takes place
in most forms ; and in only a few are insect-visits, and consequently
cross-fertilisation, so far insured that self-fertilisation is never required
and has become impossible." Similarly of Lahiatce he says, "Self-
fertilisation seems to be rendered impossible only in the species of
Ni'jKta, Thymus, Mentha, and Salvia described" (Fertilisation, etc., pp.
464. and 503). Moreover, while Mr. Darwin includes the Fox-glove and
Linaria vulgaris among his sterile plants, Miiller considers them both
to be self -fertilising.
* Exceptions occur, thus Cordia and Linum grandiflorum have little
or no diSerence in the length of the stamens.
t Leucosmia Burnettiana is remarkable for having the stigma of the
short-styled form the more papillose (Forms of Fhivers, p. 114).
HETEROSTYLISM. 217
On the other hand, the anthers of the short-styled are
usually longer and contain larger pollen grains than those
of the long-styled, the pollen of which is also often more
translucent and smoother.
Of all the species included in the above-mentioned thirty-
six species, only five seem to have the pollen of both forms
of the same size, and two in which it was reversed. The
five species are Leucosmia Burnettiana, Linum grandijlorum,
Cordia, Gilia pulchella, and Coccoeypselum. The two in which
the pollen grains of the long-styled form were the larger,
were Gilia inicrantha and PJilox suhulafa.
The presence of cases where the usnal differences are not
pronounced is just what one expects to find, in accordance
with the laws of differentiation ; whereby intermediate
conditions are to be looked for. Thus some species of
Frirmda afford great differences in the shapes of the stigmas,
P. veris being globular in the long-styled, and depressed
in the short-styled; while in P. Sinensis it is elongated:
but in other species, as P. Sihkimensis and P. farinosa, there
is but little difference between the stigmas of the two forms.
In some cases the differences reside entirely in the stamens or
pollen grains, as in Forsytliia suspensa, in which, although
(contrary to the rule) the anthers of the long-styled are in
length as 100 : 87 compared with the short-styled, yet the
pollen grains are as 91< : 100, which agrees with the rule.
With-Linum grandijlorum and Cordia and Gilia pulchella, etc.,
the difference lies in the pistil. On the other hand, the
difference may reside in the stamens, as in JEgiphila elata,
the pollen grains being as 62 : 100, i.e. in the long-styled as
compared with the short-styled.
J^giphila ohdurata has the stigmas of the long-styled
in length 100 : 55 as compared with the short-styled ; and
the length of the anthers as 44 : 100. This is, therefore,
21
218 THE STRUCTURE OF FLOWERS.
apparently truly heterostyled, but from Mr. Darwin's obser-
vations he thinks the shoi't-styled incapable of fertilisation ;
moreover the anthers of the long-styled form were " brown,
tough, and devoid of pollen." He considers that, from having
been heterostyled, it has now become dioecious, or else gyno-
dioecious.
M. W. Burck has shown* that several genera of
RubiaceoB are heterostyled in form but quite dioecious.
Faramea affords another curious difference. In the long-
styled form the stigma is short and broad ; in the short-
styled, it is long, thin, and curled. The anthers of the
short-styled are a little larger than those of the long-styled,
and the size of their pollen grains are as 100 : 67. But the most
remarkable difference (of which no other instance is known)
is in the fact that while the pollen grains of the short-styled
forms are covered with sharp points, the smaller ones are
quite smooth. The anthers, moreover, rotate outwards in
the short-styled, but do not do so in the long-styled flowers.
A similar rotation takes place in some of the Cruciferce, and
facilitates intercrossinof. A somewhat analogous torsion
occurs in some styles and stigmas, as of Linum perenne,
Luzula arvensis, Begonia, etc.
The smaller and smooth pollen, in the more degenerate
condition of the long-styled form, is suggestive of the origin
of that of wind-fertilised flowers, which has sometimes
acquired the same form. Indeed, the two forms of pollen
(figured by Mr. Darwin at p. 129 of Forms of Floivers) exactly
correspond to the very common spinescent form in inter-
crossing species of Comj^osite, and to that of the anemophilous
Artemisia of the same order, respectively.
The general conclusion, therefore, derived from the com-
* 8ur V Organisation Florale chez quelques Rubiac^es. Ann. Jard.
Bot. Buitenzorg 3, p. 105.
HETEROSTYLISM. 219
parison of these minute details, is that the long'-styled. form
of flower represents a more fully developed pistil, and
therefore a more female condition ; while the short-stjled is
more male : and, as we bave seen above, this is borne out by
the comparison of the offspi-ing ; and, lastly, by the probable
dioecious condition of jEgipliila ohJurafa, as well as by the
actual dioecism of some species of Miisscenda and Morinda
umbellata ; while Musscenda cylindrocarpa and certain other
species of Morinda are hermaphrodite without heterostylism
(Burck, I.e.).
220 THE STRUCTURE OF FLOWERS,
CHAPTER XXIV.
PARTIAL DICLINISM.
Gtnodicecism and Gynojioxcecism. * — In accounting for the
origin of certain floral structures, it must be borne in mind
that the habits and constitutions of plants are so infinitely
various, that the interpretation given for that of a structure
in one case may fail to be satisfactory when tested by
another ; and an argument apparently sound for the expla-
nation of a special phenomenon in a particular plant or
plants may not at all apply to that of others. Thus, while
the Hazel may mature its stamens befoi-e the pistils on a
slight rise of temperature in early spring, there are many
herbs, if they happen to blossom in spring earlier than is
their custom, in summer, or what may be their optimum
period, may have the staminal whorl more or less deranged,
as such plants require a relatively higher temperature to
develop them perfectly. f This is particularly characteristic
of gynodicecious plants. Thus, e.g., most of the distinctly
pi'Otandrous species of the Alslnecu are in this condition, and
* Gyinidi(rri?m signifies that the same species may have both female
and hermaphrodite plants.
Gynomonoecism signifies that the same plant may bear both female
and hermaphrodite flowers.
t This will be discussed more fully in the next chapter.
PARTIAL DICLINISM. 221
the plants with small, usually pistillate flowers are chiefly
in blossom at the beginning of the flowering period of the
larger-flowei'ed hermaphrodite plants of this section of the
Caryopliyllem. Similarly, Gaffear arabica produces small pis-
tillate flowers in Guatemala at the beginning of the season. *
It is the same with Geranium, macrorhizon and many species
of Pelargonium, etc. f
Gynodioecism also prevails in the Lahiatce, but both female
and hermaphrodite plants for the most part blossom simul-
taneously in summer. It may be noticed that the corolla is
almost invariably reduced in size in female flowers, whether
the species be strictly dioecious as in Bryony, or gj^nodioecious
as Thyme, showing the close interdependence between the
corolla and stamens, "l
That climatal conditions are likewise connected with
the Gynodioecism of the Labiatce seems probable from the
behaviour of Thymus Serpyllum ; for Delpino found that it
was trimorphic in the warmer region of Florence, having
flowers with greatly developed stamens and the pistil in
every stage of abortion or even absent (see Chapter XXV.) ;
other flowers showed the exact converse ; and, lastly, others
were hermaphrodite. Muller, however, on the other hand, in
Westphalia and Thuringia; Ascherson, in Brandenburg;
Hildebrand, in the Rhine provinces; and Mr. Darwin, in
Eno-land, never met with the purely male form ; though
Dr. Ogle found some with the pistil permanently immature. §
Similarly, Eriophorum angustifolium is gynodioecious in
Scotland and the Arctic regiogs-H
Besides temperature, the character of the soil has most
probably much effect in bringing about this kind of partial
* Muller, Fertilisation, etc., p. 304. t L.c, p. 158.
X See Forms of Flowers, pp. 307-309.
§ Muller, l.C; p. 474. U Forms of Flowers, p. 307.
222 THE STRUCTUKE OF FLOWERS.
diclinism. Mr. Darwin tliouglit " a very dry station
apparently favours the presence of the female form,"* i.e.
a lessened vegetative vigour tends to check the development
of the corolla and stamens, especially if a low temperature
accompanies it ; just as, conversely, we have seen how a
high temperature enhances it. Mr. Hart thus found that,
with Nepeta Glechoma, all the plants which he examined near
Kilkenny were females ; while all near Bath were hermaph-
rodites, and near Hertford both forms were present, but
with a preponderance of hermaphrodites. f
Both Miiller and Mr. Darwin offer theories to account for
the origin of these gynodioecious plants.
Miiller, after quoting Hildebrand's view, which he rejects, J
says,§ " Of the flowers of the same species growing together,
the most conspicuous are first visited by insects, and if the
flowers on some plants are smaller than on others, perhaps
owing to scanty nourishment, they will generally be visited
last. If the plant is so much visited by insects that cross-
fertilisation is fully insured by means of protandrous dicho-
gamy, and self-fertilisation is thus rendered quite needless,
then the stamens of the last-visited small-flowered plants
are iiseless, and Natural Selection Avill tend to make them
disappear, because the loss of useless organs is manifestly
advantageous for every organism.
" This explanation rests upon the hypotheses, (1) that
the flowers of those sjiecies in which small-flowered female
plants occur together with large-flowered hermaphrodite
plants are plentifully visited by insects and are markedly
* Forms of Floivers, p. 301
t Mature, 1873, p. 1G2; and see below, p. 239.
X FertiUsatiiw., etc., p. 473.
§ L.c, p. 484. Compare his remarks on Scahiona arvensis, I.e., pp.
310, 311.
PARTIAL DICLINISM. 223
protandrous ; (2) that variation in size of the flo\vers has
always taken place, not among the flowers on a single plant,
but between the flowers on different individuals."
Mr. Darwin suggests another view : * " As the production
of a large supply of seeds evidently is of high importance
to many plants, and . . . the females produce many more
seeds than the hermaphrodites, increased fertility seems to
me the more probable cause of the formation and separation
of the two forms."
" S. M.," reviewing Mr. Darwin's work in the Journal of
Botany, 1877, p. 375, "felt compelled to differ from the
author, and adds, " For ourselves we cannot help thinking
that gynodioecism can be better explained on the view of a
suflicieucy of pollen for the fertilisation of all the individuals
of a species being produced by only a few of the flowei'S,
so that instead of some of the anthers of all the flowers
becoming abortive — a very common occurrence — we see here
abortion of all the anthers of some of the flowers. . . . All
known instances of gynodioecism relate to species Avhich
have the maximum of stamens possessed by the orders to
which they relatively belong, and are without any complex
entomophilous structure. . . . We may also remark on the
pauciovulate condition of gynodicecious species, and ask why
do we not see this form of sexual separation in multiovulate
ones ? "
In reply to this writer's suggestions, I would remark
that in all entomophilous flowers far too much pollen is
produced and Avasted ; that Mr. Darwin's observation, that
a bee could fertilise ten pistils with pollen from one flower
of Satureia, might readily apply to hundreds of cases where
no g^-nodioecism exists ; and as long as insects visit flowers
the tendency is not to contabescence and abortion of the
* Forms of Flowers, p. 304.
224- THE STRUCTURE OF FLOWERS.
anthers, but to higher differentiations and an increase in the
quantity of pollen. Secondly, that the orders, with gyno-
dicEcism have the maximum of stamens, is not universally
true, Pelargonmm having only seven out of ten. Again, the
Labiatce are especially characterized by " entomophilous
structures." Lastly, the order Caryophyllece is multiovulate.
In the first two interpretations, those of Miiller and
Darwin, Miiller suggests scanty nourishment as a cause for
the diminished size of the female flowers, which might apply
to any or every protandrous plant and so give rise to gjno-
dioecism ; for if it be a sufficient cause in one family, why has
it not brought it about in all ? This cause alone does not
touch the question, Why is gynodioecism peculiarly common
in the Alsinece of the Caryophyllece and in Lahiatoi ? Mr.
Darwin thinks that an increased fertility of the female may
be the cause; but he seems to forget that no flower of the
Labiatce can bear more than four seeds, so that, supposing a
female plant to have the same number of flowers as a her-
maphrodite, if it bears more seeds it must be due to the
decrease in fertility of the latter, and not to any increase in the
former. * It is, in fact, a very common occuiTence for a flower
of any member of the Labiatce to bear one, two, or three only,
as well as four nutlets in an individual fruit. Mr. Darwin
" doubts much whether natural selection has come into play,"
and notices that " the abortion of the stamens ought in the
females to have added, through the laAV of compensation, to
the size of the corolla," as is the case in the ray florets of
the gynomonoecious Compositce. He, however, recognizes the
* In his experiment with Satureia hortensis, Mr. Darwin collected
seeds from the finest of ten female plants, and they weighed 78 grains ;
while those from the single hermaphrodite, which was a rather larger
plant than the female, weighed only 332 gi'ains j that is, in the ratio of
100 to 43 (Forms of Flowers,_-p. 303).
PARTIAL DICLINISM. 225
intimate connection between the corolla and androecium, and
thinks that " the decreased size of the female corollas is due
to a tendency to aboi-tion spi-eading from the stamens to the
petals."
In noting all the plants mentioned by Miiller and Mr.
Darwin as gynodioecious, there are besides the two well-
marked groups already mentioned, viz., Alsinece and Lahiatce,
the following isolated genera or species, Pelargonium, Gera-
nium macrorhizon, Slwrardia arvensis, Valeriana montana,
Scabiosa, Cnicus, Ecliium vulgare and Planfago ; to the
Compositce, I can add Achilkea millefolium; and I think
also Vines may be included in the list.
The first and important point to note about the flowering
of the Alsinem is that the female flowers are the first to open,
at the beginning of the season* It is the same with Geranium
macrohizon. Pelargonium, and Coffee in Guatemala. Kow,
Ave have already seen how sensitive the androecium and the
corolla are to a low temperature, so that we have here a direct
cause which will account for the check upon the growth and
development of these two whorls. Applying this principle
to the Labiatce, we must remember that as a group they are
correlated to a warmer climate, their "home" being the
Mediterranean and even Avarmer regions ; hence I assume
their greater hereditary sensitiveness to a low temperature
in those descendants which occapy a cooler temperate zone.
This may, I think, account for the predominance of purely
female forms, as well as the presence of stamens in every
degree of degeneracy.
How far the same principle Avill apply to the other
gynodioecious genera and species, I will not pretend to
offer an opinion, as not enough is yet known about them ;
* See Hildebraad's observation, p. 23-i, and Sexuality and Tempera-
TUKE, p. 237.
226 THE STRUCTURE OF FLOWERS.
only we must always remember that there may be a variety
of causes which may equally well bring about the same
result.
It may be also borne in mind here that another result
of low tempei'ature is, while retaining the function of the
androecium, to arrest the expansion of the corolla and to
render the flower's self-fertilising. This is peculiarly the
case with the Alsinece ; while Lamium amplexicaule fails to
open its earliest small-flowered flowers at all, being strictly
cleistogamous.
The preceding cases of gynodioecism are all associated
with a more or less degree of protandry. It is rarer to find
it accompanied with protogyny in the hermaphrodite form.
Miiller records it in Plantago lanceolata in England, which I
can corroborate, and in P. media in Germany. These plants
are anemophilous, and in a state of passage from an ento-
mophilous ancestry ; s / that it may have been retained from
an early condition.
Gynomonoecism is not particularly common, except in the
Compositcp., where the ray florets are often female, while
the disk florets are hermaphrodite. This is due to com-
pensation ; for transitional states may be seen in flowers
which are passing into the "double" condition; for as the
corolla changes its form and becomes ligulate, the stamens
are suppressed, and the style arms alter their shape.
Anemone hepatica is said to be gynomonoecious,* and also
Syringa Persica.f I have seen no case, and no description is
given of these two, so that I can only suggest that it may
be a result from degeneracy, perhaps on the road to a
petaloid condition of the stamens. Such a state I have
found in a Planfarjo which was gynodioecious.
* Dr. S. Calloni, Arch. Sci. Phys. et Nat., xiii., 1885, p. 409.
f Miiller, Fertilisation, etc., p. 393.
PARTIAL DICLIXISM. 227
Androdkecism and Andromoncecism.* — These conditions
do not appear to prevail to the same extent as the female
forms of flowers. Both of these kinds are not at all un-
common in the Uinhelli/ene, and are a result of exhaustion,
for the umbels produced at the end of the season are often
entirely male ; or, if at other periods, it is generally the
central florets which develop no pistils, as in Astrantia miiior.
Miiller has noticed how " the weaker plants usually hear but
one umbel consisting only of male flowers." This -would
make it androdioecious. I find tliat andromonoecism prevails
in Astrantia major, Carum, Smyrniuvi, and in Trinia vulgaris.
This last, growing on the Clifton downs, bore umbels Avhich
were altogether male, after the hermaphrodite ones had
formed their fruit. Dauciis grandiflora is remarkable for
having three kinds of flowers. According to Miiller, the
central ones are male; at the edge of the umbellule the
flowers are neuter, with the outermost petal greatly enlarged;
lastly, at the margin of the whole umbel, are female floi-ets
in which the outer petals attain to a gigantic size.f
* Andvodioicism signifies that the same species has both male and
hermaphrodite plants.
Andromoncecism signifies that the same plant bears both male and
hermaphrodite flowers.
t I would here remind the reader that the interpretation given
above (Chapters XI.-XIII.) of the origin of irregular corollas, applies
equally well to those cases where it is only m the outermost florets of a
cluster where the petals are enlarged, as in Iberis, many of the Com-
positce, and Umhelliferce, as well as in Hydrangea, Guelder Rose, etc. In
all these, when insects first approach the umbel and alight on the border
of it, any or each individual floret on the margin may have to carry the
burden. As soon, however, as the insect passes the edge of the cluster,
its weight is distributed over several florets ; so that they are not sub-
mitted to any special strains upon one, i.e. the outer side only. The
same remarks apply to Mentha, as compared with Lamium. The insect
visits one flower at a time in the latter, but scrambles over several in
the former, which has (presumably) degraded in consequence.
228 THE STRUCTURE OF FLOWERS.
Caltha palustris is said to be androdicecious, but no
details are given bj the observer.*
Besides the UmhellifercB,] where andromonoecism seems
to be a characteristic feature, Muller mentions Asperula
taurina and Galium Cruciata, Pulmonaria officinalis, Coriaria
myrtifolia,{nid Biospyrus Virginiana as being andromonoecious.
The hermaplirodite flowers of these species are protandrous.
In Galium Cruciata, Mr. Darwin noticed that the pistil is
suppressed in most of the lower flowers, the upper remaining
hermaphrodite.
Heterostylism may tend to produce the same result when
the stamens of the long-styled forms degenerate so far as to
become atrophied without the pistil losing its functions.
Pulmonaria angustifolia and Phlox subulata give hints of this
condition. + Asperula scoparia was at first thought by Mr.
Darwin to be heterostyled, but finding the anthers to be des-
titute of pollen, he considered it to be dioecious. A. taurina, as
figured by Mii]ler,§ shows great variability in the lengths of
the filaments and styles, and he pronounces it to be andro-
monoecious. Hence, as so many of the Pjihiacem are hetero-
styled, there seems every probability of one result of this
peculiarity, being one or other kind of this incompletely
aft'ected or partial diclinism. In the case of Coriaria myrti-
folia, Hildebrand found that it was the first flowers which
were male only. In Maples, as in Galium Cruciata, the rule is
for the three or more flowered corymb to have the central
one hermaphrodite, and the lower or outer ones male. This
* Lecoq, Geog. Bot, torn, iv., p. 488.
t Muller says that in Sanicula Europcsa the outer flowers are male,
and develop after the inner ones, which are hermaphrodite. This is so
anomalous, that one suspects an error somewhere. I have not had any
opportunity of examining fresh flowers.
X Forms of Flowers, p. 287.
§ Fertilisation, etc., p. 303.
PARTIAL DICLINISM. 229
clearly is a question of the distribution of nutrition ; the
lower, being the later ones to expand, are the weaker.*
Miiller mentions Horse-chestnuts as being also andro-
monoecious ; and. Avhat is exceptional is that the hermaphro-
dite flowers are protogynous. This, hoAvever, may be due
to the early period of flowering, like species of Primus and
Cratcegus.
The reader will now perceive that there may be several
causes at work to produce these kinds of " partial diclinism;"
and that what is required is to ascertain, if possible, by
observation and experiment, which is the one peculiar to
each species. Secondly, when any one or more causes has
been suSiciently persistent, the results become hereditary ;
so that certain species, genera, and orders become more or
less characterized by these peculiar features.
* Compare the observations on Adoxa, p. 188,
22
230 THE STRUCTURE OF FLOWERS.
CHAPTER XXV.
SEXTJALITY A2\D THE ENVIROXMENT.
General Observations. — As the environment is now known
to have most potent influences on the anatomical structure
of the vegetative system of plants, thereby affecting their
outward and visible morphological characters as well ; so are
there many causes which affect the reproductive system, at
one time influencing the andrcecium, at another the gjnce-
cium, favouring them or the reverse as the case may be ; so
that either sex or even both may be entirely suppressed, and
a hermaphrodite flower become male, female, or neuter.
With regard to the most general agency, there seems to
be a tolerably uniform consensus of opinion that the female
sex in plants is correlated with a relatively stronger vital
vigour than the male ; and this is jtist what an d 'priori
assumption would look for, as the duration of existence and
the work to be done in making fruit require a greater
expenditure of energy than the temporary function of the
stamens.
We must, however, distinguish between a healthy vital
vigour, and any excessive vegetative growth, as occurs under
high cultivation, and as is often the result of intercrossing.
If this latter surpass the requisite or optimum, conditions for
the healthy performance of the functions of all the organs
SEXUALITY AND THE ENVIRONMENT. 231
of a plant, then eitlier of the sexual organs mav beo-in
to deterioriate, till they become metamorphosed into petals
or leaves, or else degenerate and vanish.
It is true enough that we know nothing of the real nature
of life ; but it is easy to see that, of the various phases of
development, from germination to the production of seed,
each should have the proper amount of energy at its disposal,
and no more ; for if any one organ be stimulated beyond the
optimum degree, others suffer through atrophy. The first
and well-known distinction to be noticed lies, of course,
between the " vegetative energy," by means of Avhich
roots, stems, branches, and foliage are dev^eloped, and the
"reproductive energy," which brings about the formation of
flowers, fruit, and seed. If either of these be unduly excited,
the other diminishes. Thus, as long as fruit trees are
developing much wood and foliage, they either bear fruit
badly or not at all. Plants which are propagated largely
by vegetative means of multiplication, such as bulbs, corms,
tubers, etc., are notox'ious for failing to set seed as well. As
an instance in nature, Ranunculus Ficaria maybe mentioned.
This plant propagates itself by " root-tubers " and by aerial
corms, and rarely produces much fruit, for the pollen often
remains in an arrested state.* Conversely, if vegetative
energy be checked by root and branch pruning, bark-ringing,
etc., the reproductive energy is promoted, and an abundance
of fruit is the reward. Similar results follow a decrease of
energy through impoverishment, when enormous crops of
fruit may be borne by trees, as I have seen in Portugal
Laurels, when the roots had penetrated a bed of gi^avel and
the branches became decayed.
Apart from these general considerations certain special
conditions are found to favour one sex more than the other,
* See Yau Tieghem on E. Ficaria, Ann. des Sci. Nat., v., ser. 5, p. 88.
232 THE STRUCTURE OF FLOWERS.
SO that normally hermaphrodite flowers may become uni-
sexual, and every possible degree between these two extreme
cases can be met with in nature and cultivation. The
problem, thei'efore, is to discover what the immediate causes
may be in each case which stimulate or suppress the energy
required for the proper development of the stamens and
pistil respectively.
There appears to be a closer bond between the stamens
and corolla than between the two kinds of essential organs
themselves ; * thus, if the corolla degenerate, the antipetalous
stamens at least tend to follow suit, as in the Alsivece. On the
other hand, the fii'st tendency towards " doubling " appears
in a more or less pronounced petalody of the androecium.
As petals are a nearer approximation to foliar organs,
the above means that vegetative energy is more prone to
affect the stamens, when from some cause they have first
begun to lose their proper function, than the pistil.
The pistil may fail in its development from two classes
of causes : either from an undue display of the vegetative
vigour, as in completely double flowers — though it may be
unaffected in a partially double one ; or else from excessive
feebleness, under which a flower may succeed in making the
androecium, but has not sufficient energy to develop the
gynoecium ; as, e.g., often takes place in the flowers of the
Umbelliferce at the close of the season.
There is no absolute rule in these matters, and differences
result from various degrees of energy at the disposal of the
* A study of the vascular system of flowers and their axes bears this
out, as the provision made for the stamens usually arises from the
perianthial cords, while that for the pistil is mostly isolated off in rather
a more marked and independent manner. Exceptions occur, as in
Ballofa nigra, in which the four stamens originate from the same cords
as those of the placentas.
SEXUALITY AND THE ENVIRONMENT. 233
whorls, giving rise to corresponding results of different
degrees of development in the respective sexes.
The points to be clearly perceived are that a plant should
be able to develop all its organs in perfection ; that there is
an optimum degree of energy for each ; and that, though it
is customary to group these energies under the two expres-
sions, vegetative and reproductive, yet the principle may be
carried out ia detail : so that, e.g., an enlarged corolla tends
to destroy the stamens, as of the ray florets of Dahlia, or evea
the pistil too, i£ it be very large, as in Gentaurea. A stimu-
lated androecium brings about an arrest in the pistil, and
causes protandry ; and if the perianth be highly developed,
as in orchids, the enhancement of the former may cause
degeneracy in the ovules.
Sexuality and Nutritiojt. — Assuming, for the present, that
the ancestral condition of all flowers, excepting, perhaps, those
of the Gymnosperms, was hermaphrodite, many instances
exist of the same species having male, female, and herma-
phrodite flowers, such as the Ash, Silene mflata, etc., where
the aborted organs often remain more or less rudimentary.
It cannot be pretended as yet that the cause or causes can
be at all positively asserted, in each, case, for the tendency
to abortion either in the stamens or pistil ; but there are
certain well-ascertained facts which, can undoubtedly play a
part in the processes of degeneration or exaltation of the
staminal and carpellary energies respectively. If they be
sufficiently persistent the subsequent generations can, then,
become completely diclinous, without a trace of the other
sex remaining ; yet, as is well-known, any diclinous plant
may reproduce by reversion the lost sex, thereby revealing
its original hermaphroditism.
In endeavouring to trace the present condition of
diclinous flowers back to an ancestral hermaphrodite condi-
2'3i THE STRUCTURE OF FLOWERS.
tion, it will be as well to consider certain significant facts
which may help us in ascertaining the cause of their present
diclinism.
"Hildebrand has shown," writes Mr. Darwin, " that with
hermaphrodite plants which are strongly protandrous the
stamens in the flowers which open first sometimes abort, . . ,
Conversely the pistils in the flowers which open last sometimes
abort." Similarly Gartner observed that "if the anthers on a
plant are contabescent (and when this occurs it is always
at a very early period of growtli) the female organs are
sometimes precociously developed." *
A reason for this is that, on the one hand, since a higher
temperaturn is correlated with protandry, the first flowers open
when the optimum temperature has not arisen ; so that the
stamens are checked, a cooler temperature being less inimical
to the development of the gynoecium. On the other hand,
the last flowers of the seasoji are produced when the vital
energy is waning, and although the flowers may expand, they
are too feeble to develop the pistil.
Now exactly the converse may occur; thus Mr. W. G.
Smith called attention f to the seemingly unobserved fact
that Euphorbia amygdaloides always bea7\s terminal male
flowers alone at first, and subsequently the two sexes together
on lower lateral " flowers." This agrees with Castanea
Americana,^ as noticed by Mr. Median, In these two cases,
* Forms of Floivers, p. 283. I hardly think this can be always the
case ; for, of Vines growing side by side, some "will occasionally have
the anthers utterly devoid of sound pollen, but with the pistil normal ;
while others will be entirely hermaphrodite with no sign of contabescence.
I have examined such, supplied to me by Mr. Barron from the gardens
of tiie Royal Horticultural Society at Chiswick. The cause is at present
veiy obscure.
t Joiirn. ofBot., 1864, p. 196.
X Proc. Acad. N. Sci. of Philadel., 1873, p. 290.
SEXUALITY AND THE ENVIRONMENT. 235
therefore, we have instances of the plants flowering and
bearing male organs only before the highest effort of vital
energy is displayed — the preliminary and feebler effort being
capable of developing the andrcecinm alone.
With regard to diclinous trees, many examples could be
found to illustrate the principle that the female flowers are
normally produced by stronger shoots than -the male. Mr.
Meehan has particularly called attention to this fact. For
instance, " Juglans nigra* exhibits three grades of growing
buds. The largest make the most vigorous shoots. These
seem to be wholly devoted to the increase of the woody
system of the tree. Lower down, the strong last year's
shoots arise from buds not quite so large. These make
shoots less vigorous than the other class, and bear the female
flowers on their apices. Below these are numerous small
weak buds, which either do not push into grow^th at all, or
when they do, bear simply the male catkins."
Again, Castanea Americana bears two crops of male flowers,
the first of which disarticulate and are useless ; the second
appear about ten days later, accompanied by clusters of
females. Occasionall}' a tree will be entirely female.
Mr. Meehan also calls attention to the fact that isolated
trees of Birch, though producing an abundance of male and
female flowers, very often have not a perfect seed. Hazels
are sometimes protogynous, sometimes protandrous ; and if
the latter condition prevail, there may be little or no fruit,
as often occurs in Pennsylvania. After making analogous
observations on American Maples, he summarizes his remarks
on the latter as follows : —
" Male flowers do not appear on a female Maple-tree till
some of its vital power has been exhausted.
* Laws of Sex in J. Nigra, Proc. Acad. N. Sci. of Phil., 1873,
p. 290.
236 THE STllUCTURE OF FLOWERS.
" Branch-buds bearing female flowers have vital power
sufficient to develop into branches.
" Branch-buds bearing raale flowers have not vital power
enough to develop into branches, but remain as spurs, which
ever after produce male flowers only.
" Buds producing male flowers only, are more excited by
a slight rise of temperature than females, and expand at a
low temperature under which the females remain quiescent"
[i.e. when the winter temperature begins to give way to the
rise in early spring, the males are more easily excited into
maturity]. *
As another authority, I would refer to a paper by Mr,
Moore, upon the appearance of male flowei'S on female trees,
such as the Papavv, etc He alludes to Dr. Wight's views,
in that he attributes these changes " to the modifying power
of the soil and climate acting on the dormant energies of the
rudimentary ovaries and developing them into prolific fruit,
but at the cost of the male organs " In another case of the
Papaw one fertile flower was produced, and that the first
which expanded, others being all male " It wonld seem
that fertile flowers in these instances have only been de-
veloped when the greatest vital energy is present in the
plant, which is the case when they first begin to expand.
Other instances," Mr. Moore adds, " might be quoted to show
that vigour and healthiness increase the female line of vital
force in vegetables, whilst weakness is more conducive to
the male development."
This view was corroborated by a case of a young plant
of Nepenthes distillatoria, raised from seed. Mr. Moore
describes and figures it in the same paper. The lowermost
flowei'S of the raceme bore both stamens and pistil, the
* On the Relation of Heat to the Sexes of Flowers, Proc- Acad. Nat.
Sci. of Phil., 1882, p. 1.
SEXUALITY AND THE ENVIRONMENT. 237
carpels of which were somewhat dissociated. On the upper
half they were entirely male. He did not succeed in impreg-
nating any of the numerous and well-formed ovules. He
observes : " This well-authenticated case also favours the
theory that vigour in the plant is productive of the female
line of vital force." *
It is a common phenomenon for diclinous trees to change
their sex in different places or seasons. Ashes and Maples,
as well as Palms, have been known to do this. The only in-
terpretation being apparently the difference which occurs in
the climatal conditions from year to year, or the modifications
of temperature, soil, etc., consequent on different environing
circumstances.
Sexuality and Temperature. — Temperature has a marked
influence on the sexes. A relatively high temperature favours
the corolla and andrcecium, while a comparatively lower
one the gynoecium. A. Knight long ago found that Water-
melons grown with a maximum of 110° by day, usually
varying from 90° to 105°, with a minimum of 70° at night,
grew with luxuriance, but bore no fruit, though it had a
profusion of minute male blossoms. This experience is
corroborated, by present horticulturists. He was not sur-
prised, as he had for many years previously succeeded, by
long-continued low temperature, in making cucumber plants
produce female flowers only.
Mr. Median's observations on the development of buds
on certain trees appeared to coiToborate this view of
Knight's. He remarks that, in the year 1884, after a winter
of uniformly low temperature, the male and female flowers
of the nut appeared together; but in other years it was
* Trans. Irish Acad., xxiv., p. 629; see also a paper on " Sexuality,"
by Dr. M. T. Masters, Pop. Sci. Rev., xii., p. 363, 1873, and his Teratulojij,
p, 190 J also, Proc. Acad. Nat. Sci. of Phil., 1873, p. 290.
238 THE STRUCTURE OF FLOWERS.
found that a few warm days in winter would advance the
male flowers, so that they would mature some weeks before
the female flowers opened. Hence the latter were generally
unfertilised.*
That the stamens are much more sensitive to and pre-
cocious in their development under a rise of temperature, is
seen in the behaviour of plants in different countries. Thus
it is asserted f that Stratiotes aloides produces its carpels
with greater abundance towards the northern limit of its
geographical distribution, and its stamens, on the contrary,
are more frequently developed in more southern districts. J
These tendencies to check one or the other sex, may lead
to monoecious diclinism ; and even complete dioecisin seems,
at all events to some extent, due to climate, as differences
occur in widely separated countries ; thus HoncJienya peploides
is frequently hermaphrodite in America, but usually sub-
dioecious in England. §
Mr. Darwin, in his experiments, found that Mimuhis
Itifeus was very sterile in one year ; and he attributed the
fact partly to the extreme heat of the season. ||
* Proc. Acad. Nat. Sci. of Phil., 188 i, p. 116.
t Teratology, p. 196. -^
X Perhaps the propagation by apogamy of the female plants of
Chara crinita may be a resource to which this plant has been driven in
consequence of the male plants not thriving in a cool region. Sachs
says tliat the female is found throughout the whole of Northern Europe,
but the male is only known to occur in Transylvania, South of France,
and by the Caspian (Phys. of Plants, p. 801).
The idea is suggested by this that when temperature arrests the
male without checking the vegetative system, a plant may adopt
vegetative methods of multiplication. Thus, instead of regarding the
" root-tubers " and aerial corms of Ranunculus Ficaria as the cause of
the degeneracy of the pollen in that plant ; perhaps it would be more
correct to reverse the process.
§ Teratology, p. 196. || Cross and Self Fert., etc., p. 68.
I
SEXUALITY AND THE ENVIRONMENT. 239
!Mr. Darwin also records * how " a tendency to the
separation of the sexes in the cultivated Strawbeny seems
to be much more strongly marked in the United States than
in Europe ; and this appears to 4^6 the result of the direct
action of climate on the reproductive organs." Quoting
from the Gardener s Chronicle, f he adds, " Many of the
varieties in the United States consist of three forms, namely,
females, which produce a heavy crop of fruit, — of hermaphro-
dites, which 'seldom produce other than a very scanty crop
of inferior and imperfect berries,' — and of males which pro-
duce none. . . . The males bear large, the hermaphrodites
mid-sized, and the females small flowers. The latter plants
produce few runners, whilst the two other forms produce
many; ... we may therefore infer that much more vital
force is expended in the production of ovules and fruit than
in the production of pollen."
Converselv, as runners were more abuntlant with male
and hermaphrodite plants, we see here an instance of vege-
tative growth correlated with the male elements at the expense
of the female.
Sexuality and the Soil. — Miiller has given two instruc-
tive cases where it is pretty certain that the soil was a chief
cause of the separation of the sexes. J Dianthus deltoides,
near Lippstadt, offers interesting gradations from her-
maphroditism to gynodioecism and gynomonoecism. "On
the border of a meadow, of some hundred stems examined by
myself, all the flowers, without exception, proved to be pro-
tandrous, with a normal development of the anthers and
stigmas. On the grass-grown slope of a sandy hill likewise,
all the stems produced protandrous flowei-s, but on many
stems the stamens, although emerging above the petals
* Forms of Flowers, p. 293. t 1861, p. 716.
X Nature, vol. xxiv., p. 532.
240 THE STRUCTUKE OF FLOWERS.
before the development of the styles and stigmas, bore
diminished whitish anthers, not opening at all, and containing
also some shrivelled pollen-grains. Lastly, in a barren sandy
locality, many of the stems produced female flowers, with
stamens aborted in the same degree as in D. superhus, and
not infrequently such female flowers and protandrous her-
maphrodite ones are found on the same stem." Wiegman also
found the Dianthus had contabescent stamens when growing
on a dry and sterile bank. The conditions here mentioned
are very like those more than once described as associated
with double flowers, in which the stamens have also de-
generated but taken the petaloid form. Hence I think we
may directly trace the degeneracy of the anthers and pollen
to atrophy ; since chemical analyses of pollen prove that the
most important constituents required are potash, nitrogen,
and phosphorus pentoxide,* pi'obably wanting in the localities
mentioned.
" Centaurea Jacea " Midler describes f " as having its
flower-heads of the same stem aUvays of the same form, but
different stems of the same locality often present astonishing
differences in their flower-heads.
"In the most common and apparently original form, the
floAver-heads consist of florets which are all of the same
tubular shape, and all contain both fully developed anthers
and stigma, the divergence of the outer florets giving to the
whole head a diameter of 20-30 mm. From this original
form variation has gone on in two opposite dii-ections, the
final effects of this variation being, on the one side, very
conspicuous male flower-heads of 50-55 mm. diameter ; and
on the other side less conspicuous female flower-heads of
* From an analysis uf Ash blossoms, by Professor Church, Journal
of Botany, 1877, p. 36-4.
f Nature, vol. xxv., p. 2-41.
SEXUALITY AND THE ENVIKONMENT. 241
30-35 mm. diameter. In both these extreme forms the outer
row of florets possesses greatly enlarged radiating corollas
which are sexually functionless, but useful in making the
flower-mass more conspicuous. ^ In the male flower-heads,
anthers and pistils of the disk-florets are well-developed,
but the style-branches never open so as to expose their
stigmatic surfaces, and in their basal portion are grown
together. In the female flower-heads, on the contrary, only
the pistil of the disk-florets is fully developed, the anthers
being pollenless, shrivelled, and brownish coloured
" These two extreme forms are linked with the original
one by a continuous series of gradations When in the
orio-inal form variation begins in one direction, the outer
i-ow of florets gradually becomes longer and more radiating,
and in the same degree their sexual organs diminish in size
and become functionless, the anthers first aborting, and then
the pistil. Finally, the barren ray-florets continuing to
increase, the pistils of the disk-florets, too, become function-
less, and the conspicuous male flower-head is accomplished. .
" In the contrary variation some of the outer florets of
the oriodnal form besrin to diminish in size, while their
anthers become brownish and pollenless, and this change
step by step proceeds inwards and seizes a greater and
greater number of disk-florets, until the whole flower-head
is female, and reduced to a diameter of 15-18 mm. This
state bemg reached, the corollas of the marginal flowers
recommence to increase and become radiating, while at
the same time their anthers disappear without leaving any
trace, and their style-branches remain closed together."
Calendula officinalis furnishes another instance of com-
plete change of sex, most probably caused by varying con-
ditions of nutrition supplied by the soil. In the normal
" single " form the disk florets are male, but with club-
23
242 THE STRUCTURE OF FLOWERS.
shaped stigmas. The two style arms, being fused together
and strongly papillose, are only useful for thrusting out the
pollen from the anther cylinder. In " double " forms the
corollas all become ligulate, the stamens disappear altogether,
and the style arms of the pistils assume the normal form
characteristic of the ray florets. They now set seed, so that
the entire capitulum is female, and forms fruit.*
Polygamous states often occur in trees growing apparently
under the same conditions, and although we cannot doubt
that they are due to different degrees of nutrition, yet they
cannot be readily correlated to "visible differences in the
environment. Mr. Darwin thus describes the Ash : f "I
examined fifteen trees growing in the same field ; of these,
eight pi'oduced male flowers alone, and in the autumn not
a single seed; four produced only female flowers, which set
an abundance of seeds , three were hermaphrodites, and two
of them produced neai'ly as many seeds as the female trees,
whilst the third produced none, so that it was in function
a male. The separation of the sexes, however, is not com-
plete in the Ash; for the female flowers include stamens,
which drop off at an early period, and their anthers, which
never open or dehisce, generally contain pulpy matter instead
of pollen. On some female trees, however, I found a few
anthers containing pollen-grains apparently sound On the
male trees most of the flowers include pistils, but these
likewise drop off at an early period , and the ovules, which
ultimately abort, are very small compared with those in female
flowers of the same age."
It may be added that the stamens are sometimes sub-
* I found no difference whatever between the plants raised from
the larger seeds of the ray florets and the smaller ones of the disk
florets. They all gave rise to the " single " form of capitulum.
t Forms of Flowers, p. 11.
SEXUALITY AND THE ENVIRONMENT. 243
petaloid forming staminodia — another hint that " conta-
bescence " is closely akin to petalody of the androecium.
Sexuality and Heterogamy. — Another source of diclinism
may theoretically be attributed to protandry and protogyny
carried to such a degree that the opposite sex is arrested
altogether. Many plants have their flowers hovering about
homogamy, some individuals being protandrous, others proto-
gynous, according to locality, etc. Thus Saxifrages and
species of Ribes are in this condition.
We know that as soon as a flower is fertilised, the corolla
fades and mostly falls. This means that the nourishment is
now directed into the pistil. In a protogynous flower the
petals and stamens may be in a very undeveloped state, while
the stigma is ready for pollination.* If it be fertilised it
no longer requires other organs, and nourishment may be
absti-acted from the corolla and stamens, which therefore
would tend to abort. Let this procedure become hereditary,
and we get passages to female flowers. Moreover, the more
female forms tend less to degeneracy, plant for plant, than
the hermaphrodites, as Darwin showed with Satureia, and as
is known to be the case with Strawberries in the United
States, and again as is the case with the Ash, described above.
Therefore female plants might be produced abundantly which
would keep that form permanent.
Conversely, plants growing in the open with an increase
of temperature, and readily seen and visited by insects,
become strongly protandrous ; consequently the pistil is at
first delayed in development wdth a corresponding tendency
to enfeeblement in comparison with the more purely female
plants.
The results of crossing these conspicuous flowers — and
* See e.g. Miiller's figures of Saxifraga Seguieri in different stages,
Fertilisation, etc., p. 244.
244 THE STRUCTURE OF FLOWERS.
the more conspicuous the more masculine is the flower,
and the more attractive will it be — one with another, would
not therefore be so advantageous as crossing the moi-e female
plants with the conspicuous. The former, too, produce
relatively more offspring, and might tend to oust the others,
and reproduce both the "more masculine" and the "more
female " sorts. Intercrossing, therefore, coupled with en-
vironing conditions, may together bring about dioecism, as
in Strawberries. As this reasoning is rather dedticiive, it
must be only considered as a suggestion.
Sexuality and Heterosttlism. — This undoubtedly is
another source of diclinism, as already alluded to. Mr.
Darwin alludes * to Coprosma and Ilitchella as indicating
this fact. " Coprosma is dioecious, and in the male flowers
the stamens are exserted, and in the female flowers the
stigmas i so that, judging from the affinities of these genera,
it seems probable that an ancient short-styled form, beaiing
long stamens with large anthers and large pollen-grains (as
in the case of several Rubiaceous genera), has been converted
into the male Coprosma; and that an ancient long-styled
form, with short stamens, small anthers, and small pollen-
grains, has been converted into the female form. According
to Mr. Meehan,t Miicliella repens is dioecious in some
districts : for he says that one form has small sessile anthers
without a trace of pollen, the pistil being perfect ; while in
another form the stamens are perfect and the pistil rudi-
mentary. MifcJieUa, therefore, would seem to be heterostyled
in one district and dioecious in another," and this can
scarcely be due to anything but environment.
* Forms of Flowers, etc., p. 285. Sec also above, p. 228.
t Proc. Acad, of Sci. of Philadelphia, July 28, 1868, p. 183. I do not
gather from Mr. Meehan's account that he found any difference as to
locality. Dioecism appears to be a constant character.
SEXUALITY AND THE ENVIRONMENT. 245
Summarizing the various influences of the environment
as climatic^such as temperature and light, shade and
obscurity, humidity and drought, as well as varieties of soil
and degrees of nourishment, and possibly others — we soon
see how careful one must be in attributing a result to any
one or special cause alone. What we can do is, as it were,
to pick out of them, as tolerably well-ascertained, condi-
tions which seem to favour, say, the female as compared with
the male organs or flowers — such as, e.g., a mean or optimum
condition of vegetative energy, a relatively low temperature,
no excess of nutriment, a due amount of light, humidity,
etc.; or again, on the other hand, a relatively higher tempera-
ture, which favours and stimulates the staminal energies, the
androecium being more keenly sensitive and more readily
responsive to slight increments of temperature than is the
gynoecium. The duration of the male elements being shorter
than that of the female, they can come more quickly to
maturity and perish earlier, as seen, for example, in the first
flowering deciduous male catkins of Castanea Americana
mentioned above. These, having been formed at the close
of the preceding year (like many male flowers of the
JJmbelliferce late in the season), may represent the ex-
piring energy of the year's growth. They open first, as
soon as a sufficient though slight increment of temperature
occurs, but quickly fall off, quite useless, as no female
flowers are open to be benefited by them.
Again, many, if not the majority of gynodioecious plants
woiild seem to be pi'oduced by the first flowers opening
before the temperature was sufficiently high to allow of the
corolla and stamens to develop properly ; and though many
female flowers of the Lahiatce now blossom simultaneously
with the hermaphrodite flowers of the same species ; this
may be, perhaps, accounted for by hereditary influences, as
246 THE STRUCTURE OF FLOWERS.
Mr. Darwin showed that seeds of the female plants of Thyme
yielded both female and hermaphrodite plants.
Although, therefore, we are unable to fathom all the
mysteries of Nature's procedure, we can detect some of the
lines upon which she works, and perceive how, in all cases,
it is the environment — but sometimes one set of influences,
sometimes another — which, being brought to bear upon the
plant, the latter responds to it; and some form of what
may be called "incipient diclinism " is the first result. If,
then, these influences be kept up, hereditary conservatism
comes into play, and such slight beginnings towards a
separation of the sexes becomes fixed — only temporarily,
however, — which constitute the first step, to be followed by
others, till absolute and almost irrevocable dioecism is the
final result.
Dr. M. T. Masters has collected several cases in which
one or other of the sexes has been ari-ested, apparently in
consequence of the nature of the soil and other conditions of
the environment. I i-efer the reader to his " Teratology," as
my object is not merely to enumerate all the instances known,
but sufficient to establish the theory advanced, — that it is the
environment that first influences the organism, which then
responds to it ; and that, secondly, all adaptive variations
thus set up — provided the environment continue to exert its
influences — can become fixed by heredity. The consequence
is that they are ultimately recognized as constant and
specific characters.
The Origin of Sex. — If now the environment has been
proved to exert potent effects upon the development of the
sexual apparatus of flowers, there still remains the ques-
tion how far is either sex or both present, or at least poten-
tial, in the embryo. Marked differences have resulted from
sowing fresh or well-matured and older seeds of melons.
SEXUALITY AND THE ENVIRONMENT. 247
M. Arbaumont found that jomig seeds gave rise to plants of
extraordinary vegetative vigour ; moderately aged ones gave
rise to corresponding moderately vigorous plants with both
male and female flowers ; while older seeds gave rise to still
less -vigorous plants, but which, when properly nourished,
formed female buds.* M. F. Cazzuolaf also found that
melons raised from fresh seed bore a larger proportion of
male flowers than female ; while older seed bore more female
flowers : and this has been confirmed.
Another interesting result was obtained by M. Triewald,
who grew twenty-one out of twenty-four melon seeds which
were forty-one years old. The branches were yery narrow,
yet they produced early and plenty of good melons. J A
cause of the differences of vigour in the plants raised from
seeds of different age is, perhaps, connected with the fact
that fresh melon seeds contain a neutral oil, which becomes
more and more acid by keeping. This increased acidity
coincides with a diminished germinative power ; § and
proportionately, therefore, less liable to run into excessive
vegetative growth.
The next condition to be observed is that resulting from
sowing seeds of diclinous plants thickly or thinly. Hoff-
man's experiments || in this direction showed that 283 male
* Bull, de la Soc. de Bot. de Fr., 1878, p. 111.
t Bull, de Tuscan. Hort. Soc, 1877.
+ Gard. Chron., 1879, p. 470.
§ M. Ladureau in Ann. Agronomiques. Mr. Darwin also fonnd that
fresh seeds of Iheris grew at first more vigorously than others {Cross
and Self -fertilisation, etc., p. 10.3).
II Gard. Chron., 1879, p. 762; see also Bot. Zeit, xliii., 1885, p. 145,
seqq. ; also Jenaisch Zeitschr. f. Naturwiss, xix. (1885), sup. ii., pp. 108-
112. The following were the plants with which he experimented :
Lychnis diurna. L. vespertina, Valeriana dioica, Mercurialis annua, Rumex
Acetosella, Spinacia oleracea, and Cannabis sativa.
248 THE STRUCTURE OF FLOWERS.
plants appeared, and 700 female, in the thickly sown plot,
while only 76 males occurred when thinly sown. This has
been paralleled in America, where Mr. Meehan, of Phila-
delphia, has noticed how Ambrosia artemisisefvlia, if growing
vigorously, has a proportion of female flowers largely in
excess of the males ; but in fields where the grain has been
cut, and this " Rag- weed " comes up in thick masses late in
the season, the individual plants nearly starving each other,
male flowers are very numerous, and some are wholly male.
Prantl also observed that the crowded prothallia of Ferns gave
rise to more antheridia, and scattered ones more pistillidia.
Pfeffer, too, noticed the same fact with Equiseium.
In these cases we seem to have results exactly the reverse
of those of the melon seeds : but while in the latter the male
flowers were accompanied by the precocious and excessive
vegetative energy, the female were prevented from appearing
at all ; for it must be remembered that normally male
flowers of melons appear before the females. In the case
of thin sowing, the plants were in a natural and healthy
condition : but when crowded they were starved, and the
vital energy, being just enough to develop male flowers,
proved insuSicient for the female ; and, conversely, when
thinly sown, "vitality" was not checked, and females were
abundant.
The question arises, are all seeds potentially bisexual,
and one sex rather than another determined either by an
inherent vigorous constitution or by the conditions of the
environment during germination and growth ? or is there, so
to say, a determination of sex, or at least a predisposition,
at an earlier stage still ? Dr. Hoffman, judging from his
experiments, is inclined to the opinion that sex does not
reside in the seed, but depends on conditions of germination.
Mr. "W. G. Smith arrived at the same conclusion, for he says
SEXUALITY AND THE ENVIRONMENT. 24-9
in his EemarJiS on some Vicecious Plants,* " 1 think seeds
themselves are probably not either male or female, but that
after influences produce the sex ; as in animals the sex is not
developed in the early embryo life of the creature, nor till
the embryo has attained a certain age."
On the other hand, F. Heyer thought sex "was determined
at an earlier period than the ripening of the seed.f Some
differences which have been noticed in seedlings of Nutmegs
seem to countenance this idea; thus Mr. Px-estoe, in his
report on the Trinidad garden,^ says that " the leaf of the
female seedling is most perfectly elliptical, with straighter
primary veins. In the male plant it is broader towards the
point than at the middle, i.e. obovate, and furnished with a
point much longer than that of the female. The veins are
also curved in towards the point much more roundly than
in the latter."
An interesting experiment by 'Mr. I. An der.son -Henry,
recorded in the Gardener s Chronicle of 1876, may be quoted.
He sajs, " I raised a seedling Begonia having female flowera
only. It resulted from an experiment I made on the seed-
bearer by cutting off two of the three lobes which compose
the stigma, and fertilising the remaining lobe. I repeated
this experiment ; and all of the progeny which have yet
bloomed, consisting of four or five plants, have likewise all
come with female flowers only." This seems to show that
the female seedlings were due to concentration of energy to
a limited number of seeds. On the other hand, a hybrid
Begonia, "Adonis," raised by Mr. Yeitch from a summer-
flowering tuberous variety, " John Heal," crossed with a
winter-flowering variety (itself obtained fi'om B. Socotrina
crossed by a dwarf-flowering tuberous variety), bore nothing
* Journ. ofBot., 1864, p. 232 (note), t Journ. Micr. Soc, 1884, 251.
J Qard. Chron., 1884, p. 315.
250 THE STRUCTURE OF FLOWERS.
but male flowers — presumably in consequence of some weak-
ness of constitution due to hybridisation.
It would be quite foreign to my purpose to trace the
origin of sexes throughout the vegetable kingdom, as I am
solely concerned with that of flowers. But what appears to
be pretty certain is that the absorption of the pollen-nucleus
by the " egg-cell " involv^es a special form of nutrition,
coupled with certain excitant effects. Uuion between nuclei
occurs elsewhere ; and as illustrative analogies, one recalls the
fact of fusion being normal in the Gonjugatce, and among
zoospores, where no sexual differentiations are observable.
Again, in the embryo-sac there occurs the union of two nuclei,
one from each tetrad, their function being then apparently to
form endosperm. As another case, Mr. Gilburt has described
the union of the nuclei of cells constituting a " cell-gi'oup,"
which forms a wood-fibre after the absorjDtion of the septa.*
Of course one of the most essential properties of the
pollen-nucleus is to transmit to the offspring characteristics
of the male parent : but even this is paralleled in the vegeta-
tive system ; for an engrafted scion can transfer its peculi-
arities to the stock, as has occurred with Cytisus Ada-mi,
variegated Abutilons, etc.
If, however, we ask what are the actual differences which
exist between the male and female energies, and how they
have arisen, we at once find that we are completely baffled,
and that all speculations are at present futile.
* Morph. of Vej. Tiss., Journ. Roy. Micr. Soc, 1879, p. 806 (note).
Schacht observed a similar origin of liber-fibres in the Papaw, each of
which was originally composed of three or four cells, but the septa
become absorbed; their original positions being only indicated by
clusters of pores on the walls {Les Laticif. die Carica Papaya, Ann. des
Sci. Nat., 4 ser., viii., pi. 8, figs. 9, 10). Treub, on the other hand, dis-
covered the laticiferoQS vessels and liber- fibres of the Nettle, etc., to have
arisen by repeated division of the nucleus, the partitions not having been
formed at all {Arch. Neerl. des Sci. Exac. et Nat, torn, xv., 1880, p. 39).
CHAPTER XXVI.
DEGENERACY OF FLOWEKS.
Inconspicuous and Cleistogamous * Flowers. — Degeneracy
in plants is as of frequent occurrence as in animals ; and just
as it implies no pathological or anything of a constitutionally
iiijurioas character in them, so, it must be distinctly borne
in mind, does it imply nothing of the sort in plants. The
word means " down from the genus ; " like " degradation," it
is only a " step downwards." It implies retrogressive or at
least arrested conditions ; but a degraded flower often
acquires new features, qualifying it for securing self-fertili-
sation with a far greater certainty than was the case with its
more conspicuously flowering ancestors.
There are several causes which can bring about degrada-
tions in the various organs of plants, such as growth in
water, subterranean habits, parasitic and saprophytic states,
freedom from strains, compensation, etc. Though it would
be interesting to trace out the cause and effect in each case,
I must content myself with flowers, and particularly the
essential organs.
There are two principal causes which may be styled the
rationale of degradation in flowers. The first is compensa-
tion, when the vegetative system is in too great activity to
* Cleistogamous, "a closed union," i.e. when flowers are self-
fertilising without opening.
252 THE STRUCTURE OF FLOWERS.
allow of the proper amount of nutrition being at the service
of the flowering process. This is so well known that I need
not dwell upon it now. The second is the cessation of insect
fertilisation. The effect of fertilisation operates in tAvo
directions. On the one hand, if it be the result of inter-
crossing by insect agency, it stimulates the flowers till they
become thoroughly adapted to their visitors, and highly
differentiated in certain ways in consequence, but more
especially as regards the perianth and stamens ; while, in
many cases, some degree of degradation occurs simultaneously
in the pistil. Conversely, self-fertilisation and anemophily,
consequent upon the neglect of insects, are accompanied by
corresponding degradations in the perianth, stamens, and
pollen, correlated with a regained ascendancy in the powers
of reproduction. The limits of degradation, with an increase
of fertility, are seen in many cleistogamous flowers.
In tracing the progress of degeneracy from a species with
large flowers to one with inconspicuous blossoms, I do not
mean to imply that we can actually witness the process in
activity • but we can see this represented, as it were, in many
a series of what we call species of a genus ; but which we
miglit call transitional forms of one kind. It is only because
we cannot trace the actual process going on that we regard
them morphologically as distinct species. Thus, if a verifiable
demonstration be unattainable, it is a "moral conviction,"
not only that Geranium pratense is as much and obviously
adapted to insect agency as G. pusillum is to fertilise itself,
but that the latter species has been derived from the former
or from some kindred plant, through some such transitional
forms as (?. pyrenaicum and G. moUe.
This process of degradation from insect to self-fertilising
conditions, not only affects the size of all parts of the flower,
but the entire plant. Mr. Darwin showed how the stimu-
DEGENERACY OF FLOAVERS. 253
lating effect of crossing generally increased the heights and
weights and, for a time, the fertility of the plants experi-
mented upon. Conversely, self-fertilised species are alto-
gether smaller than their allied intercrossing species. Thus
SteUaria Holostea may be compared with (S. medium, Cerastium
arvense with C. tetrandrum and G. glomeratit-m, CardMviine pra-
tensis with G. Jdrsuta, Poli/gonum ampMbium with P. aviculare,
etc. Besides being thus dwarfed, self-fertilising plants are
mostly annuals. But while conspicuons flowering plants
blossom during a limited period in summer only, their
smaller, less conspicuous, and regularly self-fertilising allies
may, and often do, flower and set seed all the year round.
In my essay on " The Self-fertilisation of Plants," * I
drew up the following list of peculiarities of habitually self-
fertilising plants, all of which indicate points of degeneration
or arrest.
1. The ineonspicuousness of the flowers, even when fully
expanded.
2. The calyx and corolla are often only partially expanded,
or not at all.
3. The white or pale colours of the corollas ; while
specially coloured streaks, specks, "guides," and "path-
* I must refer the reader to the above essay for a full discussion of
this subject. The evidence there given proves conclusively that self-
fertilising and anemophilons plants are in every way the most widely
dispersed of flowering plants, and best fitted to maintain themselves
in the struggle for life. I will add here that Mr. H. 0. Forbes came
independently to a similar conclusion when studying cleistogamv in
orchids ; and remarks, at the close of his paper {Journ. Lin. Soc.,vo\. xxi.,
Box., p. 548), " The observations above given would seem, tlierefore, to
support the Rev. G. Henslow's conclusions so ably given in his ' Memoir
on the Self -fertilisation of Plants,' already published in the Transactions
of the Linnean Society. My absence abroad prevented my seeing this
paper till quite recentlv. and after I had completed these notes."
24
254 ■ THE STRUCTURE OF FLOWERS.
finders " peculiar to intercrossed flowers are more or less
reduced, if not absent.
4. The partial or total arrest of the corolla.
5. The mature stamens of the expanded flower retain in
many cases the incurved, i.e. an arrested position, which
they had in bud ; the anthers thus remain in contact with
the stigmas.
6. The stamens are often I'educed in size and number,
and the pollen in quantity.
7. The pollen tubes may often be seen to be penetrating
the stigmas, either from grains still within the anther-cells, or
evidently derived from those of the same flower.
8. The styles are shortened, and the stigmas are situated
appropriately for direct pollination from the anthers of the
same flower.
9. The partial arrest of the corolla and stamens in their
rates of development, allows the pistil to mature with com-
pai'ative rapidity.
10. The consequent early maturation of the stigma, so as
to be ready before or simultaneously with the dehiscence of
the anthers.
11. Little or no scent,
12. Decrease in size or total absence of honey glands,
with corresponding little or no secretion of honey.*
Notwithstanding these various indications of degradation,
such flowers are often correlated with special alterations
which secure self-fertilisation without a chance of failure
— a precariousness which almost always exists in flowers
adapted to insects. Thus — contrary to the old but erroneous
* Miiller, in his "General Retrospect" (Fertilisation, etc., p. 591),
also gives a number of modifications, mostly referred to in the text above,
of what he describes as " the countless ways in which plants revert to
self-fertilisation in default of sufficient insect visitors."
DEGENERACY OF FLOWERS.
255
dictum that, whether flowers were pendulous or erect, the
stigma was always heloio the anthers, so that pollen could
fall upon it — the anthers are always closely applied to the
stigmas, as may be seen in Chickweed (Fig. 52), and sraall-
a, b
Fig. 52. — Flower-bud, closed and expanded,
of Stdlaria media, showing petals reduced
ill size; stamens, three only; anthers
closely adpressed on stigmas.
tt 7)
Fig. 53. — Stamens and stigmas of
Epilobium montaniim, the hud
scarcely open, while anthers are
closely applied to the stigmas.
flowered Willow Herbs (Fig. 53), and especially in cleistoga-
mous flowers (Figs. 56-59, pp. 258-261).
The structure of the anthers and stigmas is often
greatly altered in form, besides being merely reduced in
size.
As an illustration of the above remarks, the genus Viola
is interesting as furnishing two " forms " of the same species,
V. tricolor, or Pansy, the one
being adapted to insects, the other
to self-fertilisation ; while other
species, such as F, odorata, the
Violet, bear cleistogamous buds
on the same plant as the ordinary
violet blossom.
The dimorphic flowers of Viola
tricolor were first noticed by
Miiller, who described them as follows : * "In the large
flowered form, the stigmatic cavity (Fig. 54, a, st) lies some
* Nature, Nov. 20, 1873, p. 45.
Fig. 54. — Styles and stigmas of the two
forms of Pansy • a, that of the larger
and intercrossing ; b, that of the self-
fertilising form.
256 THE STRUCTURE OF FLOWERS.
what more towards the top of the skull-like end of the style
than in the small-flowered one (&). When the skull-like knob
in the two forms is pressed against the lower petal, in the
large-flowered form the opening of the stigmatic cavitj is
directed outwards, so that the pollen-grains which have
fallen out of the anther-cone can never spontaneously fall
into the stigmatic cavity, and must be carried there by
insects ; w^hereas in the small-flowered form the opening of
the stigmatic cavity is directed, inwards, so that pollen-grains
falling out of the anther-cone spontaneously, fall directly
into the stigmatic cavity.
" In the large-flowered form, the opening of the stigmatic
cavity (st) bears, on its lower side, a labiate appendage (I)
provided with stigmatic papillae, so that a proboscis inserted
into the flower when charged with pollen from a previously
visited flowei*, rubs off this pollen on to the stigmatic lip,
thus regularly effecting cross-fertilisation ; whereas, when
withdrawn out of the flower, charged with pollen, the
proboscis presses the lip (I) against the stigmatic opening
(st), thus preventing self-fertilisation. This nice adaptation
to those visitors provided with a long proboscis (Lepidoptera,
Apidse, Rhingia) is completely wanting in the small-flowered
form (h).
" In the large-flowered form, there is a black wedge-shaped
streak (g) on the front of the style, to which Mr. A. W.
Bennett first called attention, and which he has interpreted
as a guide-mark for those visitors which are diminutive
enough to crawl entirely into the flower. This streak is
also wanting in the small-flowered form.
" In the large-flowered form, pollen-grains do not spon-
taneously fall out of the anther-cone before the flower has
been fully developed for several days ; whereas, in the small-
flowered form, in bb far the majority of cases, a great number
DEGENERACY OF FLOWERS, 257
of pollen-grains fall spontaneously out of the anther-cone
into the stigmatic cavity and there develop long pollen-
tubes, even before the opening of the flower, in much rarer
cases a short time after it has opened.
" When the visits of insects are prevented by a fine net,
the flowers of the small-flowered form wither two or three
days after opening, every one setting a vigorous seed-
capsule ; those of the lai'ge-flowered form remain in full
freshness more than two or three weeks, at length withering
without having set any capsule ; when fertilised they, too,
wither also after two or three days."
I have met with several variations in minor details of
structure in the smaller-flowered kind. Thus ia some the
stigmatic lip, probably representing one of the three stigmas,
formed a globular knob
protruding from the
orifice, as shown in Fig.
•55, a, h. In anotlier,
it protruded like a
tono-ue, C. The lateral Fig- 55.— styles and stigmas of self-fertilising forms
o ' _ ofPausy. (b'or dtsciiption, see text.)
fringes,* which help to
keep the pollen back from reaching the stigmatic chamber in
the larger flowers, are more or less retained in these ; as is
also the bent-base to the style which forms the spring,*
which keeps the globular head in a downward position.
The accompanying figures will illustrate the cleistogamous
flower-buds of Violets. They are very minute, about one-
eighth of an inch in length (Fig. 50, /). The petals are
reduced to linear and pointed structures, green or purplish
green, (a) ; or they may be altogether wanting. The spur
alone of the larger petal is sometimes present in strong-
* For the theoretical origin of " fringes " and " springs," see Chap.
XV., p. 133, and Chap. XIII., p. 123, respectively.
258
THE STRUCTURE OF FLOWERS.
growing garden plants (5). The stamens are five or less in
number, having spoon-shaped connectives, and not pointed
as in the normal form, bearing very minute oval anther-cells
at the base (c, g) * Small bundles of pollen-tubes may be
traced from the anthers into the stigma (g). The pistil has
a short curved style, and truncated stigma (d) concealed
beneath the anthers which lie imbincated over the top of
the pistil. The anthers are usually devoid of appendages,
though they are sometimes present, like the spur ; though
/ e 0
Fig. 56. — Clelstogamous Violets. (For description, see text.)
both organs are now useless. As the ovary swells it raises
the stamens up with it (e). The capsules of the violet, Mr.
Darwin observes, bury themselves in the soil, if it be loose
enough, and there ripen ; but they certainly are very, if not
more frequently not buried at all, but only concealed beneath
the foliage.
As another interesting case of a plant showing transi-
tional conditions may be mentioned Scrophularia arguta,
Ait.f " The two lowermost opposite and axillary branches
bend backwards and penetrate the soil. The next pair do
* (c) V. odorata; (g) V. canina. t Bull. Soc. Bot. de Fr., iii., p. 569.
DEGENEEACY OF FLOWERS. 259
the same, but do not always reacli the gi-ound, or else pene-
trate it very slightly. They all bear fertile flowers. The
lowest are apetalous, if completely hypogean [and pre-
sumably cleistogamous]. Those which just reach the soil
have a corolla of four lobes nearly equal, and resemble the
corolla of Veronica. A little higher up, the irregularity of
the bilabiate character of Scrophularia is pronounced."
The preceding quotation is interesting, first in showing
Low the subterranean cleistogamous form is derived from
the conspicuous flower, and also supplies a hint as to the
origin of Veronica, in that it is a 4-merous degradation from
a primitive 5-merous genus, which is lost or unrecognizable
now, unless it be some member of the subgenus Pygmcea,
which has five parts to the corolla.*
As an illustration where geographical conditions favour
the development of autogamous forms of flowers, the follow-
ing passage may be quoted : —
" Herr C. A. M. Lindman has examined the very rich
flora of the Dovrefjeld in reference to the arrangements for
fertilisation. He finds a distinct tendency to a deeper colour
in the flowers than is displayed by the same species in the
lowlands, red and blue predominating. The great length of
daylight appears to increase the size both of leaves and of
flowers, though in some species, on the other hand, the
flowers are diminutive in consequence of the low tempera-
ture. Crowded masses of small flowers are very common.
The number of scented species is comparatively small,
though the fragrance is sometimes powerful. The scarcity
of insects necessitates that there should almost always be
a provision for possible self-fertilisation ; and many species,
elsewhere heterogamous, are here homogamous. Notwith-
* For Miiller's theory of the origin of Veronica, see Fertilisation, etc.,
p. 465.
260
THE STRUCTURE OF FLOWERS.
Fig. 57. — Cleistogamous flower-buds of Oxalis
Acetosella. (For description, see text.)
standing the cold and wet summer (1886), tlie plants
observed almost invariably bore frnit."*
As an example of pure cleistogamy I will take Oxalis
Acetosella, as having special peculiarities. Mr. Darwin
alludes to M. Michalct's description of the cleistogamous
flowers of this species,t and adds some observations of his
own.J He quotes an observation of Michalet's, that the
five shorter stamens are sometimes quite aborted. This fact,
which I have also ob-
served (Fig. 57, d), is
quite in keeping with
the common process of
the reduction of the
number or parts of sta-
mens in self-fertilising
flowers. He also adds this interesting observation : " In one
case the tubes, vphich ended in excessively fine points, were
seen by me stretching upwards from the lower anthers towards
the stigmas, Avhich they had not as yet reached. My plants grew
in j)ots, and long after the perfect flowers had withered they
produced not only cleistogamic, but a iew minute open flowers,
which were in an intermediate condition between the two
kinds." This last remark is quite in accordance with the
true origin of these flowers, that they are in all cases degra-
dations from the conspicuous forms normally characteristic
of the species which produce tbera.
Fig. 57, a, clearly shows that in Oxalis Acetosella the
cleistogamous state is simply a flower-bud which has become
adapted to self-fertilisation ; and the intermediate conditions
alluded to by Mr. Darwin I should suspect were analogous to
* Journ. Boy. Micr. Soc, 1887, p. 615, and note. See below, pp. 270, 271.
t Bull. Soc. Bot. de Fr., rii. (I860), p. 465.
X Forms of Flowers, p. 32].
DEGENERACY OF FLOWERS.
2G1
Cleistogamoua
flower-bud of Impatiens
ftUva ; b, stamens (after
Bennett).
the permanent forms of the flowers of 0. cornicidata, which I
at first inferred, from the wide distribution of this species,
must be habitually self-fertilising. From Fig. 57, a, it will be
seen that the corolla just protrudes from the closed sepals,
and always remains as a " cap," b. Of the ten anthers, five
are often abortive or wanting, d ; the fertile anthers are
placed over the very short stigmas, and are bound together
by fine threads. These appear to play some part, bat the
nature of their function is obscure, c.
Impatiens fulva and I. Noli-me-tangere have also cleisto-
gamous flowers. Fig. 58, a, represents
a bud, and h two metamorphosed sta-
mens.
Lamiuin amplexicaide will furnish,
another example of cleistogamy. This Fig. 58
genus has usually flowers highly differen-
tiated, and adapted to insect fertilisation.
That the cleistogamous flowers of this, as of all other species,
are detrraded forms of the normal kind is obvious fi'om the
presence of the "lip," as well as by there being four and
didynamous stamens. The style elongates very much, and
under the pressure of the closed
summit of the corolla becomes bent,
so that the stigmas lie between the
anther-cells, and thus readily become
fertilised. Fig. 59, a, represents a
flower-bud ; b, the corolla in section ;
and c, the pistil removed. This Fig
condition of cleistogamy is found in
the earlier-flowering plants, so that it is probably a mere
result of check through a colder temperature.
Salvia clandestina may be compared with the last
described, as it is a self-fertilising form of, perhaps, S. pra-
l c
a, Cleistogamous flower-
bud of Lainium aiitplexicaule; b,
vertical section of same ; c, pistil.
59.-
262 THE STRUCTURE OF FLOWERS.
tensis. Fig. 60,* a, represents a corolla, whicli is very small,
but open ; h represents the two fertile stamens ; the anther-
lobes instead of being
horizontal are erect, and
face each other. The
stigmas curl back be-
r „n o 7 ■ 7 J ,. „ , .1 tween them, and are re-
r )g. 60. — Salvia clandestma : a, corolla ; h, anthers ; '
c, style and stigmas. mark ably long, c.
The Origin of Cleistogamy. — We are now in a position
to trace the causes of cleistogamy. Cleistogamous flowers
nearly always occur on plants otherwise, or at least their
allied species are, adapted for intercrossing, and include four
genera of anemophilous plants. The first cause or influence
is the arrest of the reproductive energy in the conspicuous
flowers, which often set no seed at all.
Whatever the primary cause of that may be, a very
common result in perennials is to increase the power of
vegetative methods of multiplication, as in the case of many
bulbous and tuberous plants.
This, however, is not a special feature of the plants which
bear cleistogamous flowers. It would seem, therefore, that
the reproductive energy being checked in one form of flower,
it, so to say, breaks out in another. But there are several
influences at work, and a very obvious one is temperature ;
for the same species may behave very differently in one
country with a high mean annual temperature, from what it
does in another with a lower one. Thus, Viola odorata does
not produce cleistogamous flowers in one part of Liguria,
where the conspicuous flowers *re perfectly fertile ; while
they are mostly barren in England. On the other hand,
cleistogamous flowers are produced by Violets near Turin,
* From a specimen growing at Kew. It is cleistogamous at Halle
(see below, p. 263).
DEGENERACY OF FLOWERS. 263
and abundantly in all parts England. Viola nana bears
normal flowers in its native home in India, but only cleisto-
gamous ones in England. Viola palustris bears only the
larger flowers near Pai'is, which are perfectly fertile, but
when it grows on mountains it bears cleistogamous flowers.
Similarly Impatiens fulva bears both kinds of flowers m Eng-
land, but the larger are usually barren. After midsummer,
in its native home in the United States, these flowers will
produce capsules. Salvia clandestina, when transplanted
from Africa to Halle, bore only cleistogamous flowers for
five years, according to Ascherson, who considered the plant
to afford an example of continuous self-fei-tilisation. He,
however, afterwards observed ordinary open flowers. It is
a species particularly common on the Continent.
Again, plants vary according to the season. Thus Mr.
Darwin found that Vandellia nummularifolia bore no perfect
flowers in one season ; so, too. Ononis columnce bore none in
1867, yet it had both kinds in 1868.
The time of the year also influences the production of
cleistogamous flowers. Thus Ononis rainuHssima, 0 parviflora,
and 0. columnce, according to Mr. Bentham, produce them
early in the spring. Godetia Gavanillesii and Lamium am-
plexicaule do the same ; while some bear a fresh crop in the
autumn, as 0. columnce.
Two cases are mentioned by Mr. Darwin in which the
period is the reverse of the above.
Viola Boxburgliiana bore abundance of cleistogamous, but
no perfect flowers, in Mr. Darwin's hothouse ; and it bears
the perfect flowers in India " only during the cold season,
and these are quite fertile. During the hot, and more
especially during the rainy season, it bears an abundance
of cleistogamous flowers."*
* Forms, etc., p. 320.
264 THE STRUCTURE OF FLOWERS.
The other example is Euellia tuherosa, of whicli Mr.
Darwin remarks, " It produces both open and cleistogamous
flowers ; the latter yield from 18 to 24, whilst the former
only from 8 to 10 seeds : these two kinds of flowers are pro-
duced simultaneously, whereas in several other members of
the family the cleistogamous ones appear only during the hot
season." From this one would infer that an excess of heat
may be a cause of cleistogamy, just as too low a temperature
appears to bring it about.
I think it probable that other influences than tempera-
ture may be brought to bear upon a plant ; which, indeed,
we may see in our own Violets. The larger flowers of this
species are oiot produced in the hottest time of the year,
while the cleistogamous buds are only borne in the summer.
On the other hand, the foliage is only developed fully, con-
temporaneously with the dwarfing of the floral organs.
Again, a poor soil has been noticed as associated with
cleistogamy by Torrey and Gray, in the case of North
American species of HeJianthemum.
Temperatui-e, however, seems to be the most important
agent; thus, while the climate of South Italy can develop
the perfect flowers and render them fertile, there cleistogamy
is suppressed; here, in England, the climate is seemingly not
sufficiently warm to do so, and the cleistogamous buds appear
in compensation. The vegetative energy, however, comes
to the fore during the summer, and perfect flowers are not
produced simultaneously with it ; so that it is not until the
vegetative period has ceased, and the materials ai'e remade for
their development, that larger flowers are again borne later in
the year, as in November, as well as in the following spring.
With regard to the anemophilous genera, Mr. Darwin
mentions Hordeum, Cryptostachys, Leersia oryzoides, and Juncus
bufonius in Russia.
DEGENERACY OF FLOWERS. 2G5
Now, the three genera of Grasses here mentioned are
characteristic of Avarmer regions, and even tropical, Leersia
oryzoides being the sole species of that genus which reaches
Europe, where it becomes cleistogamous. Therefore climatal
conditions niaj, with some reasonable presumption, be sug-
gested as the immediate cause in these cases. With regard to
Hordeum murinum, which is, perhaps, almost habitually cleis-
togamous in this country, it may be an hereditary result
issuing from a similar cause. This may also apply to Viola;
for not only are some species tropical, but all the genera
most nearly allied to Viola are tropical also. This is analo-
gous to what I have suggested as the origin of gynodioecism
in Lahiatce, which it may be noticed has at least two genera
with cleistogamous flowers in this country or Europe. Juncus
hufoniiis, according to Batalin, is exclusively cleistogamous
in Russia, hence the same cause suggests itself for this
species ; for, according to Ascherson, at Halle it has ordinary
open, lateral, hexandrous flowers in addition to terminal
cleistogamous triandrous ones.* This seems to show that
lessened vigour has also a hand in the process in this case :
the mean temperature of Halle is probably higher; if so, it
may cause the plant to bear the open flowers there.
From the above-mentioned facts, it will be seen that
there may be more than one cause to account for cleistogamy.
Hence, it must be regarded as an inevitahle result whenever
those influences are brought to bear upon the plant which
are capable of producing it ; and there is every reason to
believe that whatever effects are produced iu plants by
external stimuli, if the latter be permanently kept up they
will become hereditary, and then will be recognized by
systematists as specific or generic characters.
Anemophilous, or Wind-feetilised Plants. — The general
* Miiller, I.e., p. 561.
25
266 THE STRUCTUKE OF FLOWERS.
characters prevailing' in this group consist of elongated
papillose or plumose stigmas, or else they spread out into
laminge (Euphorbia). The filaments are usually slender and
movable, with versatile anthers, bearing incoherent and
often smooth pollen-grains. In some cases the filaments are
elastic, and project the pollen outwards ; or the whole flower
may oscillate on a slender pedicel or peduncle, as the catkins
of the Amentiferce, the flowers of Bumex, etc. Long, slender
filaments are seen in Grasses, Sedges, Rushes, Hemp and
Hop, Plantains, Littorella, and Poterium. Nettles and their
allies are remarkable for their elastic filaments, which
materially aid ia the dispersal of the pollen.
On the other hand, Palms, Bulrushes, etc., have more or
less rigidly fixed flowers and floral organs.
There is little doubt but that all wind-fertilised angio-
sperms are degradations from insect-fertilised flowers. This
is obviously so when many of the allies of an anemophilous
genns or species are constructed for insects. Thus, Miiller
says that Thalictriim oninus * is anemophilous, while T.
flavtivi is visited by several species of insects. Poterium
Sanguisorha is anemophilous ; and Sanguisorba officinalis
presumably was so formerly, but has reacquired an entomo-
philous habit ; the whole tribe Poterieai being, in fact, a
degraded group which has descended from Potentillece. Plan-
tains retain their corolla, but in a degraded form. Juncece
are degraded Lilies ; while Cyperacece and Graminece among
monocotyledons may be ranked with Amentiferce among
dicotyledons, as representing ordei'S which have retrograded
very far from the entomopbilous forms from Avhich they
were possibly and probably descended.
* I do not know on what reason ; for the stigmas are not charac-
teristic of such flowers. On d priori grounds I should have inferred its
being self -fertilising, as the anthers completely conceal the few and
small carpels.
DEGENERACY OF FLOWERS. 267
What, then, have been the causes which have given rise
to the features generally characteristic of anemophilous
flowers ? In the first place, it must be remembered that
such are far from absolute. Smooth and easily scattered
pollen,* Miiller remarks, is the only positive chai'acter
common to these plants. Mr. C. F. White, F.L.S., however,
tells me that from his researches he very much distrusts the
division so generally accepted between wind- and insect-
borne pollens. It is his opinion that there is no pollen-grain
so smooth but that the hairs on the limbs of a bee or fly can
hold it. Moreover, no pollen, however massed together, can
possibly be heavier than, say, a thistle seed and its down
attached, which the wind can carry with perfect facility ; so
that to draw any distinction on that score seems to me to
be very far-fetcbed.f With respect to the pollen of Grasses,
Mr. White observes that it is perhaps forgotten that, although
smooth in water, when dry they are notably wrinkled into
sharply angled and irregular shapes.
Mr. Eilgeworth X has figured many forms of pollen of
anemophilous genera, several of which show no signs of
smoothness or rotundity, such as Alopecurus pratensis, Carex
arenaria, and C. panica, which, like Juncus effusus, is oblong,
with sharp edges, all of which are at right angles or nearly
so. Again, Typha latifoUa and Cupressus have octahedral
pollen ; Areca Baueri, Ceratozamia, Rlieum, Mercurialis, Oak,
etc., have more or less sharply pointed spindle-shaped grains.
* See Mr. A. W. Bennett's paper, On the Form of Pollen-grains in
Reference to the Fertilisation of Flowers, Brit. Assoc. Rep., 1874.
t I would here allude to another d priori assumption. It has been
thought that the two pouches on the pollen of the Fir aid it in trans-
portation; but unless they were filled with some gas lighter than air
they only increase the weight of the grain.
X Pollen, by Mr. M. Pakenham Edgeworth, F.L.S., 1877.
268 THE STRUCTURE OF FLOWERS.
In Corylus, Alnus, and Plantago media, they are polygonal,
while Beech has them deeply three-grooved, etc.
Mr. Edgeworth, in fact, states that the different kinds of
pollen of anemophilous plants " are by no means all globular,
as Mr. Bennett asserts."
He notices, however, that " the grasses and Cyperacece,
and perhaps the Plantagineoe are without the sticky nature
of the outer coat, which obtains through all otiier pollen
grains."
With regard to the versatile condition of the anthers in
grasses, and their consequent facility of oscillating on a point,
this feature seems to be only the result of the extremely
slender filament due to degradation ; * and not quite the
same thing as the antero-posterior oscillation which the
action of bees has set up in the connectives of Salvia, species
of Calceolaria, and Curcuma Zerumbet.f Remembering how
the rigidity of the filaments of intercrossing flowers is corre-
lated to the retention of some well-defined positions for the
anthers, so that insects can be struck by them accurately,
and be again struck on the same spot by the stigmas of other
flowers, we see that when the stimulus due to intercrossincr
has been long withheld, the filaments have become slender,
easily waved about by the wind, and versatility of the
* Plantago media, which is visited, has motionless anthers ; but in
the anemophilous species of Plantain they are versatile.
+ Mr. H. O. Forbes has described and figured a very analogous case
in this species of Curcuma of Sumatra. The two anthers project for-
wards in contact, they are provided with terminal processes like horns.
The style passes between them. When a bee enters the flower it
depresses these horns with its head, and so forces the anthers down-
wards on to its thorax. The anthers bring the style and stigma down
also. In a similar way do some species of Salvia cause the style to be
brought down from the hood (4 Naturalist's Wanderings in the Eastern
Archipelago, p. 247) .
DEGENERACY OF FLOWERS. 269
anthers has followed. Those wind-fertilised plants "with stiff
filaments have presumably not yet degraded to a similar state.
With regard to the pistil, since of heterostyled plants
the stigmatic papillae are larger and longer in the long-styled
forms, we seem to get a hint as to the origin of the papillose
and plumose characters of many wind-fertilised plants ; in
that such may be due to compensatory processes on the loss
of the corolla, honey-secreting organs, etc., which have thus
favoured the development of the pistil generally, such deve-
lopments becoming emphasized in certain directions.
Protogyny or homogamy generally accompany anemo-
phily.* Thus Miiller mentions Thalictrum minus, Plantago,
Luzula, Gallitriche, Mtjriophyllum, and many Grasses as
being protogynous ; and a common characteristic feature of
such flowers is frequently noticed by Miiller, viz., that they
have all "long-lived stigmas." This seems clearly to point
to a relatively increased amount of vigour in the develop-
ment of that organ in protogynous flowers ; which becomes
especially noticeable in their enhanced size, as seen in most
anemophilous flowers. Poterium he regards as homogamous,
as well as Rye and Wheat. These conditions all agree with
the total suppression of the corolla, and may be regarded as
signs of degradation : and I have elsewhere shown, when
treating of emergence and development of the floral organs,
how a compensatory process accompanies the formation of
the coroUa and stamens on the one hand, and of the pistil
on the other ; so that when the former tend towards degra-
dation, the pistil gains the ascendancy, and matures earlier.
* Artemisia vulgaris seems to be protandrous. The style arms are
provided with papillose rosettes in the central florets, but are very
elongated, and terminate in points in the circamferential florets. In
no case could I detect pollen-tubes in unopened florets, though the
grains were shed.
270 THE STRUCTURE OF FLOWERS.
Hence, to find its stigmas enlarging under anemophily is all
in keeping with the above facts.
The Origin of Anemophilt. — With regard to the origin
of anemophilous flowers, there is every reason to believe
them to be due to the neglect or absence of insects : that as
these have brought about brilliant colours or other kinds of
conspicuousness, so their absence has allowed flowers to
degenerate and become inconspicuous, the result being
either self-fertilisation or anemophily. As two examples
of districts which illustrate this fact, are the Galapagos
Islands, visited by Mr. Darwin, and Greenland, the flora of
which is described by M. Warming.
The former observer, on landing, thought that tiiere were
few or no flowers, but, on stricter search, discovered many
to be inconspicuous. A specimen before me of Solarium
nigrum, which he bi'ought from those islands, has flow^ers
much smaller than oar ow^n native plant, and illustrates the
wide dispersion of self-fertilising plants. M. Warming
found Greenland, like the Galapagos Islands, to be poor in
insects, and " the flowers display a corresponding increased
tendency to autogamy. One hundred and thirty-eight species
of anemophilous plants are also named by him, exclusive of
Willows. The flowers appear to decrease in size with the
increase of latitude ; and the brilliancy of colour certainly
does not become greater." *
This last observation does not agree with M. Flahault's
observations ; f and possibly M. Warming is here intimating
a wrong cause of degeneracy, which I should incline to regard
as the absence of insect stimulation, with the consequent
tendency to inconspicuousness, anemophily, and autogamy.
* Overs. K. Danshe Vidensk. SelsJc., 1886, p. xxv. (quoted from Journ,
Roy. Micr. Soc, 1887, p. 433). See also above, pp. 177 and 259.
t Ann. des Sci. Nat., 6 ser., t. vii. (1877), et t. ix. (1879).
DEGENERACY OF FLOWERS. 271
Where, however, insects are abundant, whether in high
latitudes or greater altitudes, as in the Alps, there two
causes will be at work to enhance the brightness of flowers ;
viz. insect stimulation and prolonged sunlight. For Sachs
has shown that the ultra-violet and invisible rays are
specially efficacious in the development of flowers ; and as
the foliage grows more vigorously with prolonged light so
it is presumable that the flower-forming substances will be
more abundant as well.*
The genus Plantago, like Thalictrum minus, Poterium, and
others, well illustrates the change from an entomophilous to
the anemophilous state. P. lanceolata has polymorphic flowers,
and is visited by pollen-seeking insects, so that it can be
fertilised, either by insects or the wind. P. media illustrates
transitions in point of structure, as the filaments are pink,
the anthers motionless, and the pollen-grains aggregated, and
it is regularly visited by Bomhus terrestris (Delpino). On the
other hand, the slender filaments, versatile anthers, powdery
pollen, and elongated protogynous style are features of other
species indicating anemophily ; while the presence of a
degraded corolla shows its ancestors to have been ento-
mophilous. P. media therefore illustrates, not a primitive
antomophilous condition, but a return to it ; just as is the
case with Sanguisorha officinalis and Salix Caprea ; but these
show no capacity of restoring the corolla, the attractive
features having to be borne by the calyx, which is purplish
in Sanguisorha, by the pink filaments of Plantago, and by the
yellow anthers in the Sallow Willow. Plantago alpina is
self-fertilising, as the stigma does not wither until after
maturing the anthers.
If we may speculate as to why some degraded flowers
* See La Vegetation du Glohe, par Grisebach, t. i., p. 155 (trad. fran.
de Tchihatchef).
272 THE STRUCTUKE OF FLOWERS.
have become regularly autogamous, while others are now
anemophilous, it may be due to the fact that, if a flower has
been entomophilous and even strongly protandrous, the first
stage of degradation is to bring the essential organs to a
homogamous state. If they stop there, and become autoga-
raous as well, which, is the usual result, then the flower will
remain persistently self -fertilising, as, e.g., Shejiherd's-purse,
Chickweed, Knot-grass, etc.
If, however, the flower had been protogynous, such as
early-flowering Hellebores, Prunics communis or some Alpine
species, v?ith " long-lived stigmas," then this protogyny,
associated with, other degradations of the corolla, etc., which
only tend to increase it, has ended with anemophily.
In the first case the androecium of protandrous flowers
has come down from its previous highly differentiated state,
so as to be homogamous with the stigmas. From the other
or protogynous condition, the gynoecium has not been brought
back again so as to be homogamous with the anthers and
pollen, but, on the contrary, it may have become even
further differentiated, and so has now no fertiliser to depend
upon except the wind.
CHAPTER XXVir.
DEGENERACY OF FLOWERS (continued').
Degeneracy of the Andr(ecium. — The number of stamens
may decrease, as well as the quantity of pollen ; while the form
of the anthers may change and the character of the pollen
may alter ; and lastly, the position of the stamens may not
be the same as in intercrossing flowers, — all these forms of
degradation being so many adaptations or adjustments for
self-fertilisation. They are well seen in Violets and the
Wood-sorrel.
As examples, in Stellaria Holostea there are ten stamens,
in S. media only three; and in cleistogamous Violets they
vary from five to three or two. In the latter, the anthers
become spoon-shaped with a rounded connective and much
reduced anther cells ; in the cleistogamous flowers of Oxalis
Acetosella the pollen is almost deliquescent. Lastly, in all
flowers especially adapted for self-fertilisation the anthers
are in contact with the stigmas in consequence of their arrest
in sfrowth.
It must be noted here that this degeneracy in the stamens
in no way impairs their functional value. The fact is that
a very small amount of pollen is really quite sufficient for
fertilising a considerable number of ovules.
For convenience I call it degeneracy, but another view
would be to regard it as the conservation of energy, instead of
274 THE STRUCTURE OF FLOWERS.
wasting it in the production of a great deal more pollen than
is usually required.
An interesting experiment of Mr Darwin's proves this.
He placed a verj* small mass of pollen-grains on one side of
the large stigma of Ipomcea purpurea, and a great mass of
pollen over the whole surface of the stigmas of other flowers,
and the result was that the flowers fertilised with little
pollen yielded rather more capsules and seeds than did those
fertilised with an excess.* That normally intercrossing
flowers produce a great superfluity of pollen is well known.
Thus Kolreuter found that sixty gi^ains were necessary to
fertilise all the ovules of a flower of Hibiscus, while he cal-
culated that 48G3 grains were produced by a single flower, or
eighty-one times too many.f Mr. Darwin sajs, "In order
to compensate the loss of pollen in so many ways, the anthers
pi-oduce a far larger amount than is necessary for the fer-
tilisation of the same flower ; . . . and it is still more plainly
shown by the astonishingly small quantity produced by
cleistogene flowers, which lose none of their pollen, in com-
parison with that produced by the open flowers borne by the
same plants ; and yet this small quantity suffices for the
fertilisation of all their numerous seeds."
Mr. Darwin observed that when flowers were artificially
self-fertilised for several successive generations, a degeneracy
sometimes took place in the anthers and pollen ; and he seems
to attribute this to what he called the "evil efi^ects " of self-
fertilisation ; but from the above-mentioned facts, which
occur so abundantly in nature, I am inclined to regard it as
an experimental verification and illustration of a universal
principle in nature, namely the preservation of energy
wherever possible, and that such eases as appeared under his
* Crnss and Self Fertilisation of Plants, p. 25.
t Ibid., pp. 376, 377.
DEGENERACY OF FLOWEES. 275
experiments were instances of this principle at work, as the
flowers became habituated to self-fertilisation, and were then
fully fertile.
We have, then, in such cases an actual demonstration of
the first step of the changes induced by self-fertilisation
continually enforced ; and thereby a witness to one cause of
the origin of certain, and indeed, a very large number
of species. It is the converse process to that of insect
fertilisation, which itself I take to be the vera causa of the
origin of intercrossing species.
It is, perhaps, worthy of note that, while both the number
of stamens and the quantity of pollen are thus often much
reduced in some flowers the capsules of which produce many
seeds, yet in others which set but one, as Fumaria, or at
least but few seeds, the number of stamens may remain
unaltered. This seems to me to be an additional proof that
such flowers are degradations from forms originally adapted
to intercrossing when much more pollen was requisite.
Hence the present forms are retentions of former ancestral
conditions. The following cases will illustrate this : —
Sderantlius perennis and species of Medicago have ten stamens
and one seed ; Daphne Laureola has eight stamens and one
seed; Chenopodium hfiH five stamens and one seed ; similarly
is it the case with the large orders Compositce and Graminece.
The phenomenon called " contabescence " by Gartner*
would seem to have its rationale in this adaptation to self-
fertilisation in some cases, and to diclinism in others, though
there are other causes which may bring it about, when it is
a purely pathological phenomenon.
Mr. Darwin observes, "The anthers are affected at a
very early period in the flower-bud, and remain in the same
state (with one recorded exception) during the life of the
* An. and PI. under Dom.. ii., p. 165.
276 THE STRUCTURE OF FLOWERS.
plant. The affection cannot be cared by any change of
treatment, and is propagated by layers, cuttings, etc., and
perhaps even by seed. In contabescent plants the female
organs are seldom affected, or merely become precocious in
their development. The cause of this affection is doubtful,
and is different in different cases. . . . The contabescent
plants of Dianthus and Verbascum found wild by Wiegmann
grew on a dry and sterile bank." *
" Cases of an opposite nature likewise occur — namely,
plants with the female organs struck with sterility, whilst
the male organs i^emain perfect."
The constancy or prevalence of- this condition of conta-
bescence seems to be the first indication of diclinism, what-
ever the cause ; and Silene inflata may be mentioned as
frequently furnishing good examples of both kinds of
contabescence.
Degeneracy of the Pollen. — As this is a feature of
importance in the general degradation of flowei-s, a few
words may be added in reference to it. It is of frequent
occurrence in cultivated plants ; thus Potatoes are notorious
for failing to produce fruit; and some varieties are much less
liable to do so than others Mr. C F. White, F.L.S., tells
me he regards this plant as furnishing the most conspicuous
example of a form of degradation of pollen ; the pollen
grains of a normal character are very generally not to be
found at all, bat round, square, and polygonal forms abound.
On the other hand, he gathered many flowers, in a large
field in the Isle of Thanet, with scarcely a grain imperfect
in shape or reduced in size.
Mr. White has noticed, in his numerous researches
among pollens, that degenei'acy by dwarfing is mostly or
very frequently induced by inclement weather. He mentions
* A like cause produces petalody of stamens, see p. 299.
DEGENERACY OF FLOWERS. 277
the case of " Ononis, gi'owing and fioweririg abundantly on
the ' Sand-totts ' near Burnham, on the Bristol Channel, in
which plant scarcely a grain of normal form was to be
found ; many were absolutely united into gi-otesque groups
and utterly deformed. At the commencement of the cold
weather of autumn, although the corolla may appear unin-
jured, the pollen grains are often 'dirty,' unable, as it were,
to throw off the residual tissue surrounding them, and are
often irregularly reduced in size."
This sensitiveness of pollen to barren soil, inclement
weather, etc., at once throws light on a probable origin of
dielinism, such as of gyno-dioeceous plants ah^eady mentioned;
and simply confirms the idea that these differences in the
sexual systems of plants must not be looked upon as so many
beneficial arrangements, but simply inevitable results which
must follow such circumstances as give rise to them, whether
they may prove advantageous or not. The injurious effect
of over-ci'ossing, abundantly proved by florists, Mr. White
recognizes in the character of the grains of Rhododendrons
and Ericas, which exhibit a shrivelling up and occasionally
a complete " dissolution " of one and the uppermost grain of
the group of four. And this observer adds, that in more
than one species of Erica and also of Vaccinium the injury,
he thinks, has become chronic.
If the " vegetative" system be too energetic the "repro-
ductive " is sure to suffer, and one of the primary causes of
the injury is the arrested state of the pollen, as Van Tieghem
has described and figured it in Ranunculus Ficaria.* A
like result occurs in many cultivated plants, as Mr. Darwin
has pointed out when describing the " contabescence of
anthers." |
* See above, p. 231, note.
t An. and PI. under Dom., vol. ii., p. 165.
26
278 THE STRUCTURE OF FLOWERS.
DEGENERACr IX THE Gyn(ECIUM — If the theory be true
that a typical flower should contain two whorls of carpels,
or, if spirally arranged, several cycles, then it is an obvious
fact that these conditions are not the prevailing ones in
nature. In a simple type, like Ranunculus, Ave find the pistil
of many carpels, but with one ovule in each alone developed,
except in monstrous conditions , if the ovules be numerous,
then the carpels are reduced in number, as in the Helleborece.
This is a primary result of Compensation. And when
carpels have become whorled —a condition I take to be
primarily due to adaptations to insect agency, causing an
arrest of axial growth by the enhancement of the corolla,
etc., (see p. 6) — then degeneracy begins to play an important
part, in that, firstly, (theoretically, be it observed) one of
the two whorls of carpels goes altogether, sometimes the
calycine (e.g. Fuchsia), at others the petaline (e.g. Cam-
2)anula).
Secondly, the number of carpels diminishes, as in the
Gamopetalce, where less than five prevail. The following
table will show with tolerable accuracy the proportional
number of carpels and ovules that prevail in the first three
divisions of Dicotyledons.
Thalam. Calyc. Oamnp.
(1) Orders with many carpels or Ord. p.c. Ord. p.c. ' Ord. p.c.
many ovules ... ... 12 or 19 6 or 7 0 or 0
(2) Orders with 5 carpels and
many ovules ... ... 12 or 19 10 or 12 7 or 12
(3) Orders with 5 carpels and
5-10 ovules ... ... 12 or 19 14 or 17 3 or 5
(4) Orders with less than 5 carpels
and less than 5 ovules . ... 14 or 21 30 or 36 23 or 40
(5) Orders with less than 5 carpels
and many ovules ... 17 or 25 22 or 27 25 or 43
Observations. — (1) The first-mentioned correlation has two
DEGENERACY OF FLOWERS. 279
conditions, either many carpels having one or few ovules
in each, or a few carpels with many seeds, as in the
Ranunculacece. This primitive condition rapidly vanishes in
passing to Calycifloroe and Gamopetalce.
(2) Having reduced the number of carpels to a definite
quantity, five, i.e. one cycle of the prevailing t type, this
number remains tolerably persistent, but does not show a
large percentage.
(3) The combination of five carpels with a reduced number
of ovules, i.e. one or two in each cell, or 5-10 ovules in all,
is pretty uniform for the first two divisions, but almost
disnppears under Gamopetalce, the orders Sap'otacece, Nolanece,
and one or two Buhiacece, (e.g. Erithalis) representing this
condition.
(4) and (5). Here we see a steady increase in the
percentages in passing from Thalamiflorce to Gamopetalce, in
which the number of carpels is still further reduced ; but
the number of ovules runs in two directions, being either
numerous or few.
Two questions arise at this point. If one result of insect
agency is to bring about increased specialization in flowers
(yet, in proportion as they become specialized, so, inversely,
is the number and variety of insect visitors diminished),
how is it that some (e.g. Foxglove and Orchids) produce
an enormous number of seeds ; while others (e.g. Lahiatce,
Compositce, etc.) produce few or only one in each flower ?
The second question is whether a plant is better off for
having so many more seeds than another. Recognizing
reproduction as the sole end of plant life, so that a plant
should bear as many good seeds as possible, it is noticeable
that the two largest orders, Compositce and Graminece have
never more than one seed to each flower. Again, comparing
Lahiatce with Scropliularinece, according to the Genera
280 THE STRUCTURE OF FLOWERS.
Flantarum of Bentham and Hooker, while the former has
2600 species, the latter has only 1900. Lastly, comparing
two orders with regular flowers and two carpels, Boraginece
has 1200 species, and Solanece, 1250 ; while the former order
never has more than four seeds to a flower, in the latter they
are numerous.
If it were possible, we should procure statistics as to the
relative degrees of abundance in individuals of two kinds at
any place where they thrive. Casual observations certainly
have not led one to notice any such proportional abundance
of the many-seeded plants as theoretically ought to exist
if all their seeds germinated and grew to maturity ; for I
have calculated the number of apparently good seeds in a
large plant of Foxglove, and found it was one and a half
millions. If we take a typical case, that of Orchids, whose
flowers are certainly of those most highly adapted to insect
agency, it is now well known that the proportion of seedlings
to seed is infinitesimally small. Mr. Fitzgerald speaks of
a Dendrohium speciosum, which bore 40,000 flowers open at
the same time ; but though the plant was growing in the
open air and was exposed to the visits of insects, only one
flower produced a seed pod* Mr. H. 0. Forbes found the
same thing to occur in the terrestrial orchids of Portugal,
and the tropical ones of Borneo. f Exactly the same diffi-
culties are met with in cultivating plants, and especially
Orchids (with few exceptions), as Mr. Veitch has testified.
Now, when we examine the structure of the essential
organs of Orchids microscopically, their degeneracy at once
becomes apparent. First, with regard to the pollen. Instead
of its being in well-formed distinct grains, each with its
* Referred to by Mr. Veitch, Report on Orchid Conference, Journ.
Roy. Hort. Soc. Bot., vol. vii., p. 47.
t Journ. Lin. Soc. Bot., vol. xxi., p. 538.
DEGENERACY OF FLOWERS. 281
extine and intine, their development is arrested and, while
still in contact, a common extine clothes the who'e of each
massula. Moreover, it is only after the pollen mass has
been placed upon the stigma that the development is con-
tinued.* With regai'd to the pistil the first sign of degeneracy
is seen in the parietal placentation which prevails, and more
especially in the rudimentary character of the ovules, every
part of which is degraded. Even after fertilisation the
embryo cannot grow to maturity, but remains in the arrested
pro-embryonic condition. Having no albumen or nucellus-
tissue wherewith to nourish the embryo, the suspensor does
its best by elongating and escaping from the micropyle, and
then, fastening itself like a parasite upon the placentas, ex-
tracts nourishment therefrom — the result being that myriads
of seeds never succeed (at least in cultivation) in developing
even the pro-embryo ; and one can only infer that such is
the case in nature. f
In the cultivation of other flowers analogous phenomena
are met with. The more highly cultivated a florists' flower
may be, the less good seed is procurable ; wdiile the poorer
ones — that is, from a florist's point of view — or " weedy "
looking plants furnish plenty, and are highly prolific.
The rationale of these facts, whether taken from nature
or from cultivation, I believe to be fundamentally the same,
viz. the adaptation to insect agency and the result of repeated
intercrossing, which enhances the development and form of
the perianth especially, and generally of the stamens as well.
At least the kinds of energy which are concerned in the
manufacture of these whorls are more especially forced into
activity by the stimulus received from without. On the
other hand, the pistil suffers proportionately in all its parts
* Mr. B. T. Lowne, Orchid Conference, etc., I.e., p. 48.
t M. Guignard has drawn similar conclusions. See above, p. 172.
282 THE STRUCTURE OF FLOWERS.
throug-li compensation and atrophy, the ovules being appa-
rently particularly sensitive. To meet this difficulty nature
seems, to speak metaphorically, to have tried two methods,
either to make an immense number of seeds, so that at least
a few might be perfect, or else to attempt no more than four
or even one, so that at least they should be vigorous, and
survive in the struggle for life during the critical periods of
germination and seedling existence. To judge by results,
this latter method turns out to be the best.
The interpretation, then, I would offer of inconspicaous-
ness and all kinds of degradations is the exact opposite to
that of conspicuousness and great differentiations ; namely,
that species wath minute flowers, rarely or never visited by
insects, and habitually self-fertilised, have primarily arisen
through the neglect of insects, and have in consequence
assumed their present floral structures. The external
stimulus or irritations derived from the weights, pressures,
and punctures of insects being no longer applied, the
secretion of honey has failed, the corolla ceasing to be
subject to hypertrophy has atrophied. A like procedure has
obtained with the stamens, while a large proportion of pollen
has become effete, the anthers being partly contabescent, as
it is called. What remains, though often altered in cha-
racter, is amply sufficient to set an abundance of seed.
With regard to the pistil, however, the reverse of this
has in some respects taken place. The corolla and androecium
no longer putting a check upon the rapid development of
the gynceciura, the latter has a strong tendency to gain the
ascendancy; so thq^t the result is homogamy or protogyny,
with an extraordinary fertility of all plants which have
inconspicuous and regularly self-fertilising flowers.
If the seed be not always -in great quantity in one and
the same capsule, an ample progeny is secured by the
DEGENERACY OF FLOWERS. 283
extremely rapid maturation of the fruits in succession ; as
may be remai-kably well seen in Chickweed.
The general result is that all these " -weed-like " plants,
with which wind-fertilised herbs must be associated as equally
independent of insects, of all flowering plants are by far the
most widely dispersed, and are, in fact, cosmopolitan ; * and
although they be small and annuals, are yet best capable of
holding their own in the great struggle for life.
Rudimentary Organs. — These are the ultimate result of
atrophy and degeneracy in flowers. They are so well known
as occui'ring in all parts of plants, vegetative and repro-
ductive, that I need not describe them now. The reader
will doubtless gather from all that has been said about
hypertrophy and atrophy as causes of development and
degeneration respectively, that they are just what one
would expect to find. Indeed, every organ can be met with
in every stage of degeneration till it has completely vanished ;
and even when all visible trace is wanting, the vascular cord
belonging to it may in some cases still be detected. Last of
all, this vanishes as well. These diiferences, for instance,
can be witnessed in the presence or absence of the " trace "
of the fifth stamen of the Labiatae.
It is thought by some that a rudimentary organ may
become a honey-secreting gland, as Robert Brown suggested
for some Cruciferous plants. Glands mostly consist of epider-
mal and sub-epidermal tissues only, and if they occupy the
place of an organ, the latter has the vessels arrested before
they reach into the glai\,d, whicb therefore is still of the same
nature. In the male flower of Lychnis dioica the disk sur-
rounds the rudimentary pistil, which in no way contributes
* In my essay referred to, I have given a long list of self-fertilising
plants which have been discovered in widely distant localities over the
northern and southern hemispheres.
28-t THE STRUCTURE OF FLOWERS.
to it. On the other hand, a gland may have its own proper
vascular system, as in Lamium album, in which case a
circular horizontal ring of vascular cords is formed from the
pistillary cords ; from this are given off a series of vertical
cords, running up into the gland itself.
There can be no a priori objection to the supposition that
an organ, when degenerating and becoming rudimentary,
may acquire a new foi-m and function ; for such, indeed, is
not infrequently the case. But what perhaps may be more
usual, is that some other organ becomes moi-e highly de-
veloped through compensation. Thus, for example, the
leaflets of the Pea, in becoming tendrils, lose all trace of a
blade, retaining only their mid-ribs. These, however, now
elongate and acquire sensitiveness, for the use of climbing.
On the other hand, in compensation for the loss of a certain
amount of leaf surface, the stipules are very broad and
foliaceons. Again, in the ray florets of Centaurea the essen-
tial organs have vanished altogether, but the corolla is
greatly enlarged in comparison with those of the disk
florets.*
* For a discussion upon " rudimentary organs," and their bearing
upon the theory of Evolution, I would refer the reader to my work on
Evolution and Religion (the " Actonian " Prize Essay for 1872), chap,
xiii., p 197.
CHAPTER XXYIII.
PTIOGKESSIVE METAMORPHOSES.
Homology. — The theory of homology has long been main-
tained, and has met with such an overwhelming mass of
evidence in its favour, that it is now regarded as a well-
established morphological doctrine. The belief that every
individual member of a flower, whether sepal, petal, stamen,
or carpel, may be interchangeable with a leaf, and. that they
are therefore all phy Homes or foliar appendages to the axis,
scarcely requires proof. Secondly, any one organ may
theoretically be substituted for any other, so that although a
suflScient number of interchanges has not yet been met with
to make a complete series of permutations, yet they have
gone far towards strengthening the probability that such
might be possible.*
I propose giving a very abbreviated series to illustrate,
first, progressive changes from leaves through bracts to
* The metamorphosis, with the exception of the substitution of
petals for other organs, is rarely more than tentative ; for it is, as it
were, a mere attempt to effect a change, so that wherever a " monstrous"
organ bears ovules they are almost always rudimentary and quite
incapable of beiug fertilised. I have said "rarely," for M. Brongniart
succeeded in obtaining fertile seeds from artificial impregnation of
ovuliferous stamens in Polemonium cceruleum {Bull. Soc. de Bot. Fr., t.
viii., p. 453).
286
THE STRUCTURE OF FLOWERS."
carpels; and, secondly, a retrogressive series from carpels to
bracts, and thence to leaves ; finally deducing some important
conclusions.
Progressive Changes in Bracts. — Bracts are in many
cases very obviously modifications of leaves, being sometimes
simply complete leaves reduced only in size, as in Epilohiam ;
or a bract consists either of the blade alone, as in Buttercups,
or else of the petiole only,
but now expanded and
blade-like in form, as may
be well seen in Hellebores,
where transitional states
occur between the normal
pedate leaf and true lan-
ceolate bracts (Fig 61,
a, h, c).
When bracts are
coloured otherwise than
green, they then approach nearer to members of the repro-
ductive or floral series rather than the veg'etative, and in
many cases are actually continuous in a spiral series with
the sepals and petals, as in Cactus, Cahjcanthus, etc., and so
assist in rendering the flower attractive. Several species of
the genus Salvia, e.g. S. splendens, S. Bruantii, as well as of
Bromeliacece, are remarkable for having brilliantly coloured
bracts at the base of the flower. In some cases the bracts
may be so arranged as to mimic a corolla, and indeed func-
tionally replace it, as in species of Cornus (Fig. 62), Danvinia
(Fig. 63), and the so-called Everlastings.
The presence of bright colours in bracts, as also in sepals,
to be described, I take to be due to the same influence as
of the normal attractiveness in corollas ; viz., the visits
of insects : the immediate cause being nourishment ; the
Fig. 61. — Transitional form?, a, h, from a leaf to a
true bract, c, of HdLtborus viriUis.
PROGRESSIVE METAMORPHOSES.
287
stimulus required to bring the extra flow to the bracts, etc.,
being presumably the irritation induced by insect visitors.
The next progressive state is for bracts to assume a more
Fig. 62, — Inflorescence of Connis florida,
■n ith luur white petaloid bracts.
Fig. 63. — Inflorescence of Darunnia, with
coloured petaloid bracts.
or less staminoid character. This is rare, but it has been
noticed in Abies excelsa* A substitution of anthers for
bracts has been seen in. Melianthus major,-f concerning which
Sig, Licopoli remarks that the flowers of chiefly the terminal
racemes were impei'fect, the summit of the floriferous axis
bearing a tuft of perfect and imperfect anthers the petals
and the two carpels of the flower having been atrophied or
arrested.
Fig. 64 represents an involucral bract of Nigella, bearing
an anther on one side of it; while Fig. 65, a, is that of a
glume of Lolium perenne with an anther. That bracts should
ever assume a pistilloid character is, a priori, still more
unlikely, as being further removed from the central organ of
the flower. Dr. M. T. Masters has, however, described % a
* Teratology, p. 192. f Bull. Soc. de Eot. Fr., Rev. hih., t. xiv., p. 253.
X Journ. of Lin. Soc. Bot., vol. vii., p. 121.
288
THE STRUCTURE OF FLOWERS.
malformed Lolium peremie, in which the flowering glumes
had styles and stigmas (Fig. 65, a, b) ; the essential organs
being absent, were replaced by a tuft of minute scale-like
Fig. 64. — Involucral bract of
Nigella, with autlier (after
Masters).
a b
Fig. 65.— Glumes of Lolium, with anther
and stigmas (after Masters).
organs, some of which were prolonged into styliform pro-
cesses, the sexual organs being otherwise suppressed.
In a proliferous case of Delphinium elatum described
and figured by Cramer,* the parts of the flowers were all
metamorphosed into open rudimentary carpels. The axis
was elongated and terminated above, in one case, by a
similar abortive flower ; in another, by an umbel of such
flowers, every part of which was more or less carpellary ;
while all the hrads on the prolonged axis, even those out of
the axils of which the branches of the umbel sprang, were
similarly made of open carpels.
Progressive Changes in the Caltx. — The sepals are
usually homologous with the petiole of a leaf. This is obvi-
ously the case with the Rose, where the rudiments of the
* Bildungsabweichungen, etc., heft, i., taf. 10. The figure is repro-
duced iu Teratology, p. 126.
PROGRESSIVE METAMORPHOSES.
289
compound blades are retained (see Fig. 24, p. 93). In
Pedicularis the blades are present as a minute fringe on the
edge. In Ranunculus, Potent ilia, etc., the broad base of the
petiole is the only part present, for in abnormal conditions
the blade may be borne above (Fig. i5>5). Similarly, in a
gamosepalous calyx the teeth as a rule seem to be all that
remain to represent the blades ; for in TrifoUum repens, when
virescent, true unifoliate blades ai'e developed on elongated
pedicels, all arising from the border of the calyx-tube (Fig.
Q7), in which the teeth become pinnately nerved blades.
Fig. 66. — Riinunculus with foliaceous
sepal.
Fig. 67. — Foliaceous calyx of Tn'folium
repens, with stipulate leaflets (after
Baillon).
The venation may in some cases assist in furnishing a clue
as to the real nature of a part. Thus in Hellebore, as already
seen (Fig. 61), the bracts are homologous with petioles,
their venation being palmate, and not pinnate as in the
divisions of the blades of the leaves. It is the same in the
sepals, which are presumably therefore homologous with
petioles as well. The sepals of Galtha resemble them in
their venation, but in this plant the leaf is of a more
primitive type, not being lobed, and has also a palmate
venation.
A similar difference between the venation of the sepals
27
290
THE STRUCTURE OF FLOWERS.
and blades of the leaves is seen in JDlpterocarpus and Mus-
scenda (Fig. 68). Transitional states from a single to a
double flower of Saxifraga decipiens, described and figured
by M. C. Morren,* shows that the newly formed petals in
the place of stamens, as also the normal petals of the flower,
exactly correspond, both in shape and venation, with the
cotyledons. Palmate venation thus simply represents a more
primitive type ; and, since fl»wers are constructed out of
metamorphosed leaves — the vegetative being replaced by
reproductive energies, — one naturally expects to find the
calyx and corolla, which more nearly approach leaves in
structure, to show arrested foliar con-
ditions, as, e.g., are seen in palmate
nervation and absence of blade or
petiole, as the case may be.
In Musscenda (Fig. 68) the teeth
of the sepals are usually subulate and
acuminate ; but in the one foliaceous
and subpetaloid sepal it is di^awn out
into a long petiolar form, which then
expands into a palmately nerved
lamina. The fact that a "tooth " is
in this case prolonged into a " petiole "
seems to imply that the sepal arises
at once from the receptacular tube,
which, therefore, one would infer to
be axial. A somewhat analogous pro-
cedure is in the monstrous Trifolium,
where the unifoliate blades, supported on long pedicels with
stipular appendages as well, all arise from the border of the
so-called calyx-tube (Fig. 67). There the inference would
be the same, only that the receptacular t^^be is free from the
* Les Bull, de I'Acad. Roy. de Bruxelles, t. xvii., p. i., p. 415.
Fig. 63. — Flower and leaf of
Mass(Enda.
PROGRESSIVE METAMORPHOSES.
291
pistil, and not adherent as in the case of Musscenda. In both
instances it will pi^esumably be purely axial in character.
Progressive changes in the calyx ai-e not uncommon by
its assuming a petaloid character. This is normal in some
genera of Batiunculacece, in Fuchsia, Bhodochiion, as well as in
some members of the Incompletce, as in Mirahilis, Polygonum,
Daphne, etc. Normally coloured sepals are most frequent
in polysepalous genera. Abnormal colorisation, with or
without any metamorphosis of the organ, is
most frequent in gamosepalous flowers, as in
the cultivated " hose-in-hose " varieties of
Primula, Mimidus and Azalea. The calyx
may be petaloid either wholly or in part
only. In Musscenda (Fig. 68), one sepal only
is normally sub-petaloid. Calceolaria has
occasionally one or more sepals petuloid.
Similarly Linaria (Fig. 69) and other in-
stances might be mentioned. These condi-
tions, brought about by cultivation, clearly Fig. 69.— Mnajta,
. J 1 1 T • 1 • 1 with one sepal
show the important part that high nourish- petaloid.
ment plays as an external stimulus or factor in the produc-
tion of colour.
Staminoid sepals appear to be very rare. It is recorded
by M. Gris that they have occurred in Philadelphus speciostis*
Pistiloid sepals are nearly equally as rare as staminoid.
They have been observed by Mr. Laxton in double flowers
of the Garden Pea (Fig. 70), in which there was a five or
six-leaved calyx, some of the segments of which were of a
carpellary nature, and bore imperfect ovules on their mar-
gins, the extremities being drawn out into sub-stigmatiferous
styles. t
* Bull. Soc. de Bot. Fr., t. v., p. 330.
t Gard. Chron. 1886, p. 897 ; and Teratology, p. 302.
292
THE STRUCTURE OF FLOWERS,
I have also found the sepals ovuliferous in a monstrous
form of Violet, which was almost entirely virescent (Fig. 71).
Progressive Changes of the Corolla. — For petals to
become staminoidis far from uncommon. It is a normal con-
dition in Atragene (Fig. 44, p. 141), which illustrates the
transition, and in Water-lilies, where a gradual development
of the anther cells is accompanied by a gradual reduction of
the petal to a filament. As abnormal instances may be men-
tioned, a case of Foxglove which I have elsewhere * described
as having the corolla split up into strap-shaped antheriferous
processes (Fig. 72), and a Columbine in which the spurs
Fig. 70.— Calyx of Garden Pea,
with carpellary lobes (after
Masters).
Fig. 71. — Ovuliferous
sepal of Violet.
Fig. 72.— Corolla of Fox
glove, with staminate
tube.
became curiously coiled and bore pollen within the tissue of
the coils (Fig. 73).
Pistiloid petals are of rare occurrence. As an example is
Begonia (Fig.- 74, a), in which the apex of the petal was
green and stigmatiform, the basal part being broad, coloured,
and ovuliferous. Fig. 74, &, shows a petal, ovuliferous below,
stigmatiferous at the summit, and antheriferous midway ;
c is a rudimentary ovule.
Progressive Changes in the Stamens. — The only change
* Journ. Linn. Soc. Bot., vol. xv., p. 86, tab. 3.
PROGRESSIVE METAMORPHOSES.
293
that stamens can undergo in this direction is to be more
or less converted into pistillaiy structures. This is bj no
means uncommon. Either the filament alone, or the anther
alone, or both together may be affected. The reader is
Fig. 73. — Aquilegia, with poUeniferous spurs
(after W. G. Smitb).
Fig. 74.— Ovuliferous petals, etc. ,
of Begonia (after Masters).
referred to Dr. Masters's Teratology for a description, with
figures of several kinds.* It is more usual for the filament
to become enlarged into the ovarian part bearing rudimentary
ovules ; but when the anther is involved, it may be partially
or wholly transformed. In these cases the connective is
usually prolonged into a stigmatiferous process, f As an
example often described is that of the Houseleek, in which
the margins of the anther cells become ovuliferous in various
degrees ; as in Fig. 75, where ovules are borne by the pos-
terior sides only, instead of pollen. In other cases the
filament bears rudimentary ovules as well. Dr. Masters
points out that " where there is a combination of the
* Page 303.
f In Aristolochia this change seems to be permanent and functional.
See above, p. 83.
294.
THE STRUCTURE OF FLOWERS.
attributes of the stamen and of the pistil in the same organ,
the pollen is formed in the upper or inner surface of the leaf
organ, while the ovules arise from the opposite surface from
the free edge." Begonia is a genus which is peculiarly liable
to pi-oduce malformations in the stamens (Fig. 76).* Bosa
(^J)
Fig. 15. — Ovuliferous anthers of
Sempervivum (after Masters).
Fig. 76.— Stigmatiferous and ovuliferous
stamens of Begonia.
arvensis'\ affords a case in which the ovules were borne by
the anthers, and then they themselves produced pollen. In
these cases, where the anthers are ovuliferous, the connective
is often more or less stigmatiferous, as in Begonia (Fig. 76),
which shows various degrees of metamorphosis in this way ;
but the anthers may sometimes be stigmatiferous, as in
Poppies, X or styliform as well, as in Bamboos. §
The complete substitution of carpels for stamens occurs
in many plants, as in Mains a])etala,\\ Tulips, etc., and is
extremely common in Wallflowers,^ while it is by no means
an uncommon occurrence to find male plants of normally
dioecious or monoecious character bearing female organs,
though perhaps in these cases it is often an addition, rather
than a substitution of one organ for another.
Bot. Zeit. (1870), vol. xxviii.,
X Teratology, p. 304.
* See Journ. of Lin. Soc. xi. 472;
p. 150, tab. ii.
t Journ. of Bot., 1867, p. 318, tab. 72.
§ Col. Munro, Trans. Lin. Soc, vol. xxvi., p. 7.
(1 Poiteau et Turpin, Arhr. Fruit., t. xxxvii., I'eferred to by Moqnin-
Tandon, TSratologie, p. 220.
% Called " Rogues " by the market-gardeners, as the corolla is want-
ing or green. See Ann. des Sci. Nat., 5 ser., xiii., p. 315, pi. 1.
CHAPTER XXIX.
RETROGRESSIVE METAMORPHOSES.
The Pistil. — Commencing with tlie pistil, there may be
changes in the ovary, ovules, style, and stigmas, separately
or collectively. Instead of one or more
ovules, a pistil may be formed within
an ovary, as sometimes occurs in Wall-
flowers, Grapes, Oranges, etc.* A sin-
gular instance is described by Dr.
Masters f of a Carnation, " the placenta
of which bore not only ovules but also
carpels, the latter originating in a per-
verted development of the former ; so
that many intermediate stages could be
traced between the ordinary ovule and
the ovary. Some of these carpels, thus
derived from ovules, themselves bore
secondary ovules on a marginal pla-
centa " (Fig. 77, a, carpel and section), the secundine, how-
ever, being the only part developed (b).
Stamens within an apparent ovary have occurred in
* Teratology, p. 182.
t L.c, p. 267. Perhaps the supposed " ovule within an ovule " may
have been the nucellus only, more or less free from the secundine.
Fig. 77. — Carpels and ovules
on placenta ot Carnation
(after Masters).
296
THE STRUCTURE OF FLOWERS.
BcecJcia diosmcefoUa ; * but as they grew on the interior of
the wall and not on an axile placenta, as is the normal con-
dition in the Myrtacece, I expect that it was due to the
staminal vascular cords branching off and coming out of the
tissue within instead of at the summit of the hollow recepta-
cular tube, the carpels being more or less arrested. A not
uncommon instance is to find the pistils of Willows with
open ovaries and bearing one or more anthers on the margins
(Fig. 78, a). I have met with a" similar occurrence in
Ranunculus auricomus (Fig. 78, &). Pistils of other flowers
<v
Fig. 78. — Stameniferous carpels of AVillow
(.a) and Ranunculus auricomus (,6).
Fig. 79. — o, Petaliferous placenta? of Car-
(lamine pratensis ; b, of RhodUxUndron.
in a similar waj,
as
have been known to bear anthers
Chamoerops humilis, Primus, f etc.
Pollen within ovules has been met with occasionally, as
in Passiflora and Bosa arvensis.X
In some members of the Cruciferoe, as Cardamine pratensis
(Fig. 79, a), round pods are formed instead of the usually
* Teratology, p. 184. Possibly the ovaiy was entirely absent, and the
stamens would then be growing on the interior of a closed receptacular
tube, just as carpels grow upon the inside of the hip of a rose.
+ See Weber, Verhandlung des Nat. Hist. Vereines der Preuss Rhein-
und Westph., 1860, p. 381.
X Teratologrj, p. 185.
RETROGRESSIVE METAMORPHOSES. 297
long siliquas. These are full of petals, and if carefully
examined appear to be whorled, with traces of stamens and
pistil within them ; so that they represent flower-buds, but
of which petals form the greater part ; similarly, Rhodo-
dendrons and other flowers are known to bear imperfect
flower-buds within the ovary (Fig. 79, b).
Anthers occupying the place of stigmas appear to have
occurred in Campanula,* Snowdrop, and double Tulips.
The substitution of stamens for the entire pistil is of a
less usual occurrence than the staminody of its parts : for
cases, the reader may consult Masters's Teratology .j In a
species of Orchis, probably 0. Morio, the ovaries were wanting
altogether, a long pedicel taking their place, and within
the reduced and regular perianth were huo anthers on
opposite sides (Fig. 23, a, p. 92), an apparent compensation
in lieu of the pistil.
The next and most frequent case of metamorphosis is
that of conversion of carpels, and usually the stamens as well,
into petals, or the so-called "doubling" of
flowers. This is usually accompanied by a
change from whorls to spirals with a multi-
plication of the parts. Thus, in a double
Wallflower, I have counted more than fifty
petals spirally arranged. With regard to
the petalody of the pistil, as Dr. Masters
observes, " this is much less common than
the corresponding change in the stamens. ^'y^i-^^^/tSoM
It generally affects the style and stigma wi of myan-
only, as happens normally in Petalostylis,
Iris, etc." X Fig. 80 illustrates a metamorphosed carpel of
Polyanthus, with a broad coloured appendage to the style.
In some double flowers the carpels only are petaloid.
* Teratology, p. 300. t Ibid., p. 299. t md., p. 296.
298 THE STRUCTURE OF FLOWERS.
This has been observed in Anemone nemorosa, cultivated
varieties of Ranunculus, Violet, and Gentiana Amarella.
Retrogressive Metamorphoses of Stamens. — For the
stamens to become petaloid, it is extremely common, as in
double flowers, and such a change may represent what
is normally the case in Water-lilies, Canna, and Atragene
(Fig. 44, p. 141). Changes may apply to the anther lobes,
connective, or filament, or to all together. Fuoiisias often
bear filaments with petaloid expansions of the apex, at the
base of which are one or two anthers showing varying
degrees of degeneration. This is a very similar condition to
one in Petunia, described by Dr. Masters, in which the con-
nective had developed into a green roundish blade bearing
two anther cells at the base (Fig. 81).* In such cases, it
seems to be the connective which has expanded outwards
and become the blade of the petal or leaf. Similarly, in the
Fig. 81. — Foliaceous connective of Petunia Fig. 82. — Petalody, or "liose-in-hose'Torm,
(after Masters). of counectives in a double Columbine.
double Columbine petalody of the connective sometimes takes
place (Fig. 82). f Commelina alba has also furnished a case
of an anther lobe becoming petaloid.
Causes of " Doubling." — There can be no doubt that
petalody results from a weakened reproductive energy, espe-
cially that of the androecium, which can become constitu-
tional and may be hereditary and transmissible by crossing.
* rerafo?o<7j/, p. 254. ^ Ihid., p. 293
RETROGRESSIVE METAMORPHOSES. 299
Cases seem clearly to show that a barren and dry soil, as
well as a very dry atmosphere, are prominent causes for its
appearance. Thus Mr. Darwin described a double Gentiana
Amarella* growing " on a very hard, dry, bare, chalky
bank." T. S. speaks f of a double Fotentilla as " grow-
ing along a high wall, on a dry raised bank close to a
beaten path, adjoining a gravelly field." Again, a writer in
Gartenzeitung J alludes to the raising of double Stocks, and
says that they should only have " just enough water for
their preservation," and that " the starved state of the
plants " causes doubling. He alludes to Camellias, also, as
becoming double when grown in a dry soil. Kerria Japonica
becomes double in Europe, in consequence of its missing the
wet season of Japan. It is well known that double flowers
are more easily raised on the continent than in England,
probably from a like cause, as our atmosphere is considerably
more charged with moisture than a continental one. In
raising double Stocks, it is customary to procure seed from
the flowers on axillary shoots which have a weaker repro-
ductive energy than those growing on the primary or central
axis, the seeds being smaller and often misshapen. The
above causes are, therefore, suggestive ; in that if a some-
what elevated, dry, and poor soil, one devoid of phosphates,
etc., be provided, the probability is that petalody will ensue.
Having once shown a trace of the malady, florists know how
to proceed in order to propagate and transmit the affection.
There remains one other floral metamorphosis, and that
is of petals into sepals. This condition approximates to
virescence of the corolla, so that in many cases such a
change could scarcely be called sepalody. But M. Godron
has shown that when Hannnculus auricomus appears to be
* Gard. Chron., 18-4.3, p. 628 t Ibid., 1866, p. 973.
X Ibid., 1886, p. 197.
300 THE STRUCTURE OF FLOWERS.
apetalous or to have a corolla consisting of a few petals only,
it is dae to the fact that the petals which ax'e wanting are
really present, but have become calycine.
Origin of Homology. — Though we cannot penetrate into
the arcana of life, nor trace the workings of its forces which
bring about the development of any organ whatever, I
think we can at least reach the physiological starting-point,
so to say, of all these changes which I have briefly described.
I have already mentioned that we may consider a vascular
cord as the fundamental " floral unit," and as all cords are
identical in character as long as they are within a pedicel,
and, as far as one can observe, identical also in character
even when they have penetrated the different organs, we at
once see that there is a common source for each and all.
Secondly, when we trace these cords from the receptacle or
axis into the floral members, we soon discover that any cord
can supply two, three, or more totally different organs with
their respective branches, as in the case of Campanula
medium described above (p. 43). Indeed, starting, say, with
five cords in a pedicel, they can supply any number of organs
ad libitum, however diverse in character and however
numerous they may be. Hence, although normally each
whorl is stamped with its own individuality, it is easy to
imagine, in accordance with the principles of evolution, that
others may partake of it ; and so the charactei'istic features
peculiar to one whorl can transcend its limits, and influence
others as well.
Beyond some such interpretation as this, I do not think
it is possible to go.
In saying that a fibro- vascular cord can "give rise" to a
sepal, or petal, or other organ, I need hardly remind the
reader that I am only speaking metaphorically, in describing
what one observes in studying the anatomy of flowers.
CHAPTER XXX.
PHYLLODY * OF THE FLORAL WHORLS.
ViRESCENCE AND FOLIACEOUS CONDITIONS — SePALS, PeTALS, AND
Stamens. — The last changes to be described, which are
common to all the members of a flower, are virescence, when
they retain their normal forms, but are simply green ; and
foliaceous conditions, when they assume more or less a truly
leaf -like form.
Dr. Masters has given descriptions t of several of each
kind of floral members as well as of foliaceous bracts, to
which I must refer the reader for details. There are certain
particulars, however, to which I would especially draw
attention as throwing light upon the ordinary structure of
floral whorls, and especially that of ovules.
Taking the Alpine Strawberiy as an illustrative case, the
petals, stamens, and carpels are often more or less foliaceous ;
but the petals retain a palmate venation, though the three
leaflets of the ternate leaf are pinnately nerved (Pig. 83, a,
h). In the case of stamens the connective may be foliaceous,
as in Petunia (Fig. 81) ; J also in the Alpine Strawberry
(Fig. 83, a) and in the " Green Rose " the anthers are often
persistent on either edge of a leaf-like intermediate part
* The abnormal assumption of a leaf-like character.
t Teratology, p. 241, seqq.
t Ibid., p. 254.
28
302
THE STRUCTURE OF FLOWERS.
(Fig. 83, c). A curious foliaceous modification is described
bj Miiller and figured bj Masters,* in which tbe metamor-
a
Fig. 83.— o, Foliaceous stamen, and b, petal of the Alpine Strawberry (jfter Le Maout
au(i DecaisQe) ; c, stamen ot " Green Ruse."
phosed stamen had the appearance of two leaves united by
their mid-ribs. It occurred in Jatroplm Pohliana (Fig. 84).
This will be alluded to again, as pecu-
liarly significant.
Phyllodt of the Carpels and
' lUl "X/" Ovules. — This is of much more frequent
l//f T^^, occurrence than of the stamens. The
first condition of change is to leave the
ovary open and to expose the ovules ;
the style may still be stigmatiferous.
Fip.84.-Foiiaceous stamen of ^he ovules then undergo phylloidal
Misters) ^''^''■''"'* ^'^^^"^ chauges of different degrees, and much
discussion has arisen as to whether the
coats of ovules should be regarded as homologous with leaves,
the nucellus being axial, or not, etc.f
Since, however, anatomical observations clearly prove
that both the primine and secundine issue out of tangential
* Teratology, p. 255.
t L.c, p. 262.
PHYLLODY OF THE FLORAL WHORLS. 303
divisions of the epidermal layer of the nueellus, one can
hardly consider these of themselves as homologous with a
true phyllome. But when we find that each of the two sides
of an anther cell can develop Into a foliaceous structure, as
in the case of the Jatroplia alluded to above (Fig. 84), we
seem to have discovered a power of converting what is
originally and simply an epidermal layer into a truly folia-
ceous structure. Moreover, this jDrocess is not infrequent
in certain raonstrous states of ovules, so that it would appear
that any question of homology is, strictly speaking, out of
court in these cases. When the whole of an appendicular
organ becomes foliaceous, then, of course, a true case of
homology may be recognized.
Origiji, Dbvelopment, and Homologies of Ovules. — Tera-
tology, here, I think, assists us greatly. With regard to the
structure of an ovule, it first appears as a papilla upon the
placenta, the cellular tissue of which, with its epidermal
layer, constitutes the first stage. Such may, perhaps, be
considered as the rudimentary condition of the funicle alone,
as the true ovule is formed at the summit of it. One or
more of the apical sub-epidermal cells gradually develop into
the nueellus, while the secundine is first formed by tan-
gential division of the epidermis commencing at a certain
place below the apex ; the primine, if present, subsequently
following suit in the same manner.* It is a noticeable fact
that while an ovule thus complete is elsewhere general in
flowering plants, the Gymnosperms and most orders of the
Ganwpetalce form remarkable exceptions, as having only one
coat to the ovule. In the former of these two groups it is
doubtless due to a primitive condition being accompanied
by other features showing afiinities with cryptogams. In
* See paper by Warming, De I'Ovule, Ann. des Sci. Nat., v. (1877),
p. 177.
304 THE STEUCTUKE OF FLOWERS.
the latter, it is due to reversion by arrest, and is likewise
accompanied by a simpler origin of the nucellus and embryo-
sac, as Warming has shown. The suggestion I would offer
to account for this anomaly is that such arrest is due to
compensation. The Gaviopetulce, as a whole, are the most
advanced of all flowers through adaptations to insect agency ;
and as this invariably brings about an exalted condition of
the corolla and stamens, the consequence is that the pistil
has to suffer ; the first visible result being protandry, accom-
panied by a temporal arrest in the development of the pistil.
If this tendency to arrest be carried to the ovule, it may
be affected too, and the result is that one, the last-formed
coat, may be ai'rested altogether. Orchids, as shown above,
illustrate this principle remarkably well, as their ovules,
though possessing two coats, are as degenerate as in many
parasitic plants (see above, pp. 172 and 281).
Tracing the ozngin of an ovule, then, from its birth, it
first appears as a papilla on the placenta of the carpel. A
branch from the marginal fibro-vascular cord of the carpel
enters it from below, and reaches at least as far as the
chalaza, or base of the nucellus. It may go no further, as in
rudimentary ovules of Orchis ; or be arrested in the form of
cambium in the degraded state seen in the parasitic Thesium.
On the other hand, as the ovule becomes a seed and the coats
go to form the seed-skin, fibro-vascular branchings may occur
all through the latter, being developed from the original cord.
Such may be well seen in Mustard, Acorns, Beans, and the
Coco-nut.
Although the coats of the ovule were originally formed
by tangential division of the cells of the epidermis of the
nucellus, when united to form a seed-skin, this has become
thickened by a cellular growth between them, through which
the cords then ramify.
PHYLLODY OF THE FLORAL WHORLS.
805
Pistils which, hare reverted to a more or less foliaceous
character bear ovules which often become foliaceous as
well ; and then a not uncommon procedure is the develop-
ment of a cup-like structure, probably composed of the tAvo
ovular coats, on an elongated stalk, with a rudimentary
nucellus within, but more or less perfectly free from it ; or
it may not exist at all.
The late Professor Henslow described a monstrous con-
dition of Mignonette with figures of ovules in this condition.*
They were sometimes
replaced by minute
leaves (Fig. 85, c) ; or
else in the place of
each was a cup-like
structure, elevated
on a long stalk, with
an egg-like nucellus
within, but quite free
from it. He likened
it to the theca of a
moss with its central
columella. Comparing these two modifications, i-epresented
by Fig. 85, a and h with c, — or, again, those of Fig. 86, a
and h, — the interpretation seems to be that the fibro-vascular
cord passing up the funicle of the ovule becomes a petiole,
and its prolongation constitutes the mid-rib. The secundine
and primine with intermediate tissue become the blade, as
seen in the foliaceous states of ovules, and constitute the
" cup " when they assume that form.
A similar process, I think, quite explains the origin of
the foliaceous processes of the stamen of JatropJia, repre-
sented by Fig. 84. The entire stamen is, of course, really
* Tra7iS. Camh. Phil. Soc, vol. v.
Fig. 85.
-Foliaceous and metamorphosed ovules of Migno-
nette (after Prof. J. S. Henslow).
306
THE STRUCTUEE OF FLOWERS.
homologous with one leaf alone ; but the membranes belong-
ing to each anther, being of, at least, two layers of cells,
have become foliaceous, just as the epidermis of the nucellus
has done in the cases herein described; so that, in the
Jatroplia, two leafy expansions were
developed out of one.
Other instances are known of ovules
being represented by leaves, as Primula
Sinensis, Symphytum officinale,* and
Sisymhrium Alliaria (Fig. 86).
Theoretically, it might be objected
that a leaf (carpel) should give rise to
a leaf (ovule or, at least, ovular coat) ;
but foliaceous excrescences from a leaf-
Fig. se.-Metamorphosed ovules surface are not at all uncommon, as,
^^H ^Srt^m'S: for example, frequently occur in Cab-
ncea, xvii.. t. 20). bages,t where, in consequence of high
nourishment inducing hypertrophy, any " rib " or " vein "
may throw off a branch which can form a leafy expansion,
which not at all infrequently becomes
funnel-shaped, like the abortive ovules of
the Mignonette. Similar funnel-shaped or
tubular productions are found on corollas
of semi-double flowers, as in Primulas,
Cyclamens, Antirrliinum, etc., sometimes
externally. Fig. 87 represents a like out-
th'e7abeUumTf growth from the labellum of Cattleya
Mossiece; and I have seen the posterior
sepal of Vanda ccerulea replaced by a pedicel with a cup at
the apex exactly like the terminal process in Fig. 85, a. In
all these cases I would regard such productions as due to
hypertrophy.
* Teratology, p. 263. t I^id., p. 312, fig. 166.
Fig. 87. — Tubular excres-
cence on "
Cattleya MossieoB.
PHYLLODY OF THE FLORAL WHORLS. 307
As another carious instance a remarkable form of the
Sun-dew, Drosera o-otundifoUa, may be alluded to here, as
throwing additional light apon the origin of ovules. It has
been described and figured by Naudin,* and also by Plan-
chon.f In this monstrosity the ovular coats were represented
by " tentacles." These, as is well known, are not epidermal
trichomes, but structures issuing from branches arising from
the fibro-vascular cords of the leaf, and are thei^efore strictly
homologous with the "funnels " on cabbage leaves.^
The conclusion, therefore, which seems deducible from
the foregoing observations is that an ovule is simply an
appendage (not a bud) to the fibro-vascular cord of the
margin of the carpel, and under monstrous conditions can
grow into foliaceous excrescences to the carpellary leaf. It
is not, therefore, axial in its character. Since all that is
required to start from is a fibro-vascular cord, this may be
furnished by any cord, even the mid-rib ; and such is the case
in some monstrous states of Primula, in which rudiments of
ovules are found on the mid-ribs as well as on the margins of
separate carpels.
As the " funnels " on the mid-ribs and lateral veins of
cabbage leaves are due to an abnormal condition of hyper-
trophy, so ovules I consider as arising in a similar way, and
take them to be due to the same influence, though of course
it is normal in their case. The very presence of the large
cords running up the margins of carpellary leaves, direct from
the axis below, — being often, indeed, larger than the dorsal
cord, — which then ramify, not only into each ovule, but often
backwards within the carpellary walls till they reach and
* Ann. des Sci. Nat., 2'^ ser., vol. xiv., p. 14.
t Ihid., 3" ser., voL ix., p. 86, tab. 5, 6.
X The " pitchers " of Nepenthes, perhaps, originate in much the
Bame way, from the original water-gland at the apex of the leaf.
808 THE STRUCTURE OF FLOWERS.
anastomose with tlie dorsal cord ; these, together with the
greatly thickened cellular margins now constituting the
placentas which snj)ply the conducting tissue for the pollen-
tubes, all show a form of hypertrophy in the edges of the
carpellary leaves, a condition of things widely different from
the usually thin and more or less impovei-islied margins of .
true leaves.
If we may recognize a fibro- vascular cord as the " funda-
mental unit," and as a basis for the construction of any
organ, and moreover as also containing within it poten-
tially the power of evolving any number of similar organs by
repeatedly branching; then, when hypertrophy affects such a
" unit," it may branch once, twice, or any number of times,
when each branch passing off to tbe surface can lay the founda-
tion of a repetition of the organ from which it takes its rise.*
Attention has already been called to this origin of the
numerous stamens of the Malvacece, and how certain forms
of double flowers originate from the multi-
plication of the petaline cords, each branch
of which issues in a distinct petal, as in
Snowdrops.
Similai'ly for cai'pels and ovules, the
process of multiplication can be witnessed
both normally and abnormally. On the
Fig. 88.— Multifold carpels one hand, that of carpels into five groups
with ovullferous margins . i ,i
from a malformed rrim- occurs m the Hollyhock through the
chorisis of the original carpellary cord ; on
the other. Fig. 88 represents a multifold carpel of a Pi'im-
rose, due, there is no doubt, to a like chorisis of the cords
belonging to one individual carpel.
Similarly for ovules, while two only are normally charac-
* I must again remind the reader that I am here speaking meta-
phorically ; as we do not know wherein this potentiality really lies, but
can only describe what is actually visible.
PHYLLODY OF THE FLORAL WHORLS. 809
teristic of the Plum, and Orchis has an inmimeraWe quantity
arising by repeated chorisis of the original placentary cords,
so in monstrous Primroses, etc., as represented in Fig. 88,
many additional ovular processes may be formed, not only on
the margins, but even, as stated, on the mid-ribs.
One other point may be here noticed, a propos to the
following curious discovery by M Baillon. I have regarded
a vascular cord as a " unit," as being capable of giving rise
to any appendage whatever ; and as long as it is in an axis
as a "trace," the cords of all organs are absolutely indistin-
guishable. Furthei', there is no difference between a cord
which will enter an appendage and one which will form a
pedicel from a peduncle. In the latter case, several cords
are usually required for the pedicel ; while one, the most
external of the " horseshoe " group given off at one side of
the peduncle {i.e. as seen in a transverse section), enters the
bract. In Erodium cicutarium, which has three flowers to
the umbel with very slender pedicels, one single cord is all
that the peduncle contributes to supply each of the pedicels,
and one very small cord for a bract. The cord for the pedicel
increases by radial chorisis, and so passes from the form of a
wedge to that of a fan, when the outermost parts increase
till they meet, and so a circle is established.
This shows that an "axis" and an "appendage" are
fundamentally due to the same kind of " unit."
The reader will now see that in the following case *
the funicular cord, which is normally that of a foliar, i.e.
appendicular organ, supplied an axial cord ; just as many
leaves can give rise to buds which are often utilized for pi'o-
pagative purposes.
* Sur le Developpement et la Germination des Grains Bulhiformes des
Amaryllidees,Tpar. M. Baillon, Bull. Soc. de Fr., t. xxi., 30 (pub. en Revue
des Cours Sci. Lyon, Aout 30, 1873).
810 THE STRUCTUEE OF FLOWERS.
" Les bulbilles des Amaryllidees ne sont pas toujours des
graines veritables modifiees seulement quant a I'epaisseur et
a la consistance de leurs diverses couches naturelles, notam-
ment des phis esterieures. Temoin le Calostemma Cunning-
hamii. Ici, par una singuliere transformation de I'ovule ea
bulbe, la cbalaze, en s'epaississant, joue le role d'un veritable
plateau, sur leqnel se prodiiisent une, puis plusieurs racines
adventives. Les enveloppes ovulaires tienne alors lieu
d'ecailles bulbaires tandis qu'il s'eleve dans le sac embryon-
naire un veritable bourgeon parti de la chalaze comma
sujDport et s'echappant par son sommet de la cavite ovulaira
pour se comporte eusuite comma une plante complete."
An analagous case of bulbs arising from a foliar organ
occurred with Scilla Sibirica. Some plants dug up in October,
1887,* were found to have taken the form of the so-called
" droppers " not uncommon in tulips. Their peciiliarity
resides in the fact that the tubular leaf-sheath bends and
grows downwards, thereby carrying the axillary bulbil to a
greater depth in the soil than usual. In February, 1888, on
re-examining them, Dr. Masters discovered that from one to
four bulbils had been developed at different heights within
the tissue of the tubular sheath, being in connection with the
cords of the latter by means of a transverse nexus of tracheids.
I refer to these cases as being curious instances of axial
structures proceeding from foliar — i.e., by the change of
character of the fibro-vascular cords from being at first
foliar and then axial. They support the theory of homology
of leaf and axis, which is, of course, otherwise quite efficiently
substantiated by such plants as XylopJiylla, Huscus and the
Cactacece.
* Gard. Chron. for Oct. 15, 1887, p. 475, fig. 98, " droppers ; " also, for
March 3, 1888, p. 27S, fig. 45, ditto, with bulbils.
CHAPTER XXXI.
THE VARIETIES OF FERTILISATION.
There are at least seven kinds of union : — (1) self-fertilisa-
tion, or the fertilisation of a pistil by the pollen from the
same flower (Autogamy) ; (2) crossing different flowers on
the same plant ; (3) crossing flowers on different plants of
the same stock ; (4) crossing flowers of different plants, but
of different stocks ; all the preceding being of exactly the same
form or variety of species ; (5) crossing varieties of the same
species ; (6) crossing different species of the same genus ;
(7) crossing different genera of the same order.
When a knowledge of the floral sexes was first acquired,
the idea maintained was that hermaphrodite flowers were
specially adapted for self-fertilisation ; but it was, I believe,
Dean Herbert who first observed the importance of crossing,
in his work on the AmarylUdacefe (1836). He says, " I am
inclined to think that I have derived advantage from im-
pregnating the flowers from which I wished to obtain seeds
with pollen fi'om another individual of the same variety, or,
at least, from another flower rather than its own, and espe-
cially from an individual grown in a different soil or aspect."
Mr. Darwin's work. On the Cross and Self Fertilisation
of Plants (1876), placed on a scientific basis, by means of
experimental verifications, the exact values of such crossings.
His conclusions, however, require considerable modifications.
312 THE STRUCTURE OF FLOWERS.
They are true for at least the first few years ; as in but four
or five cases only did he exceed the third generation ;
and when he prolonged them to seven generations, as in
Mimulus luteus, and ten in Ipomcea purpurea, his results
began to assume a very different complexion.
The inference deducible fi-om his experiments is that
careful and artificial crossing generally introduces a remark-
able stimulus for a time; but the effects are not permanent.
On the other hand, a perseverance in self -fertilisation pro-
duces results which are much more stable ; so that, finally,
self-fertilised plants (i.e the successive off-spring of this
process) outstrip their competitors. Florists also find that by
continued crossing the flowers of a species they soon reach
the end of their tether, and no further progress is obtainable.
Secondly, ]Mr. Darwin failed to realize the fact that self-
fertilisation predominates in nature with the vast majority of
hermaphrodite plants, whether they be adapted to insects or
are inconspicuous and adapted for autogamy.
Thirdly, he misinterpreted the meaning of degeneracy,
which often accompanies self-fei-tilisation ; thinking that it
involved constitutional injuriousness, of which there is no
trace whatever in nature.
Lastly,* he, and other writers who have followed him,
wrongly inferred that adaptations to insect agency implied
a converse " purpose," viz. to avoid self -fertilisation, instead
of regarding them as the inevitahle results of the stimulus of
intercrossing and of the visits of insects. The danger of
this a 'priori, deductive, or teleological reasoning, without any
attempt at verification, lies in the fact that it is untrust-
* I must refer the reader to my paper on The Self-fertilisation of
Plants, in which I have dealt with these points. It was written in 1877,
but I have met with nothing since to invalidate the above conclusions,
but, on the contrary, very much in support of them.
THE VARIETIES OF FERTILISATION. 313
worthy. It may or may not be true ; but it is of no value
unless thoroughly tested by experiment aud verified. Thus,
for example, Mr. Darwin, in speaking of tlie movements of
the stigmatic lobes of Mimulics, says " Mr. Kitchener has
ingeniously explained the use of these movements, namel}^,
to prevent the self- fertilisation of the flower." He, however,
experimented with this plant, and then discovered that " if
insects are excluded the flowers fertilise themselves perfectly,
and produce plenty of seed." *
Again, it has been argued that we are justified in assum-
ing that the remarkable adaptations to insects, which are so
obvious in many flowers, must he of some use to the plant,
even though we may not be able to discover it. This state-
ment, however, is just as much an a priori and deductive
assumption as the preceding, and is quite valueless until
verified ; and it is only by means of such experiments as Mr.
Darwin laboi'iously carried out, that the real value of inter-
crossing and self-fertilisation or other kind of union can be
ascertained. Thus, e.g., the Garden Pea is undoubtedly
adapted to insects, like other irregular flowers ; but experi-
ments proved that " a cross between two individuals of the
same variety does not do the least good to the offspring,
either in height or fertility." f
* Cross a7id Self Fertilisation, p. 64. As another instance of an d
Xiriori deduction, Sachs says of Epipadis latifolia, " The flower left to
itself does not get fertilised, for the pollen-masses do not spontaneously
fall out of the anther; and even if they did, would not come on to the
stigmatic surface " (Veg. Phys., p. 796). Mr. A. D. Webster, however, has
observed that E. latifolia is very imperfectly fertilised, for, although
visited by insects, cross-fertilisation seldom takes place ; that " self-
fertilisation by the pollen falling spontaneously on the stigma is not
uncommon, as the pollen-masses . . . become friable, and before the plant
withers, either spontaneously or by the action of the wind fall on the
stigma" (Bot. Gaz., sii., p. 104).
t L.c, p. 264.
29
314 THE STRUCTURE OF FLOWERS.
Moreover, however greatly we may feel impressed with
the truly wonderful adaptations of flowers, a careful and
critical study of tliem reveals many features which seem
to counterbalance, to some degree at least, the " good " we
may in the first instance be inclined to assume as self-
evident. Indeed, the disadvantages accruing from great
differentiations in adaptation to insect agency are really too
important not to have been frequently noticed. Such are,
"hercogamy," or the mechanical obstruction to self-fertilisa-
tion, as in Orchids ; the physiological barrier, as in Linum
perenne; the absence of insects required to fertilise a flower,
as is the case with Convolvulus sepinm in England, which
rarely sets seed, as Sphinx Convolvuli is a rare insect ; the
frequent absence of bees, etc., in inclement weather, when
Clover sets but little seed, to the great loss of the farmer ;
when certain flowers are neglected for greater attractions,
as may be often seen when bees keep persistently to one
species of plant and pass over others ; the frequency with
which bees perforate tubular flowers without pollinating
them at all. Again, Muller points out* that while hone}'-
seeking insects may legitimately cross heterostyled plants,
pollen-seeking insects have no need to thrust their heads or
proboscides down to the stigma of the short-styled forms ;
hence such tend to bring about illegitimate unions of the
long-styled forms only. This, he thinks, may be a cause of
the greater fertility of that kind of union j Lastly, the
more highly differentiated a flower is, the less is its number
of insect visitors and the rarer may it become in nature.
Thus orders of plants with easy access to the honey are
some of the most abundant, as Eaimnculacece, Compositce^X
* Fertilisation, etc., p. 387. t See above, p. 206.
X The enormous number of species and -"vide diffusion of the Cmn-
positm are proofs of the advantages accruing to it from the pecuh'ar
THE VARIETIES OF FERTILISATION. 315
and Umhelliferce ; as well as are those dependent upon tlie
wind, which never fails, such as Willows, Cyperacece, and
Grasses. On the other hand, all regularly self-fertilising
plants are abundant, and, trogether with certain wind-
fertilising plants, are cosmopolitan.
Although the idea that self-fertilisation is injurious is
certainly not held now by botanists in so absolute a form as
Mr. Darwin often stated it, yet it will not be amiss to point
out the want of agreement between his conclusions and his
own experiments.
In a chapter on " General Results," * he commences by
saying : " The first and most important of the conclusions
which may be drawn from the observations given in this
volume, is that cross-fertilisation is generally beneficial, and
self-fertilisation injurious. This is shown by the difference
in height, weight, constitutional vigour, and fertility of the
offspring from crossed and self-fertilised flowers, and in
structure of the flowers ; first, in being adapted to a great variety of
insects. Thus, on ten species of plants, Miiller detected 546 species of
insects, in the following proportions, Lepidoptera, 15 p.c. ; Apidse, 41
p.c. ; Diptera, 27 p.c. ; other short-tongued insects, 17 p.c. Bees,
therefore, are the chief visitors. This is almost invariably the rule : the
only species mentioned by Miiller in his table in which short-lipped
insects surpass in number the Apidge is Chrysanthemum leucanthemum,
which has a corolla tube, 3 mm. in length, in which the honey rises
up into the widening throat and is easily accessible. The number of
Lepidoptera is in the proportion of 6-9 p.c. ; Apidae, 16*6 p.c. ; Diptera,
38-9 p.c. ; others, 37"5 p.c. In Achillea Millefolium, with a corolla tube
of 3 mm., Lepidoptera are 6-9 p.c; Apidaj, 34*5 p.c; Diptera, 24-1
p.c, and others, 34*5 p.c. Lastly, in Centaurea Jacea, with a tube of 7 to
10 mm., the Lepidopf?era rise to 27 p.c. ; Apidae, 58*7 p.c ; while Diptera
sink to 12-5 p.c, and other short-lipped insects are only 2 p.c.
The Compositce thus well illustrate the fact that tubes are propor-
tionate in length to the more specialized insects, a universal feature
seen in all other orders as well.
* Cross and Self Fertilisation of Plants, p. 436.
81G THE STRUCTURE OF FLOWERS.
the number of seeds produced by the parent plants. With
respect to the second of these two propositions, namely, that
self-fertilisation is generally injurious, we have abundant
evidence. The sfcructui'e of the flowers in such plants as
Lobelia ramosa, Digitalis purpurea, etc., (1) renders the aid
of insects almost indispensable for their fertilisation ; and
bearing in mind the pi'epotency of pollen from a distinct
individual over that from the same individual, such plants
will almost certainly have been crossed during many or all
previous generations. So it must be, owing merely to the
prepotency of foreign pollen, with cabbages and various
other plants, the varieties of which almost invai'iably in-
tercross when grown together. The same inference may
be drawn still more sui'ely with respect to those plants, such
as Reseda (2), and Eschscholtzia (3), which are sterile with
their own pollen, but fertile with that from any other
individual. These several plants must therefore have been
crossed during a long series of previous generations, and the
artificial crosses in my experiments cannot have increased
the vigour of the offspring beyond that of their progenitors.
Therefore the difference between the self-fertilised and
crossed plants raised by me cannot be attributed to the
superiority of the crossed, but to the inferiority of the self-
fertilised seedlings, due to the injurious effects of self-
fertilisation."
Mr. Darwin then proceeds to discuss the first proposition,
" that cross-fertilisation is generally beneficial," so that we
may conclude that the preceding quotation represents the
author's reasoninsr and conclusions on the idea of there
being some " injuriousness " in self-fertilisation.
In the first place, it may be observed that the reason
why Mr. Darwin's crossings yielded at first more marked
results in height, fertility, etc., is because plants are never
THE VARIETIES OF FERTILISATIOJST. 317
SO carefully ci'ossed iu nature, nor self-fertilisation so carefully
prevented, as was the case in his experiments. The probability
is that the two processes are much more mixed in nature in
the case of most plants. Therefore, by his experiments the
more unalloyed influence of crossing brought about a much
more enhanced stimulus than ever occurs in the wild state.
Moreover, the prepotency of foreign pollen, upon which he
lays stress, is a purely relative phenomenon ; for whenever
self-fertilisation yields more seeds than intercrossing, as is
often the case, it is a just inference that the pollen " of the
same flower " is then prepotent, in its turn. Indeed, Mr.
Darwin actually found that in some cases intercrossing did
no " good " at all, as in the case of the Garden Pea mentioned
above, and in Canna Warscewiczi, etc.
I will now add some observations upon certain points
I have numbered in this paragraph.
(1) That Lobelia raviosa and Digitalis ptirpnrea, and many
others given in a "List of Plants Sterile without Insect-aid," *
cannot readily fertilise themselves unless the flower be
disturbed in some way, is, per se, no proof that self- fertilisa-
tion is injurious ; for the flowers of many of such plants are
fully self-fertile when artificially assisted. Thus, Mr. Darwin
says that although L^lpinus luteus and L. pilosus seed freely
when insects are excluded ; yet Mr. Swale, of Christchurch
in New Zealand, found Lupins only formed pods of seed
when the stamens were artificially released, as they are not
there visited at all by bees.f The interpretation of this
fact, so well known that the term " hercogamous " J has
been invented for it, I take to be an immediate result of
* Cross and Self Fertilisation, etc., p. 357.
t i.e., p. 150, note.
J If I remember rightly, by Errera ; see Bull, de la Soc. Bot. de Belg.,
xvii. (1887). The term means a " fenced-off union."
SI 8 THE STRUCTURE OF FLOWERS.
the action of insects. I have given reasons for believing, and
the reader can readily suggest other instances, that structural
peculiarities have grown in response to pressures and thrusts
made upon the floral organs bj the insects themselves ;
and that such have sometimes produced protuberances or
obstructions in the way of the emission of the pollen upon
the stigma of the same flower, is no more than might be
anticipated to be extremely probable. Thus one of the
most remarkable is the rostellum of Orchids, believed to be
a modified stigma now converted to a new use. In nearly
all Orchids this blocks up the way of access to the stigmatic
chamber, while the pollen masses recline on the roof over
it, so to say; but when Orchids become self-fertilising or
even cleistogamous as well, this is often brought about by the
degradation of the rostellum ; so that the pollen masses can
then easily slide over the summit of the stigmatic chamber
and fall into it at once. When they do so they are fully
self-fertile, as Mr. Henry 0. Forbes has shown.*
Some few plants are quite barren with their own pollen,
even when artificially placed upon the stigma ; though
Lobelia and Digitalis do not belong to the group. These,
as shown elsewhere, can and often do become fully fertile
at other places and seasons, and are thereby benefited by
acquiring the possibility of setting seed by self-fertilisation,
as otherwise they might set none at all.
There are, then, three kinds of barriers to self-fertilisation:
one mechanical, as in Orchids ; a second, that of time, when
e.g. a flower is so strongly protandrous that the pollen is all
shed before the stigmas are mature ; and, thirdly, a physiolo-
gical one, when the pollen is actually impotent on the
stigma of the same flower, even though it be homogamous.
* On the Contrivances for insuring Self. fertilisation in some Tropical
Orchids, Journ. Linn. Soc, xxi., p. 538.
THE VARIETIES OF FERTILISATION. 319
In no case is it logical to say that sucli ari'angements are to
prevent self-fertilisation. We may well ask why are a
comparatively few plants thus provided for, and yet the
vast majority are not. If, however, we regard them as
results of differentiation brought about by the stimulus of
insect agency — so that in certain places hypertrophy has set
in and rendered the flov/er hercogamous, in others the
androecium is so stimulated and its development so hurried
on that the flower becomes protandrous, or its pollen so
highly differentiated as to become like that of a distinct
species, — we have a reasonable interpretation for these
phenomena. Moreover, not one of them is absolute or stable.
Thus a hercogamous Orchid can become self-fertilising ; *
* Since the above was in type, Mr. H. N. Ridley has read a paper,
at a meeting of the Linnean Society (Feb. IG, 1888), on "The Self-
fertilisation of Orchids," in which he arrives at the same conclusions
as Mr. H. 0. Forbes (see above, p. 253, note), finding- that the process
is effected in several ways, especially, perhaps, by the degeneration of
the rostellum. Moreover, the Orchids which he discovered to be capable
of fertilising themselves are not only the most numerous in individuals,
but are also the most widely dispersed of the genera to which they
respectively belong. He also corroborates Mr. Forbes's observations, that
Orchids set but a small percentage of their fruit, although fully exposed
to the visits of insects.
Mr. H. Veitch has also contributed a valuable paper on the
" Hybridisation of Orchids," in which he appears to corroborate M.
Guignard's observations in every particular (see above, Chap. XVIII.).
The reader will take note of the significance of the fact that when
Mr. Darwin published his work on " The Fertilisation of Orchids," it
was thonght that no flowers could equal them in theii- remarkable
adaptations for securing the benefits of intercrossing by insect agency,
and in their methods of "preventing self-fertilisation." Yet, of all
flowering plants, evidence now tends to show that they set the least
amount of seed, even when fully exposed to insects ; while the order
has furnished materials for two important papers on the many forms
and ways by which self-fertilisation is secured in different genera.
820 THE STRUCTURE OF FLOWERS.
the strongly protandrous Carnation can be made to be
biglily self-fertile, as Mr. Darwin showed; and Linum perenne
can have its pollen so modified as to set seed abundantly in
the same flower, as occurred with Mr. Meehan in Philadephia,
though it was physiologically impotent in England,
It is, in fact, so to say a mere accident that mechanical
and physiological barriers exist at all ; and it is only by
experiment that one can discover whether a flower so
conditioned may not be really capable of self-fertilisation all
the time. Indeed, Mr. Darwin's experiments have abundantly
shown that self-fertilising properties are quickly reacquired,
whenever the process is persevered with. For example,
E sells choltzia Californica was "absolutely self-sterile" in
Brazil. Mr. Darwin, however, by self-fertilising it in Eng-
land, raised the fertility in two genei-ations to nearly 87 p.c.
"When he asserts that his artificial crossings could not have
increased the vigour of the offspring, and therefore all differ-
ences must be attributed to the inferiority of the self-fer-
tilised, this argument w^ould apply to a certain number of his
experiments in different degrees, viz., with plants normally
self-sterile ; but he ignores the fact that, as soon as he tried
to raise a stock of self-fertilised plants, the latter steadily
gained upon the offspring of the crossed, till they equalled
or surpassed them, or else would have done so had the
experiments been continued.
Thus, with regard to Lobelia ramosa, the ratio of heights
of the " intercrossed " to the " self-fertilised " offspring of
first generation was 100 : 82 ; and the proportion of seeds as
100 : 60. In the second year, those growing under what he
had proved to be the most disadvantageous condition for
self-fertilised seedlings, namely, being crowded, the ratio
of the heights became as 100 : 88-3. The experiment,
unfortunately, was not continued further.
THE VARIETIES OF FERTILISATION. 321
Comparing this plant witli i. fulgens, wliict is also qnite
sterile without aid, and, according to Gartner, is " quite
sterile with pollen from the same plant, though this pollen
is efficient on any other individual," * Mr. Darwin suc-
ceeded in raising self-fertilised plants by keeping the pollen
of a floAver in paper till the stigmas were ready, as it is
strongly protandrous. The heights of the offspring were as
100 : 127, and Mr. Darwin adds, " the self-fertilised plants
[in two out of four pots] were in eveiy respect very much
finer than the crossed plants."
In the next generation he used pollen from a different
flower on the same plant to represent self-fertilisation. In
this case those " self-fertilised " were only 4 p.c. below the
crossed, the ratio being as 100 : 96. The conclusion, then, is
that self-fertilisation pure was the best ; intercrossing distinct
plants, less so ; and crossing on the same plant, the least.
Bianthus, like Lobelia fulgens, is strongly protandrous ;
but in the third generation the proportional number of seeds
per capsule was as 100 : 125. " This anomalous result is
probably due to some of the fertilised plants having varied
so as to mature their pollen and stigmas more nearly at
the same time than is proper to the species " (p. 135).
Exactly so.
The conclusion I would draw is, therefore, not that self-
fertilisation is per se in any way injurious, but that flowers
which are normally sterile, by having become so highly
differentiated through insect stimulation, do not now spon-
taneously set seed ; and self-fertilisation is not so efficient
as crossing. As soon, however, as the former process is
persevered with, signs are not wanting of nature's showing
even an eager response to it, till the results are often far
superior to those normally obtained by intercrossing.
* Cross and Self Fertilisation, eiG.,Tp.Vi9.
322 THE STRUCTUEE OF FLOWERS.
If flowers, unlike the preceding, are normally very self-
fei'tile, as Ipomma and Mimulus pi^oved to be, then it appears
that intercrossing supplies a remarkable stimulus, and the
intercrossed beat the self-fertilised for a time. Sooner or
later, however, the effect of the stimulus gradually dis-
appears, and self-fertilisation reasserts itself. Thus with
Iponuea purpurea Mr. Darwin raised crossed and self- ferti-
lised plants for ten generations ; and the heights of the
latter were 24, 21, 32, 14, 25, 28, 19, 15, and 21 p.c.,* respec-
tively, less than the crossed. Grouping these into threes,
the ratios become 100 : 74-3 ; 100 : 77-6 ; 100 : 81-6. That is to
say, the intercrossed were steadily declining ; for if the self-
fertilised be regarded as 100, then the ratios of these to
the crossed appear as follows : 100 : 134 ; 100 : 129 ; 100 : 121
Similarly with regard to fertility, the ratio of that of the
intercrossed plants to the self-fertilised was for the first and
second generations as 100 : 93 ; for the third and fourth, as
100 : 94 ; for the fifth, as 100 : 106 ; and the eighth, as
100 : 113. Hence the self-fertilised were superior.
Mimulus liitens gave analogous results. The crossed
plants {i.e. offspring of crossings) surpassed the self-ferti-
lised until the fourth generation, when several plants of the
latter assumed a taller character, with whiter blossoms.
This self -fertilising form "increased in the later self-ferti-
lised generations, owing to its great self-fertility, to the com-
plete exclusion of the original kinds." f " It transmitted its
character faithfully, and as the self-fei"tilised plants consisted
exclusively of this variety, it was manifest that they would
always exceed in height the crossed plants." X
* These numbers correspond to the first nine years. The tenth gives
46; but Mr. Darwin thinks this number to have been accidental (p. 41).
t Cross and Self Fertilisation, p. 67.
j Ibid., p. 70.
THE VARIETIES OF FERTILISATION. 323
(2) Witli regard to Reseda and EschsclwUzia, liis observa-
tions are also somewhat misleading'. ^Ir. Darwin experi-
mented with B. lutea and R. odorata. They are both very-
capricious. Of R. lutea some individuals were absolutely
self-sterile, whether left to themselves or artificially polli-
nated, while a few produced self- fertilised capsules. Simi-
larly with R. odorata, when protected by a net some plants
were loaded with self- fertilised capsules, others produced a
few, and others, again, not a single one. Miiller,* however,
found that " plants which are kept protected from insects,
yielded capsules filled with good seed." The inference from
this variability in the fertility of different individuals in the
same year, is that it is an accidental peculiarity of some to
be more or less self-fertile than others ; and that it was due
to varying degrees of nutrition affecting the essential
organs. We know row that plants frequently vary in their
degi-ees of fertility, both at different seasons of the year,t
and in different years or localities, according to climate, con-
ditions of soil, etc. In any case, the self-sterility of these
plants is by no means so absolute as to justify the belief of
their having never been self- fertilised for years.
Let us now turn to Mr. Darwin's experiments.
Reseda lutea. The ratio between the heights of the crossed
plants and those of the self -fertilised were as 100 : 85, the
weights as 100 : 21, when the plants were grown in pots.
When grown in open ground they were nearer equality, viz.,
in height, as 100 : 82, and in weight (a better test than
height), as 100 : 40. Differences in fertility are not given,
and, therefore, presumably not striking.
* Fertilisation, etc., p. 116.
t Mr. Darwin says Papaver vagum, inclnded in tte list of j^lants
sterile without insect aid, produced a few capsules in the early part
of the summer ; see above, Chap. XXV., on Sexuality and Environment.
324 THE STRUCTURE OF FLOWERS.
Reseda odorata. The results of plants grown in pots
were as follows, the proportions being taken as before. The
heights were as 100 : 82; weights as 100 : 67; while their
heights when the plants were grown in the open were as
100:105.*
He next raised seed by crossing some flowers and self-
fertilising othei-s on the same plant of a particular semi-
self-sterile individual. From these the seedlinsrs sfave the
following results : heights as 100 : 92 ; weights as 100 : 99 ;
fertility as 100 : 100.
These results show that the differences have practically
vanished ; the weight being a much better test than height,
as it points to greater assimilative powers, and leaves nothing
to be desired.
It is difficult, then, to see how Eeseda furnishes data for
any argument raised to prove the existence of injuriousness
in the self-fertilisation of plants. Indeed, Mr. Darwin him-
self observes : " I expected that the seedlings from this
semi-self-sterile plant would have profited in a higher degree
* Mr. Darwin remarks upon this result as follows : " We have here
the anomalous result of the self-fertilised plants being a little taller
than the crossed, of which fact I can offer no e.'cplanation. It is, of
course, possible, but not probable, that the labels may have been inter,
changed by accident " (Cross, etc., p. 121). In my paper (p. 383) referred
to I have shown that it was most generally the case that -while a close
competition in the same pot proved disadvantageous to the self-fertilised
seedlings, yet, when they had no competition, the differences were not
nearly so marked. There are apparently but two alternatives to
appeal to in order to account for tlie fact that intercrossed plants are
not so greatly superior to the self-fertilised when jjlanted in open
ground, as when in competition in pots ; viz., either the intercrossed
plants become deteriorated on being planted in open ground, which is
absurd, or else the self-fertilised must regain or acquire vigour in a
relatively greater degree than do the intercrossed, and thus would seem
to evince what might be called a greater " elasticity " of growth than
their intercrossed competitors.
THE VARIETIES OF FERTILISATION. 325
from a cross tban did the seedlings from the fully self-fertile
plants. But my anticipation was quite wrong, for they
profited in a less degree : " * — really not at all, for the self-
fertilised were superior. " An analogous result followed in
the case of Esclisclioltzia, in which the offspring of the plants
of Bi'azilian parentage (which were partially [said to be
" absolutely " so, on p. Ill] self-sterile) did not profit more
from a cross, than did the plants of the far more self-fertile
English stock." *
Mr. Darwin commenced his experiments by saying, " This
plant is remarkable from the crossed seedlings not exceeding
in height or vigour the self-fertilised. On the other hand,
a cross greatly increases the productiveness of the flowers on
the parent-plant, and is sometimes necessary in order that
they should produce any seed. Moreover, plants thus de-
rived are themselves much more fertile than those raised
from self-fertilised flowers ; so that the whole advantage of
a cross is confined to the reproductive system." t
Twelve flowers crossed produced eleven good capsules,
containing 17'4 grains of seeds; eighteen self-fertilised
flowers produced twelve good capsules, containing 13"61
grains : therefore the ratio of fertility was as 100 : 71. In
the first season the heights were as 100 : 86. Being cut
down, the next season, they were reversed, " as the self-
fertilised plants in three out of four pots were now taller
than and flowered before the crossed plants."
"In the second generation, eleven pairs were raised and
grown in competition in the usual manner. The two lots
were nearly equal during their whole growth, or as 100:101.
There was no great difference in the number of flowers and
capsules produced by the two lots, when both were left freely
exposed to the visits of insects."
* Gross and Self Fertilisation, p. 121. t L.c, p. 109.
30
826 THE STRUCTURE OF FLOWERS.
This concludes his experiments with English plants; and
though crossing did little or no good, and the first average
of heights, viz. 100 : 82, he thinks were accidental, the
converse proposition, that self- fertilisation was injurious, is
in no way proved. It would be just as logical to say that,
since the self-fertilised plants grew more vigorously after
both were cut down, that crossing must have Aveakened the
constitution of the crossed seedlings. Or, again, from the
second year's results, we might justly conclude that the two
effects were quite identical.
He next experimented with seed the parents of which
had been cultivated in Brazil, in which country Fi-itz
Miiller had found them to be "absolutely self-sterile with
pollen from the same plant, but perfectly fertile when ferti-
lised with pollen from any other plant." Seeds raised from
these in England " were found not to be so completely self-
sterile as in Brazil." The average number of seeds produced
in the capsules borne on the intercrossed and self-fertilised
plants of Brazilian origin were 80 and 12 respectively in the
first year; that is in the ratio of 100 : 15.
With regard to the second generation, or grandchildren,
next raised, Mr. Darwin observes : " As the grandparents in
Brazil absolutely required cross-fertilisation in order to
yield any seeds, I expected that self- fertilisation would have
proved very injurious to these seedlings, and that the crossed
ones would have been greatly superior in height and vigour
to those raised from the self-fertilised flowers. But the
result showed that my anticipation was erroneous ; for as in
the last experiment with plants of the English stock, so in
the present one, the self-fertilised plants exceeded the crossed
by a little in height, viz., as 100 : 101."
In the next year the average number of seeds per capsule
of the crossed and self-fertilised was as 100 : 86-6 ; so that the
THE VAEIETIES OF FERTILISATION. 327
relative fertility of the self-fertilised had risen from zero in
Brazil to 15, and then to 866 pc, in comparison with the
crossed regarded as 100.
He now made crossings between the offspring of the
Brazilian plants and the English-grown plants, with the
following results : —
First, as to heights, —
The English-crossed to the self-fertilised plants ... ... 100:109
The English-crossed to the intercrossed * plants ... ... 100: 9-1
The intercrossed to the self-fertilised plants ... ... ... 300:116
Secondly, as to w^eights, —
The English-crossed to the self-fertilised plants ... ... 100 : 118
The English-crossed to the intercrossed plants ... ... 100 : 100
The intercrossed to the self -fertilised plants ... 100:118
Three rows of plants of each kind grew in the open ; and
here also the self-fertilised grew taller than the others.
Moreover, all except three of the self-fertilised were killed
by the winter.
" We thus see that the self-fertilised plants which were
grown in the nine pots were superior in height (as 116 : 100)
and in weight (as 118 : 100), and apparently in hardiness, to
the intercrossed plants derived from a cross between the
grandchildren of the Brazilian stock. The superiority is
here much more strongly marked than in the second trial
with the plants of the English stock, in which the self-
fertilised were to the crossed in height as 101 : 100. It is
a far more remarkable fact . . . that the self-fertilised plants
exceeded in height (as 109:100), and in weight (as 118 : 100),
the offspring of the Brazilian stock crossed by the English
stock."
* "Intercrossed" signifies the offspring of the Brazilian plants
crossed with one another.
328 THE STRUCTUEE OF FLOWERS.
When we look back and remember that tlie plant was
" absolutely self-sterile " in Brazil, and compare that fact
with these final results, it is difficult to see how self-fertilisa-
tion can be charged in any way with injuriousness. Though
the results may have shown little or no advantage from
crossing, it does not follow " that the differences," namely
greater height, weight, or fertility of the self-fertilised, were
attributable " to the inferiority of the self-fertilised seedlings,
due to the injurious effects of self -fertilisation."
On the other hand, the facts appear to warrant the
conclusion that this north-temperate plant became barren
in Brazil in consequence of the hot climate ; that the
recovery of its self-fertilising powers was due to the English
climate better suiting it ; that it at once responded to the
effort, so that its self-fertility rose in two generations from
0 to 86"6 p.c. The plants, too, thus raised showed nothing to
indicate any constitutional derangement that might, with
any show of reason, be attributable to self- fertilisation.
From the preceding observations upon Mr. Darwin's
reasoning, I think the reader will now see that it is not so
conclusive in proving the existence of any injuriousness in
self-fertilisalion as he appeared to think.
This chapter was already in type when I met with the
following passage in " The Life and Letters of C. Darwin,"
written in May, 1881 : " I now believe . . . that I ought to
have insisted more strongly than I did on the many adap-
tations for self-fertilisation, though I was well aware of
many such adaptations."
With regard to the values of other kinds of fertilisation,
1 must refer to Mr. Darwin's works ; for it is beyond my
purpose to discuss them, as they have no special bearing
upon the origin of floral structures.
CHAPTER XXXII.
FERTILTSATIOK AND THE ORIGIN OF SPECIES.
The Origin of Species by Insect Agency. — The attractive
features of flowers being now well recognized as correlated
with insect agency in fertilisation, the question arises, How
have they come into existence ? We may suppose that a plant
bore seedlings, some of which had, we will say, the corolla
accidentally (that means from some unknown cause ai-ising
from ivifliiu) larger on one side than another ; and then such
a flower, being selected by insects, left offspring which, by.
gradual improvement through repeated selection, ultimately
reached the form it now possesses.
As an alternative, we may suppose that the first impulse
came from loithoat, and induced by the insect itself; so that
the variation once set up in a definite direction, went on
improving under the constantly i"epeated stimulus of insect
visitors until the form of the flower was actually con-
formable to the insect itself.
The process of evolutionary development might perhaps
be much the same under either supposition, but the latter
hypothesis has more than one advantage. First, in the
assignment of a direct physical cause for the incipient change,
instead of some incidental and unaccountable variation,
which must be assumed by the former. Secondly, the theory
does not require the plant to make an indefinite number of
830 THE STRUCTURE OF FLOWERS.
less useful changes or variations, only to be discarded at
each generation for the one form that was wanted. Thirdly,
as a great number of flowers would be visited, both on one
plant and on many surrounding individuals in the neigh-
bourhood, great numbers might bear offspring advancing
more or less in the same direction ; and there would be no
fear of extermination, even if some happened to be crossed
by the parent form. Indeed, the varying offspring would
largely supersede the parent form in number altogether, if
they sprang up at one place without emigration. If we
supply the additional aid of isolation, many other influences
would be brought to bear upon them, and they would be fi'ee
to vary without any interference from the parent stock.
Mr. Darwin has abundantly shown that when a plant is
crossed, and its seedlings strugi^le in a confined place with
those derived from flowers which have not been crossed but
artificially self-fertilised, they generally succeed in mastering
the latter; so that if there be any struggle with the seedlings
of a self-fertilised parent, such a struggle for life is mainly
during the early period of growth, before any varietal or
specific characters of the flowers have put in an appearance
at all. For it is only in the youthful stages that the greatest
contest is maintained ; and the result depends largely upon
constitutional, and not at all upon specific., that is morpho-
logical characters, mostly taken from the flowers. N"ow,
Mr. Darwin has shown that such constitutional vigour does
very generally accompany at least the first few years of
crossing. So that we have a vera causa of the success
of such newly ci'ossed plants in the preliminary struggle
for life. It need hardly be remarked that if insects thus
start a new variety, they are crossing the flowers at the
same time.
It is true that the stimulus of crossing does not last for
FERTILISATION AND THE ORIGIN OF SPECIES. 831
many years ; but it is probably all that is wanted to give
the crossed plant the ascendancy when starting on an evolu-
tionary career.
As an illustrative case of a struggle between two varieties,
I took the same quantity of English-grown " Revett's "
wheat and Russian " Kubanka," the former having a pre-
ponderance of starch and the latter of gluten, being a smaller
and harder grain. I sowed them as thickly as possible on a
square yard, the two kinds having been previously well
mixed together. They all germinated, and the struggle of
course became intense. About twenty ears only were pro-
duced, which were all Kubanka. The experiment was
repeated a second year, with the same result. This is what
I would consider as, therefore, due to " constitutional
selection."
Survivors, however, are by no means entirely dependent
upon constitution, much less on specific differences ; for seeds
which fall on the circumference of the crowd, or on a better
soil than that upon which others may happen to lie, as on
stony ground, are thereby " selected," but it is through no
merit of their own, as in any way being the fittest, for they
survive only because they are the " luckiest ; " just as out of
the thousands of eggs of a salmon a few only escape the
jaws of their enemies : so that simply " good luck " plays an
important part in determining which shall survive and come
to maturity in both kingdoms alike.
Hence, during the period of life when the struggle for
existence is most intense, there are various circumstances
which determine what plants shall survive ; and in probably
few cases, generally no case, have the morphological variations
or specific characters any voice in the matter of selection
whatever, excepting indirectly, as stated above, whenever
constitutional vigour is correlated with first crossings.
332 THE STRUCTURE OF FLOWERS.
The difficulty wliicli Mr. Romanes has felt in. the struggle
for life through the swamping effect of a varying offspring
being crossed with the parent form, seems to me to be illusory
as far as most flowering plants are concerned.* For not only
do the majority of new forms arise through transport of
seeds to a new and distant locality, but even at home, if the
plant be at all responsive, so many seedlings, perhaps all,
will tend to be differentiated at the same time and in the
same way, that the parent form will soon be in a minority,
and if now neglected by insects may die out through " insect-
selection " of the new form.
According to the old view, that plants are varying spon-
taneously in all directions, and that only a few are selected
by insects, the difficulty has long been felt that dangers of
all sorts must surround the offspring of those few. Let us
reverse the process, however, and let the insects themselves
be the cause of changes set up in the flowers in the adaptive
directions, and the responsive power of the flower itself will
soon develop the best forms. These run no risk of being lost,
through the multitude of offspring. Hence, if my theory be
true, physiological selection, which I cannot find horticul-
turists are inclined to accept, is not needed at all.
Suppose some prevailing insect to have begun to set up
incipient changes for a new variety, which then becomes dis-
persed ; since many of the offspring will possess the new
adaptation, and several other kinds of insects will visit the
flower in different places, as the seeds happen to get trans-
ported, the result will be, that while the original species
of insect induces the descendants of the plant at home to
vai'y in adaptation to itself, others are at work elsewhere,
* Fritz Miiller found the genus Abutilon and a species of Bignonia to
be more or less sterile with parental pollen. See Miiller's Fertilisation,
etc., pp. 145, 466.
FERTILISATION AND THE ORIGIN OF SPECIES. 333
modifying the same incipient alterations to suit themselves.
Hence, as soon as isolation by migration has taken place, it
is the presence of other insects which determines the develop-
ment of other varieties. All, however, are based on the
same plan of departure.
In this way many varietal and subsequently specific forms
of the same genus will arise; and the further they travel
from the parental home the greater, perhaps, will be the
specific difi"erences; and thus can representative species be
accounted for, especially among conspicuously flowering
plants.
On the other hand, the perpetually self-fertilising species
whicli alone, as a rule, are cosmopolitan, are almost identical
in form, or at least have a minimum of differences between
them, and such as may possibly be accounted for by climatal
causes alone.
Difficulties of Natural Selection. — The greatest diffi-
culty I have always felt in the idea that a plant was selected
because it had some floral structures more appropriate than,
others, lay first in the fact that the principal period of the
struggle for life takes place in the seedling stage, before any
varietal and specific characters have appeared ; and, unless
there were a large number of the seedlings which would
ultimately bear the improved flower, or else a superior con-
stitutional vigour be guaranteed to be correlated with the
particular varietal characters to be preserved, these alone
could have nothing to do with the survival of the fittest.
Secondly, granting that the plant has succeeded in sur-
viving till the flowering period, then why should so many
minute details of floral structure be necessarily correlated ?
If the loss of three out of five carpels in the Labiatce w^ere
due to natural selection, why should this go band-in-hand
with a multiplication of the ribs of the calyx, and the
834! THE STRUCTURE OF FLOWERS.
peculiar lipped and hooded corolla with the lateral position,
of the flower, etc. ? We find in selecting peas and beans
great varieties among them, but next to none in the calyx
and corolla, to which the horticulturist pays no attention.
In nature, however, we often find in flowers regularly
visited by insects innumerable and minutely correlated adap-
tations in all the whorls, which must have all varied together
to form such existing flowers. Now, the difficulty of their
doing so without some common cause, which affects them
all simultaneously, seems to me insuperable.
If my theory, however, be accepted, it solves the whole
mystery at once, as all the changes are set up by one prime
cause, namely, the irritations of the insect in the case of all
flowers adapted to insect-fertilisation ; while the absence of
insects in regularly self-fertilised flowers, as well as anemo-
philous ones, is sufficient to account for the atrophy which
has affected them, the present condition of such flowers
having been the inevitable result.
Hence, instead of speaking of the Origin of Species of
Plants by Natural Selection, I would regard the survival of
the fittest as first issuing from " Constitutional Selection ; " *
while the origin of the floral specific characters is the result
of the responsive power of protoplasm to external stimuli.
These latter ai'e infinitely various in kind and degree, as has
been shown in the early part of this book. The result is, that
while high differentiations occur in some directions, degrada-
tions are met with in others, sometimes seen in different parts
of the entire plant ; but not at all infrequently are both
features observable simultaneously in one and the same floral
* Of course the chances of less competition by growing on the circum-
ference of the batch of seedlings, by receiving a little more light, etc.,
aid in selecting, and sometimes may determine, as stated above, those
which shall survive.
FERTILISATION AND THE ORIGIN OF SPECIES. 335
whorl. The phrase " natural selection " will therefore have
been noticed as conspicuous by its absence throughout this
book. This is not because I would in the least deny the
fact that vast numbers of seedlings perish while others sur-
vive through that form which I have called " constitutional
selection," which are thus " selected," and arrive at the
flowering and fruiting stages ; and, again, that of these latter
many may set no seed through the neglect of insects, etc., and
so perish entirely and leave no offspring, while others again
survive and are selected. Why, however, I do not refer any
particular structure to the action of natural selection is
because I have always felt or perceived a danger in doing so.
Natural selection is, as thus styled, an abstraction ; and as
long as we hide our ignorance of its concrete representatives,
that is to say, the real causes at work to induce a change, w^e
may fancy we understand all about it, while we may be in
reality in pi'ofound ignorance.
Professor Huxley remarked, in his lectures on the Origin
of Species, that what we want is " a good theory of varia-
tion." It is in the attempt to fill this hiatus that I have,
step by step throughout this book, preferred to give what
seemed to me a direct cause, mechanical, physiological,
climatal, etc., for every structure ; which may bring us
nearer to a comprehension of the direct interaction of cause
and effect than the vague term " natural selection " seems
capable of doing Thus, to take an example, Miiller refers
the loss of the fifth stamen in Labiates to natural selection,
but makes no statement hoiv he supposes selection to have
done it. On the other hand, I would prefer to attribute its
absence to atrophy, in compensation with the hypertrophy
of the corolla on the posterior side. I may be -n-rong, of
course, but at all events I give a reasonable cause, which is
a fertile one in bringing about alterations in the structure
336 THE STRUCTURE OF FLOWERS,
of flowei'S ; whereas "natural selection" leaves us exactly
where we were before. Moreover, natural selection is made
to cover exactly opposite processes ; for the formation of the
enlarged lip, on the one hand, would be attributed to it, just
as much as the elimination of a stamen altogether, on the
other. Instead, therefore, of using this term as the cause of
anything and everything, I prefer to attribute eifects to
hypertrophy, atrophy, resistance to strains, responsive action
to irritations, and so on. If it be thought that natural selec-
tion somehow underlies all this, the reader is at liberty
to substitute the phrase ; but, I must confess, it conveys
nothing definite to my mind, while the others undoubtedly do.
I do not wish the reader to suppose that my theory is
altogether in opposition to Mr. Darwin's ; for it must not be
forgotten that he himself laid great stress on the environ-
ment as a cause of variability upon which, when once brought
about, natural selection could then act. Thus he remarks :
" To sum up on the origin of our domestic races of animals
and plants. Changed conditions of life are of the highest
importance in causing variability, both by acting directly on
the organisation, and indirectly by affecting the reproductive
system. It is not probable that variability is an inherent
and necessary contingent, ander all circumstances. . , . Vari-
ability is governed by many unknown laws, of which corre-
lated growth is probably the most important. Something,
but how much we do not know, may be attributed to the
definite action of the conditions of life. [Under this I would
include the definite action of insects exerted mechanically
upon the organs of flowers.] Some, perhaps a great, effect
may be attributed to the increased use or disuse of parts.
[Compensation plays undoubtedly a very important part]. . .
Over all these causes of Change, the accumulative action
of Selection, whether applied methodically and quickly, or
FERTILISATION AND THE ORIGIN OF SPECIES. 837
unconsciously and slowly, but more efficiently, seems to have
been the predominant Power." *
If thus the variations of floral sti'uctures can be reasonably
referred directly to extei-nal agencies, and we may speak of each
as a cause instead of using the abstract expresssion " natural
selection," there still remains the question, What has brought
into existence the primary flowers themselves, which insects
have subsequently modified into their present conditions ?
The Origin of Flowers. — There are good reasons for
regarding Gymnosperms — both from their extreme antiquity,
as well as from points of structure showing affinity with
the higher Cryptogams ; such, for example, as the Lycopodl-
acece — as standing in some sort of way intermediate between
the latter and Dicotyledons. Yet the connecting links are
much wanted on both sides of them. As far as Coniferce
and Cycadece can help us, we are strongly led to believe that
they were primitively, just as they are now, anemophilous
and diclinous ; though the subdioecious (?) WehvitscMa has
points of structure which seem to indicate its being a
degraded state of an hermaphrodite plant. This remarkable
monotypic genus is, however, too isolated and unique to afford
any safe point of departure on the road to Dicotyledons, so
that with regard to the latter we are still driven to specu-
lation alone.
If, then, we are right in assuming Gymnosperms to
have been always diclinous, and Dicotyledons to have arisen
from some member of that group, then it is presumable that
the first were diclinous, perhaps dioecious, and anemophilous
as well. The general opinion seems to be that they were
dioecious; and Mr. Darwin thought that monoecism was the
next step, and thence hermaphroditism was ultimately
reached.
* Origin of Species, 6th ed., p. 31.
31
338 THE STRUCTURE OF FLOWERS.
"Now, we must not forget that when a female flower is
pollinated the effect of the impregnation by the pollen-tube
is not only to create an embryo in the ovule, but to endow it
potentially with its own sexuality ; so that the sexless embryo
becomes potentially both male and female ; in as much as it
may subsequently grow up to be solely a male or solely a
female plant ; or else it may combine the sexes, either as a
monoecious or hermaphrodite plant.
Moreover, we novsr know that the resulting sex which
appears in dioecious plants on maturity is largely, if not
entirely, dependent upon conditions of nutrition, possibly
aided by other and unknown influences.
Consequently, we cannot say for certain whether the
first Dicotyledons were not at least monoecious, if not
hermaphrodite, since the former of these states prevails
already in Gymnosperms, as in Piiius; while the latter is
hinted at in not infrequent monstrous conditions when the
lowermost scales of the spiral series in cones of Abies excelsa,
etc., are antheriferous, instead of being ovuliferous. * Such
cases show that one (the male) sex can stiddenly appear in
the same spiral series as the other. And this is all that is
wanted to form an hermaphrodite flower; for continuously
spirally-arranged sexual organs are characteristic of many
plants, such as of the Hanunculaceoe ; and such a monstrous
condition 7)iay simply be a reversion to a pi'imitive her-
maphrodite state. Hence appears the inherent possibility
of the production of hermaphroditism without any slow
evolutionary process at all ; but simply as a result of the
conveyance of the male energy to the female plant, by the
very act of pollination itself.
Mr. Darwin, when speculating on the origin of herma-
phroditism, wrote as follows : " By what graduated steps
* Teratology, p. 192.
FERTILISATION AND THE ORIGIN OF SPECIES. 339
an hermaplirodite condition was acquired we do not know.
But we can see that if a lowly organisecl form, in which the
two sexes were represented by somewhat different individuals,
were to increase by budding either before or after conjugation,
the two incipient sexes would be capable of appearing by
buds on the same stock, as occasionally occurs with various
characters at the present day. The organism would then be
in a monoecious condition, and this is probably the first
step towards hermaphroditism ; for if very simple male and
female flowers on the same stock, each cousistinar of a sinofle
stamen or pistil, were brought close together and surrounded
by a common envelope, in nearly the same manner as with
the florets of the Compositce, we should have a hermaphrodite
flowex"." *
It is a singular fact that Mr. Darwin never seems to have
thought of Euphorbia, which tallies exactly with his hypo-
thetical origin of a hermaphrodite flower ; but, unfortunately,
a " blossom " of an Eujohorhia is 7iot regarded by botanists
as a flower, but an inflorescence. It consists of a " single
pistil," on its own pedicel, surrounded by many " single
stamens," each on their own pedicels ; and are " brought
close together and surrounded by a common envelope."
Mr. Darwin's mistake resides in his supposition that
hermaphroditism must have arisen from dioecism, by passing
through moncecism ; so that he is obliged by this order of
progress to consider a flower with stamens and a pistil to be
made of separate flower-buds, i.e. to be axial structures with
their appendages reduced to at least one of each kind. But
from phyllotactical reasons, it is clear that the origin and
arrangements of the floral members are entirely foliar.
All that seems necessary for us to assume as the origin of
a flower with a conspicuous corolla or perianth, is a leaf -bud
* Cross and Self Fertilisation of Plants, p. 410.
340 THE STRUCTURE OF FLOWERS.
of which some of the members have already differentiated
into carpellary, others into staminal organs, the outer
appendages being simply bracts, like, we will say, those
surrounding the stamens or ovule of the Yew.
As insects often come for pollen alone — as in honeyless
flowers of Laburnum, Poppies, St. John's Wort, and Roses, — •
and then pierce the juicy tissues for moistening the honey, as
they have been seen to do in Ane'mo7ie, Laburnum, Hyacinths,
Orchis, etc., we may, I think, infer with some probability
that they did the same with the primitive flowers.
Having once attracted insects to come regularly, then a
multitudinous series of differentiations would follow. The
corolla would in all probability be the first to issue out of the
bracts, as being the next whorl to the stamens and as a
result of stimulus ; other changes, already described under
the Principles of Variation, would follow by degrees and in
different combinations ; but in every case they would be due
to the responsive action of the protoplasm in consequence of
the irritations set up by the weights, pressures, thrusts,
tensions, etc., of the insect visitors.
Thus, then, do I believe that the whole Floral World has
arisen.
INDEX.
Adelphous filaments, 57; imitated,
59 ; and nectaries, 58
Adhesion, analogies in animal king-
dom of, 48, 88; principle of, 5, 78,
seqq. ; rationale of, 80 ; of stamen to
perianth, and origin of, 81, and to
style (?), Aristolochia, (fig. 21) 83
jEstivations and phyllotaxis, (fig. 3)
15
Alpine, flowers, colours of, 176 ;
strawberry, phyllody of, 301
Amaryllis, appendage to perianth,
(fig. 41) 134
Androdioecism, examples, explanation
and origin of, 227
AndrcEcium, explained, 4 ; irregu-
larity in, origin of, 109
Anemophilous flowers, 265, seqq. ;
characters of, 268; cosmopolitan,
283 ; " long-lived " stigmas of,
269 ; pollen of, 266
Anemophily, and Greenland flora,
270; and cleistogamy, 264; and
degeneracy, 266, 272 ; and hete-
rogamy, 269 ; origin of, 266, 270,
272; and protogyny, 200, 269,
272
Anisomerous whorls, explained, 5 ;
causes of disarrangement of, 45
Anthers, on bracts, (fig. 64) 288;
connivent, of Violet, 60 ; conta-
beseent, 275 ; on glumes, (fig. 65)
288 ; metamorphosed, 293, (fig. 81)
298, (figs. 83, 84) 302; stigma-
tiferous, (fig. 76) 294 ; syngene-
sious, and mterpretation of, (fig.
11) 60; versatile, 266. 268
Ant-plants, hereditary efl'ects of irri-
tation in, 115, 142,' 157
Appendages, in Amaryllis, (fig. 41)
134; and axis, homology between,
309 ; origin of floral, 133
Aquilegia vulgaris, arrangement of
floral whorls of, 22 ; number of
parts in, 22
Arahis albida, leaf-traces of, (fig. 7)
39
Arctic flora, and anemophily, 270 ;
and self-fertilisation, 259
Aristolochia, structure of flower, (fig.
21) 83
Arrangement, causes of, 47 ; displace-
ment of, by anisomery, and substi-
tution, 45 ; illustrations of, in
HamcnculacccB, 21, seqq.; principle
of, 5, 139
Arrest, of carpels, 4, 8, 278 ; of
carpels in Campanulacew, 44; of
floral axis, 6 ; in free-central pla-
centas, 72, seqq. ; of growth of
ovary and seeds in Orchids, 169,
281, and in Willows, 170
Atragene, staminal nectaries of, (fig.
44) 141
Atrophy and hypertrophy in animal
kingdom, 88 ; as causes of irregu-
larities, 108 ; in compensation, 105 ;
in zygomorphism, 116, seqq.
342
INDEX.
Autogamy, explained, 198, 311. See
Selt'-fertiHsation.
Axis, and appendage, homology be-
tween, 309 ; floral, cause of arrest
of, 6
B
Beta, formation of ovule of, (fig. 16)
73
Boughs, curvature of, due to strain,
(fig. 39) 125
Bracts, petaloid, 286, (figs. 62, 63)
287 ; pistiloid (glumes), (fig. 65)
288 ; progressive changes in, 286 ;
transitional forms of, in Hellebore,
(fig. 61)286
Bulbs, origin of, from funicle, 310;
from leaf-sheath, 310
Cabbages, excrescences on, homologous
with ovules, 307
Calyx, arrest of, 8, 184, 194; pro-
gressive metamorphosis of, 288 j
-tube, 89, seqq. See Sepals.
Campanula medium, anatomy of flower
of, (fig. 8) 43, (fig. 15) 71
Campanulacea;, arrangement of carpels
in genera of, 44
Capparidece, androecium of, and sym-
metry in flower of, 33
Carpels, arrest of, 4, 8, 278 ; in Cam-
panulacece, 44 ; cohesion of, 62 ;
decrease by compensation, 21, 278 ,
phyllody of, 302; superposition of,
44, seqq. ; typical number of whorls
of, 4. See Pistil.
Carpophore, placental origin of, 72
Cell-division and light, 154
Cell-wall, thickening of, to resist
pressure, 127
Centaurea, adaptations for fertilisa-
tion, (fig. 11) 60; and sexuality,
240
Chauge of symmetry, 18, 186
Chorisis, and arrangement, 24, 39, 44,
46 ; multiplication of stamens by,
44, and of carpels by, 44, 308, and
of ovules by (in Orchids), 309
Cleistogamy, and anemophily, 264 ;
and degeneracy, 251, seqq. ; and en-
vironment, 263 ; explained, 198 ; in
flowers, 251 ; illustrations of 257-
262; in Impatiens, (fig. 58) 261 ;
in Lamium, (fig. 59) 261 ; origin
of, 262-264; in Oxalis, (fig. 57)
260; in Silvia, (fig. 60) 262; in
Violets, (figs. 55, 56) 257, 258
Cohesion, of carpels, 62 ; illustrations
of, 49, 50 ; origin of, 50 ; of petals,
56 , in Phyteuina, (fig. 9) 50 ;
principle of, 5, 48 , of sepals, 54 ,
of stamens, 57 , to resist strains,
51, 53 ; varieties of, congenital and
by contact, 48
Colours, of Alpine flowers, 176 ;
changes in, 176 ; and darkness, 177 ;
effect of crossing on, 178 ; effect of
salts on, 175 ; of flowers, 174 , and
insects, 182 ; laws of, 174 ; nutri-
tion and, 178; origin of, 178 ; as
pathfinders, 178, and arrest of,
253 , white and pale tints, aud
self-fertilisation, 253 ; whole, and
self-fertilisation, 183
Compensation, in adaptations of
flowers, 105, 117 ; atrophy and
hypertrophy in, 105 ; increase of
seeds and decrease of carpels by,
21, 278; in irregular flowers, 103,
seqq. ; in rudimentary organs, 284
Conducting tissue, of Orchids, 165;
origin of, by irritation of pollen-
tube, 165, seqq. ; structure of, (fig.
50) 164
Conifera:, foliage of, adnata and free,
84; origin of flowers and the, 337
Connivent anthers, of Violet, 60
Contabescence of anthers, 275
Cords, fibro-vascular, alteration in
orientation of, 64, 65 ; as floral
units, 300, 308, 309 ; iu flower of
Campanula, (fig. 8) 43, (fig. 15)
71 ; increase in number of, bb-hl ;
orientation of phloem and tracheae
INDEX.
843
in, 63 ; in receptacular tubes, (fig.
14) 6S, (tig. 28) 95, (fig. 30) 97 ;
sepaline, of Salvia, 55 ; as origiu
of the staminal and carpellary, in
MalvacecB, 43, 44
Corollas, appendages to, origin of, 133,^
seqq. ; form of, 101, seqq. ; meta-
morphoses of, 292, 301 ; movements
in, of Genista, (fig. 47) 160 ; of
Lopezia, (fig. 48) 161 ; origin of,
irreguhir, 103, seqq.; petals of,
displacement of, by insects, (figs.
.33-35) 110, 111; polliniferous,
292, 293 ; progressive metamor-
phoses of, 292 ; reduction of size
of,9, 254, in Geranium, 252; regular
and irregular, 101, seqq.; sensi-
tiveness in, Ypomaa, \6\ ; stameni-
ferous. (figs. 72, 73) 292, 293;
strains, effect of, on the formation
of, 101, seqq., 126; structure of
bilateral, 116, seqq. ; virescence of,
(figs. 83, 84) 301, seqq. i'et? Petals.
Correlation of growth, 112, 113,
117 ; irregularities by, 108
Cross-fertilisation, advantages of, in
evolution of species, 330, and in
horticulture, 311; colour, effects
ou, 178; disadvantages of, 314;
rationale of, 312 ; stimulus pro-
duced by, 312 ; views of Mr. Darwin
on, 315
CrucifercB, anatomy of floral recep-
tacle, (fig. 6) 32 ; symmetry of,
32
D
Darkness and colours, 177
Declinate stamens, in Dictamnus, (fig.
33) 110; distribution of forces in,
of Echium, (fig. 20) 82 ; of Epilo-
hium, (fig. 34) 111 ; origin of, due
to weight of insects, 110, 111
Degeneracy and degradation, of an-
drcecium, 273 ; and androdioecisra,
227 ; and anemophily, 266 ; of
flowers, 251, seqq.; in inconspicuous
flowers, cause of, 251 ; in Orchids,
172, 281,319; origin of, 282 ; and
self- fertilisation, 252, seqq.
Development, of floral whorls, 191, and
continuous during flowering, l'J2 ;
order of, of parts of flowers, relative
only, 195; rates of, in pistil, 192,
193
Dialysis, explained, 5, 50 ; in Mhnu-
lus, (fig. 10) 51
Diclinism, and heterostylism, 228 ;
partial, 220 ; in primitive flowers,
337
Dimorphism, and fertilisation in Viola
tricolor, 255 ; and heterostylism,
203 ; in stamens, (fig. 37) 121
Dioecism, and heterostylism as cause
of, 218; of primitive flowers, 337
Domatia, hereditary formation of,
115, 142, 157
Doubling, causes of, 298
Drosera, metamorphoses of tentacles
of, into ovules, 307
Duvernoia, zygomorphism of, origin
of, (fig. 31) 107
E
Electricity, effects on protoplasm, (fig.
45) 152, on nucleus, 154
Emergence, alteration in order of, in
regular and in irregular flowers,
187 ; and development of ovules,
195, and interpretation of, 196; of
floral whorls, 184; order of, 184
Energy, reproductive and vegetative,
231, seqq.
Environment, action of, Mr. Darwin's
views on, 336; influence of, 158;
origin of species through, 329,
seqq. See Preface.
Epidermis, origin of i-oot hairs on,
(fig. 42), 137
Eranthis, ari'angement and number of
parts in flower of, 22
Exclusion, of insects from flowers,
102, 133, seqq.
Excrescences, on corolla, (fig. 87)
306 ; on cabbage-leaves, as homo-
logues of ovules, 307
344
INDEX.
Fasciation, 51, 85 ; of petioles of pear,
(fig. 26) 94
Fertilisation, cross- (see s.v.) ; and
origin of species, 329 ; by pollen-
tube (see S.V.); varieties of, 311;
self- (see s.v.)
Fibro-vascular cord, as a fundamental
unit, 300, 308, 309. See Cord.
Flora, of Dorrefjeld, and self-fertilisa-
tion, 259 ; of Galapagos Islan is,
270 ; of Greenland, 270
Floral symmetry, correlation with
pliyllotaxis, 14; explained, 4, 5;
variations in, 12
Floral whorls, development of, order
of, 191; emergence of, 184; sym-
metrical decrease and increase in,
18 ; unsymmetrical, 20. See Whorls.
Flowers, conspicuous, developmeut of
parts of, 191; degeneracy in, 251 ;
inconspicuous, origin of, 251 ; origin
of, 337 ; typical, structure of, (Hg.
1)3
Forces, effects of mechanical, etc.
See Mechanical forces.
Forms, of floral organs, 101, seqq. ;
dimorphic, of stamens, (fig. 37)
121; principle of, 5; transitional,
118, seqq.
Funicle, bulb arising from, 310 ; as
origin of ovule, 303
Galls, analogous to tumours, 144 ;
due to irritation, 144; hairs of,
138
Garidella, arrangement and number
of parts in, (fig. 4) 21
Glands and rudimentary organs, 283.
See Nectaries.
Growth of organs, continuous during
flowering period, 122 ; correlation
of, 112, 333
Guides, degeneracy of, in self-fertil-
ised flowers, 253 ; origin of, 178
Gymnosperms, and the origin of
flowers, 337
Gynandrous, 82 ; Aristolochia, (fig.
21)83
Gynodicecism, causes of, 221, seqq. ;
and climate, 221 ; explained, 220 ;
origin of, 222, seqq. ; and soil, 221
Gyncecium, degeneracy of, 278 ; ex-
plained, 4 ; unsymmetrical decrease
in, 20. See Carpels and Pistil.
Gynomonoecism, examples of, 226 ;
explained, 220
H
Hairs, on filaments, origin of, 136
(see fig. 11, 60); in galls, 138; on
roots, origin of, 137 ; on seeds,
170 ; within styles, origin of, 139 ;
tangles and wheels, origin of, 133,
seqq.
Heliotrope, stigma of, cause of ano-
malous, 135
Hellebore, alteration in orientation of
cords, (fig. 12) 64; arrangement
and number of parts of floral
whorls (fig. 5), 22
Hercogamy, explained, 317 ; in
Orchids, 314; relative character
of, 319
Hermaphroditism, origin of, Mr.
Darwin's theory of, and observa-
tions on, 339
Heterogamy, explained, 198 ; and
sexuality, 243
Heteromorphic flowers explained,
203
Heterostylism, explained, 203 ; and
diclinism, 228 ; and dioecism. 218
and degrees of fertility, 204, seqq.
origin of, 213 ; and sexuality, 244
structure of stigmas 111,216; un
stable, in stamens of Jfarcissits
cernuus, (fig. 37) 121
Homogamy, explained, 198 ; and
anemophily, 269; fluctuating con-
ditions about, 201
Homology, of appendages and axis,
INDEX.
345
309 ; explained, 285 ; origin of,
300
Homomorphic conJitions, 203
Homostyled, flowers, explained, 203 ;
form.s of Auricula, 208 ; of Primula
Sinensis, 209
Hooks of Uncaria, (fig. 46) 156
H\-pertrophy, in animal kingdom, 88 ;
cause of, 51, 88 ; effects of, in
unions, 86, 87 ; form, a cause of,
105, seqq. ; 116, seqq. ; in Orchids,
87 ; of placentas, 307
Illegitimate, or homomorphic unions
206
Tmpatiens, secretive stipules of, (fig.
43) 140
Impregnation, a form of nutrition,
250
Inconspicuous flowers, 251, seqq. ;
anemophilous, 265 ; due to degene-
racy, 251, seqq. ; origin of, 282 ;
self-fertilising, 253, seqq.
Insects, origin of species by agency
of, 329 ; relative proportion of, in
regular and irregular flowers, 102,
103, 314; visitors to Compositas,
315
Irregularity, origin of, 103
Irritability. See Ant-plants, Appen-
dages, Form, Protoplasm, Zygo-
morphism.
Laws, of alternation, 41 ; of colour,
174 ; of superposition, 41
Leaf, cabbage, excrescences on, 307 ;
of Coniferce, adnate and free, 84,
85 ; opposite and verticillate, 9 ;
transition from opposite to verti-
cillate, (fig. 2) 11, 17, 18. See
Phyllotaxis.
Leaf-traces, of Arabia albida, (fig. 7)
39 ; compared with floral, 40
Liber-fibre, origin of, 250
Light, and cell-division, 154 ; in-
fluences of, on leaves, 154; on
roots of Ivy, 155 ; on nucleus, 154 ;
and sleep of calyx and corolla, 155
Lysimachia, anatomy of floral re-
ceptacle of, (fig. 19) 77
M
Mechanical forces, action on boughs,
125; on corolla, 126; on pear
growth, 124; on stamens, 81, 82,
126 ; tissues, formation of, by, 155,
seqq. See Irritability.
Metamorphosis, of bracts, 286 ; of
calyx, 288 ; of corolla, 292, 302 ;
of flowers, 285, 295 ; of pistil, 295 ;
of stamens, 292, 298 ; of tentacles
of Drosera, 307
Movements, in corolla, 160; of fila-
ments, 159, 161, 162 ; of pistil,
162; of stamens, 162; of staminode,
161 ; of stigmas and styles, 159,
162
N
Narcissus cermms, unstable hetero-
stylism of, 121
Natural selection, difl^culties of, 333 ;
forms of, 330, seqq. ; insufficient
as a cause, 335. See Selection.
Nectaries, 140, seqq. ; and adelphous
stamens, 58 ; irritation, an origin
of, 141, 143 ; and pollination, 148 ;
position of, 140, seqq. ; stamiual in
Atragene, (fig. 44) 141 ; stipular
in Tmpatiens, (fig. 43) 140
Nepenthes, origin of pitcher of, 146
Nucleus, effect of electrical irritation
on, 154, of light on, 154 ; of pollen-
tube, effect of, 250
Numbers, illustrations of special, 25—
38 ; origin of, 9 ; principle of 4, 7
346
INDEX.
O
Obdiplostemony, 188 ; cause of, 190 ;
origin of, 150
Opposite and verticillate leaves, 9 ;
as origin of alternate, 11
Orchids, adhesive roots of, (fig. 42)
137 ; conducting tissue of, l65 ; de-
generacy in, 172, 280, 319 ; effect
of irritations on, mechanical, 114,
of larva;, 171, physiological, of
pollen-tubes, 165, seqq. ; hyper-
trophy in, 87 ; monstrous, 87 ; self-
fertilising, 253, 318
Order of development of floral whorls,
relative only, 195
Organs, floral, slow development of,
122 ; rudimentary, 283
Origin of species, fertilisation and,
329 ; by natural selection, 333 ; by
response of protoplasm to environ-
ment, 3, 50, 51, 84, seqq., 88, 103,
seqq., 112, seqq., 116, seqq., 126,
133, seqq.
Ovary, arrest of, 169; growth from
irritation of larva;, 171, from me-
chanical irritations, 114 ; from
pollen-tube, 170, seqq.
Ovules, basilar, interpretation of, 74;
of Beta (fig. 16), 73 ; emergence
of, 195; homology of, 303, seqq.;
foliaceous, (fig. 85) 305; meta-
morphoses of, 305, seqq. ; of Or-
chids, 166, seqq., 281 ; order of de-
velopment, interpretation of, 196;
origin of, 303, seqq. ; phvllody of,
302, (fig. 85) 305, (fig. 86) 306
Pansy, stigma and style of, (fig. 54)
255 ; self-fertilising forms, (fig. 55)
257
Pathfinders and colours, 178
Pear, cause of obliquity at base of,
(fig. 38) 124 ; interpretation of re-
ceptacular tube of, 86, (fig. 22, a)
90, (fig. 26) 94 ; effect of tension
and weight of, upon form of, 124
Pedicel, origin from peduncle in
Erodium, 309
Pelarqonium, anatomv of floral recep-
tacle, (fig. 13) 65-67
Peloria, 128, seqq. ; causes of, 130 ;
and generic characters, 132 ; he-
reditary, 131 ; and hypertrophy,
131; induced by Tingkhc, 130
Perianth, excrescence on, (fig. 87)
306 ; form of, 101
Perigynous condition, 78
Petals, adhesion of, 78, seqq. ; co-
hesion of, 56, seqq. ; colours of,
174, seqq. ; 253, 270, (see Colours) ;
irritabihtv of, 158, (fig. 47) 160,
(fig. 49) 162. See Corolla.
Phyllody, of carpels, 302; of floral
whorls, 301, seqq. ; of ovules, 302.
See Ovule.
Phyllotaxis, and aestivation, (fig. 3)
15 ; and arrangement, 39, seqq. ;
and number, 9, seqq. ; and origin
of flowers, 339
Phi/teuma, cohesions of, (fig. 9) 50
Pistil, carpels, number of, 4, 7, seqq. ;
superposition of, 46, 47, in Cain-
pamilacecB, 44 ; degeneracy in, 278 ;
development of, rate of, 192 ; fibro-
vascular cords of, (figs. 12, 13, 14,
16) 64, 65, 68, 71, 73 ; metamor-
phoses of, 295, seqq. ; movements
of, 162 ; rationale of superposition
in, 46, 47 ; syncarpous, 62, seqq.
See Carpel, Gyncecium, Ovary, Re-
cejitacular Tube.
Pitclier of Nepenthes, origin of, 146,
307
Placenta, axile, 62 ; as a carpophore,
72; cords of, 64-77; free-central,
72, 76, (fig. 19) 77; hypertrophy
of, 307 ; parietal, of Orchids, a
sign of degeneracy, 281
Pollen, of anemophilous flowers, 267 ;
of cleistogamous flowers, 258,
seqq. ; degeneracy of, 273, 276 ; of
Orchids, 173 ; in ovules, 296 ; quan-
INDEX.
347
tity, reduction of, 273; of self-
fertilising plants, 254
PuUen-tube, efiects of, 166, 167 ;
irritation due to, 164, seqq. ; in
Orchids, 166, seqq. ; in Oxalis, 260 i
in Verbascum. 168 ; in Violets, 258 ;
in Willows, 170
Pollination and nectaries, correlation
between, 148
Polygamous flowers and environment,
242
Pressure, effects of mechanical, 101,
seqq., 116, seqq., 123, seqq., 156,
seqq. ; resistance to, by cell-wall,
127
Primine and secundine, foliacious, 306
Primulacece, free-central placenta of,
interpretation of, (figs. 18, 19) 76,
77
Principles, general, 1 ; of variation, 4
Protaudry, cause of, 198 ; explained,
198; illustrations of, 191, seqq.;
in Echium, (fig. 20) 82 ; and self-
fertilisation, 272, 273, seqq.
Protogyny, anemophily as a cause of,
200,' 269 ; causes of, 199, seqq. ;
emergence and order of develop-
ment of flowers with, 195; ex-
plained, 198 ; inconspicuousness of
many flowers with, 195
Protoplasm, common to animal and
vegetable kingdoms, and pheno-
mena same in both, 147 ; irrita-
bility of, to electricity, 152, to
temperature, 153, to touch, 153,
seqq. ; origin of sj)ecies due to
responsive powers of (see Origin of
Species) ; transmission of efiects of
irritation by continuity of, 163
E
Eanunculacea, arrangement in, illus-
trations of, 21 ; symmetry in, illus-
trations of, 21
Receptacle, floral, anatomy of, in
Cruciferce, (fig. 6) 32 ; in Helle-
bore, (fig. 12)^64; in Ivy, (fig. 14)
68 ; in Lysimachia, (fig. 19) 77 ;
in Pelargonium, (fig. 13) 65 ; in
Primula, (fig. 19) 77
Receptacular tube, 89, seqq. ; ana-
tomy of, in Alstrcemeria, (fig. 30)
97 ; arrested conditions in, 91, 100 ;
with calvx foliaceous, (fig. 67)
289 ; of Cherry, (fig. 29) 97 ; of
Cotoneaster, (fig. 22, b) 90; of
Fuchsia, (fig. 27) 94 ; of GalantJius,
98; of Hawthorn, (fig. 25) 93;
interpretation of, 86 ; morphologi-
cal investigations of, 90 ; of AIus-
scemla, (fig. 68) 290 ; of Narcissus,
98 ; of Orchids, (fig. 23) 92 ; of
Pear, 86, (fig. 22, a) 90, (fig. 26)
94; oi Prunus, (fig. 28) 95; of
Rose, (fig. 24) 93 ; teratologiual in-
vestigations of, 92 ; views of, 89
Regularity, acquired, 128 ; explained,
5 ; observations on, 101 ; position
of flowers with, 101 ; TingiJcc as
causiug, 130. See Peloria.
Resupination, origin of, 107
Roots, adhesive, of Orchids, (fig. 42)
137; origin of hairs on, 137; of
Ivy, effects of light on, 155
Rudimentary organs, 283
S
Salvia, cleistogamous species, 2G2,
263; cords of sepals of, 55; fila-
ments of, 268; self-fertilising spe-
cies, 261
Scent, absence of, in self-fertilising
flowers, 254
Secretive tissues, as conducting, 164,
seqq.; irritation as a cause of, 142 ;
of milk, 147 ; as nectaries, 140,
seqq.; in Nepenthes, 146; origin
of, 141
Secundine, and primine, foliaceous,
306
Seeds, chai'acter of, for double flowers,
299; number of, compared with
carpels, 21, 278, with stamens,
275 ; prof)ortion of, to seedlings in
Orchids, 280
348
INDEX.
Selection, constitutional, 330, 334;
experiment lu, 331 ; by injects,
335 ; of the luckiest, 331 ; natural,
333. See Natural Selection.
Self-fertilisation, and the flora of
Dovrefjeld, 259 : cosmopolitan,
283 ; Mr. Darwin's views on, 215,
and review of, 315, seqq. ; and de-
£;eneracy, 252 ; of Epitobmm, (fig.
53) 255; general, 192, 199, 216';
and honiomorphism, 214; illustra-
tions of, (figs. 52-60) 255-262 ;
injuriousness of, disproved, 315,
seqq.; misinterpretations regard-
ing, 312, seqq. ; of Orchids, 253,
318; peculiarities of, 253; rapid
recovery of, 320; oi Stellaria media,
(fig. 52) 255; and whole colour-
ing, 183
Sensitiveness, 151. Sec Protoplasm.
Sepaline cords, source of staminal
and carpellary, 42, seqq. ; in Cam-
panula, (fig. 8) 43, and (fig. 15)
71 ; Labiata; increase of, m calyx
of, 56 ; Salvia, in calyx of, 55
Sepals, arrest of, 8 ; carpellary lobes
of, in Pen, (fig. 70) 292 ; cords of,
in Campanula, (fig. 8) 43, (fig. 15)
71, and in Hollyhock, 44; de-
velopment of, order of, 191 seqq. ;
emergence of, 184, seqq., and in
CrucifcrcB, 32 ; foliaceous, in Ra-
nunculus (fig. 66), in Tvifolium
(fig. 67), 289 : homologous with
petioles, 288 ; lateral pair of, in
Crucifers, first to emerge, (fig. 6)
32, 185 ; nectaries superposed to,
in Hellebore, (fig. 5) 22; nnmbers
of, in whorls, 25, seqq. : ovulife-
rous, in Violet, (fig. 71) 292 ; pe-
taloid, one abnormallv in Linaria,
(fig. 69) 291, normally in Mus-
scenda, (fig. 68) 290 ; petals super-
posed to, in Garidella, (fig. 4) 21 ;
pistiloid, 291 ; staminoid, 291 ; ve-
nation of, 289
Septa, absorption of, in liber and
wood-fibres, 250; formation of, in
pistils, 70, seqq.
Sex, sudden appearance of, 338;
arrest of, 246 ; change of, in Calen-
dula, 241 ; origin of, 246, 249 ; of
seeds, 247; and soil, 239; and
temperature, 237
Sexuality, in Calendula, 241 ; in Cen-
taurea, . 240 ; and environment,
230, 245 ; and heterogamy, 243 ;
and heterostylism, 244 ; anil nutri-
tion, 233, seqq. ; and soil, 239
Solution, explained, 5
Spring, in corolla of Genista, (fig. 47)
160; of stamens in Medicago, (fig.
49) 162; of styles 125, of Viola,
(fig. 54) 255 •
Stamens, adelphons, and nectaries, 58;
adhesion of, and mechanical forces,
81 ; cohesion of, 57 ; decliuate,
110, 125, in Dictamnus, (fig. 33)
110; in Echium, (fig. 20), 82 ; in
Epilohium, (fig. 34), 111; dimorphic,
(fig;37) 121; distribution of forces
in, 81, 126; with heterostylism,
203, seqq. ; irregularity in, origin of,
109 ; irritability of, 159, 161 ; move-
ment of, 162 ; metamorphoses of,
292, 298; petaline, cause of absence
of, 7, 20; whorls, number of, 8
Staminode, movement of, in Lopezia,
(fig. 48) 161
Stigmas, of anemnphilous flowers,
269; of Aristolochia, (fig. 21) 83;
of heterostyled flowers, 216 ; irri-
tability of, 115, 163; long-lived,
269 ; movements of, 162 ; by pro-
toplasmic continuity, 163
Stimulus, produced by crossing, ad-
vantages of, 330 ; temporary effect
of, 312, 330
Stipules, of Acacia spharocephala, due
to irritation, 157 ; nectariferous,
of Tmjxiticns, (fig. 43) 140
Strains, effect on boughs, (fig. 39) 125;
and cohesions, 51, 53 ; hypertrophy
by, in pears, (fig. 38) 124, in pedi-
eels, 123, on stems, 123, on struc-
tures, 123 seqq.
Struggle for existence in seedlings,
period of greatest, 330
INDEX.
349
Styles, hairs within, origin of, 139;
of heterostyled plants, 203, seqq. ;
movement of springs in, of Pau^y,
(fig. 54) 255; piston-action of,
(fig. 11) 60; of self-fertilising
plants, 254
Stylopod, placental origin of, 72
Super])osition, of carpels, 44; laws
of, 41
Supportive tissues, 127
Symmetry, floral, changes in, 1 86 ;
decrease and increase of, 18; illus-
trations of, in Eanunculacecc, 21 ;
and phyllotaxis, 14 ; variations of,
12
Syncarpous pfstil, 62
Syngenesious anthers, 59
Tendrils, of Ampehpsis, 145 ; of
Cucurhilaceoe, 145 ; thickening of,
due to irritation, 156
Teratology, 2, 285, seqq. ; 295, seqq. ;
301, seqq.
Teucrium, structure of flower in adap-
tation to insects, 56, (fig. 36) 117
Trichomes, origin of, 133, seqq.
Trimorphic flowers, 210, seqq.
Typical flower, diagram and structure
'of, (fig. 1) 3
U
Uncaria, hook of, (fig. 46) 156
Unions, cause of, 84 ; effect of hyper-
trophy in, 86 ; illegitimate, 206 ;
legitimate, 204
Unsymmetrical, corolla, 5 ; decrease
in floral whorls, 20
Variation, principles of, in flowers, 4
Vascular cords, in Campanula, {fig,. 8)
43 ; as floral units, 300, 308, 309 ;
in Malvacecc, 43 ; origin of, 42. See
Cords.
Versatile anthers, cause of, 268 ; in
wind-fertilised flowers, 266, seqq.
Verticillate and opposite leaves, 91
Vessels and cells, constructed to resist
pressure, 127 ; as supportive, 127
Violet, cleistogamous, (fig. 56) 258 ;
style and stigma of, in self- fertilising
forms, (fig. 55) 257
Virescence, explained, 301
W
Weeds, and fertilisation, 281 ; self-
fertilising, cosmopolitan, 283
White flowers, 180; efl'ect of crossing
with, 180 ; and self-fertilisation,
182
Whorls, floral, alternation of, 39, seqq. ;
arrangement of, 39, seqq. ; examples
of one to twelve membered, 25,
seqq. ; illustrations from Jtanun-
culacece, 21, seqq. ; origin of, in
Cruciferw, (fig. 6) 32 ; projected
cycles, 38 ; superposition of, 39,
seqq. ; symmetrical increase and
decrease of, 18, and cause of, 19;
of typical flower, (fig. 1) 3
Wind-fertilised flowers. See Ane-
mophilous and Anemophily.
Wood-fibre, origin of, 250
Zygomorphism, origin of, 102, 116,
seqq.
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BINDING SECT. ^ n 3 1 1972
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UNIVERSITY OF TORONTO LIBRARY
QK Hen slow, George
653 The origin of floral
H4 structure through insect
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