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FLOWERS, FRUITS,

LEAVES.

NATURE SERIES.

FLOWERS, FRUITS,

AND

\

LEAVES.

SIR JOHN LUBBOCK, BART., F.R.S., M.P.,
D.C.L, LL.D.

WITH NUMEROUS ILLUSTRATIONS.

Bonbon :
MACMILLAN AND CO.

AND NEW YORK.
1888.

The Right of Translation and Reproduction is Reserved.

RICHARD CLAY AND SONS
LONDON AND BUNGAY.

First edition printed i88&
Reprinted 1888.

PREFACE.

THE volume of my Scientific Lectures which contains a
chapter on Flowers being now almost out of print, Messrs.
Macmillan have proposed to me that I should reprint
that chapter, together with two subsequent Lectures, one
on Fruits and Seeds, the other on Leaves, as an additional
volume in their Nature Series, under the title of " Flowers,
Fruits, and Leaves." To this I have gladly assented, and
have taken the opportunity to make several corrections
and additions, as well as to insert several new illustrations.

For permission to use Figs. 80, 82-87, 88-90, and 95,
I am indebted to the courtesy of Messrs. Lovell Reeve
and Co.

HIGH ELMS, DOWN, KENT.

CONTENTS.

CHAPTER I.

The Dead-nettle — Cross-fertilisation — The writings of Sprengel,
Darwin, Hooker, Bennett, Delpino, Hildebrand, Kerner, Miiller,
&c. — Relations of Plants and Insects — Insectivorous Plants —
Drosera, Pinguicula, Utricularia, Sarracenia — Fertilisation of
Flowers by Insects — Structure of a Flower — Geranium — Economy
of Pollen — Prevention of Self-fertilisation — Vallisneria — Wind-
fertilised Plants — Industry of Bees and Wasps — Bees and Colours
— Use of Scent to Flowers — Structure of Flowers — Malva —
Geranium — Scrophularia — Aristolochia — Arum — Use of Honey —
Explanation of Dead-nettle — Salvia Pages i — 22

CHAPTER II.

The Antirrhinum — Heath — Chervil — Daisy — Chrysanthemum — Lotus
— Furze — Broom — Cleistogamous Flowers — Dimorphous Flowers
— Primrose and Cowslip — The Use of Honey — Attraction of
Insects by Honey — Protection of Plants by Insects — Protection of
Plants against Insects — Chevaux de Prises — Glandular Hairs —
Slippery Surfaces — Barriers — Sleep of Plants — Sleep of Leaves —
Relation of the Sleep of Flowers to the Habits of Insects —
The Scent of Flowers — Bee Flowers and Fly Flowers — The
Origin of Flowers Pages 23 — 44

CONTENTS.

CHAPTER III.

Structure of Fruits and Seeds — Differences in Fruits and Seeds —
Reasons for Differences of Structure — Protection of Seeds — Edible
Fruits and Seeds— Movements of Plants — Arrowroot — Dandelion
— Linaria — Vallisneria — Dispersion of Seeds — Seeds thrown by
Parent Plant — Seeds sown by Parent Plant — Viola canina and
Hirta — Reason of Differences — Seeds thrown by Geraniums —
Herb Robert — Other species of Geranium — Vetch — Cardamine —
Squirting Cucumber — Other Plants which throw Seeds — Poppy —
Campanula — Swimming Spores — Eye-Spot — Vaucheria — Elaters
of Equisetum — Seeds carried by Wind — Valerianella — Spinifex —
Rose of Jericho — Winged Seeds — Maple — Sycamore — Lime —
Hornbeam — Elm — Birch — Pine — Fir — Ash — Feathered Seeds —
Clematis — Anemone — Dryas — Thrincia — Epilobium — Willow —
Cotton — Cotton Grass — Seeds adapted to be Wafted by Water —
Cocoa-nut Pages 45 — 72

CHAPTER IV.

Edible Fruits, Colours of — Sense of Colour in Animals — Seeds carried
by Animals — Hooked Seeds — Burdock — Agrimony — Bur Parsley
— Enchanter's Nightshade — Cleavers — Forget-me-Not — Harpago-
phyton — Martynia — Sticky Seeds — Winged Seeds on Trees —
Hooked Seeds on Bushes and Herbs — English Trees in Relation
to their Fruits and i- eeds — Modes of Dispersion in one Natural
Order — Rosaceae — Sticky Seeds especially suitable to Epiphytes —
Mistletoe — Arceuthobium — Myzodendron — Seeds sown by Parent
Plant — Trifolium — Viola — Cardamine — Ground-nut - — Vetch —
Lathyrus — Other Species — Moving Seeds — Erodium — Stipa —
Species with more than one kind of Seed — Thrincia — Corydalis —
Alisma — Seeds which mimic Insects and other Animals — Scorpiu-
rus, resemblance of, to Caterpillars.Biserrula to a Centipede, Ricinus
to a Mite, Jatropha and Martynia to Beetles, pod of Trichosanthes
to a Snake — Interest and variety of Problems still remaining for
solution Pages 73—96

CONTENTS.

CHAPTER V.

Beauty of Leaves — Variety of Forms — Causes of Variety — Size of
Leaves— Hornbeam, Beech, Elm, Sycamore, Lime, Chestnut,
Mountain Ash, Elder, Ash, Walnut, Ailanthus, Horse Chestnut —
Rowan — Forms of Leaves — Lime — Beech Nut — Spanish Chestnut
— Elm — Conifers — Yew — Length of Leaves in Conifers — Horse
Chestnut — Maple — Structure of Leaf — Stomata — Poplars — Black
and White Poplar— Plants with Vertical Leaves — Lettuce —
Compass Plants Pages yj— 118

CHAPTER VI.

Tropical Vegetation — Australian Acacias — Acacia Melanoxylon with
two types of Leaves — Eucalyptus — Juniperus Sinensis — Ivy — Fall
of the Leaf — Length and Longevity of Coniferous Leaves — Ever-
green Leaves — Functions of Hairs — Hairs as a Protection — Rela-
tion of Hairs and Honey — Water-Plants often Glabrous — Mimicry
— Mayweed and Chamomile — Stinging-nettle and Dead-nettle —
Yellow Bugle — Form of Leaves in Water Plants — Floating and
Submerged Leaves — Plants with two forms of Leaves — Ranunculus
aquatilis — Much Divided Leaves frequent in Herbaceous Plants —
Entire Leaves frequent in Shrubs and Trees — Broad and Narrow
Leaves — Attitude of Leaves — Drosera and Plantago — Daphne
— Vegetation of Dry Regions — Succulent Plants — Various Forms
of Leaf in Lathyrus — Lathyrus Aphaca and Nissolia — Lobed and
Heart-shaped Leaves — Possible Modes of accounting for the
Difference — Leaves of Seedlings — Lobed Leaves often preceded
by Heart-shaped ones — Cephalandra — Hibiscus — Passiflora — Ex-
planation of Forms of Leaves — Form of Leaf has Relation to
Requirements of Plant — Senecio — Herbaceous Species — Shrubby
Species — Climbing Species — Succulent Species — Tree Species —
Great variety of Forms — Conclusion Pages 119 — 147

LIST OF ILLUSTRATIONS.

FIG. PAGE

1. Lamium album i

2. Flower of Lamium album 2

3. Section of ditto 2

4. Drosera rotundifolia 4

5. Geranium pratense (young flower) 8

6. Geranium pratense (older flower) 8

7. Malva sylvestris 14

8. Malva rotundifolia 14

9. Stamens and stigmas of Malva sylvestris 15

10. Ditto of Malva rotundifolia 15

11. Epilobium angustijolium 1 6

12. Epilobium parviflorum 1 6

13. Diagrammatic section of Arum 18

14. Salvia officinalis. Section of a young flower 21

15. Ditto, visited by a Bee 21

16. Ditto, older flower 21

17. Stamens in their natural position 22

18. Stamens when moved by a Bee 22

19. Wild Chervil (Chcerophyllum sylvestre) 23

20. Floret of Chrysanthemum parthenium, just opened 26

21. Ditto, somewhat more advanced 26

22. Ditto, with the stigmas expanded 26

23. Lotus corniculatus 27

24. Flower of Lotus corniculatus seen from the side and in front . 29

25. Ditto, after removal of the standard 29

26. Ditto, after removal of the standard and wings 29

27. Ditto, after removal of one side of the keel 29

28. Terminal portion of Fig. 27 more magnified 29

29. Primula (long-styled form) 31

LIST OF ILLUSTRATIONS.

FIG. PAGE

30. Primula (short-styled form) 31

31. Knautia dipsacifolia 38

32. Linncea 39

33. Carltna 39

34. Silene nutans 41

35. Cat-famine chenopodifolia 45

36. Vallisneria spiralis 51

37. Viola hirta 54

38. Viola canina 55

39. Ditto, Seed-vessel with seed 56

40. Ditto, Seed-vessel after ejecting the seed 57

41. The Herb Robert (Geranium robertianttm] 58

42. Geranium dissectum 59

43. Geranium rob rtianum 61

44. Common Vetch. Vicia septum 62

45. The Squirting Cucumber (Momordica elateriuni) 63

46. Seed-head of Poppy (Papaver} 65

47. Seeds of Maple, Sycamore, Lime, Hornbeam, Elm, Birch,

Pine, Fir, Ash 68

48. Seeds of Willow Herb, Thrincia hitta, Tawarix, Willow,

Cotton-grass, Bullrush 71

49. Myzodendron (after Hooker) 73

50. Seeds of Burdock, Agrimony, Bur Parsley, Enchanter's Night-

shade, Cleavers, Forget-me-nots 76

51. Seeds of Harpa^ophyton procumbens and Marty nia proboscidea. 77

52. Vicia amphicarpa 86

53. Lathy rus amphicarpus (after Sowerby) 87

54. Eurodium glaucophyllum (after Sweet) 89

55. Seed of Stipa pennata 91

56. Seeds of Corydalis heterocarpa 92

57. Pod of Scorpiurus subvillosa and S. vermiatlata 94

58. Pod of Biserrula 95

58^. Seed of Castor Oil (Ricinus) 95

58*:. Seed of Jatropha 95

59. Leaves of Beech 97

60. Leaves of Lime 103

61. Leaves of Beech 104

62. Leaves of Elm 1^5

63. Leaves of Castanea 106

64. Leaves of Castanea and Beech 106

65. Leaves of Yew 107

66. Leaves of Box 107

LIST OF ILLUSTRATIONS.

FIG. PAGE

67. Leaves of Horse Chestnut 108

68. Ditto 109

69. Leaves of Acer no

70. Leaves of Castanea 112

71. Maple Leaver on Chestnut 113

72. Ditto 114

73. Black Poplar (P. nigra) Il6

74. Acacia melanoxylon 119

75. Seedling of Acacia salicina I2O

76. Eucalyptus (young) 122

77. Eucalyptus (old) 122

78. Pupa of Eunomia eagrus 1 26

79. Lamium and Urtica 128

80. Ranunculus aquatilis 130

81. Bupleurum fructicostim 132

82. Senedo vulgaris 133

83. Drosera rotundifolia 134

84. Drosera anglica 134

85. Plantago media 134

86. Plantago lanceolata 134

87. Daphne 135

88. Lathyrus niger 137

89. Lathyrus aphaca 137

90. Lathyrus nissolia 138

91. Furze (Ulex). Seedling 141

92. Cephalandra palmata. Seedling 142

93. Hibiscus pcdunculatus. Seedling 143

94. Passiflora carulea. Seedling 144

95. Senedo campestris 146

FIG. i. — Lainium album.

FLOWERS.

CHAPTER I.

THE flower of the common White Dead nettle
(Lamium album, Fig. i) consists of a narrow tube,
somewhat expanded at the upper end (Fig. 2), where
the lower lobe of the corolla forms a platform, on each
side of which is a small projecting lobe (Fig. 3, ;;z).
The upper portion of the corolla is an arched hood
(Fig. 3 co), under which lie four anthers (ad), in pairs,
while between them, and projecting somewhat down-
wards, is the pointed pistil (st). At the lower part,
the tube contains honey, and above the honey is a
row of hairs almost closing the tube.

Now, why has the flower this peculiar form ?
. S B

2 THE DEADNETTLE. [CHAP.

What regulates the length of the tube ? What is
the use of this arch ? What lessons do these lobes
teach us ? What advantage is the honey to the
flower ? Of what use is the fringe of hairs ? Why
does the stigma project beyond the anthers ? and
why is the corolla white, while the rest of the plant
is green ?

FIG. 2. — Flower of Lainium alktm. FIG. 3. — Section of ditto.

Similar questions may of course be asked with
reference to other flowers. Let us now see whether
we can throw any light upon them.

At the close of the last century, Conrad Sprengel
published a valuable book on flowers, in which he
pointed out that the forms and colours, the scent,
honey, and general structure of flowers, have reference
to the visits of insects, which are of importance in
transferring the pollen from the stamens to the pistil.
This admirable work, however, did not attract the
attention it deserved, and remained almost unknown
until Mr. Darwin devoted himself to the subject. Our
illustrious countryman was the first clearly to perceive
that the essential service which insects perform to
flowers consists not only in transferring the pollen

I.] CROSS-FERTILISATION. 3

from the stamens to the pistil, but in transferring it
from the stamens of one flower to the pistil of another.
Sprengel had indeed observed in more than one in-
stance that this was the case, but he did not altogether
appreciate the importance of the fact.

Mr. Darwin, however, has not only made it clear
from theoretical considerations, but has also proved it,
in a variety of cases, by actual experiment. More
recently Fritz Miiller has even shown that in some
cases pollen, if placed on the stigma of the same
flower, has no more effect than so much inorganic
dust ; while, and this is perhaps even more extra-
ordinary, in others, the ppllen placed on the stigma of
the same flower acted on it like a poison. This he
observed in several species ; the flowers faded and fell
off, the pollen masses themselves, and the stigma in
contact with them, shrivelled up, turned brown, and
decayed ; while flowers on the same bunch, which were
left unfertilised, retained their freshness.

The importance of this " cross-fertilisation," as it
maybe called, in contradistinction to "self-fertilisa-
tion," was first conclusively proved by Mr. Darwin in
his remarkable memoir on Primula (Linnean Journal,
1862), and he has since illustrated the same rule by
researches on Orchids, Linum, Lythrum, and a variety
of other plants. The new impulse thus given to the
study of flowers has been followed up in this country
by Hooker, Ogle, Bennett, and other naturalists, and
on the Continent by Axell, Delpino, Hildebrami,
Kerner, F. Miiller, and especially by Dr. H. Muller.
who has brought together the observations of others,
and added to them an immense number of his own.

B 2

4 RELA TION OF PLANTS AND INSECTS. [CHAP.

In by far the majority of cases, the relation between
flowers and insects is one of mutual advantage. In
some plants, however, as for instance in our common
Drosera, we find a very different state of things, and
the plant catches and devours the insects.1 The first
observation on insect-eating flowers was made about
the year 1768, by our countryman Ellis. He observed
that in Dionaea, a North American plant, the leaves

FIG. 4. — Drosera rotnndifolia.

have a joint in the middle, and thus close over, kill,
and actually digest any insect which may alight 01
them.

In our common Sundew (Drosera rotundifolia,
Fig. 4) the rounded leaves are covered with glutinous
glandular hairs or tentacles — on an average about 200
on a full-sized leaf. The glands are each surrounded

1 See Danvin's Insectivorous Plants.

T.J INSECTIVOROUS PLANTS. 5

by a drop of an exceedingly viscid solution, which,
glittering in the sun, has given rise to the name of the
plant If any object be placed on the leaf, these
glandular hairs slowly fold over it, though if it be inor-
ganic they soon unfold again. On the other hand, if
any small insect alights on the leaf it becomes en-
tangled in the glutinous secretion, the glands close
over it, their secretion is increased, and they literally
digest their prey. Mr. Frank Darwin has recently
shown that plants supplied with insects grow more
vigorously than those not so fed. It is very curious
that while the glands are so sensitive that even an
object weighing only -rgTrcr of a grain placed on them
is sufficient to cause motion, yet they are " insensible
to the weight and repeated blows of drops " of even
heavy rain.

Drosera, however, is not our only English insect-
ivorous plant. In the genus Pinguicula, which fre-
quents moist places, the leaves are concave with
incurved margins, and the upper surfaces are covered
with two sets of glandular hairs. In this case the
naturally incurved edges curve over still more if a
fly or other insect be placed on the leaf.

Another case is that of Utricularia, an aquatic
species, which bears a number of utricles or sacs,
which have been supposed to act as floats. Branches,
however, which bear no bladder float just as well as
the others, and there seems no doubt that their real
use is to capture small aquatic animals, which they do
in considerable numbers. The bladders in fact act on
the principle of an eel-trap, having an orifice closed
with a flap which permits an easy entrance, but

6 FLOWERS FERTILISED BY INSECTS. [CHAP.

effectually prevents the unfortunate victim from
getting out again.

I will only allude to one foreign case, that of the
Sarracenia.1 In this genus some of the leaves are in
the form of a pitcher. They secrete a fluid, and are
lined internally with hairs pointing downwards. Up the
outside of the pitcher there is a line of honey glands
which lure the insects to their destruction. Flies
and other insects which fall into this pitcher cannot
get out again, and are actually digested by the plant.
Bees, however, are said to be scarcely ever caught.

Every one knows how important floj£ers_are_±a
insects.; every one knows that bees, butterflies, etc.,
derive the main part of their nourishment from the
honey or pollen of flowers, but comparatively few are
aware, on the other hand, how much the flowers them-
selves are dependent on insects. Yet it has, I think,
been clearly shown that if insects have been in some
respects modified and adapted with a view to the
acquirement of honey and pollen, flowers, on the other
hand, owe their scent and honey, their form and
colour, to the agency of insects. Thus the lines and
bands by which so many flowers are ornamented have
reference to the position of the honey ; and it may be
observed that these honey-guides are absent in night
flowers, where they of course would not show, and
would therefore be useless, as for instance in Lychnis
vespertina or Silene nutans. Night flowers, moreover,
are generally pale ; for instance, Lychnis vespertina is
white, while Lychnis diurnat which flowers by day,
is red.

See Hooker, British Association Journal, 1874.

i.] FLOWERS FERTILISED BY WIND. 7

Indeed, it may be laid down as a general rule that
those flowers which are not fertilised by insects, as for
instance those of the Beech and most other forest
trees, are smallin size, and do not possess either
colour, scent, or honey.

Before proceeding further let me briefly mention
the terms used in describing the different parts of a
flower.

If we examine a common flower, such for instance
as a Geranium, we shall find that it consists, firstly,
of an outer envelope or calyx:, sometimes tubular,
sometimes consisting of separate leaves called sepals ;
secondly, an inner envelope or corolla, which is gener-
ally more or less coloured, and which, like the calyx,
is sometimes tubular, sometimes composed of separate
leaves called petals ; thirdly, of one or more stamens,
consisting of a stalk or filament, and a head or anther,
in which the pollen is produced ; and fourthly, a pistil,
which is situated in the centre of the flower, and
consists generally of three principal parts ; one or
more compartments at the base, each containing one
or more seeds ; the stalk or style ; and the stigma,
which in many familiar instances forms a small head
at the top of the style or ovary, and to which the
pollen must find its way in order to fertilise the
flower.

But though the pistil is thus surrounded by one
or more rows of stamens, there are comparatively few
cases in which the pollen of the latter falls directly
on the former. On the contrary this transference is
in most cases effected in other ways — generally by
means of the wind, of insects, or, in some cases, of

WASTE OF POLLEN.

[CHAP.

birds. In the former case, however, by far the
greater part of the pollen is wasted ; and much more
must therefore be produced than in those cases where
the transference is effected by insects.

One advantage, of course, is the great economy of
pollen. We have not much information on the sub-
ject, but it would seem, from the few observations
that have been made, that half a dozen pollen grains
are sufficient to fertilise a seed. But in plants in

FIG. 5. — Geranium pratense (young
flower). Five of the stamens are
erect.

FIG. 6. — Geranium prateme (older
flower). The stamens have retired,
and the stigmas are expanded.

which the pollen is carried by the wind, the chances
against any given grain reaching the pistil of another
flower are immense. Consequently by far the greater
part of the pollen is lost. Every one, for instance,
must have observed the clouds of pollen produced by
the Scotch fir. In such flowers as the Pacony the
pollen is carried by insects, and far less therefore is
required ; yet even here the quantity produced is still
large ; it has been estimated that each flower produces

I. ] PRE VENTION OF SELF-FER TILISA TION. g

between 3,000,000 and 4,000,000 grains of pollen.
The Dandelion is more specialised in this respect,
and produces far less pollen ; according to Mr.
Hassall about 240,000 grains to each flower ; while
in Geum urbanum, according to Gaertner, only ten
times more pollen is produced than is actually used
in fertilisation.

It might, however, be at first supposed that where
stamens and pistil co-exist in the same flower, the
pollen from the one could easily fall on and fertilise
the other. And in fact in some species this does
occur ; but as we have seen, it is a great advantage to
a species that the flower should be fertilised by pollen
from a different stock. How then is self-fertilisation
prevented ?

There are three principal modes.

Firstly, in many species the stamens and pistil are
in separate flowers, sometimes situated on different
plants.

Secondly, even when the stamens and pistil are in
the same flower, they are in many species not mature
at the same time ; this was first observed by Sprengel
in Epilobium angustifolium as long ago as 1790; in
some cases the stigma has matured before the anthers
are ripe, while in other and more numerous cases the
anthers have ripened and shed all their pollen before
the stigma has come to maturity.

Thirdly, there are many species in which, though
the anthers and stigma are contained in the same
flower and are mature at the same time, they are so
situated that the pollen can hardly reach the stigma
of the same flower.

io COLOUR, SCENT, AND HONEY. [CHAP.

The transference of the pollen from one flower to
another is, as already mentioned, effected principally
either by the wind or by insects, though in some cases
it is effected by other agencies, as for instance, by
birds, or by water. For instance, in the curious Val-
lisneria spiralis (Fig. 36) the female flowers are
situated on long stalks which are spirally twisted,
and grow very rapidly, so that even if the level of
the water alters, provided this be within certain
limits, the flowers float on the surface. The male
flowers on the contrary are minute and sessile, but
when mature they detach themselves from the plant,
rise to the surface, and float about freely like little
boats among the female flowers.

Wind-fertilised flowers as a rule have no colour,
emit no scent, produce no honey, and are symmetri-
cal in form. Colour, scent, and honey are the three
characteristics by which insects are attracted to
flowers.

As already observed, wind-fertilised flowers gene-
rally produce much more pollen than those which
are fertilised by insects. This is necessary, because
it is obvious that the chances against any given pollen
grain reaching the stigma are much greater in the one
case than in the other.

Again, it is an advantage to wind-fertilised plants
to flower early in the spring before the leaves are out,
because the latter would catch much of the pollen
and thus interfere with its access to the stigma.
In these plants the pollen is less adherent, so that
it can easily be blown away by the wind, which
would be a disadvantage in most plants which are

I.] INDUSTRY OF THE BEE. n

fertilised by insects. Such flowers generally have the
stigma more or less branched or hairy, which evidently
must tend to increase their chances of catching the
pollen.

Moreover, as Mr. Darwin has observed, there does
not appear to be a single instance of an irregular
flower which is not fertilised by insects or birds.

The evidence derivable from the relations of bees
to flowers is probably sufficient to satisfy most
minds that bees are capable of distinguishing colours,
but the fact had not been proved by any conclusive
experiments. I therefore tried the following. If you
bring a bee to some honey, she feeds quietly, goes
back to the hive, stores away her honey, and returns
with or without companions for another supply.
Each visit occupies about six minutes, so that there
are about ten in an hour, and about a hundred in a
day. I may add that in this respect the habits of
wasps are very similar, and that they appear to be
quite as industrious as bees.

I once tested this by training a bee and a wasp to
come to some honey, and then timing them through
a whole day. Knowing they would be early I went
into my study a few minutes after four in the morning,
but the wasp was already at work, and continued
without a moment's intermission until 7.46 in the
evening, working without a moment's rest for nearly
sixteen hours and making no less than 116 visits to
the honey. The bee began at 5.45 A.M., or somewhat
later than the wasp, and left cff also rather earlier.
Perhaps I may give the record of the morning's work
of this wasp.

INDUSTRY OF THE WASP.

[CHAP.

At each

visit she sucked up as much honey

as she

could carry off to the nest and returned at

once.

She came,

as already mentioned, for the first time,

At 4.13,

returning at At 8.29, returning

at

4-32

11

8.36

4.50

11

8.40

5-5

11

8-45

5-15

.,

8.56

5.22

11

9-7

5.29

11

9- '4

5-36

11

9-20

5-43

11

9.26

5.50

,.

9-39

5-57

„

9-43 „

6.5

11

9-50

6.14

11

9-57

6.23

11

io-4

6.30

11

10.10

6.40

11

10.15

6.48

11

10.24 „

6.56

„

10.29

7-5

11

io-37

7.12

11

10-45

7.18

11

10.50

.7-25

n

10.59

7-31

1!

1 1.6 „

7.40

11

11.15

7.46

11

11.22

7.52

11

11-30

8.0

11

"•35

8.10

11

"•47

8.18

11

n-55

8.24

12.6

The visits were continued till dusk.
This, however, was in autumn ; in summer they make
more overtime, and work on even late in the evening.

i.] BEES AND COLOURS. 13

In fine weather bees visit often more than twenty
flowers in a minute, and so carefully do they economise
the sunny hours, that in flowers with several nectaries
if they find one dry, they do not waste time by ex-
amining the others on the same plant. Mr. Darwin
watched carefully certain flowers, and satisfied him-
self that each one was visited by bees at least thirty
times in a day. The result is, that even where flowers
are very numerous — as, for instance, on heathy plains
and clover fields — every one is visited during the day.
Mr. Darwin has carefully examined a large number of
flowers in such cases, and found that every single one
had been visited by bees.

In order to test the power of bees to appreciate
colour, I placed some honey on a slip of glass, and
put the glass on coloured paper. For instance, I put
some honey in this manner on a piece of blue paper,
and when a bee had made several journeys, and thus
become accustomed to the blue colour, I placed some
more honey in the same manner on orange paper
about a foot away, Then during one of the absences
of the bee I transposed the two colours, leaving the
honey itself in the same place as before. The bee
returned as usual to the place where she had been
accustomed to find the honey; but though it was
still there, she did not alight, but paused for a
moment, and then dashed straight away to the blue
paper. No one who saw my bee at that moment
could have had the slightest doubt of her power of
distinguishing blue from orange.

Again, having accustomed a bee to come to honey
on blue paper, 1 ranged in a row other supplies of

FLIES AND COLOURS.

FCHAP.

honey on glass slips placed over paper of other colours,
yellow, orange, red, green, black, and white. Then I
continually transposed the coloured paper, leaving
the honey on the same spots ; but the bee always
flew to the blue paper, wherever it might be. Bees
appear fortunately to prefer the same colours as we
do. On the contrary, flowers of a livid yellow, or
fleshy colour are most attractive to flies ; and more-
over while bees are attracted by odours which are
also agreeable to us, flies, as might naturally be

FIG. 7. — Alalva sylvestris.

FIG. 8. — Malva. rotundifolia.

expected from the habits of their larvae, prefer some
which to us seem anything but pleasant.

Among other obvious evidences that the beauty
of flowers is useful in consequence of its attracting
insects, we may adduce those cases in which the
transference of the pollen is effected in different man-
ners in nearly allied plants, sometimes even in the
same genus.

Thus, as Dr. H. Miiller has pointed out, Malva

I.]

MALVA. EPILOBIUM.

sylvestris (Fig. 7) and Malva rotundifolia (Fig. 8)
which grow in the same localities, and therefore must
come into competition, are nevertheless nearly equally
common.

In Malva sylvestris, however (Fig. 9), where the
branches of the stigma are so arranged that the plant
cannot fertilise itself, the petals are large and conspi-
cuous, so that the plant is visited by numerous insects ;
while in Malva rotundifolia, the flowers of which are
comparatively small and rarely visited by insects, the

FIG 9. — Stamens and stigmas of
Malva sylvestris.

FIG. 10. — Ditto of Macva rotundifolia-

branches of the stigma are elongated, and twine them-
selves (Fig. 10) among the stamens, so that the flower
readily fertilises itself.

Another interesting case is afforded by the genus
Epilobium. Epilobium angustifolium has large pur-
plish flowers in conspicuous heads (Fig. n), and is
much frequented by insects; while E. parvifloruvt
(Fig. 12) has small solitary flowers and is seldom
visited by insects. Now in the former species their
visits are necessary, because the stamens ripen and

16 GERANIUM. [CHAP.

shed their pollen before the pistil, so that the flower
is consequently incapable of fertilising itself. In E.
parviflorum, on the contrary, the stamens and pistil
come to maturity at the same time.

Let us take another case — that of certain Geraniums.
In G. pratense (Figs. 5 and 6, p. 8) all the stamens
open, shed their pollen, and wither away before the
pistil comes to maturity. The flower cannot therefore
fertilise itself, and depends entirely on the visits of

FIG. ii. — EpiloMum angustifoliunt. FIG. 12. — Epilobium paivijlorum.

insects for the transference of the pollen. In G.
pyrenaicum, where the flower is not quite so large,
all the stamens ripen before the stigma, but the in-
terval is shorter, and the stigma is mature before
all the anthers have shed their pollen. It is there-
fore not absolutely dependent on insects. In G.
molle, which has a still smaller flower, five of the
stamens come to maturity before the stigma, but the
last five ripen simultaneously with it. Lastly, in G.
pusillum, which is least of all, the stigma ripens even
before the stamens. Thus, then, we have a series more

i.] SCROPHULARIA. 17

or less dependent on insects, from G.pratense to which
they are necessary, to G. pusillum, which is quite
independent of them ; while the size of the corolla
increases with the dependence on insects.

In those species in which self-fertilisation is pre-
vented by the circumstance that the stamens and
pistil do not come to maturity at the same time, the
stamens generally ripen first.

The advantage of this is probably connected with
the visits of bees. In those flowers which grow in
bunches the lower ones naturally open first. Con-
sequently in any given spike the flowers are at first all
male ; subsequently the lower ones, being the older,
have arrived at the female stage, while the upper ones
are still male. Now it is the habit of bees to begin
with the lower flowers of a spike and work upwards.
A bee, therefore, which has already dusted herself with
pollen from another flower, first comes in contact with
the female flowers, and dusts them with pollen, after
which she receives a fresh supply from the upper male
flowers, with which she flies to another plant.

There are, however, some few species in which the
pistil ripens before the stamens. One is our common
Scrophularia nodosa. Now why is this ? Mr. Wilson
has given us the answer. .S. nodosa is one of our few
flowers specially visited by wasps ; the honey being
not pleasing to bees. Wasps, however, unlike bees,
generally begin with the upper flowers and pass down-
wards, and consequently in wasp flowers it is an ad-
vantage that the pistil should ripen before the stamens.
But though the stamens generally ripen before the
pistil, the reverse sometimes occurs. Of this a very

i8

ARISTOLOCHIA—ARUM.

[CHAP

interesting case is that of the genus Aristolochia. The
flower is a long tube, with a narrow opening closed by
stiff hairs which point backwards, so that it much re-
sembles an ordinary eel-trap. Small flies enter the
tube in search of honey, but from the direction of the
hairs it is impossible for them to return. Thus they
are imprisoned in the flower, until the stamens have
ripened and shed their pollen, by which the flies get

FIG. 13. — Diagrammatic section of Arum, ft, hairs ; a, anthers ; sf, stigmas.

thoroughly dusted. Then the hairs of the tube shrivel
up, thus releasing the prisoners, which carry the pollen
to another flower.

A"-ain, in our common Arums — the Lords and

iO r

Ladies of village children — the well-known green leaf
incloses a central pillar, near the base of which are
arranged a number of stigmas (sf, Fig. 13), and above

I.] EXPLANATION OF THE DEADNETTLE. 19

them several rows of anthers (a). It might be sup-
posed therefore that the pollen from the anthers
would fall on and fertilise the stigmas. This, how-
ever, is not what occurs. In fact the stigmas come
to maturity first, and have lost the possibility of fer-
tilisation before the pollen is ripe. The pollen must
therefore be brought by insects, and this is effected by
small flies, which enter the leaf, either for the sake of
honey or of shelter, and which, moreover, when they
have once entered the tube, are imprisoned by the
fringe of hairs (//). When the anthers ripen, the pol-
len falls on to the flies, which in their efforts to escape
get thoroughly dusted with it. Then the fringe of
hairs withers, and the flies, thus set free, soon come
out, and ere long carry the pollen to another plant.

Now let us return to our White Deadnettle and see
how far we can answer the questions which I began
by asking.

In the first place, the honey attracts insects. If
there were no honey, they would have no object in
visiting the flower. The bright colour is useful in
rendering the flower conspicuous. The platform serves
as an alighting stage for bees. The length of the tube
has reference to that of their proboscis, and prevents
the smaller species from obtaining access to the honey
which would be injurious to the flower, as it would
remove the source of attraction for the bees, without
effecting the object in view. The upper arch of the
flower protects the stamens and pistil, and also presses
them firmly against the back of the bee ; so that,
when the bee alights on the stage and pushes its pro-
boscis down to the honey, its back comes into contact

C 2

20 SALVIA. [CHAP.

with them. The row of small hairs at the bottom of
the tube prevents small insects from creeping down
the tube and stealing the honey. Lastly, the small
processes on each side of the lower lip are the rudi-
mentary representatives of parts, formerly more largely
developed, but which, having become useless, have
almost disappeared.

In the Deadnettle, it would appear that the pistil
matures as early as the stamens, and that cross-fertili-
sation is attained by the relative position of the stigma,
which, as will be seen in the figure, hangs down below
the stamens ; so that a bee, bearing pollen on its back
from a previous visit to another flower, would touch
the pistil and transfer to it some of the pollen, before
coming in contact with the stamens. In other species
belonging to the same great group (Labiatae) as La-
mium, the same object is secured by the fact that the
stamens come to maturity before the pistil ; they shed
their pollen, and shrivel up before the stigma is mature.

Fig. 14 represents a young flower of Salvia officinalis
in which the stamens (a a) are mature, but not the
pistil (/), which, moreover, from its position, is un-
touched by bees visiting the flower ; as shown in
Fig. 15. The anthers, as they shed their pollen,
gradually shrivel up ; while, on the other hand, the
pistil increases in length and curves downwards, until
it assumes the position shown in Fig. 16, st, where, as
is evident, it must come in contact with any bee
visiting the flower, and would touch just that part of
the back on which pollen would be deposited by a
younger flower. In this manner cross-fertilisation is
effectually secured.

I.]

SALVIA.

21

There are, however, several other curious points in
which vS. officinal is differs greatly from the species last
described.

FKJ.

FIG. 16

FIG. 15

Fin. i4.—Satvia officinal^. Section of a young flower.
FIG. 15. — Ditto, visited by a Bee,
FIG. 16.— Ditto, older flower.

The general form of the flower, indeed, is very simi-
lar. We find again that, as generally in the Labiates,
the corolla has the lower lip adapted as an alighting
board for insects, while the arched upper lip covers
and protects the stamens and pistils.

22

SALVIA.

[CHAP. i.

The arrangement and structure of the stamens is,
however, very peculiar and interesting. As in Lamium,
they are four in number, but one pair is quite rudi-
mentary (Fig. 14). In the other (a a) the two anthers,
instead of being attached close together at the sum-
mit of the filament, are separated by a long movable
rod, or connective (Figs. 17, 18, m\ so that they can
play freely on the stalk of the stamen. In a natural
position, this connective is upright, so that the one

FIG. 17. — Stamenf in their uatural
position.

FIG. 18. — Stamens when moved
by a Bee.

anther is situated (Fig. 14) in the neck of the tube,
the other under the arched hood. The lower anther,
moreover, is more or less rudimentary. Now when a
bee comes to suck the honey, it pushes the lower
anther out of the way with its head ; the result of
which is that the connective swings round, and the
upper fertile anther comes down on to the back of the
bee (Figs. 15 and 18), and dusts it with pollen, just at
the place where, in an older flower (Fig. 16) it would
be touched by the stigma, st.

FIG. 19. — Wild Chervil (£Jutrophylliiin sylvtstre)

CHAPTER II.

AT first sight, it may seem an objection to the
view set forward in the preceding chapter, that some
flowers — as, for instance, those of the common Antir-
rhinum— which, according to the above-given tests,
ought to be fertilised by insects, are entirely closed.
A little consideration, however, will suggest the reply.
The Antirrhinum is especially adapted for fertilisation
by humble bees. The stamens and pistil are so ar-
ranged that smaller species would not effect the object.
It is therefore an advantage that they should be ex-
cluded, and in fact they are not strong enough to move
the spring. The Antirrhinum is, so to say, a closed
box, of which the humble bees alone possess the key.

The common Heath (Erica tetralix] offers us a very
ingenious arrangement. The flower is in the form of

24 HEATH— CHERVIL. [CHAP

an inverted bell. The pistil represents the clapper,
and projects a little beyond the mouth of the bell.
The stamens are eight in number, and form a circle
round it, the anthers being united by their sides into
a continuous ring. Each anther has a lateral hole,
but as long as they touch one another, the pollen
cannot drop out. Each also sends out a long process,
so that the ring of anthers is surrounded by a row of
spokes. Now when a bee comes to suck the honey,
it first touches the end of the pistil, on which it could
hardly fail to deposit some pollen had it previously
visited another plant. It then presses its proboscis
up the bell, in doing which it would pass between
two of the spokes, and pressing them apart, would
dislocate the ring of anthers : a shower of pollen
would thus fall from the open cells on to the head of
the bee.

In many cases the effect of the colouring and scent
is greatly enhanced by the association of several
flowers in one bunch, or raceme ; as for instance in
the wild hyacinth, the lilac, and other familiar species.
In the great family of Umbelliferae, this arrangement
is still further taken advantage of, as in the common
Wild Chervil (CJuzropJiyllum sylvestre, Fig. 19).

In this group the honey is not, as in the flowers
just described, situated at the bottom of a tube, but
lies exposed, and is therefore accessible to a great
variety of small insects. The union of the florets
into a head, moreover, not only renders them more
conspicuous, but also enables the insects to visit a
greater number of flowers in a given time.

It might at first be supposed that in such small

ii.] DAISY— CHRYSANTHEMUM. 25

flowers as these self-fertilisation would be almost un-
avoidable. In most cases, however, the stamens ripen
before the stigmas.

The position of the honey on the surface of a more
or less flat disc renders it much more accessible than
in those cases in which it is situated at the end of a
more or less long tube. That of the Deadnettle, for
instance, is only accessible to certain humble-bees;
while H. M tiller has recorded no less than seventy-
three species of insects as visiting the common
Chervil, and some plants are frequented by even a
larger number.

In the Composites, to which the common Daisy
and the Dandelion belong, the association of flowers
is carried so far, that a whole group of florets is ordi-
narily spoken of as one flower. Let us take, for
instance, the common Feverfew, or large white Daisy
^Chrysanthemum partJienium, Figs. 20 — 22). Each
head consists of an outer row of female florets, in
which the tubular corolla terminates on its outer side
in a white leaf-ovary, which serves to make the flower
more conspicuous, and thus to attract insects. The
central florets are tubular, and make up the central
yellow part of the flower-head. Each of these florets
contains a circle of stamens, the upper portions of
which are united at their edges and at the top
(Fig. o), so as to form a tube, within which is the
pistil. The anthers open inwards, so as to shed the
pollen into this box, the lower part of which is formed
by the stigma, or upper part of the pistil. As the
latter elongates, it presses the pollen against the upper
part of the box, which at length is forced open, and

26

CHR YSANTHEMUM.

[CHAP.

the pollen is pushed out (Fig. 21). Any insect then
alighting on the flower would carry off some of the
pollen adhering to its under side. The upper part of
the pistil terminates in two branches (Fig. 22, st],
each of which bears a little brush of hairs. These
hairs serve to brush the pollen out of the tube ; while

FIG. 21.

FIG. 20. — Floret of Chrysanthemum #ar//ienium, just opened, X 20.
FIG. 21. — Ditto, somewhat more advanced.
FIG. 22. — Ditto, with the stigmas expanded.

in the tube the two branches are pressed close to-
gether, but at a later stage they separate, and thus
expose the stigmatic surfaces (Fig. 21), on which an
insect, coming from a younger flower, could hardly
fail to deposit some pollen. The two stigmas in the
ray florets of Parthenium have no brush of hairs ',

II.]

LOTUS.

and they would be of no use, as these flowers have no
stamens.

The Leguminosae, or Pea-tribe, present a number
of beautiful contrivances. Let us take a common
little Lotus corniculatus (Fig. 23). The petals are five
in number ; the upper one stands upright, and is known
as the standard (Fig. 24, std) ; the two lateral ones
present a slight resemblance to wings (Figs. 24, 25, w}

FIG. 23. — Lotus cotnicidatits.

while the two lower ones are united along their edges,
so as to form a sort of boat, whence they are known
as the "keel" (Figs. 25, 26 k}. The stamens, with
one exception, are united at their bases, thus forming
a tube (Figs. 27, 28 t), surrounding the pistil, which
projects beyond them into a triangular space at the
end of the keel. Into this space the pollen is shed

28 FURZE— BROOM. [CHAP.

(Fig. 28, p°). It must also be observed that each of
the wings has a projection (c) which locks into a cor-
responding depression of the keel, so that if the wings
are depressed they carry the keel with them. Now
when an insect alights on the flower, its weight de-
presses the wings, and as they again carry with them
the keel, the latter slips over the column of stamens
thus forcing some of the pollen out at the end of the
keel and against the breast of the insect. As soon
as the insect leaves the flower, this resumes its natural
position, and the pollen is again snugly protected.
The arrangement in the Sweet Pea is very similar,
and if the wings are seized by the fingers, and pressed
down, this out-pumping of the pollen may be easily
effected, and the mechanism will then be more clearly
understood.

It will be observed (Fig. 28) that one stamen is sepa-
rated from the rest. The advantage of this is that it
leaves a space through which the proboscis of the bee
can reach the honey, which is situated inside the tube
formed by the united stamens. In those Leguminosae
which have no honey, the stamens are all united to-
gether. Such flowers are, nevertheless, in spite of the
absence of honey, visited by insects for the sake of the
pollen.

In other Leguminosae, as, for instance, in the Furze
(Ulex europ(Eiis\ and the Broom (SarotJiamnus scopa-
rius), the flower is in a state of tension, but the differ-
ent parts are, as it were, locked together. The action
of the bee, however, puts an end to this ; the flower
explodes, and thus dusts the bee with pollen.

Whole volumes might be filled with the various

II.

LOTUS.

29

FIG. 24.

FIG. 25.

FIG. 24 — Flower of Lotus corniciilatits seen from the side and in front

FIG. 25. — Ditto, after removal of the standard.

FIG. 26. — Ditto, after removal of the standard and wings.

FIG. 27. — Ditto, after removal of one side of the keel.

FIG. 28. — Terminal portion of Fig. 27 more magnified.

a, the free stamen ; c, the place where the wings lock with the keel ;

f, filaments of stamens ; g; tip of keel ; fa, pollen ; st, stigma ;

std, standard ; iv> wing ; k, keel ; /, combined bases of stamens.

interesting arrangements by which cross-fertilisation
is secured in this great order of plants.

It is indeed impossible not to be struck by the

30 CLEISTOGAMOUS FLOWERS. [CHAP.

marvellous variety of contrivances found among
flowers, and the light thus thrown upon them, by
the consideration of their relations to insects ; but I
must now call attention to certain very curious cases,
in which the same species has two or more kinds of
flowers. Probably in all plants the flowers differ
somewhat in size, and in some species there are two
distinct classes of flowers, one large, and much visited
by insects, the other small, and comparatively neg-
lected ; while in others, as, for instance, some of the
Violets, these differences are carried much further. The
smaller flowers have no scent or honey, the corolla is
rudimentary, and, in fact, an ordinary observer would
not recognise them as flowers at all Such "cleisto-
gamic " flowers, as they have been termed by Dr.
Kuhn, are already known to exist in over fifty genera.
Their object probably is to secure, with as little ex-
penditure as possible, the continuance of the species
in cases when, from unfavourable weather or other
causes, insects are absent ; and under such circum-
stances, as scent, honey, and colour are of no use, it is
an advantage to the plant to be spared from the effort
of their production.

As the type of another class of cases in which two
kinds of flowers are produced by the same species
(though not on the same stock) we may take our
common Cowslips and Primroses. If you examine a
number of them, you will find that they fall into two
distinct series. In some of the flowers, the pistil is as
long as the tube, and the button-shaped stigma (Fig.
29, sf) is situated at the mouth of the flower ; the
stamens (a <z) being half-way down the tube; while

II.j

DIMORPHISM.

in the other set, on the contrary, the anthers are at the
mouth of the flower, and the stigma half-way down.
The existence of these two kinds of flowers had long
been known, but it remained unexplained until Mr.
Darwin devoted his attention to the subject. Now
that he has furnished us with the clue the case is
clear enough.

An insect visiting a plant of the short-styled form
would dust its proboscis at a certain distance from the
extremity (Fig. 30, a], which, when the insect passed

FIG. 29. — Primula (long-styled form). FIG. 30.— Primula (uhort-styled form).

to a long-styled flower, would come just opposite to
the pistil (Fig. 2Q,st\ At the same time, the stamens
of this second form (Fig. 29, a) would dust the pro-
boscis at a point considerably nearer to the extremity,
which in its turn would correspond to the position of
the stigma in the first form (Fig. 30, sf). The two
kinds of flowers never grow together on the same stock,
and the two kinds of plants generally grow together
in nearly equal proportions. Owing to this arrange-
ment, therefore, insects can hardly fail to fertilise each
flower with pollen from a different stock.

32 COWSLIP AND PRIMROSE. [CHAP

The two forms differ also in some other respects. In
the long-styled form, the stigma (st) is globular and
rough, while that of the short-styled is smoother, and
somewhat depressed. These differences, however, are
not sufficiently conspicuous to be shown in the figure.
Again, the pollen of the long-styled form is consider-
ably smaller than the other, a difference, the import-
ance of which is obvious, for each pollen grain has to
give rise to a tube which penetrates the whole length
of the style, from the stigma to the base of the
flower; and the one has therefore to produce a tube
nearly twice as long as that of the other. The
careful experiments made by Mr. Darwin have shown
that, to obtain the largest quantity of seed, the flowers
must be fertilised by pollen from the other form.
Nay, in some cases, the flowers produce more seed, if
fertilised by pollen from another species, than by
that from the other form of their own.

This curious difference in the Primrose and Cowslip,
between flowers of the same species, which Mr. Dar-
win has proposed to call Dimorphism, is found in most
species of the genus Primula, but not in all.

The Cowslip and Primrose resemble one another in
many respects, but the honey they secrete must be
very different, for while the Cowslip is habitually visited
during the day by humble-bees, this is not the case
with the Primrose, which, in Mr. Darwin's opinion, is
fertilised almost exclusively by moths.

The genus Lythrum affords a still more complex
case, for here we have three sets of flowers. The
stamens are in two groups ; in some plants, the pistil
projects beyond them ; in the second form it is shorter

II.] THE PURPOSE OF HONEY. 33

than any of the stamens, and in the third it is inter-
mediate in length, so that the stigma lies between the
two sets of anthers.

The real use of honey now seems so obvious that it
is curious to see the various theories which were once
entertained on the subject. Patrick Blair thought that
the honey absorbed the pollen, and then fertilised the
ovary. Pontedera thought it kept the ovary in a
moist condition. Linnaeus confessed his inability to
solve the question. Other botanists considered that
it was useless material thrown off in the process of
growth. Krianitz thought he observed that in meadows

o *->

much visited by bees the plants were more healthy,
but the inference he drew was, that the honey, unless
removed, was very injurious, and that the bees were of
use in carrying it off.

Kurr observed that the formation of honey in
flowers is intimately associated with the maturity of
the stamens and pistil. He lays it down, as a general
rule, that it very seldom commences before the open-
ing of the anthers, is generally most copious during
their maturity, and ceases so soon as the stamens
begin to wither and the development of the fruit com-
mences. Rothe's observations also led him to a
similar conclusion, and yet neither of these botanists
perceived the intimate association which exists
between the presence of honey and the period at;
which the visits of insects are of importance to the
plant. Sprengel was the first to point out the real
office of honey, but his views were far from meeting
with general assent, and, even as lately as 1833,
were altogether rejected by Kurr, who came to the

D

34 ATTRACTION OF INSECTS BY HONEY. [CHAP.

conclusion that the secretion of honey is the result of
developmental energy, which afterwards concentrates
itself on the ovary.

No doubt, however, seems any longer to exist that
Sprengel's view is right ; and that the true function of
honey is to attract insects, and thus to secure cross-
fertilisation. Thus, most of the Rosaceae are fertilised
by insects, and possess nectaries ; but, as Delpino has
pointed out, the genus Poterium is anemophilous, or
wind-fertilised, and possesses no honey. So also the
Maples are almost all fertilised by insects, and produce
honey ; but Acer negundo is anemophilous, and honey-
less. Again, among the Polygonaceae, some species are
insect-fertilised and melliferous, while, on the other
hand, certain genera, Rumex and Oxyria, have no
honey, and are fertilised by the wind. At first sight
it might appear an objection to this view, and one
reason perhaps why the earlier botanists missed the
true explanation, may have been the fact, that some
plants secrete honey ou other parts than the flowers.
Belt and Delpino have, I think, suggested the true
function of these extra floral nectaries.1 The former
of these excellent observers describes a South
American species of Acacia : this tree, if unprotected,
is apt to be stripped of the leaves by a leaf-cutting
ant, which uses them, not directly for food, but,
according to Mr. Belt, to grow mushrooms on. The
Acacia, however, bears hollow thorns, while each leaf-
let produces honey in a crater-formed gland at the

1 I, by no means, however, -wish to suggest that we as yet fully under-
stand the facts. For instance, the use of the nectary at the base of tb.2
leaf of the Fern is still quite unexplained.

ii.] PROTECTION OF PLANTS BY INSECTS. 35

base, and a small, sweet, pear-shaped body at the tip.
In consequence, it is inhabited -by myriads of a small
ant, which nests in the hollow thorns, and thus finds
meat, drink, and lodging all provided for it. These
ants are continually roaming over the plant, and con-
stitute a most efficient body-guard, not only driving
off the leaf-cutting ants, but, in Belt's opinion, render-
ing the leaves less liable to be eaten by herbivorous
mammalia. Delpino mentions that on one occasion
he was gathering a flower of Clerodendron fragrans,
when he was suddenly attacked by a whole army of
small ants.

I am not aware that any of our English plants are
protected in this manner from browsing quadrupeds,
but not the less do our ants perform for them a very
similar function, by keeping down the number of small
insects, which would otherwise rob them of their sap
and strip them of their leaves.

Forel watched, from this point of view, a nest of
Formica pratensis. He found that the ants brought in
dead insects, small caterpillars, grasshoppers, cercopis,
&c., at the rate of about twenty-eight a minute, or
more than one thousand six hundred in an hour.
When it is considered that the ants work not only
all day, but in warm weather often all night too,
it is easy to see how important a function they fulfil
in keeping down the number of small insects.

Some of the most mischievous insects, indeed —
certain species, for instance, of aphis and coccus-
have turned the tables on the plants, and converted
ants from enemies into friends, by themselves develop-
ing nectaries, and secreting honey, which the ants

D 2

36 PROTECTION OF PLANTS. [CHAP.

love. We have all seen the little brown garden ant,
for instance, assiduously running up the stems of
plants, to milk their curious little cattle. In this
manner, not only do the aphides and cocci secure
immunity from the attacks of the ants, but even turn
them from foes into friends. They are subject to the
attacks of a species of ichneumon, which lays its eggs
in them, and Delpino has seen ants watching over the
cocci with truly maternal vigilance, and driving off the
ichneumons whenever they attempted to approach.

But though ants are in some respects very useful to
plants, they are not wanted in the flowers. The great
object is to secure cross-fertilisation ; but for this
purpose winged insects are almost necessary, because
they fly readily from one plant to another, and
generally, as already mentioned, confine themselves
for a certain time to the same species. Creeping
insects, on the other hand, naturally would pass from
each floret to the next ; and, as Mr. Darwin has shown
in his last work, it is of little use to bring pollen from
a different flower of the same stock ; it must be from
a different plant altogether. Moreover, creeping in-
sects, in quitting a plant, would generally go up another
close by, without any regard to species. Hence, even
to small flowers (such as many cruciferae, compositae,
saxifrages, &c.), which, as far as size is concerned,
might well be fertilised by ants, the visits of flying
insects are much more advantageous. Moreover, if
larger flowers were visited by ants, not only would
these deprive the flowers of their honey, without ful-
filling any useful function in return, but they would
probably prevent the really useful visits of bees. If

ii.J CHEVAUX DE FRISE. 37

you touch an ant with a needle or a bristle, she is
almost sure to seize it in her jaws ; and if bees, when
visiting any particular species, were liable to have the
delicate tip of their proboscis seized on by the horny
jaws of an ant, we may be sure that such a plant
would soon be deserted.

On the other hand, we know how fond ants are of
honey, and how zealously and unremittingly they
search for food. How is it, then, that they do not
anticipate the bees, and secure the honey for them-
selves ? Kerner has recently published a most in-
teresting memoir on this subject, and has pointed out
a number of ingenious contrivances by which flowers
protect themselves from the unwelcome visits of such
intruders. The most frequent are the interposition of
chevaux de frise, which ants cannot penetrate, glutin-
ous surfaces which they cannot traverse, slippery
slopes which they cannot climb, or barriers which
close the way.

Firstly, then, as regards clievaux de frise. In some
respects these are the most effectual protection, since
they exclude not only creeping insects, but also other
creatures, such as slugs. With this object, it will be
observed that the hairs which cover the stalks of so
many herbs usually point downwards. A good
example of this is afforded, for instance, by a plant,
Knantia dipsacifolia (Fig. 31), allied to our common
blue scabious. The heads of the common carline,
Carlina vulgaris (Fig. 33), again, present a sort of
thicket, which must offer an almost impenetrable
barrier to ants. Some species of plants are quite
smooth, excepting just below the flowers. The

GLANDULAR HAIRS.

[CHAP.

common but beautiful Cornflower (Centaurea cyanus)
is quite smooth, but the involucres forming the
flower-head are bordered with recurved teeth. In
this case, neither the stem rior the leaves show a trace
of such prickles.

The same consideration throws light on the large
number of plants which are more or less glutinous, a
condition generally produced, as, for instance, in the

FIG. 31. — Kntiutia dipsacifalia.

flowers of the Gooseberry and of Linncza borealis
(Fig. 32), by the presence of glandular hairs. Kerner
has called attention to a very interesting illustration
afforded by Polygonum amphibium. In this species
the stigma projects about one-fifth of an inch above
the flower, so that if ants could obtain access, they
would steal the honey without fertilising the flower;
a flying insect, on the contrary, alighting on the
flower, could scarcely fail to touch the stigma. %

II.] GLANDULAR HAIRS. 39

The beautiful rosy flowers of this species' are rich
in nectar : the stamens are short ; the pistil, on the
contrary, projects considerably above the corolla.
The nectar is not protected by any special arrange-
ment of the flower itself, and is accessible even to
very small insects. The stamens ripen before the
pistil, and any flying insect, however small, coming
from above, would assist in cross-fertilisation. Creep-
ing insects, on the contrary, which in most cases
would enter from below, would rob the honey with-
out benefiting the plant. P. amphibium, as its name

FIG. 32. — Linncra.

denotes, grows sometimes in water, sometimes on
land. So long, of course, as it grows in water, it is
thoroughly protected, and the stem is smooth ; while,
on the other hand, those specimens which live on
land throw out certain hairs which terminate in sticky
glands, and thus prevent small insects from creeping
up to the flowers. In this case, therefore, the plant is
not sticky, except just when this condition is useful.
All these viscous plants, as far as I know, have
upright or horizontal flowers.

4o SLIPPERY SURFACES. [CHAP.

On the other hand, where the. same object is
effected by slippery surfaces, the flowers are often
pendulous ; creeping creatures .being thus kept out of
them, just as the pendulous nests of the weaver-bird
are a protection from snakes and other enemies.
As instances of this kind, I may mention the common
Snowdrop and the Cyclamen.

Many flowers close their petals during rain, and this
is obviously an advantage, since it prevents the honey
and pollen from being spoilt or washed away. I have
elsewhere suggested that the so-called " sleep " of
flowers has reference to the habits of insects, on the
ground that flowers which are fertilised by night-
flying insects would derive no advantage from being
open in the day ; while, on the other hand, those
which are fertilised by bees would gain nothing by
being open at night. I confess that I suggested this
with much diffidence, but it may now, I think, be
regarded as well established.1

Silene nutans (Fig. 34), the Nottingham Catchfly, is
a very instructive species from this point of view, and
indeed illustrates a number of interesting points in the
relations between plants and insects. Its life history
has recently been well described by Kerner. The
upper part of the flowering stem is viscid ; from which
it has derived its English name, the Nottingham
Catchfly. This prevents the access of ants and other
small creeping insects. Each flower lasts three
days, or rather three nights. The stamens are ten in
number, arranged in two sets, the one set standing in

1 The so-called sleep of leaves is a different problem, and probably
enables the plant to support better the cold of night.

jr.] SLEEP OF PLANTS. 41

front of the sepals, the other in front of the petals.
Like other night flowers, it is white, and opens
towards evening, when it also becomes extremely
fragrant. The first evening, towards dusk, the five
stamens in front of the sepals grow very rapidly for
about two hours, so that they emerge from the
flower ; the pollen ripens, and is exposed by the
bursting of the anther. So the flower remains through
the night, very attractive to, and much visited by,
moths. Towards three in the morning the scent

FIG. 34. — Silcne nutans.

ceases, the anthers begin to shrivel up or drop off, the
filaments turn themselves outwards, so as to be out of
the way, while the petals, on the contrary, begin to
roll themselves up, so that by daylight they close the
aperture of the flower, and present only their brownish-
green undersides to view ; which, moreover, are thrown
into numerous wrinkles. Thus, by the morning's
light, the flower has all the appearance of being faded.
It has no smell, and the honey is covered over by
the petals. So it remains all day. Towards evening,
however, everything is changed. The petals unfold

42 SLEEP OF PLANTS. [CHAP.

themselves ; by eight o'clock the flower is as fragrant
as before, the second set of stamens have rapidly
grown, their anthers are open, and the pollen again
exposed. By morning the flower is again " asleep,"
the anthers are shrivelled, the scent has ceased, and the
petals rolled up as before. The third evening, again
the same process occurs, but this time it is the pistil
which grows: the long spiral stigmas on the third
evening take the position which on the previous two
had been occupied by the anthers, and can hardly fail
to be dusted by moths with pollen brought from
another flower.

An objection to the view that the sleep of flowers is
regulated by the visits of insects, might be derived
from the cases of those flowers which close early in
the day, the well-known Tragopogon pratense, or "John
Go-to-bcd at Noon," for instance ; still more, such
species as Lapsana communis, or Crepis pulchra, which
open before six and close again before ten in the
morning. Bees, however, are very early risers, while
ants come out later, when the dew is off; so that it
might be an advantage to a flower which was quite
unprotected to open early for the bees, and close
again before the ants were out, thus preserving its
honey exclusively for bees.

Thus then I have endeavoured to show in a variety
of cases how beautifully flowers are constructed, so as
to secure their fertilisation by insects. Neither plants
nor insects would be what they are, but for the in-
fluence which each has exercised on the other. Some
plants, indeed, are altogether dependent on insects for
their very existence. We know now, for instance, that

II.] THE SCENT OF FLOWERS. 43

certain plants produce no seeds at all, unless visited by
insects. Thus, in some of our colonies, the common
Red Clover sets no seeds, on account of the absence
of humble bees ; for the proboscis of the hive bee is
not long enough to effect the object. According to
Mr. Belt, the same is the case, and for the same reason,
in Nicaragua, with the scarlet-runner. But even in
those instances in which it is not absolutely necessary,
it is an advantage that the flowers should be fertilised
by pollen brought from a different stock, and with
this object in view insects are tempted to visit flowers
for the sake of the honey and pollen ; while the
colours and scents are useful in making the flowers
more easy to find.

Fortunately for us, bees like the same odours as we
do ; and as the great majority of flowers are adapted
for bees, they are consequently sweet ; but it might
have been otherwise, for flies, as already mentioned,
prefer unpleasant smells, such as those of decaying
meat, and other animal substances on which they
live as larvae, and some flowers, consequently, which
are fertilised by them are characterised by very evil
odours. Colours also are affected in the same man-
ner, for while bee-flowers (if I may coin such an
expression) have generally bright, clear colours, fly-
flowers are usually reddish or yellowish brown.

Nevertheless although flowers present us with these
beautiful and complex contrivances, whereby the
transfer of pollen from flower to flower is provided for,
and waste is prevented, yet they appear to be imperfect,
or at least not yet perfect in their adaptations. Many
small insects obtain access to flowers and rob them of

44 THE ORIGIN OF FLOWERS. [CHAP. n.

their contents. Malva rotundifolia can be, and often
is, sucked by bees from the outside, in which case the
flower derives no advantage from the visit of the
insect. In Medicago sativa, also, insects can suck the
honey without effecting fertilisation, and the same
flower continues to secrete honey after fertilisation
has taken place, and when, apparently, it can no
longer be of any use. Fritz Muller has observed that
though Posoqueriafragrans is exclusively fertilised by
night-flying insects, many of the flowers open in the
day, and consequently remain sterile. It is of course
possible that these cases may be explained away ;
nevertheless, as both insects and flowers are con-
tinually altering in their structure, and in their geo-
graphical distribution, we should naturally expect to
find such instances. Water continually tends to find
its own level ; animals and plants as constantly tend
to adapt themselves to their conditions. For it is
obvious that any blossom which differed from the
form and size best adapted to secure the due trans-
ference of the pollen would be less likely to be
fertilised than others ; while on the other hand, those
richest in honey, sweetest, and most conspicuous,
would most surely attract the attention and secure the
visits of insects ; and thus, just as our gardeners, by
selecting seed from the most beautiful varieties, have
done so much to adorn our gardens, so have insects,
by fertilising the largest and most brilliant flowers,
contributed unconsciously, but not less effectually, to
the beauty of our woods and fields.1

1 I have treated the subject of the?e chapters at greater length in a
little book on Flowers and Insects, forming one of the present series.

FIG. 35. — Cardainine chenopodijolia.
a a, ordinary pods ; b, subterranean pods.

CHAPTER III.

FRUITS AND SEEDS.

FRUITS and Seeds, though not generally so con-
spicuous as flowers, are not less interesting.

In considering them, it is fortunately not necessary
to use many technical terms, though it is impossible

46 STRUCTURE OF SEED. [CHAP.

to avoid them altogether. In order to understand the
structure of the seed, we must commence with the
flower, to which the seed owes its origin. Now I
have already mentioned, but it may be convenient to
repeat here, if you take such a flower as, say a
Geranium, you will find that it consists of the /bllowing
parts : Firstly, there is a whorl of greenjjeaves, known
as the sepals, and together forming the calyx
secondly, a whorl of coloured leaves, or petals,
generally forming the most conspicuous part of the
flower, and called the corolla ; thirdly, a whorl of
organs more or less like pins, which are called stamens,
in the heads, or anthers of which, the pollen is
produced. These anthers are in reality, as Goethe
showed, modified leaves ; in the so-called double
flowers, as, for instance, in our garden roses, they are
developed into coloured leaves like those of the corolla,
and monstrous flowers are not unfrequently met with,
in which the stamens are green leaves, more or less
resembling the ordinary leaves of the plant. Lastly,
in the centre of the flower is the pistil, which also is
theoretically to be considered as constituted of one or
more leaves, each of which is folded on itself, and
called a carpel. Sometimes there is only one carpel.
Generally the carpels have so completely lost the
appearance of leaves, that this explanation of their
true nature requires a considerable amount of faith,
though in others, as for instance in the Columbine
(Aquilegia), the original leaf-form can still be traced.
The base of the pistil is the ovary, composed, as I
have just mentioned, of one or more carpels, in which
the seeds are developed. I need hardly say that many

1 1 i.l PROTECTION OF SEEDS. 4?

so-called seeds are really fruits ; that is to say, they
are seeds with more or less complex envelopes.

We all know that seeds and fruits differ greatly in
different species. Some are large, some small ; some
are sweet, some bitter ; some are brightly coloured ;
some are good to eat, some poisonous ; some spherical,
some winged, some covered with bristles, some with
hairs ; some are smooth, some very sticky.

We may be sure that there are good reasons for
these differences. In the case of flowers much light
has been thrown on their various interesting pecu-
liarities by the researches of Sprengel, Darwin, Mliller,
and other naturalists. As regards seeds also, besides
Gaertner's great work, Hildebrand, Krause, Stein-
brinck, Kerner, Grant Allen, Wallace, Darwin, and
others, have published valuable researches, especially
with reference to the hairs and hooks with which so
many seeds are provided, and the other means of
dispersion they possess. Nobbe also has contributed
an important work on seeds, principally from an agri-
cultural point of view, but the subject as a whole offers
a most promising field for investigation. It is rather
with a view of suggesting this branch of science to you,
than of attempting to supply the want myself, that I
now propose to call your attention to it. In doing so
I must, in the first place, express my acknowledg-
ments to Mr. Baker, Mr. Carruthers, Mr. Hemsley,
and especially to Mr. Thiselton Dyer and Sir Joseph
Hooker, for their kind and most valuable assistance.

It is said that one of our best botanists once observed
to another that he never could understand what was
the use of the teeth on the capsules of mosses. " Oh,"

43 EDIBLE FRUITS AND SEEDS. [CHAP.

replied his friend, " I see no difficulty in that, because
if it were not for the teeth, how could we distinguish
the species ? "

We may, however, no doubt, safely consider that
the peculiarities of seeds have reference to the plant
itself, and not to the convenience of botanists.

In the first place, then, during growth, seeds in
many cases require protection. This is especially the
case with those of an albuminous character. It is
curious that so many of those which are luscious when
ripe, as the Peach, Strawberry, Cherry, Apple, &c.,
are stringy, and almost inedible, till ripe. Moreover,
in these cases, the fleshy portion is not the seed itself,
but only the envelope, so that even if the sweet part
is eaten the seed itself remains uninjured.

On the other hand, such seeds as the Hazel, Beech,
Spanish Chestnut, and innumerable others, are pro-
tected by a thick, impervious shell, which is especially
developed in many Proteaceae, the Brazil-nut, the so-
called Monkey-pot, the Cocoa-nut, and other palms.

In other cases the envelopes protect the seeds, not
only by their thickness and toughness, but also by
their bitter taste, as, for instance, in the Walnut.
The genus Mucuna, one of the Leguminosae, is remark-
able in having the pods covered with stinging hairs.

In many cases the calyx, which is closed when the
flower is in bud, opens when the flower expands, an<i
then after the petals have fallen closes again until the
seeds are ripe, when it opens for the second time.
This is, for instance, the case with the common Herb
Robert (Geranium robertianuni). In Atractylis can-
cellata, a South European plant, allied to the thistles,

in.] MOVEMENTS OF PLANTS. 49

the outer envelopes form an exquisite little cage.
Another case, perhaps, is that of Nigella, the " Devil-
in-a-bush," or, as it is sometimes more prettily called,
" Love-in-a-mist," of old English gardens.

Again, the protection of the seed is in many cases
attained by curious movements of the plant itself.
In fact, plants move much more than is generally
supposed. So far from being motionless, they may
almost be said to be in perpetual movement, though
the changes of position are generally so slow that they
do not attract attention. This is not, however, always
the case. We are all familiar with the Sensitive Plant
which droops its leaves when touched. Another
species (Averrhoa bilimbi] has leaves like those of an
Acacia, and all day the leaflets go slowly up and down.
Desmodium gyrans, a sort of pea living in India, has
trifoliate leaves, the lateral leaflets being small and
narrow ; and these leaflets, as was first observed by
Lady Monson, are perpetually moving round and
round, whence the specific name gyrans. In these two
cases the object of the movement is quite unknown
to us. In Dioncea, on the other hand, the leaves form
a regular fly-trap. Directly an insect alights on them
they shut up with a snap.

In a great many cases leaves are said to sleep ;
that is to say, at the approach of night they change
their position, and sometimes fold themselves up,
thus presenting a smaller surface for radiation, and
being in consequence less exposed to cold. Mr.
Darwin has proved experimentally that leaves which
he prevented from moving suffered more from cold
than those which were allowed to assume their natural

E

50 ARROWROOT. DANDELION. [CHAP.

position. He has observed with reference to one
plant, Maranta arnndinacea, the Arrowroot, a West
Indian species allied to Canna, that if the plant has
had a severe shock it cannot get to sleep for the next
two or three nights.

The sleep of flowers is also probably a case of the
same kind, though, as I have already attempted to
show, it has, I believe, special reference to the visits
of insects ; those flowers which are fertilised by bees,
butterflies, and other day insects, sleep by night,
if at all ; while those which are dependent on moths
rouse themselves towards evening, as already men-
tioned, and sleep by day. These motions, indeed,
have but an indirect reference to our present subject.
On the other hand, in the Dandelion (Leontodon), the
flower-stalk is upright while the flower is expanded,
a period which lasts for three or four days ; it then
lowers itself and lies close to the ground for about
twelve days, while the fruits are ripening, and then
rises again when they are mature. In the Cyclamen
the stalk curls itself up into a beautiful spiral after
the flower has faded.

The flower of the little Linaria of our walls (L.
cymbalarid) pushes out into the light and sunshine,
but as soon as it is fertilised it turns round and
endeavours to find some hole or cranny in which it
may remain safely ensconced until the seed is ripe.

In some water-plants the flower expands at the
surface, but after it is faded retreats again to the
bottom. This is the case, for instance, with the
Water Lilies, some species of the Potamogeton, Trapa
natans. In Valisneria, again, the female flowers

VALISNERIA.

51

(Fig. 36, a) are borne on long stalks, which reach to the
surface of the water, on which the flowers float The
male flowers (Fig. 36, £), on the contrary, have short,

FIG. 36. — Valisnerii sfiralis.
a, female flower ; b, male flower ; c, floating pollen.

straight stalks, from which, when mature, the pollen
(Fig. 36, c) detaches itself, rises to the surface, and,
floating freely on it, is wafted about, so that it comes

E 2

52 DISPERSION OF SEEDS. [CHAP.

in contact with the female flowers. After fertilisation,
however, the long stalk coils up spirally, and thus
carries the ovary down to the bottom, where the seeds
can ripen in greater safety.

The next points to which I will direct your attention
are the means of dispersion possessed by many seeds.
Farmers have found by experience that it is not
desrrable to grow the same crop in the same field
year after year, because the soil becomes more or less
exhausted. In this respect, therefore, the powers of
dispersion possessed by many seeds are a great
advantage to the species. Moreover, they are also
advantageous in giving the seed a chance of germi-
nating in new localities suitable to the requirements
of the species. Thus a common European species,
Xanthium spinosum, has rapidly spread over' the whole
of South Africa, the seeds being carried in the wool
of sheep. From various considerations, however, it
seems probable that in most cases the provision does
not contemplate a dispersion for more than a short
distance.

There are a great many cases in which plants
possess powers of movement directed to the dissemina-
tion of the seed.

I have already referred to the case of the common
Dandelion. Here the flower-stalk stands more or less
upright while the flower is expanded, a period which
generally lasts for three or four days. It then lowers
itself, and lies more or less horizontally and concealed
during the time the seeds are maturing, which in our
summers occupies about twelve days. It then again
rises, and, becoming almost erect, facilitates the

in.] SEEDS THRO WN B Y THE PARENT PLANT. 53

dispersion of the seeds, or, speaking botanically, the
fruits, by the wind. Some plants, as we shall see,
even sow their seeds in the ground, but these cases
will be referred to later on.

In other cases the plant throws its own seeds to
some little distance. This is the case with the common
Cardamine hirsuta, a little plant, I do not like to call
it a weed, six or eight inches high, which comes up of
itself abundantly on any vacant spot in our kitchen-
gardens or shrubberies, and which much resembles
that represented in Fig. 17, but without the subter-
ranean pods b. The seeds are contained in a pod
which consists of three parts, a central membrane, and
two lateral walls. When the pod is ripe the walls are
in a state of tension. The seeds are loosely attached
to the central piece by short stalks. Now, when the
proper moment has arrived, the outer walls are kept
in place by a delicate membrane, only just strong
enough to resist the tension. The least touch, for
instance, a puff of wind blowing the plant against a
neighbour, detaches the outer wall, which suddenly
rolls itself up, generally with such force as to fly
from the plant, thus jerking the seeds to a distance of
several feet.

In the common Violet, beside the coloured flowers,
there are others in which the corolla is either absent
or imperfectly developed. The stamens also are
small, but contain pollen, though less than in the
coloured flowers. In the autumn large numbers of
these curious flowers are produced. When very young
they look like an ordinary flower-bud (Figs. 37 and 38,
a), the central part of the flower being entirely covered

S4 SEEDS SOWN BY THE PARENT PLANT. [CHAP.

by the sepals, and the whole having a triangular form.
When older (Figs. 37 and 38, *) they look at first sight
like an ordinary seed capsule, so that the bud seems
to pass into the capsule without the flower-stage.

* IG. 37- — Viola kirta.
a, young bud ; 6, ripe seed capsule.

The Pansy Violets do not possess these interesting
flowers. In the Sweet Violet ( V. odorata and V. kirta,
Fig. 37) they may easily be found by searching among
the leaves nestling close to the ground. It is often
said, for instance by Vaucher, that the plants actually

111.]

VIOLA HIRTA AND CAN IN A.

55

force these capsules into the ground, and thus sow
their own seeds. I have not, however, found this to
be the case, though as the stalk elongates, and the
point of the capsule turns downwards, if the earth be
loose and uneven, it will no doubt sometimes so

FIG. 38. — Viola, canina.

a, bud ; b, bud more advanced ; c, capsule open, some of the seeds are already
thrown.

happen. When the seeds are fully ripe, the capsule
opens by three valves and allows them to escape.

In the Dog Violet ( V. canina, Fig. 38) the case is
very different. The capsules are less fleshy, and,
though pendent when young, at maturity they erect
themselves (Fig. 38, c), stand up boldly above the
rest of the plant, and open by the three equal valves

56 REASON OF DIFFERENCES. [CHAP.

(Fig. 39) resembling an inverted tripod. Each valve
contains a row of three, four, or five brown, smooth,
pear shaped seeds, slightly flattened at the upper, wider
end. Now the two walls of each valve, as they become
drier, contract, and thus approach one another, thus
tending to squeeze out the seeds. These resist some
time, but at length the attachment of the seed to its
base gives way, and it is ejected several feet, this
being no doubt much facilitated by its form and
smoothness. I have known even a gathered specimen

FJG. 39. — Viola canina. Seed vessels with seed.

throw a seed nearly 10 feet. Fig. 40 represents a
capsule after the seeds have been ejected.

Now we naturally ask ourselves what is the reason
for this difference between the species of Violets ;
why do V. odorata and V. hirta conceal their capsules
among the moss and leaves on the ground, while V.
canina and others raise theirs boldly above their heads,
and throw the seeds to seek their fortune in the world ?
If this arrangement be best for Viola canina, why has
not Viola odorata also adopted it ? The reason is, I
believe, to be found in the different mode of growth

in.] SEEDS THROWN BY GERANIUMS. 57

of these two species. Viola canina is a plant with an
elongated stalk, and it is easy therefore for the capsule
to raise itself above the grass and other low herbage
among which violets grow.

V. odorata and V. hirta, on the contrary, have, in
ordinary parlance, no stalk, and the leaves are radical,
i.e. rising from the root. This is at least the case in
appearance, for, botanically speaking, they rise at the
end of a short stalk. Now, under these circumstances,

FIG. 40. — Viola canina. Seed vessel after ejecting the seed.

if the Sweet Violet attempted to shoot its seeds, the
capsules not being sufficiently elevated, the seeds
would merely strike against some neighbouring leaf,
and immediately fall to the ground. Hence, I think,
we see that the arrangement of the capsule in each
species is that most suitable to the general habit of
the plant.

In the true Geraniums again, as, for instance, in the
Herb Robert (Fig. 41), after the flower has faded, the
central axis gradually elongates (Fig. 41, a, c, d). The

HERB ROBERT.

[CHAP.

seeds, five in number, are situated at the base of the
column, each being inclosed in a capsule, which

FIG. 41. — HERB ROBERT (Geranium robertianutn).

a, bud ; b, flower ; c, flower after the petals have fallen : d, flower with seeds nearly
ripe ; e, flower with ripe seeds ; f, flower after throwing seeds.

terminates upwards in a rod-like portion, which at
first forms part of the central axis, but gradually
detaches itself. When the seeds are ripe the ovary

III.]

OTHER SPECIES OF GERANIUM.

59

raises itself into an upright position (Fig. 41, e] ; the
outer layers of the rod-like termination of the seed-
capsule come to be in a state of great tension, and
eventually detach the rpd with a jerk, and thus throw
the seed some little distance. Fig. 41, f, represents
the central rod after the seeds have been thrown. In

Diagram,

FIG. 42. — Qerattiunt dissectmit.

a, just befors throwing seed ; 6, just after throwing seed ; c, the capsule still attached
to the rod ; d, the seed.

some species, as for instance in Geranium dissectum,
Fig. 42, the capsule-rod remains attached to the central
column and the seed only is ejected.

It will, however, be remembered that the capsule is,
as already observed, a leaf folded on itself, with the
edges inwards, and in fact in the Geranium the seed-

60 SPECIES OF GERANIUM. [CHAP.

chamber opens on its inner side. You will, therefore,
naturally observe to me that when the carpel bursts
outwards, the only effect would be that the seed
would be forced against the outer wall of the carpel,
and that it would not be ejected, because the opening
is not on the outer but on the inner side. This
remark is perfectly just, but the difficulty has been
foreseen by our Geraniums, and is overcome by them
in different ways. In some species, as for instance
in Geranium dissectum, a short time before the
dehiscence, the seed-chamber places itself at right
angles to the pillar (Fig. 42, a). The edges then
separate, but they are provided with a fringe of hairs,
just strong enough to retain the seed in its position,
yet sufficiently elastic to allow it to escape when the
carpels burst away, remaining attached, however, to
the central pillar by their upper ends (Fig. 42, c).

In the common Herb Robert (Fig. 43), and some
other species, the arrangement is somewhat different.
In the first place the whole carpel springs away (Fig.
43, b and c}. The seed-chamber (Fig. 43, c] detaches
itself from the rod of the carpel (Fig. 43, b}, and when
the seed is flung away remains attached to it. Under
these circumstances it is unnecessary for the chamber
to raise itself from the central pillar, to which accord-
ingly it remains close until the moment of disruption
(Fig. 41, e). The seed-chamber is moreover held in
place by a short tongue which projects a little way
over its base ; while, on the other hand, the lower end
of the rod passes for a short distance between the
seed-capsule and the central pillar. The seed-capsule
has also near its apex a curious tuft of silky hair

III.]

VETCH.

61

(Fig. 43, f), the use of which I will not here stop to
discuss. As the result of all this complex mechanism
the seeds when ripe are flung to a distance which is
surprising when we consider how small the spring is.
In their natural habitat it is almost impossible to
find the seeds when once thrown. I therefore brought

Diagram.

FIG. 43. — Geranium robertianum.
a, just before throwing the seed ; b, tha rod ; c, the seed inclosed in the capsule.

some into the house and placed them on my billiard-
table. They were thrown from one end completely
beyond the other, in some cases more than twenty feet.
Some species of Vetch, again, and the common
Broom, throw their seeds, owing to the elasticity of
the pods, which, when ripe, open suddenly with a jerk.

62 CARDAMINE. [CHAP.

Each valve of the pod contains a layer of woody cells,
which, however, do not pass straight up the pod, but
are more or less inclined to its axis (Fig. 44). Conse-
quently, when the pod bursts it does not, as in the case
of Cardamine, roll up like a watch-spring, but twists
itself more or less like a corkscrew.

I have mentioned these species because they are
some of our commonest wild flowers, so that during

FIG. 44. — COMMON VETCH (Vicia septum).
The line a b shows the direction of the woody fibres.

the summer and autumn we may in almost any walk
observe for ourselves this innocent artillery. There
are, however, many other more or less similar cases.
Thus the Squirting Cucumber (Momordica elateriunt),
a common plant in the south of Europe, and one
grown in some places for medicinal purposes, effects
the same object by a totally different mechanism.

III.]

SQUIRTING CUCUMBER.

The fruit is a small cucumber (Fig. 45), and when
ripe it becomes so gorged with fluid that it is in a
state of great tension. In this condition a very slight
touch is sufficient to detach it from the stalk, when
the pressure of the walls ejects the contents, throwing
the seed some distance. I have seen them even in
this country sent nearly twenty feet; but in a hotter
climate the plant grows more vigorously, and they

FIG. 45. — THE SQUIRTING CUCUMBER (Momordica elateriuni).

would doubtless be thrown further. In this case of
course the contents are ejected at the end by which
the cucumber is attached to the stalk. If any one
touches one of these ripe fruits, they are often thrown
with such force as to strike him in the face.

In Cydanthera, a plant allied to the Cucumber,
the fruit is unsymmetrical, one side being round and
hairy, the other nearly flat and smooth. The true apex

64 OTHER PLANTS WHICH THROW SEEDS. [CHAP.

of the fruit which bears the remains of the flower, is also
somewhat eccentric, and, when the seeds are ripe, if
it is touched even lightly, the fruit explodes and the
seeds are thrown to some distance. The mechanism
by which this is effected has been described by
Hildebrand. The interior of the fruit is occupied by
a loose cellular structure. The central column, or
placenta, to which the seeds are attached, lies loosely
in this tissue. Through the solution of its earlier
attachments, when the fruit is ripe, the column adheres
only at the apical end, under the withered remains of
the flower, and at the swollen side. When the fruit
bursts the placenta unrolls, and thus hurls the seeds to
some distance, being even itself sometimes also torn
away from its attachment.

Other cases of projected seeds are afforded by
Impatiens, Hitra, one of the Euphorbia, Collomia,
Oxalis, some species allied to Acanthus, and by
Arceuthobium, a plant allied to the Mistletoe, and
parasitic on Juniper, which ejects its seeds to a
distance of several feet, throwing them thus from
one tree to another.

Even those species which do not eject their seeds
often have them so placed with reference to the
capsule that they only leave it if swung or jerked by
a high wind. In the case of trees, even seeds with
no special adaptation for dispersion must in this
manner be often carried to no little distance ; and
to a certain, though less extent, this must hold good
even with herbaceous plants. It throws light on the,
at first sight, curious fact that in so many plants with
small, heavy seeds, the capsules open not at the

III.]

POPPY. CAMPANULA.

bottom, as one might perhaps have been disposed to
expect, but at the top. A good illustration is afforded
by the well-known case of the common Poppy
(Fig. 46), in which the upper part of the capsule
presents a series of little doors (Fig. 46, a), through
which, when the plant is swung by the wind, the
seeds come out one by one. The little doors are

FIG. 46. — SEED-HEAD OF POPPY (Palaver).

protected from rain by overhanging eaves, and arc
even said to shut of themselves' in wet weather. The
genus Campanula is also interesting from this point
of view, because some species have the capsules
pendent, some upright, and those which are upright
open at the top, while those which are pendent do
so at the base.

F

66 SWIMMING SPORES. EYE-SPOT. [CHAP.

In other cases the dispersion is mainly the work of
the seed itself. In some of the lower plants, as, for
instance, in many seaweeds, and in some allied fresh-
water plants, such as Vaucheria> the spores1 are
covered by vibratile cilia, and actually swim about
in the water, like infusoria, till they have found a
suitable spot on which to grow. Nay, so much do
the spores of some seaweeds resemble animals, that
they are provided with a red " eye-spot " as it has
been called, which, at any rate, seems so far to
deserve the name that it appears to be sensitive to
light. This mode of progression is, however, only
suitable to water plants. One group of small, low-
organised plants, Marchantia, develop among the
spores a number of cells with spirally thickened walls-
which, by their contractility, are supposed to dis-
seminate the spores. In the common Horsetails
(Equisetuvi), again, the spores are provided with
curious filaments, terminating in expansions, and
known as " elaters." These move with great vigour,
and probably serve the same purpose.

In much more numerous cases, seeds are carried by
the wind. For this of course it is desirable that they
should be light. Sometimes this object is attained
by the character of the tissues themselves, sometimes
by the presence of empty spaces. Thus, in V alerianella
auricula, the fruit contains three cells, each of which
would naturally be expected to contain a seed. One
seed only, however, is developed, but, as may be seen
from the figure given in Mr. Bentham's excellent

1 I need hardly observe that, botanically, these are not true seeds,
hut rather motile buds.

in.] SEED CARRIED BY WIND. 67

Handbook of the British Flora, the two cells which
contain no seed actually become larger than the one
which alone might, at first sight, seem to be normally
developed. We may be sure from this that they
must bs of some use, and, from their lightness, they
probably enable the wind to carry the seed to a
greater distance than would otherwise be the case.

In other instances the plants themselves, or parts
of them, are rolled along the ground by the wind.
An example of this is afforded, for instance, by a kind
of grass (Spinifex sqnarrosus), in which the mass of
inflorescence, forming a large round head, is thus
driven for miles over the dry sands of Australia until
it comes to a damp place, when it expands and soon-
strikes root.

So, again, the Anastatica hierochuntica, or " Rose
of Jericho," a small annual with rounded pods, which
frequents sandy places in Egypt, Syria, and Arabia,
when dry, curls itself up into a ball or round cushion,
and is thus driven about by the wind until it finds a
damp place, when it uncurls, the pods open and sow
the seeds.

These cases, however, in which seeds are rolled by
the wind along the ground, are comparatively rare.
There are many more in which seeds are wafted
through the air. If you examine the fruit of a
Sycamore you will find that it is provided with a
wing-like expansion, in consequence of which, if there
is any wind when it falls, it is, though rather heavy,
blown to some distance from the parent tree. Several
cases are shown in Fig. 47 ; for instance, the Maple a,
Sycamore b, Hornbeam d, Elm e, Birch f,

F 2

63

WINGED SEEDS.

[CHAP.

JL

FIG. 47.

a, maple ; b, sycamore ; c, lime ; d, hornbeam ; e, elm ; /, birch ; g, pine ; h, fir ;
i, ash.

Fir h, and Ash 2, while in the Lime, c, the whole
bunch of fruits drop together, and the ': bract," as it

in.] WINGED SEEDS FREQUENT ON TREES. 69

is called, or leaf of the flower-stalk, serves the same
purpose.

In a great many other plants the same result is
obtained by flattened and expanded edges. A beauti-
ful example is afforded by the genus Thysanocarpus,
a North American crucifer ; T. laciniatus has a dis-
tinctly winged pod ; in T. curvipes the wings are
considerably larger ; lastly, in T. elegans and T.
radians the pods are still further developed in the
same direction, T. radians having the wing very
broad, while in T. elegans it has become thinner and
thinner in places, until at length it shows a series of
perforations. Among our common wild plants we
find winged fruits in the Dock (Rumex] and in the
common Parsnip (Pastihacd). But though in these
cases the object to be obtained — namely, the dispersion
of the seed — is effected in a similar manner, there are
differences which might not at first be suspected.
Thus in some cases, as, for instance, the Pine, it is the
seed itself which is winged ; in Thlaspi arvense it is
the pod ; in Entada, a leguminous plant, the pod
breaks up into segments, each of which is wringed ;
in Nissolia the extremity of the pod is expanded into
a flattened wing ; lastly, in the Lime, as already
mentioned, the fruits drop off in a bunch, and the
leaf at the base of the common flower-stalk, or
"bract," as it is called, forms the wing.

In Gouania retinaria of Rodriguez the same object
is effected in another manner ; the cellular tissue of
the fruit crumbles and breaks away, leaving only the
vascular tissue, which thus forms a net inclosing
the seed.

70 FEATHERED SEEDS. WILLOW. [CHAP.

Another mode, which is frequently adopted, is
the development of long hairs. Sometimes, as in
Clematis, Anemone, and Dryas, these hairs take the
form of a long feathery awn. In others the hairs
form a tuft or crown, which botanists term a pappus.
Of this the Dandelion and John Go-to-bed-at-noon,
so called from its habit of shutting its flowers about
mid-day, are well-known examples. Tufts of hairs,
which are themselves sometimes feathered, are de-
veloped in a great many Composites, though some,
as, for instance, the Daisy and Lapsana, are without
them ; in some very interesting species, of which the
common TJirincia hirta of our lawns and meadows
is one, there are two kinds of fruits, as shown in
Fig. 48, b, one with a pappus and one without. The
former are adapted to seek " fresh woods and pastures
new," while the latter stay near the parent plant and
perpetuate the race at home.

A more or less similar pappus is found among
various English plants — in the Epilobium (Fig. 48, a),
Thrincia (Fig. 48, &), Tamarix (Fig. 48, c], Willow
(Fig. 48, d}, Cotton Grass (Fig. 48, e), and Bulrush
(Fig. 48, /) ; while in exotic species there are many
other cases — as, for instance, the beautiful Oleander.
As in the wings, so also in that of the pappus, it
is by no means always the same part of the plant
which develops into the crown of hairs. Thus in the
Valerians and Composites it is the ^alyx ; in the
Bulrush the perianth ; in Epilobium the crown of the
seed , in the Cotton Grass it is supposed to represent
the perianth ; while in some, as, for instance, in the
Cotton plant, the whole outer surface of the seed is

HI.] WILLOW HERB. THRINC1A. BULRUSH. 71

clothed with long hairs. Sometimes, on the contrary,
the hairs are very much reduced in number, as, for
instance, in some species of ALschynanthus, where

FIG 48.

a, willow herb {Epilobiuiii) ; b, two forms of seed of Thrincia hirta : c, Tdmarix ,
d, willow (Salix) ; e, cotton grass (Eriopkortttti) ; f, bulrush {Typha).

there are only three, one on one side and two on the
other. In this case, moreover, the hairs are very

72 SEEDS WAFTED BY WATER. [CH. in.

flexible, and wrap round the wool of any animal with
which they may come in_ contact, so that they form a
double means of dispersion.

In other cases seeds are wafted by water. Of this
the Cocoa-nut is one of the most striking examples.
The seeds retain their vitality for a considerable time,
and the loose texture of the husk protects them and
makes them float. Every one knows that the Cocoa-
nut is one of the first plants to make its appearance
on coral islands, and it is, I believe, the only palm
which is common to both hemispheres. •

The seeds of the common Duckweeds (Lemnd)
sink to the bottom of the water in autumn, and re-
main there throughout the winter ; but in the spring
they rise up to the surface again and begin to grow.

FIG. 49. — Myzodendron. (After Hooker.)

CHAPTER IV.

IN a very large number of cases the diffusion of
seeds is effected by animals. To this class belong
the fruits and berries. In them an outer fleshy
portion becomes pulpy, and generally sweet, inclosing
the seeds. It is remarkable that such fruits, in order,
doubtless, to attract animals, are, like flowers, brightly
coloured — as, for instance, the Cherry, Currant, Apple,
Peach, Plum, Strawberry, Raspberry, and many others.
This colour, moreover, is not present in the unripe
fruit, but is rapidly developed at maturity. In such
cases the actual seed is generally protected by a

74 EDIBLE FRUITS. COLOURS. [CHAP.

dense, sometimes almost stony, covering, so that it
escapes digestion, while its germination is perhaps
hastened by the heat of the animal's body. It may
be said that the skin of apple and pear pips is com-
paratively soft ; but then they are embedded in a
stringy core, which is seldom eaten.

These coloured fruits form a considerable part of the
food of monkeys in the tropical regions of the earth,
and we can, I think, hardly doubt that these animals
are guided by the colours, just as we are, in selecting
the ripe fruit. This has a curious bearing on an
interesting question as to the power of distinguishing
colour possessed by our ancestors in bygone times.
Magnus and Geiger, relying on the well-known fact
that the ancient languages are poor in words for
colour, and that in the oldest books — as, for instance,
in the Vedas, the Zendavesta, the Old Testament,
and the writings of Homer and Hesiod — though
the heavens are referred to over and over again,
its blue colour is never dwelt on, have argued that
the ancients were very deficient in the power of
distinguishing colours, and especially blue. In our
own country Mr. Gladstone has lent the weight of his
great authority to the same conclusion. For my part
I cannot accept this view. There are, it seems to me,
very strong reasons against it, into which I cannot,
of course, now enter ; and though I should rely
mainly on other considerations, the colours of fruits
are not, I think, without significance. If monkeys
and apes could distinguish them, surely we may infer
that even the most savage of men could do so too.
Zeuxis would never have deceived the birds if he had
not had a fair perception of colour.

iv.] HOOKED SEEDS. 75

In these instances of coloured fruits, the fleshy edible
part more or less surrounds the true seeds ; in others
the actual seeds themselves become edible. In the
former the edible part serves as a temptation to
animals ; in the latter it is stored up for the use of the
plant itself. When, therefore, the seeds themselves
are edible they are generally protected by more or
less hard or bitter envelopes, for instance the Horse
Chestnut, Beech, Spanish Chestnut, Walnut, &c.
That these seeds are used as food by squirrels and
other animals is, however, by no means necessarily an
evil to the plant, for the result is that they are often
carried some distance and then dropped, or stored up
and forgotten, so that in this way they get carried
away from the parent tree.

In another class of instances animals, unconsciously
or unwillingly, serve in the dispersion of seeds.
These cases may be divided into two classes, those in
which the fruits are provided with hooks, and those in
which they are sticky. To the first class belong,
among our common English plants, the Burdock
(Lappa, Fig. 50, a) ; Agrimony (Agrimonia, Fig. 50, I?) •
the Bur Parsley (Caucalis, Fig. 50, c] ; Enchanter's
Nightshade (Circ<za, Fig. 50, d] ; Goose Grass or
Cleavers (Galium, Fig. 50. e), and some of the Forget-
me-nots (My0s0tis,.Fig. BO,/"). The hooks, moreover^
are so arranged as to promote the removal of the
fruits. In all these species the hooks, though beauti-
fully formed, are small; but in some foreign species
they become truly formidable. Two of the most
remarkable are represented on page 77, — Martynia
proboscidea (Fig. 51, b] and HarpagopJiytonprocumbens
(Fig. 51, a). Martynia is a plant of Louisiana, and if

76 BURDOCK. AGRIMONY. FORGET-ME-NOT. [CH

*

FIG 50

a, burdock (^Lappa); b, agrimony (Afrimonia); c, bur parsley (_Caucalis)\ d, en-
chanter's nightshade (Circita) ; e, cleavers (Galiuni) ; f, forget-me-nots (JMyosotis)

its fruits once get hold of an animal it is most difficult
to remove them. Harpagophytum is a South African
genus. The fruits are most formidable, and are said

iv.l HARPAGOPHYTON. MARTYNIA. 77

FIG. 51.
a, Harpagophyton proc umbens (natural size) ; b, Martyniaproboscidea.(patoX2\ size).

sometimes even to kill lions. They roll about over the
dry plains, and if they attach themselves to the skin,

STICKY SEEDS. [CHAP.

the wretched animal tries to tear them out. and some
times getting them into his mouth perishes miserably.

The cases in which the diffusion of fruits and seeds
is effected by their being sticky are less numerous, and
we have no well-marked instance among our native
plants. The common Plumbago of South Europe is
a case which many of you no doubt have observed.
Other genera with the same mode of dispersion are
Pittosporum, Pisonia, Boerhavia, Siegesbeckia, Grin-
delia, Drymaria, &c. There are comparatively few
cases in which the same plant uses more than one of
these modes of promoting the dispers:on of its seeds,
still there are some such instances. Thus in the
common Burdock the seeds have a pappus, while the
whole flower-head is provided with hooks which
readily attach themselves to any passing animal.
Asterothrix, as Hildebr.and has pointed out, has three
provisions for dispersion ; it has a hollow appendage,
a pappus, and a rough surface.

But perhaps it will be said that I have picked out
special, cases ; that others could have been selected,
which would not bear out, or perhaps would even
negative, the inferences which have been indicated ;
that*[ have put the cart before the horse ; that the
Ash fruit has not a wing in order that it may be
carried by the wind, or the Burdock hooks that the
heads may be transported by animals, but that
happening to have wings and hooks these seeds are
thus transported. Now doubtless there are many
points connected with seeds which are still un-
explained ; in fact it is because this is so that I was
anxious to direct attention to the subject. Still I

iv.] WINGED SEEDS ON TREES. 79

believe the general explanations which have been
given by botanists will stand any test.

Let us take for instance fruits formed on the same
type as that of the Ash— that is to say, with a long
wing, known to botanists as a Samara. Now such a
fruit would be of little use to low herbs, which,
however, are so numerous. If the wing was accidental,
if it were not developed to serve as a means of dis-
persion, it would be as likely to occur on low plants
and shrubs as on trees. Let us then consider on what
kind of plants these fruits are found. They occur on
the Ash, Maple, Sycamore, Hornbeam, Pines, Firs
and Elm ; while the Lime, as we have seen, has also a
leaf attached to the fruits, which answers the same
purposes. Seeds of this character therefore occur on
a large proportion of our forest trees, and on them
alone. But more than this : I have taken one or
two of the most accessible works in which seeds
are figured, for instance Gaertner's De Fructibus et
Seminibus, Le Maout and Decaisne (Hooker's transla-
tion) Descriptive and Analytical Botany, and Baillon's
Histoire des Plantes. I find thirty genera, belonging
to twenty-one different natural orders, figured as
having seeds or fruits of this form. They are all
trees or climbing shrubs, not one being a low herb.

Let uS take another case, that of the plants in which
the dispersion of the seeds is effected by means of
hooks. Now, if the presence of these hooks were, so
to say, accidental, and the dispersion merely a result,
we should naturally expect to find some species with
hooks in all classes of plants. They would occur, for
instance, among trees and on water-plants. On the
other hand, if they are developed that they might

8o

HOOKED SEEDS ON BUSHES. [CHAP.

adhere to the skin of quadrupeds, then, having
reference to the habits and size of our British
mammals, it would be no advantage for a tree or for
a water-plant to bear hooked seeds. Now, what are
the facts ? There are about thirty English species in
which the dispersion of the seeds is effected by means
of hooks, but not one of these is aquatic, nor is one of
them more than four feet high. Nay, I might carry
the thing further. We have a number of minute
plants, which lie below the level at which seeds would
be likely to be entangled in fur. Now none of these,
ao-ain, have hooked seeds or fruits. It would also

o

seem, as Hildebrand has suggested, that in point of
time, also, the appearance of the families of plants in
which the fruits or seeds are provided with hooks
coincided with that of the land Mammalia.

Again, let us look at it from another point of view.
Let us take our common forest-trees, shrubs, and tall
climbing plants ; not, of course, a natural or botanical
group, for they belong to a number of different orders,
but a group characterised by attaining to a height
of say over eight feet. We will in some cases only
count genera ; that is to say, we will count all the wil-
lows, for instance, as one. These trees and shrubs are
plants with which we are all familiar, and are about
thirty-three in number. Now, of these thirty-three
no less than eighteen have edible fruits or seeds, such
as the Plum, Apple, Arbutus, Holly, Hazel, Beech,
and Rose. Three have seeds which are provided with
feathery hairs ; and all the rest, namely, the Lime,
Maple, Ash, Sycamore, Elm, Hop, Birch, Hornbeam,
Pine, and Fir are provided with a wing. Moreover,
as will be seen by the following table, the lower trees

iv.] FR U1TS AND SEEDS OF ENGLISH TREES. 8 1

and shrubs, such as the Cornel, Guelder Rose, Rose,
Thorn, Privet, "Elder, Yew, and Holly have generally
e,dible berries, much eaten by birds. The winged seeds
or fruits characterise the great forest trees.

TREES, SHRUBS, AND CLIMBING SHRUBS NATIVE OR NATURALISED
IN BRITAIN.

Seed or Fruit.

Edible.

Hairy.

Winged. Hooked.

X

X.
X
X
X
X
X
X
X
X
X
X
X
X
X

X

X
X
X

X

X

X
X

X
X

X

X

X

X
X

X

X

Berber is vulgaris

Lime ( Tilia Europaa) . .
Maple {Acer)

Spindle Tree (Euonymus) .
Buckthorn {jRhamnus) . .
Sloe (Prunus)

Rose (Rosa)

Apple (Pyrus)

Hawthorn (Crotegut) . . .
Medlar (Mespilus) ....
Ivy (ffedera) ... . .

Cornel (Cornus)

Elder (Sambucus) ....
Guelder Rose ( Viburnum) .
Honeysuckle (Lonicera) . ,
Arbutus (Arbutus) ....
Holly (Ilex)

Ash (Fraxinus)

Privet (Ligustrum) ....
Eltn (Ulmus)

Hop (Humulus)

Alder (Alnus) *

Birch (Bttuli)

Hornbeam ( Carpinus] . . .
Nut (Corylus)

Beech (JPagus)

<">ak (Quercus)

Willow (Salix) . ...

Poplar (Populus)

Pine (Pinus)
Fir (Abies)

Yew (Taxus) . . . .

1 Some species of Alder have winged fruits.

82 VARIOUS MODES OF DISPERSION. [CHAP.

Or let us take one natural order. That of the
Roses is particularly interesting. In the genus Geurn
the fruit is provided with hooks ; in Dryas it
terminates in a long feathered awn, like that of
Clematis. On the other hand, several genera have
edible fruits ; but it is curious that the part of a plant
which becomes fleshy, and thus tempting to animals^
differs considerably in the different genera. In the
Blackberry, for instance, and in the Raspberry, the
carpels constitute the edible portion. When we eat a
Raspberry we strip them off and leave the receptacle
behind ; while in the Strawberry the receptacle con-
stitutes the edible portion ; the carpels are small,
hard, and closely surround the seeds. In these genera
the sepals are situated below the fruit. In the Rose
on the contrary, it is the peduncle that is swollen and
inverted, so as to form a hollow cup, in the interior of
which the carpels are situated. Here we must re-
member that the sepals are situated above, not below,
the fruit. Again, in the Pear and Apple, it is the
ovary which constitutes the edible part of the fruit,
and in which the pips are embedded. At first sight
the fruit of the Mulberry — which, however, belongs to
a different family — closely resembles that of the
Blackberry. In the Mulberry, however, it is the
sepals which become fleshy and sweet.

The next point is that seeds should be in a spot
suitable for their growth. In most cases, the seed
lies on the ground, into which it then pushes its little
rootlet. In plants, however, which live on trees, the
case is not so simple, and we meet some curious
contrivances. Thus, the Mistletoe, as we all know, is

iv.] VISCID SEEDS. 83

parasitic on trees. The fruits are eaten by birds, and
the droppings often therefore fall on the boughs ; but
if the seed was like that of most other plants it would
soon fall to the ground, and consequently perish.
Almost alone among those of English plants it is
extremely sticky, and thus adheres to the bark.

I have already alluded to an allied genusi
Arceutkobium, parasitic on Junipers, wrhich throws its
seeds to a distance of several feet. These also are
very viscid, or, to speak more correctly, are embedded
in a very viscid mucilage, so that if they come in
contact with the bark of a neighbouring tree they
stick to it.

Dr. Watt has described a curious peculiarity in
another species of the same family. The fruit, like
that of the Mistletoe and of most other species of this
order, consists of a mass of viscid pulp surrounding
a single seed, and when detached from the parent
plant it adheres to whatever it may fall on. There it
germinates. The radicle when it has grown to about
an inch in length develops on its extremity a flattened
disc, and then curves about until the disc is applied to
some neighbouring object. If the spot to which the
disc has fastened is suitable, the development of the
plant proceeds there. If on the contrary the spot be not
suitable, the radicle straightens itself, tears the viscid
berry away from whatever it has adhered to, and
raises it in the air. The radicle then again curves, and
the berry is carried by it to another spot where it
again adheres. The disc then detaches itself, and by
the curving of the radicle is advanced to another spot
where it again fixes itself. Dr. Watt says he has seen

G 2

84 A WALKING SEED. [CHAP.

this happen several times, and thus the young plant
seems to select certain places in preference to others.
They have been observed for instance to quit the
leaves, on which they must often alight, and move on
to the stem.

Another very interesting genus, again of the same
family, is Myzodendron (Fig. 49), a Fuegian species, de-
scribed by Sir Joseph Hooker, and parasitic on the Beech.
Here the seed is not sticky, but is provided with four
flattened flexible appendages. These catch the wind
and thus carry the seed from one tree to another. As
soon, however, as they touch any little bough the arms
twist round it and there anchor the seed.

In many epiphytes the seeds are extremely numer-
ous and minute. Their great numbers increase the
chance that the wind may waft some of them to the
trees on which they grow ; and as they are then fully
supplied with nourishment they do not require to
carry any store with them. Moreover their minute
size is an advantage, as they are carried into any
little chink or cranny in the bark ; while a larger or
heavier seed, even if borne against a suitable tree,
would be more likely to drop off. In the genus
Neumannia, the small seed is produced at each end
into a long filament which must materially increase its
chance of adhering.

Among terrestrial species there are not a few
cases in which plants are not contented simply to
leave their seeds on the surface of the soil, but actually
sow them in the ground.

Thus in Trifolium subterraneum, one of our rarer
English Clovers, only a few of the florets become

iv.] TRI FOLIUM CARDAMINE GROUND-NUT. 85

perfect flowers ; the others form a rigid pointed head
which at first is turned upwards, and as their ends are
close together, constitute a sort of spike. At first, I
say, the flower-heads point upwards like those of
other Clovers, but as soon as the florets are fertilised,
the flower- stalks bend over and grow downwardsj
forcing the flower-head into the ground, an operation
much facilitated by the peculiar construction and
arrangement of the imperfect florets. The florets are,
as Darwin has shown, no mere passive instruments.
So soon as the flower-head is in the ground they
begin, commencing from the outside, to bend them-
selves towards the peduncle, the result of which of
course is to drag the flower-head further and further
into the ground. In most Clovers each floret produces
a little pod. This would in the present species be
useless, or even injurious ; many young plants growing,
in one place would jostle and starve one another
Hence we see another obvious advantage in the fact
that only a few florets perfect their seeds.

I have already alluded to our Cardamines, the pods
of which open elastically and throw their seeds some
distance. A Brazilian species, C. chenopodifolia, Fig.
35, p. 45, besides the usual long pods, Fig. 35, a a,
produces also short pointed ones, Fig. 35, b b, which it
buries in the ground.

Arachis hypog&a is the ground-nut of the West
Indies. The flower is yellow and resembles that of a
pea, but has an elongated calyx, at the base of which,
close to the stem, is the ovary. After the flower has
faded, the young pod, which is oval, pointed, and very
minute, is carried forward by the growth of the

86

V1C1A.

[CHAP.

stalk, which becomes several inches long and curves
downwards so as generally to force the pod into the
ground. If it fails in this, the pod does not develop,

FIG ^z.—Vicia amfihicarpa.
a. a, ordinary pods ; b b, subterranean pods.

but soon perishes ; on the other hand, as soon as it is
underground the pod begins to grow and develops two
large seeds.

In Vicia amphicarpa, Fig. 52, a South European

IV.]

LATHYRUS.

species of Vetch, there are two kinds of pods. One
of the ordinary form and habit (a), the other (6) oval,

FIG 53. — Lnthyrus amphicarpos. (After Sowerby.)
a, ordinary pods ; 6, subterranean pods.

pale, containing only two seeds borne on underground
stems, and produced by flowers which have no corolla,
Again, a species of the allied genus Lathyrus,
Fig. 53, L. amphicarpos, affords us another case of the
same phenomenon.

88 MOVING SEEDS. [CHAP.

Other species possessing the same faculty of bury-
ing their seeds are Okenid hypogaa, several species
of Commefyna, and of Amphicarpaa, Voandzeia sub-
terranea, Scrophularia arguta, &c. ; and it is very
remarkable that these species are by no means nearly
related, but belong to distinct families, namely, the
Crucifertz, Leguminoscz, Commelynacece, Violariece, and
Scrophulariacea.

Moreover it is interesting that in L. amphicarpos, as
in Vicia amphicarpa and Cardamine chenopodifolia, the
subterranean pods differ from the usual and aerial form
in being shorter and containing fewer seeds. The reason
of this, is, I think, obvious. In the ordinary pods the
number of seeds of course increases the chance that
some will find a suitable place. On the other hand
the subterranean ones are carefully sown, as it were,
by the plant itself. Several seeds together would
only jostle one another, and it is therefore better that
one or two only should be produced.

In the Erodiums, or Crane's Bills, the fruit is a1
capsule which opens elastically, in some species
throwing the seeds to some little distance. The seeds
themselves are more or less spindle-shaped, hairy
and produced into a twisted hairy awn as shown in
Fig. 54, representing a seed of E. glaucophyllum.
The number of spiral turns in the awn depends upon
the amount of moisture ; and the seed may thus be
made into a very delicate hygrometer, for if it be
fixed in an upright position, the awn twists or un-
twists according to the degree of moisture, and its
extremity thus maybe so arranged as to move up and
down like a needle on a register. It is also affected by

iv.]

EROD1UM.

heat. Now if the awn were fixed instead of the seed,

it is obvious that during the process of untwisting, the

seed itself would be pressed downwards, and, as M.

Roux has shown, this mechanism thus serves actually

to bury the seed. His observations were made on an

allied species, Erodium cincoium, which he chose on

account of its size. He found that

if a seed of this plant is laid on the

ground, it remains quiet as long as it

is dry ; but as soon as it is moistened

— i.e. as soon as the earth becomes

in a condition to permit growth —

the outer side of the awn contracts,

and the hairs surrounding the seed

commence to move outwards, the

result of which is gradually to raise

the seed into an upright position with

its point on the soil. The awn then

commences to unroll and consequently

to elongate itself upwards, and he

suggests that as it is covered with

reversed hairs, it will probably press

against some blade of grass or other

obstacle, which will prevent its moving

up, and will therefore tend to drive

the seed into the ground. If then

the air becomes drier, the awn will again roll up,

in which action M. Roux thought it would tend to

draw up the seed, but from the position of the hairs

the feathery awn can easily slip downwards, and

would therefore not affect the seed. When moistened

once more, it would again force the seed further

(After sweet.)

90 ST1PA. [CHAP.

downwards, and so on until the proper depth was
obtained. A species of Anemone (A. montana)
again has essentially the same arrangement, though
belonging to a widely separated order.

A still more remarkable instance is afforded by a
beautiful South European grass, Stipa pennata (Fig.
55), the structure of which has been described by
Vaucher, and more recently, as well as more com-
pletely, by Frank Darwin. The actual seed is small,
with a sharp point, and stiff, short hairs pointing
backwards. The upper end of the seed is pro-
duced into a fine twisted corkscrew-like rod, which is
followed by a plain cylindrical portion, attached at
an angle to the corkscrew, and ending in a long and
beautiful feather, the whole being more than a foot
in length. The long feather, no doubt, facilitates the
dispersion of the seeds by wind ; eventually, however,
they sink to the ground, which they tend to reach,
the seed being the heaviest portion, point downwards.
So the seed remains as long as it is dry, but if a
shower comes on, or when the dew falls, the spiral
unwinds, and if, as is most probable, the surrounding
herbage or any other obstacle prevents the feathers
from rising, the seed itself is forced down and so
driven by degrees into the ground.

I have already mentioned several cases in which
plants produce two kinds of seeds, or at least of pods,
the one being adapted to burying itself in the ground.
Heterocarpism, if I may term it so, or the power of
producing two kinds of reproductive bodies, is not
confined to these species. There is, for instance, a
North African species of Corydalis (C. heterocarpa of

IV.]

ST1PA.

FIG. 55.— Seed of Stipa. pennaia. (Natural sue.)

92 PLANTS WITH TWO KINDS OF SEEDS. [CHAP.

Durieu) which produces two kinds of seed (Fig. 56),
one somewhat flattened, short and broad, with rounded
angles ; the other elongated, hooked, and shaped like
a shepherd's crook with a thickened staff. In this case
the hook in the latter form perhaps serves for dispersion.
Our common Thrincia hirta (Fig. 48$) also pos-
sesses, besides the fruits with the well-known feathery
crown, others which are destitute of such a provision,
and which probably therefore are intended to take
root at home.

FIG. 56. — Seeds oiCorydalis heterocarpa.

Mr. Drummond, in the volume of Hookers Journal
of Botany for 1842, has described a species of(
Alismacea which has two sorts of seed-vessels* the'
one produced from large floating flowers, the other at
the end of short submerged stalks. He does not,
however, describe either the seeds or seed-vessels in
detail.

Before concluding I will say a few words as to the
very curious forms presented by certain seeds and

iv.] SEEDS WHICH MIMIC ANIMALS. 93

fruits. The pods of Lotus, for instance, quaintly
resemble a bird's foot, even to the toes ; whence the
specific name of one species, ornithopodioides ; those
of Hippocrepis remind one of a horse-shoe ; those of
Trapa bicornis have an absurd resemblance to the
skeleton of a bull's head. These likenesses appear
to be accidental, but there are some which probably
are of use to the plant. For instance there are two
species of Scorpiurus, Fig. 57, the pods of which lie
on the ground, and so curiously resemble the one
(5. subvillosa, Fig. 57, a) a centipede, the other (S.ver-
miculata, Fig. 57, U] a worm or caterpillar, that it is
almost impossible not to suppose that the likeness
must be of some use to the plant. May it not
be possible that in these cases birds carry the seeds
some little distance before they find out that they
are not really insects ?

The pod of Biserrula pelecinus (Fig. 58) also
has a striking resemblance to a flattened centipede ;
while the seeds of Abrns precatorius, both in size and
in their very striking colour, mimic a small beetle,
A rtemis circumusta.

Mr. Moore has recently called attention to other
cases of this kind. Thus the seed of Martynia
diandra much resembles a beetle with long antennae;
several species of Lupins have seeds much like spiders,
and those of Dimorphochlamys, a gourdlike plant,
mimic a piece of dry twig. In the common Castor
Oil plants (Fig. 58^), though the resemblance is not
so close, still at a first glance the seeds might readily
be taken for beetles or ticks. In many Euphorbi-
aceous plants, as for instance in Jatropha (Fig.

94

SEEDS WHICH MIMIC ANIMALS. [CHAP.

the resemblance is even more striking. The seeds
have a central line resembling the space between the

FIG. 57.
a. pod of Scorpivna tuoviUata; b, Scorpinrus verimculata.

elytra, dividing and slightly diverging at the end,
while between them the end of the abdomen seems

IV.]

BISERRULA, RICINUS, JATROPHA.

95

to peep ; at the anterior end the seeds possess a small
lobe, or caruncle, which mimics the head or thorax of
the insect, and which even seems specially arranged
for this purpose ; at least it would seem from ex-
periments made at Kewthat the carunculus exercises
no appreciable effect during germination. In Tri-
chosantlies anguina the long pods hang down, and
alike in size, form, colour and attitude closely resemble
snakes, as the specific name denotes.

These resemblances might benefit the plant in one
of two ways. If it be an advantage to the plant

FIG. 58.— Pod of
Bisernda.

FIG. y'M.— Seed of
Castor Oil (.Ricimts),

FIG. 58*.— Seed of
Jatropha.

that the seeds should be swallowed by birds, their
resemblance to insects might lead to this result. On
the other hand if it be desirable to escape from
graminivorous birds, then the resemblance to insects
would serve as a protection. We do not, however,
yet know enough about the habits of these plants
to solve this question.

Indeed, as we have gone on, many other questions
will, I doubt not, have occurred to you, which we arc
not yet in a position to answer. Seeds, for instance,
differ almost infinitely in the sculpturing of their

96 PROBLEMS STILL UNSETTLED. [CHAP. iv.

surface. But I shall vvofully have failed in my object
if I have given the impression that we know all about
seeds. On the contrary, there is not a fruit or a
seed, even of one of our commonest plants, which
would not amply justify and richly reward the most
careful study.

In this, as in other branches of science, we have
but made a beginning. We have learnt just enough
to perceive how little we know. Our great masters
in natural history have immortalised themselves by
their discoveries, but they have not exhausted the
field ; and if seeds and fruits cannot vie with flowers
in the brilliance and colour with which they decorate
our gardens and our fields, still they surely rival, it
would be impossible to excel, them, in the almost
infinite variety of the problems they present to us,
the ingenuity, the interest, and the charm of the
beautiful contrivances which they offer for our study
and our admiration.

FIG. 59.— The Beech.

CHAPTER V.

LEAVES.

MR. RUSKIN, in one of his most exquisite passages,
has told us that " Flowers seem intended for the
solace of ordinary humanity : children love them ;
tender, contented, ordinary people love them. They
are the cottager's treasure ; and in the crowded town
mark, as with a little broken fragment of rainbow,
the windows of the workers in whose heart rests the
covenant of peace." I should be ungrateful indeed

H

93 VARIETY OF FORMS. [CHAP.

did I not fully feel the force of this truth ; but
it will be admitted that the beauty of our woods
and fields is due at least as much to foliage as to
flowers.

In the words of the same author, "The leaves of
the herbage at our feet take all kinds of strange
shapes, as if to invite us to examine them. Star-
shaped, heart-shaped, spear-shaped, arrow-shaped,
fretted, fringed, cleft, furrowed, serrated, sinuated, in
whorls, in tufts, in spires, in wreaths, endlessly ex-
pressive, deceptive, fantastic, never the same from
footstalk to blossom, they seem perpetually to tempt
our watchfulness and take delight in outstripping our
wonder."

Now, why is this marvellous variety, this inex-
haustible treasury of beautiful forms ? Does it result
from some innate tendency of each species ? Is it
intentionally designed to delight the eye of man ? or
has the form, and size, and texture, some reference to
the structure and organization, the habits and re-
quirements, of the whole plant ?

Ido not propose now to discuss any of the more
unusual and abnormal forms of leaves : the pitchers
of Nepenthes or Cephalotus, the pitfalls of Sarracenia
or Darlingtonia, the spring-trap leaves of Dionaea,
the scarcely less effective though less striking con-
trivances in our own Drosera or Pinguicula, nor the
remarkable power of movement which many leaves
present, whether in response to an external stimulus,
as in certain species of Mimosa, Oxalis, &c., or as a
spontaneous periodic movement, such as the " sleep "

v.] CA USES OF DIFFERENCES. 99

of many leaves, or the nearly continuous rotation of
the lateral leaflets of Desmodium. I propose, rather,
to ask you to consider the structure, and especially
the forms, of the common every-day leaves of our
woods and fields.

In talking the subject over with friends, I have
found a widely prevalent idea that the beauty and
variety of leaves are a beneficent arrangement made
specially with reference to the enjoyment and delight
of man. I have, again, frequently been met by the
opinion that there is some special form, size, and
texture of leaf inherently characteristic of each
species ; that the cellular tissue tends to " crystal-
lize," as it were, into some particular form, quite
irrespective of any advantage to the plant itself.

Neither of these views will, I think, stand the test
of careful examination.

In the first place, let us consider the size of the
leaf. On what does this depend ? In herbs we very
often see that the leaves decrease towards the end of
the shoot, while in trees the leaves, though not identical,
are much more uniform in size.

Again, if we take a twig of Hornbeam, we shall find
that the six terminal leaves have together an area of
about 14 square inches, and the section of the twig
has a diameter of *o6 of an inch. In the beech the
leaves are rather larger, six of them having an area
of perhaps 18 inches, and, corresponding with this
greater leaf-surface, we find that the twig is somewhat
stouter, say '09 of an inch. Following this up, we
shall find that, cateris paribus, the size of the leaf has

II 2

I00 SIZE OF LEA VES. [CHAP.

relation to the thickness of the stem. This is clearly
shown in the following table : —

Impression of Stalk below the Sixth Leaf.

beam. Beech. Elm. Nut Sycamore. Lime. Chestnut.

Elder. Ash. Walnut Ailanthus. Chestnut.

Diameter Approximate

of Area

Stem of Six Upper Leaves
in inches. in inches.

Hornbeam ...... '06 14

Beech ....... '09 18

Elm ......... •" 34

Nut ....... : . -13 ••• 55

Sycamore ..... '13 60

Lime ........ 'H 60

Chestnut ....... '15 72

Mountain Ash .... '16 ... 60

Elder ........ '18 ... 93

Ash ......... 'i8 ... too

Walnut ....... -25 220

. Ailanthus ...... '3 ... 240

Horse Chestnut .... '3 ... 300

In the Elm the numbers are TI and 34, in the
Chestnut '15 and 72, and 'in the Horse Chestnut the
stem has a thickness of '3, and the six leaves have
an area often of 300 square inches. Of course, how-
ever, these numbers are only approximate. Many
things have to be taken into consideration. Strength,
for instance, is an important element. Thus the
Ailanthus, with a stem equal in thickness to that of

v.] STRENGTH OF STEM. 101

the Horse Chestnut, carries a smaller area of leaves,
perhaps because it is less compact. Again, the
weight of the leaves must doubtless be taken into
consideration. Thus in some sprays of Ash and
Elder of equal diameter, which I examined, the
former bore the larger expause of leaves ; not only,
however, is the stem of the Elder less compact, but
the Elder leaves, though not so large, -were quite as
heavy, if not indeed a little heavier. I was for some
time puzzled by the fact that, while the terminal
shoot of the Spruce is somewhat thicker than that of
the Scotch Fir, the leaves are not much more than $
as long. May this not perhaps be due to the fact that
they remain on the tree more than twice as long, so
that the total leaf area borne by the branch is greater,
though the individual leaves are shorter ? Again, it
will be observed that the leaf area of the Mountain
Ash is small compared to the stem, and it may,
perhaps, not be unreasonable to suggest that this
may be connected with the habit of the tree to grow
in bleak and exposed situations. The position of the
leaves, the direction of the bough, and many other
elements would have also to be taken into consi-
deration, but still it seems clear that there is a
correspondence between thickness of stem and size
of leaf. This ratio, moreover, when taken in relation
with the other conditions of the problem, has, as we
shall see, a considerable bearing not only on the size,
but also on the form of the leaf.

The Mountain Ash has been a great puzzle to me ;
it is, of course, a true Pyrus, and is merely called Ash
from the resemblance of its leaves to those of the

io2 ROWAN. SYCAMORE. [CHAP.

common Ash. But the ordinary leaves of a Pear are,
as we all know, simple and ovate, or obovate. Why,
then, should those of the Mountain Ash be so entirely
different? May, perhaps, some light be thrown on
this by the arrangement of the leaves ? They are
situated some distance apart, and though, as shown
in the table, they are small in comparison to the
diameter of the stem, still they attain a size of 15
square inches, or even more. Now, if they were of
the same form as the ordinary Pear leaf, they would
be about 7 inches long by 2 to 3 in breadth. The
Mountain Ash, as we know, lives in mountainous
and exposed localities, and such a leaf would be
unsuitable to withstand the force of the wind in such
situations. From this point of view, the division into
leaflets seems a manifest advantage.

Perhaps it will be said that in some trees the leaves
are much more uniform in size than in others. This
is true. The Sycamore, for instance, varies greatly ;
in the specimen tabulated, the stem was "13 in diameter,
and the area of the six upper leaves was 60 square
inches. In another, the six upper leaves had an area
of rather over 100 inches, but in this case the diameter
of the stem was "18.

Another point is the length of the internode. In
such trees as the Beech, Elm, Hornbeam, &c., the
distance from bud to bud varies comparatively little,
and bears a tolerably close relation to the size of the
leaf. In the Sycamore, Maple, &c., on the contrary,
the length varies greatly.

Now, if, instead of looking merely at a single
leaf, we consider the whole bough of any tree, we

LIME. 103

shall, I think, see the reason of their differences of
form.

Let us begin, for instance, with the common Lime
(Fig. 60). The leaf-stalks .are arranged at an angle of
about 40° with the branch, and the upper surfaces of
the leaves are in the same plane with it. The result
is, they are admirably adapted to secure the maxi-
mum of light and air. Let us take, for instance, the
second or third leaf in Fig. 60. They are 4^ inches long

FIG. 60. — Lime.

and very nearly as broad. The distance between the
two leaves on each side is also just 4! inches, so that
they exactly fill up the interval. In Tilia parvifolia
the arrangement is similar, but leaves and inter-
nodes are both less, the leaves, say \\ inch, and the
internodes '6.

In the Beech, the general plane of the leaves is
again that of the branch (Fig. 61), but the leaves
themselves are ovate in form, and smaller, being only

104 BEECH. NUT. [CHAP.

from 2 to 3 inches in length. On the other hand, the
distance between the internodes is also smaller, being,
say, i£ inch against something less than 2 inches.
The diminution in length of the internode is not,
indeed, exactly in proportion to that of the leaf, but,
on the other hand, the leaf does not make so wide an
angle with the stem. To this position is probably
due the difference of form. The outline of the basal
half of the leaf fits neatly to the branch, that of the
upper half follows the edge of the leaf beyond, and

FIG. 61. — Beech.

the form of the inner edge being thus determined,
decides the outer one also.

In the Nut (Corylus), the internodes are longer
and the leaves correspondingly broader. In the Elm
the ordinary branches have leaves resembling, though
rather larger than, those of the Beech ; but in vigorous
shoots (Ulmus, Fig. 62), the internodes become longer
and the leaves correspondingly broader and larger,
so that they come nearly to resemble those of the
Nut.

But it may be said that the Spanish Chestnut

v.]

ELM. CHESTNUT.

(Castanea vulgaris, Fig. 63) also has alternate leaves
in a plane parallel to that of the branch, and with in-
ternodes of very nearly the same length as the Beech.
That is true ; but, on the other hand, the terminal
branches of the Spanish Chestnut are stouter in pro-
portion. Thus, immediately below the sixth leaf, the
Chestnut stalk may be "15 of an inch in thickness, that

FIG. 62. — Elm

of the Beech not much more than half as much.
Consequently, the Chestnut could, of course supposing
the strength of the wood to be equal, bear a greater
weight of leaf; but, the width of the leaf being de-
termined by the distance between the internodes, the
leaf is, so to say, compelled to draw itself out. In
Fig. 64 I have endeavoured to illustrate this by placing
a spray of Beech over one of Spanish Chestnut.

io6

CHES TNUT. YE W.

[CHAP.

Moreover, not only do the leaves on a single twig thus
admirably fit in with one another, but they are also
adapted to the ramification of the twigs themselves.
Fig. 59 shows a bough of Beech seen from above, and
it will be observed that the form of the leaves is such
that, while but little space is lost, there is scarcely
any over-lapping. Each fits in perfectly with the
rest.

FIG. 63. — Castanea.

FIG. 6 4 — Casianea and Beech.

The leaves of the Yew (Fig. 65) belong to a type
very different from those which we have hitherto been
considering. They are long, narrow, and arranged all
round the stem, but spread right and left, so that
they lie in one plane, parallel to the direction of the
branchlet, and their width bears just such a relation
to their distance apart that when so spread out their
edges almost touch.

The leaves of Conifers are generally narrow and
needle-like. I would venture to suggest that this may
be connected with the greater uniformity in the struc-
ture of the wood as compared with that of Dicoty-

V-]

CONIFERS. BOX,

107

ledons, such as the Beech, Oak, &c. The leaves of
the Scotch Pine (Pinus sylvestris] are needle -like,
i^ inch in length and -Jg- in diameter. They are
arranged in pairs, each pair enclosed at the base in a
sheath. One inch of stem bears about fifteen pairs
of leaves. Given this number of leaves in such a
space, they must evidently be long and narrow. If I

FIG. 65.— Yew.

FIG. 66.— Box.

am asked why they are longer than those of the Yew,
1 would suggest that the stem, being thicker, is able
to support more weight. In confirmation of this, we
may take for comparison the Weymouth Pine, in
which the leaves are much longer and the stalk
thicker.

Fig. 66 represents a sprig of Box. It will be
observed that the increase of width in the leaves

,oS MAPLE. HORSE CHESTNUT. [CHAP.

corresponds closely with the greater distance between
the points of attachment.

When we pass from the species hitherto considered,
to the Maples (Fig. 69), Sycamores, and Horse
Chestnuts (Figs. 67 and 68), we come to a totally
different type of arrangement. The leaves are placed
at right angles to the axis of the branch instead of
being parallel to it, have long petioles, and palmate

FIG. 67.— Horse Chestnut.

instead of pinnate veins. In this group the mode of
growth is somewhat stiff ; the main shoots are per-
pendicular, and the lateral ones nearly at right angles
to them. The buds, also, are comparatively few,
and the internodes, consequently, at greater distances
apart, sometimes as much as a foot, though the two
or three at the end of a branch are often quite short.
The general habit is shown in Figs. 67 and 68. Now,
if we were to imagine six Beech or Elm leaves on these
three internodes, it is obvious that the leaf surface

v.] HORSE CHESTNUT. 109

would be far smaller than it is at present. Again, if
we compare the thickness of an average Sycamore
stem below the sixth leaf, with that of a Beech stern,
it is obvious that there would be a considerable waste
of power. Once more, if the leaves were parallel to
the branch, they would, as the branches are arranged,
be less well disposed with reference to light and air,
A glance at Figs. 67, 68, and 69, however, will show

FIG. 68. — Horse Chestnut.

how beautifully the leaves are adapted to their
changed conditions. The blades of the leaves of the
upper pair form an angle with the leaf-stalks, so as to
assume a horizontal position, or nearly so ; the leaf-
stalks of the second pair decussate with those of the
first, and are just so much longer as to bring up that
pair nearly, or quite, to a level with the first; the
third pair decussate with the second and are again

no MAPLE. [CHAP.

brought up nearly to the same level, and immediately
to the outside of the first pair. In well-grown shoots
there is often a fourth pair on the outside of the
second. If we look at such a cluster of leaves directly
from in front, we shall see that they generally appear
somewhat to overlap ; but it must be remembered
that in temperate regions the sun is never vertical.
Moreover, while alternate leaves are more convenient
in such an arrangement as that of the Beech, where

FlG. 69. — Acer.

there would be no room for a second leaf, it is more
suitable in such cases as the Sycamores and Maples
that the leaves should be opposite, because if, other
things remaining the same, the leaves of the Sycamore
were alternate, the sixth leaf would require an incon-
venient length of petiole.

Perhaps it will be said that the Plane-tree, which has
leaves so like a Maple that one species of the latter
genus is named after it (Acer platanoides, Fig. 69), has,
nevertheless, alternate leaves. In reality, however, I
think this rather supports my argument, because the

v.] PLANE. in

leaves of the Plane, instead of being at right angles to
the stem, lie more nearly parallel with it. Moreover,
as any one can see, the leaves are not arranged so
successfully with reference to exposure as those of the
species we have hitherto been considering, perhaps
because, living as it does in more southern localities,
the economy of sunshine is less important than in
more northern regions.

The shoot of the Horse Chestnut is even stouter
than that of the Sycamore, and has a diameter below
the sixth leaf of no less than f\ of an inch. With this
increase of strength is, I think, connected the greater
size of the leaves, which attain to as much as eighteen
inches in diameter, and this greater size, again, has
perhaps led to the dissection of the leaves into five or
seven distinct segments, each of which has a form
somewhat peculiar in itself, but which fits in admir-
ably with the other leaflets. However this may be,
we have in the Horse Chestnut, as in the Sycamore
and Maples, a beautiful dome of leaves, each standing
free from the rest, and expanding to the fresh air and
sunlight a surface of foliage in proportion to the
stout, bold stem on which they are borne.

Now, if we place the leaves of one tree on the
branches of another, we shall at once see how unsuit-
able they would be. I do not speak of putting a
small leaf such as that of a Beech on a large-leaved
tree such as the Horse Chestnut ; but if we place, for
instance, Beech on Lime, or vice versd, the contrast
is sufficiently striking. The Lime leaves would over-
lap one another, while, on the other hand, the Beech
leaves would leave considerable interspaces. Or let us

112 RELATION OF LEAVES TO BRANCHES. [CH.

in the same way transpose those of the Spanish
Chestnut (Castanea} and those of Acer platanoides,
a species of Maple. I have taken specimens in which
the six terminal leaves of a shoot of the two species
occupy approximately the same area. Figs. 63 and
69 show the leaves in their natural position, those
of the Spanish Chestnut lying along the stalk, while
those of the Maple are ranged round it. In both

FIG. 70. — Leaves pf Castanea.

cases it will be seen that there is practically no over-
lapping and very little waste of space. In the Spanish
Chestnut the stalks are just long enough to give a
certain play to the leaves. In the Maple they are
much longer, bringing the leaves approximately to
the same level, and carrying the lower and outer ones
free from the upper and younger ones.

Now, if we arrange the Spanish Chestnut leaves
round a centre, as in Fig 70, it is at once obvious how

v.] RELATION OF LEAVES TO BRANCHES. 113

much space is wasted. On the other hand, if we
place the leaves of the Maple on the stalk of a
Spanish Chestnut at the points from which the leaves
of Chestnut came off, as in Fig. 71, we shall see that
the stalks are useless, and even mischievous as a
cause of weakness and of waste of space ; while, on
the other hand, if we omit the stalks, or shorten them
to the same length as those of the Chestnut, as in
Fig. 72, the leaves would greatly overlap one another.

FIG. 71. — Maple leaves on Chestnut.

Once more, for leaves arranged as in the Beech the
gentle swell at the base is admirably suited ; but in a
crown of leaves such as those of the Sycamore, space
would be wasted, and it is better that they should ex-
pand at once as soon as their stalks have borne them
free from those within. Moreover, the spreading lobes
leave a triangular space (Fig. 69) with the insertion of
the stalk at the apex which seems as if expressly
designed to leave room for the pointed end of the leaf
within.

114

STRUCTURE OF LEAF.

fCHAP.

Hence we sec how beautifully the whole form of
these leaves is adapted to the mode of growth of the
trees themselves and the arrangement of their buds.

Before we proceed to consider the next series of
species to which I wish to direct attention, it will be
necessary for me to say a few words on the micro-
scopical structure of the leaf. Although so thin, the
leaf consists of several layers of cells. Speaking
roughly, and as a general rule, we may say that on
each side is a thin membrane, or epidermis, underneath

FIG. 72. — Maple leaves on Chestnut.

which on the upper side are one or more layers of
elongated cells known from their form as " pallisade
cells," beneath which is a parenchymatous tissue of
more or less loose texture. The leaf is strengthened
by ribs of woody tissue. From this general type there
are, of course, numerous variations. For instance,
many water plants have no epidermis. The structure
of the leaf has been described in a number of memoirs
by Bonnet, Haberlandt, Areschoug, Stael, Pick, Hein-
richer, Vesque, Tschirch, Hentig, and other writers.

v.] POPLAR. 115

If the surface of the leaf be examined with a
tolerably high power, small opaque spots will be ob-
served, resembling button-holes, with a thick rim or
border composed of two more or less curved cells, the
concavities being turned inwards. When dry, they
are nearly straight, and lie side by side ; but when
moistened they swell, become somewhat curved, and
gape open. It is difficult to realise the immense num-
ber of these orifices, or "stomata" as they are called,
which a single bush or tree must possess when we
remember that there are sometimes many thousand
stomata to a square inch of surface. In a large pro-
portion of herbs the two sides of the leaf are under
conditions so nearly similar that the stomata are al-
most equally numerous on the upper and on the lower
side. In trees, however, as a general rule, they are
found exclusively on the under side of the leaf, which is
the most protected ; they are thus less exposed to the
direct rays of the sun, or to be thoroughly wetted by
rain, so that their action is less liable to sudden and
violent changes.

There are, however, some exceptions ; for instance,
in the black Poplar the stomata are nearly as
numerous on one side of the leaves as on the other.
Now, why is this ? If we compare the leaves of the
black and white Poplar, we shall be at once struck by
the fact that, though these species are so nearly allied,
the leaves are very different. In the white Poplar
(Populus alba), the upper and under sides are very
unlike both in colour and texture, the under side being
thickly clothed with cottony hairs. In the black
Poplar (P. nigra, Fig. 73) the upper and under surfaces

I 2

n6

POPLAR.

[CHAP.

arc, which is not frequent, very similar in colour
and texture. The petioles or leaf-stalks, again, are
unlike ; those of P. nigra presenting the peculiarity
of being much flattened at the end towards the leaf.
The effect of the unusual structure of the petiole is
that the leaf, instead of being horizontal as in the P.
alba and most trees, hangs vertically, and this again
explains the similarity of the two surfaces, because

FIG. 72.— Black Poplar (P. nigra).

the result is that both surfaces are placed under nearly
similar conditions as regards light and air. Again, it
will be observed that, if we attempt to arrange the
leaves of the black Poplar on one plane, they generally
overlap one another ; the extent is larger than can be
displayed without their interfering with one another.
In foliage arranged like that, for instance, of the Beech,
Elm, Sycamore, or, in fact, of most of our trees, this

v.] COMPASS PLANT. 117

would involve a certain amount of waste ; but in
the black Poplar, as Fig. 73 shows, the leaves when
hung in their natural position are quite detached from
one another.

Another interesting case of a species with vertical
leaves is the Prickly Lettuce (Lactuca scariola], while
those of other species of Lettuce (L. muralis and
L. mrosd] are horizontal. With this position of the
leaves is connected another peculiarity, especially
well marked in the so-called " compass " plant of the
American prairies (Silphium laciniatum\ a yellow
Composite not unlike a small Sunflower, and which
is thus named because the leaves turn their edges
north and south. This has long been familiar to the
hunters of the prairies, but was first mentioned by
General Alvord, who called Longfellow's attention
to it, and thus inspired the lines in " Evangeline : "

" Look at this delicate plant, that lifts its head from the meadow,
See how its leaves are turned no th, as true as the magnet ;
This is the compass flower, that the finger of God has planted
Here in the houseless wild to direct the traveller's journey
Over the sea-like,- pathless, limitless waste of the desert."

The advantage of%,this position, and consequently
the probable reasoh for its adoption, is that in con-
sequence of it the two faces of the leaf are about
equally illuminated by th€v sun ; and in connection
with this we find that the structure of the leaf is
unusual in two respects. The stomata are about
equally abundant on both surfaces, while pallisade
cells, which are generally characteristic of the upper
surface, are in this species found on the lower one
also.

ii8 COMPASS PLANT. [CHAP. v.

Stahl and Pick have pointed out that even in the
same species, leaves growing in shade differ somewhat
in these respects from those which are exposed to
bright light.

The leaves of the Prickly Lettuce (Lactuca
scariold) have also, when growing in sunny situations,
a tendency to point north and south. Under such
circumstances also they have a layer of pallisade
cells on each side.

FIG. 74. — Acacia melanoxylon.

CHAPTER VI.

HITHERTO I have dealt with plants in which one
main consideration appears to be the securing as
much light and air as possible. Our English trees
may be said as a general rule to be glad of as much
sun as they can get. But a glance at any shrubbery
is sufficient to show that we cannot explain all leaves
in this manner, and in tropical countries some plants
at any rate find the sun too much for them. I
will presently return to the consideration of other
characteristics of tropical vegetation. In illustration,
however, of the present point, perhaps the clearest
evidence is afforded by some Australian species,
especially the Eucalypti and Acacias. Here the
adaptations which we meet with are directed, not
to the courting, but to the avoidance, of light.

I2O

A US TRALIAN A CA CIA.

[CHAP.

The typical leaves of Acacias are pinnate, with a
number of leaflets. On the other hand, many of the
Australian Acacias have leaves (or, to speak more
correctly, phyllodes) more or less elongated or willow-
like. But if we raise them from seed we find, for
instance, in Acacia salicina, so called from its re-
semblance to a Willow, that the first leaves are
pinnate (Fig. 75), and differ in nothing from those

FIG. 75. — Seedling of Acacia salicina.

characteristic of the genus. In the later ones, how-
ever, the leaflets are reduced in number, and the
leaf-stalk is slightly compressed laterally. The fifth
or sixth leaf, perhaps, will have the leaflets reduced
to a single pair, and the leaf-stalk still more flattened,
while, when the plant is a little older, nothing remains
except the flattened petiole. This in shape, as already
observed, much resembles a narrow willow-leaf but
flattened laterally, so that it carries its edge upwards

vi.] EUCALYPTUS. IVY. 121

and consequently exposes as little surface as possible
to the overpowering sun. In some species the long
and narrow phyllodes carry this still further by hang-
ing downwards, and in such cases they often assume
a scimitar-like form. This I would venture to
suggest may be in consequence of one side being
turned outwards, and therefore under more favourable
conditions.

In one very interesting species (Acacia melan-
oxylon, Fig. 74), the plant throughout life produces
both forms, and on the same bough may be seen
phyllodes interspersed among ordinary pinnate
leaves, the respective advantages being, it would
appear, so equally balanced that sometimes the
one, sometimes the other, secures the predominance.

In the case of the Eucalyptus, every one who has
been in the South of Europe must have noticed
that the young trees have a totally different aspect
from that which they acquire when older. The leaves
of the young trees (Fig. 76) are tongue-shaped, and
horizontal. In older ones, on the contrary (Fig. 77),
they hang more or less vertically, with one edge towards
the tree, and are scimitar-shaped, with the convex
edge outwards, perhaps for the same reason as that
suggested in the case of Acacia. There are several
other cases in which the same plant bears two kinds
of leaves. Thus, in some species of Juniper the
leaves are long and pointed, in others rounded and
scale-like. Juniperus chinensis has both.

In the common Ivy the leaves on the creeping
or climbing stems are more or less triangular, while
those of the flowering stems are ovate lanceolate ; a

122

FALL OF THE LEAF.

[CHAP.

difference, the cause of which has not, I think, yet
been satisfactorily explained, but into which I will
not now enter.

We have hitherto been considering, for the most
part, deciduous trees. It is generally supposed that
in autumn the leaves drop off because they die.
My impression is that most persons would be very
much surprised to hear that this is not altogether

FIG. 75. — Eucalyptus — Young.

FIG. 77.— Eucalyptus— Old.

the case. In fact, however, the separation is a vital
process, and, if a bough is killed, the leaves are not
thrown off, but remain attached to it. Indeed, the
dead leaves not only remain in situ, but they are
still firmly attached. Being dead and withered, they
give the impression that the least shock would detach
them ; on the contrary, however, they will often
bear a weight of as much as two pounds without
coming off.

vi.] LENGTH AND LONGEVITY OF LEAVES. 123

In evergreen species the conditions are in many
respects different from those affecting deciduous
species. When we have an early fall of snow in
autumn the trees which still retain their leaves are
often very much broken down. Hence, perhaps,
the comparative paucity of evergreens in temperate
regions, and the tendency of evergreens to have smooth
and glossy leaves, such as those of the Holly, Box,
and Evergreen Oak. Hairy leaves especially retain
the snow, on which more and more accumulates.

Again, evergreen leaves sometimes remain on the
tree for several years ; for instance, in the Scotch
Pine three or four years, the Spruce and Silver Fir six
or even seven, the Yew eight, Abies pinsapo sixteen
or seventeen, Araucaria and others even longer. It
is true that during the later years they gradually
dry and wither; still, being so long-lived, they
naturally require special protection. They are, as a
general rule, tough, and even leathery. In many
species, again, as is the case with our Holly, they
are spinose. This serves as a protection from brows-
ing animals ; and in this way we can, I think, explain
the curious fact that, while young Hollies have spiny
leaves, those of older trees, which are out of the reach
of browsing animals, tend to become quite unarmed.

In confirmation of this I may also adduce the
fact that while in the Evergreen Oak the leaves on
well-grown trees are entire and smooth-edged like
those of the Laurel, specimens which are cropped
and kept low form scrubby bushes with hard prickly
leaves.1

1 Bunbury, Botanical Fragments, p. 320.

124 EVERGREEN LEAVES. [CHAP.

Mr. Grindon, in his Echoes on Plant and Flower
Life (p. 30), says that " the occurrence of prickles only
here and there among plants shows them to be un-
connected with any general and ruling requirement
of vegetation. We can only fall back upon the
principle laid down at the outset, that they are
illustrations of the unity of design in Nature, leading
us away from the earth to Him who is ' the end of
problems and the font of certainties.' " Surely,
however, it is obvious that the existence of spines
and prickles serves as a protection.

Another point of much importance in the economy
of leaves is the presence or absence of hairs. I have
already observed that most evergreens are glossy and
smooth, and have suggested that this may be an
advantage, as tending to prevent the adherence of
snow, which might otherwise accumulate and break
them down.

The hairs which occur on so many leaves are ot
several different types. Thus, leaves are called silky
when clothed with long, even, shining hairs (Silver
Weed) ; pubescent or downy, when they are clothed
with soft, short hairs (Strawberry) ; pilose, when the
hairs are long and scattered (Herb-robert) ; villous,
when the hairs are rather long, soft, white, and close
(Forget-me-not) ; hirsute, when the hairs are long
and numerous (Rose-campion) ; hispid, when they are
erect and stiff (Borage) ; setose, when they are long,
spreading, and bristly (Poppy); tomentose, when they
are rather short, soft, and matted ; woolly, when long,
appressed, curly, but not matted (Corn-centaury) ;
velvety, when the pubescence is short and soft to the

vi.] FUNCTION OF HAIRS. 125

touch (Foxglove) ; cobwebby, when the hairs are
long, very fine, and interlaced like a cobweb (Thistle,
cobwebby House- leek). The arrangement of the
hairs is also interesting. In some plants there is a
double row of hairs along the stem. In the Chick-
weed only one. This, perhaps, serves to collect rain
and dew, and it is significant that the row of hairs
is always opposite to the flower-stalk, which also has
a single row. Now, the flower-stalk is for a con-
siderable part of its life turned downwards, with the
row of hairs outwards. This, perhaps, may account
for the absence of hairs on that side of the stem.

Many leaves are clothed with woolly hairs while in
the bud, which afterwards disappear. Thus, in the
Rhododendron, Horse Chestnut, and other species, the
young leaves are protected by a thick felt, which
when they expand, becomes detached and drops off.
Many leaves are smooth on the upper side, while
underneath they are clothed with a cottony, often
whitish, felt. This probably serves as a protection
for the stomata. In some cases the hairs probably
tend to preserve the leaves from being eaten. In
others, as Kerner has suggested, they serve to keep off
insects — apparently with the special object of pre-
venting the flowers from being robbed of their honey
by insects which are not adapted to fertilise them.
Fritz Miiller, to whom we are indebted for so many
ingenious observations, gives an interesting case.
The caterpillar of Eunomia eagrus, when about to
turn into the chrysalis (Fig. 78), breaks off its hairs
and fastens them to the twig which it has selected, so
as to form on each side of itself about half a dozen

126 HAIRS AS A PROTECTION. HONEY. [CHAP.

stiff fences, to protect it during its helpless period of
quiescence.

Vaucher long ago observed, though he gave no
reason for the fact, that among the Malvacece
(Mallows) the species which produce honey are hairy,
and those which do not are glabrous.

Is we make a list of our English plants, marking
out which species have honey and which have hairs,
we shall find that we may lay it down as a general
rule that honey and hairs go together. The ex-
ceptions, indeed, are very numerous, but when we

FIG. 78. — Pupa of Eunoinia eagnis.

come to examine them we shall find that they can
generally be accounted for. I have made a rough
list of the species in the English .flora which have
honey and yet are glabrous. It does not profess to be
exactly correct, because there are some species with
reference to which I was unable to ascertain by per-
sonal examination, or by reference to books, whether
they produce honey or not. My list, however, com-
prised no species.

Now, in the first place, in sixty of these no
species the entrance to the honey is so narrow that

vi.] WATER PLANTS OFTEN GLABROUS. 127

even an ant could not force its way in : twenty are
aquatic, and hence more or less protected from the
visits of ants and other creeping insects; thus we
shall frequently find that if, in a generally hairy
genus, one or more species are aquatic, they are also
glabrous — as, for instance, Viola palustris, Veronica
anagailis, V. beccabunga, and Ranunculus aquatilis.
Polygonum amphibium is peculiarly interesting,
because, as Kerner has pointed out, aquatic speci-
mens are glabrous ; while in those living on land the
base of the leaf produces hairs. Half a dozen are
early spring plants which flower before the ants are
roused from their winter sleep ; about the same
number are minute ground plants to which hairs
could be no protection ; three or four are night
flowers ; there still remain a few to be accounted for,
which would have to be considered individually, but
probably the evidence is sufficiently complete to
justify the general inference.

Lastly, I must not omit to mention the hairs which
have a glandular character.

The next point to which I would call attention is
the remarkable manner in which certain forms repeat
themselves. In some cases, there seems much reason
to suppose that one plant derives a substantial ad-
vantage from resembling another. For instance,
Chrysanthemum inodorum, the scentless Mayweed,
very closely resembles the Chamomile in leaves,
flowers, and general habit. The latter species, how-
ever, has a strong, bitter taste, which probably serves
as a protection to it, and of which also, perhaps, the
scentless Mayweed may share the advantage. These

128 STINGING AND DEAD NETTLES. [CHAP.

two species, however, are nearly allied to one another,
and I prefer, therefore, to take as an example of
mimicry the Stinging-nettle ( Urtica) and the common
Dead-nettle (Lamium albittn). These two species
belong to totally different families ; the flowers are
altogether unlike, but the general habit and the
form of the leaves are extremely similar.

How close the similarity is may be seen by the
following illustration (Fig. 79), taken from an excellent

FIG. 79. — Laiiiinm and Urtica.

photograph made for me by Mr. Harman, of Bromley.
The plants on the left are true Stinging-nettles;
those on the right are the white Dead-nettle, one of
which is in flower. So close was the resemblance
that, after getting the photograph, I went back to the
spot on which they were growing to assure myself
that there was no mistake. It cannot be doubted
that the true Nettle is protected by its power of sting-
ing ; and, that being so, it is scarcely less clear that
the Dead-nettle must be protected by its likeness to

vi.] YELLOW BUGLE. 129

the other. Moreover, though I was fortunate in
lighting on so good an illustration as that shown in
the figure just when I had the opportunity of photo-
graphing it, still every one must have observed that
the two species are very commonly found growing
together. Assuming that the ancestor of the Dead-
nettle had leaves possessing a faint resemblance to
those of the true Nettle, those in which the likeness
was greatest would have the best chance of survival,
and consequently of ripening seeds. There would be
a tendency, therefore, according to the well-known
principles of Darwin, to a closer and closer resem-
blance. I am disposed to suggest whether these re-
semblances may not serve as a protection, not only
from browsing quadrupeds, but also from leaf-eating
insects. On this part of the subject we have as yet,
however, I think, no sufficient observations on record.

Ajuga champcBpitys, the yellow Bugle, has leaves
crowded and divided into three linear lobes, the lateral
ones sometimes again divided. They differ, therefore,
greatly from those of its allies, and this puzzled me
much until one day I found it growing abundantly on
the Riviera among Euphorbia cyparissias. and I was
much struck by the curious likeness. The Euphorbia
has the usual acrid juice of the genus, and it struck
me that the yellow Ajuga was perhaps protected by
its resemblance.

Leaves which float on the surface of still water
tend to be orbicular. The water-lilies are a well-
known illustration. I may also mention Limnan-
themim nymphcsoides, which, indeed, is often taken
for a water-lily, though it really belongs to the family

K

1 30 LEAVES OF WATER-PLANTS. [CHAP.

of Gentians, and Alisma natans, a species allied to
the Plantains. In running water, on the contrary,
leaves tend to become more or less elongated.

Subaqueous leaves of fresh-water plants have a
great tendency either to become long and grass-like
or to be divided into more or less hair-like filaments.
I might mention, for instance, Myriophyllum ; Hip-
puris, or Mares-tail, a genus which among English
plants comes next to Circaea, the enchanter's night-
shade, with totally different leaves; Ranunculus
aquatilis, a clos2 ally of the Buttercup ; and many
others.

FIG. 2o. — Ranunculus aquatilis.

Some, again, which, when mature, have rounded,
floating leaves, have long, narrow ones when young.
Thus in Victoria regia the first leaves are filiform, then
come one or more which are sagittate, and lastly
follow the great orbicular leaves.

Another interesting case is that in which the same
species has two forms of leaf (Fig. 80) — namely, more
or less rounded ones on the surface, and a second
series which are subaqueous and composed of more
or less linear or finely-divided segments.

Mr. Grant Allen has suggested that this tendency

vi.] FLOATING AND SUBMERGED LEAVES. 131

to subdivision in subaqueous leaves is due to the
absence or paucity of carbonic acid. I have ventured
to suggest a different explanation. Of course it is
important to expose as large a surface as may be to
the action of the water. We know that the gills of
fish consist of a number of thin plates, which while in
water float apart, but have not sufficient consistence
to support even their own weight, much less any ex-
ternal force, and consequently collapse in air. The
same thing happens with thin, finely-cut leaves. In
still water they afford the greatest possible extent
of surface with the least expenditure of effort in
the formation of skeleton. This is, I believe, the
explanation of the prevalence of this form in sub-
aqueous leaves.

Again, in still air the conditions, except so far as
they are modified by the weight, would approximate
to those of water; but the more the plant is exposed
to wind the more would it require strengthening.
Hence, perhaps, the fact that herbs so much oftener
have finely-cut leaves than is the case with trees. In
the Umbellifers, for instance, almost all the species
have the leaves much divided — more, I need hardly
say, than is the case with trees. Shrubs and trees
are characterised by more or less entire leaves, such
as those of the Laurel, Beech, Hornbeam, Lime, or
by similarly shaped leaflets as in the Ash, Horse
Chestnut, Walnut.

There are, however, many groups of plants, which,
while habitually herbaceous, contain some shrubby
species, or vice versa. Let us take some groups of this
description in which the herbaceous species have their

K 2

132 ENTIRE LEAVES AND SHRUBS. [CHAP.

leaves much cut up, and see what is the character of
the foliage in the shrubby species.

The vast majority of Umbellifers, as I have just ob-
served, are herbaceous, and with leaves much divided,
the common Carrot being a typical example. One
European species, however, Bupleurum fructtcosum,
is a shrub attaining a height of more than six feet,
and has the leaves (Fig. 81) coriaceous, and oblong
lanceolate.

FIG. Zi.—Bnpleurntn fnict'icosmn.

a

The common Groundsel (Fig. 82), again, is a low
herb with much-cut leaves. Some species of Senecio,
however, are shrubby, and the:r leaves assume
totally different character, Senetio laurifolius and 5.
populifolins having, as their specific names denote,
leaves respectively resembling the Laurel and Poplar.
In the genus Oxalis, again, to which the Shamrock
belongs, there is a shrubby species, O. laureola, with
leaves like those of a Laurel.

I would venture, then, to suggest these consideration

VI.]

BROAD AND NARRO W LEA VES.

133

as throwing light on the reason why herbaceous plants
so often have their leaves much cut up.1

Next let me say a few words on the reasons why
some plants have broad and some narrow leaves.
Both are often found within the limits of a single
genus. I have ventured to indicate the distance
between the buds as a possible reason in certain
cases. It would not, however, apply to herbaceous

FIG. 82. — Senecio

genera such as Plantago or Drosera. Now, Drosera
rotundifolia (Fig. 83) has the leaves nearly orbicular,
while in D. anglica (Fig. 84), they are long and narrow,
Plantago media (Fig. 85) has ovate leaves, while in
P. lanceolate (Fig. 86) they are lanceolate, and in

1 Mr. Grant Allen, who had been also struck by the fact that
herbaceous plants so often have their leaves much cut up, has suggested
a different explanation, and thinks it is .due to "the fierce competition
that goes on for the carbon of the air between the small matted under-
growth of every thicket and hedgerow. "

i34 DROSERA AND PLANT AGO. [CHAP.

FIG. 83. — Drosera. rotundijotia.

FIG. 84. — Drosera anglica..

FIG. 85. — Plantago media..

FIG. 86. — Plantago lanieolata.

vi. I DAPHNE. 135

P. maritima nearly linear. More or less similar cases
occur in Ranunculus.

These differences depend, I believe, on the attitude
of the leaf, for it will be found that the broad-leaved
ones are horizontal, forming a rosette more or less
like that of a daisy, while the species with narrower
leaves carry them more or less erect. In the Daisy
the rosette lies on the ground, but in other cases, as
in Daphne (Fig. 87), it is at the end of a branch.

FIG. Zj.—Dafhne

In hot, dry countries the general character of the
vegetation differs from that which prevails in a climate
like ours. There is a marked increase of prickly,
leathery, waxy, and aromatic species. The sap also
in many cases is mucilaginous or somewhat salt,
which probably tends to check evaporation. The
first two characteristics evidently tend to protect the
leaves. As regards the third, Mr. Taylor1 in his
charming book on Flowers, has pointed to the power

1 Page 311.

136 VEGETATION OF DRY REGIONS. [CHAP.

which, as Tyndall has shown, the spray of perfume
possesses to bar out the passage of heat rays, and
has suggested that the emission of essential oils from
the leaves of many plants which live in hot climates
may serve to protect themselves against the intensely
dry heat of the desert sun.

I am rather disposed to think that the aromatic
character of the leaves protects them by rendering it
less easy for animals to eat them.

In still drier regions, such as the Cape of Good
Hope, an unusually large proportion of species are
bulbous. These, moreover, do not belong to any
single group, but are scattered among a large number
of very different families : the bulbous condition
cannot, therefore, be explained by inheritance, but
must have reference to the surrounding circumstances.
Moreover, in a large number of species the leaves
tend to become succulent and fleshy. Now in
organisms of any given form the surface increases as
the square, the mass as the cube, of the dimensions.
Hence, a spherical form, which is so common in
small animals and plants, and which in them offers a
sufficient area of surface in proportion to the mass,
becomes quite unsuitable in larger creatures, and we
find that both animals and plants have orifices leading
from the outside to the interior, and thus giving- an

* o o

additional amount of surface. But in plants which
inhabit very dry countries it is necessary that they
should be able to absorb moisture when opportunity
offers, and store it up for future use. Hence, under
such circumstances fleshy stems and leaves are an
advantage, because the surface exposed to evaporation

vi. j FORMS OF LEAF IN LATHYRUS. 137

is smaller in proportion than it would be in leaves of
the ordinary form. This is, I believe, the reason why
succulent leaves and stems are beneficial in very
dry climates, such as the Canaries, Cape of Good
Hope, &c.

The genus Lathy r us, the wild pea, contains two
abnormal and interesting species in which the
foliaceous organs give the plant an appearance very

FIG. £8. — Lathyrns niger.

FIG. 89. — JLathyrus aphaca.

unlike its congeners. Fig. 88 represents L. niger with
leaves of the ordinary type. In the yellow pea
(L. apJiaca, Fig. 89), the general aspect is very
different, but it will be seen on a closer inspection
that the leaves are really absent, or, to speak more
correctly, are reduced to tendrils, while the stipules,
on the contrary, are, in compensation, considerably
enlarged. They must not, therefore, .be compared

1 38 LA TH YRUS AP HA CA AND N1SSOUA . [CHAP.

with the leaves, but with the stipules of other species,
and from this point of view they are of a more
normal character, the principal difference, indeed,
being in size. It is interesting that the young plant
has one or two leaves composed of a pair of leaflets,
not unlike those of L. niger

FIG. 90. — Lathyrus nissolia.

The grass pea (L. nissolia, Fig. 90) is also a small
species. It lives in meadows and the grassy borders
of fields, and has lost altogether, not only the leaves,
but also the tendrils. Instead, however, of enlarged
stipules, the functions of the leaves are assumed by
the leaf-stalks, which are elongated, flattened, linear,
ending in a fine point, and, in fact, so like the leaves
of the grasses among which the plant lives, that it is
almost impossible to distinguish it except when ip

vi.J LOBSD AND HEART-SHAPED LEAVES. 139

flower. For a weak plant growing among close grass,
a long linear leaf is, perhaps, physically an advantage ;
but one may venture to suggest that the leaves would
be more likely to be picked out and eaten if they
were more easily distinguishable, and that from this
point of view also the similarity of the plant to the
grass among which it grows may also be an advantage.

In looking at foliage I have often been much
puzzled as to why the leaves of some species are
tongue-shaped, while others are lobed. Take, for
instance, the black Bryony (Tamus communis) and
the common Bryony (Bryonia dioicd}. Again, why
are the veins in some leaves pinnate, like those of the
Beech and Elm, and others palmate, as in the Maple
and Sycamore ?

My first idea was that this might have reference to
the arrangement of the woody fibres in the leaf-stalk.
If we make a section of the stalk of a leaf, we shall
find that in some cases the woody fibres are collected
in the middle, while in others there are several distinct
bundles, separated by cellular parenchyma. My first
idea was that each of the primary ribs of a leaf might
represent a separate woody fibre in the leaf-stalk, so
that leaves with a single bundle of woody fibres
would be pinnate ; those with several distinct bundles
palmate.

The first species which I examined favoured this
view. The Melon, Geranium, Mallow, Cyclamen, and
other species with palmate leaves had, sure enough,
several woody fibres; while, on the contrary, the
Laurel, Rhododendron, Privet, Beech, Box, Castanea,
Arbutus, Phillyrea, and other leaves with pinnate

1 40 REASONS FOR THE DIFFERENCE. [CHAP.

veins, had one central bundle. But I soon came
across numerous exceptions, and had to give up the
idea. I then considered whether the difference could
be accounted for by the mode of growth of the leaf,
and I am still disposed to think that it has some
bearing on the subject, though this requires further
study.

The next suggestion which occurred to me was
that it might be connected with the " prefoliation " or
arrangement of the leaves in the bud. The first
palmate leaves which I examined were what is called
" plicate," or folded up more or less like a fan ; while
the leaves with pinnate veins were generally "con-
duplicate," or had the one half applied to the other.
But, though this was true in many cases, it was not a
general rule, and I was obliged to give up this idea
also. It then occurred to me to take climbing plants,
and see whether I could find any relation between
palmate and tongue-shaped leaves on the one hand,
and the mode of growth on the other — whether, for
instance, the one turned generally up, the other down ;
whether the one were generally twining and the other
clasping, or vice versa. All these suggestions one by
one broke down.

Among Monocotyledons, however, the tongue-
shaped preponderates greatly over the palmate form
of leaf. With very few exceptions, the form's of the
leaves of climbing Monocotyledons are in fact just
such as would be obtained by widening more or less
the linear, grass-like leaf which is so prevalent in
the class.

This, then, raises the question whether the heart

VI.]

LEA VES OF SEEDLINGS.

141

shaped leaf is the older form from which the palmate
type has been gradually evolved. Let us see whether
we can find any evidence bearing on this question in
what may be called the embryology of plants. The
Furze, with its spiny prickles, belongs to a group of
plants which, as a general rule, have trifoliate or
pinnate leaves. Now, if we examine a seedling Furze
(Fig. 91), we shall find that the cotyledons are

FIG 91.— FURZE (.Ulex). Seedling.

succeeded by several trifoliate leaves, with ovate
leaflets. These gradually become narrower, more
pointed, and stiffer, thus passing into spines. Hence
we can hardly doubt that the present Furze is
descended from ancestors with trifoliate leaves. I
have already referred to other cases in which the
young plants throw light on the previous condition
of the species (ante, p. 120).

142

CEPHALANDRA.

[CHAP.

Now we shall have no difficulty in finding cases
where, while in mature plants the leaves are more or
less lobed and palmate, the first leaves succeeding the
cotyledons are entire. This would seem to point to
the fact that when in any genus we find heart-shaped
and lobed leaves, the former may represent the earlier
or ancestral condition.

In support of this it will be sufficient here to give
three instances belonging to three distinct families —
namely, Cephalandra palmata (Fig. 92), one of the

FIG. 92 —Cephalandra falmata. Seedlu.g.

Cucurbitaceae ; Hibiscus pedunculatus (Fig. 93), belong-
ing to the Malvaceae ; and, one of the most striking
of all, Passiflora ccerulea (Fig. 94). Other species of
Passiflora show the same passage from entire to
trifid leaves, while on the contrary in P. van Volscenii
even the leaves just following the cotyledons are more
or less divided. The advantage of the palmate form
may perhaps consist in its bringing the centre of
gravity nearer to the point of support.

Broad leaves, moreover, are of two types : cordate,

VI.]

HIBISCUS.

with veins following the curvature of the edge ; and
palmate, or lobed leaves with veins running straight
to the edge. The veins contain vascular bundles
which conduct the nourishment sucked up by the
roots, and it is clearly better that they should hold a
straight course, rather than wind round in a curve.

FIG. 93. — Hibiscus fcduncnlatits. Seedling.

Moreover, as the nourishing fluids pass more rapidly
along these vascular bundles, the leaf naturally grows
there more rapidly, and thus assumes the lobed form,
with a vein running to the point of each lobe.

On the whole, we see, I think, that many at any
rate of the forms presented by leaves have reference
to the conditions and requirements of the plant. If

1 44 EX PLAN A TION OF FORMS OF LEA VES. [CHAP.

there was some definite form told off for each species,
then, surely, a similar rule ought to hold good for
each genus. The species of a genus might well differ

I'IG. 9(.— rassijlora cteruiea. Seedling.

more from one another than the varieties of any
particular species ; the generic type might be, so to
say, less closely limited ; but still there ought to be
some type characteristic of the genus. Let us see
whether this is so. No doubt there are many genera
in which the leaves are more or less uniform, but in

vi.] EXPLANA TION OF FORMS OF LEA VES. 145

them the general habit is also, as a rule, more or less
similar. Is this the case in genera where the various
species differ greatly in habit ? I have already
incidentally given cases which show that this is not
so, but let us take some group — for instance, the
genus Senecio, to which the common Groundsel
(Fig. 82) belongs, as a type well known to all of us
— and look at it a little more closely.

The leaves of the common Groundsel I need not
describe, because they are familiar to us all. This
type occurs in various other species of more or less
similar habit. On the other hand, the fen Senecio
(S. paludosus] and the marsh Senecio (S. pahistris],
which live in marshy and wet places, have long, narrow,
sword-shaped leaves, like those of so many other
plants which are found in such localities. The field
Senecio (S. campestris. Fig. 95), which lives in mea-
dows and pastures, has a small terminal head of
flowers springing from a rosette of leaves much like
those of a common Daisy (Bellis perennis] ; a
Madagascar species, as yet I believe unnamed, is
even more like a Daisy. Senecio junceus looks much
like a Rush ; 5. hypocharideus of South Africa
strikingly resembles a Hypochaeris, as its name denotes.
A considerable number of species attain to a larger
size and become woody, so as to form regular bushes ;
S. biixifolhis has very much the generaUlook of a
Box, 6". vagans of a Privet, .S. laurifolius of a Laurel,
eric&folius of a \\z?A.\\, pinifolius of a Fir, or rather,
a Yew.

Again, some species are climbers ; 5. scandens
and >S. macroglossus have leaves like a Bryony ;

L

i46 TREE SPECIES. SUCCULENT SPECIES. [CHAP.

5. araneosus and 5. tamoides like a smilax or tamus
(Yam) ; 5. tropaolifolius like a tropaeolum.

Among the species inhabiting hot, dry regions are
some with swollen fleshy leaves, such as S. haworthii
from the Cape of Good Hope, and 5. pteroneura,
from Mogador. Senecio rosmarinifolius, of the Cape;
is curiously like a Rosemary or Lavender. Lastly,
some species may almost be called small trees, such

FIG. 95. — Senecio catnpestris.

as 5. populifolius, with leaves like a Poplar ; and
5. amygdaloides, like an Almond.

I might mention, if space permitted, many other
species which, as their names denote, closely resemble
forms belonging to other groups — such, for instance,
as Senecio lobelioides, erysimoides, bupleurioides,
verbascifolius, juniperinus, ilicifolius, acanthifolius,
linifolius, platanifolius, graminifolius, verbenefolius,

vi.] CONCLUSION. 147

rosmarinifolius, coronopifolius, chenopodifolius, lavan-
deriaefolius, salicifolius, mesembryanthemoides, digit-
alifolius,abietinus,arbutifolius,malvaefolius,erodiifolius,
halimifolius, hakeaefolius, resedaefolius, hederaefolius,
acerifolius, plantigineus, castaniaefolius, spiraeifolius,
bryonisefolius, primulifolius, and many more. These
names, however, indicate similarities to over thirty
other perfectly distinct families.

It seems clear, then, that these differences have
reference not to any inherent tendency, but to the
structure and organisation, the habits and require-
ments, of the plant. Of course it may be that the
present form has reference not to existing, but to
ancient, conditions, which renders the problem all the
more difficult. Nor do I at all intend to maintain
that every form of leaf is, or ever has been, necessarily
that best adapted to the circumstances, but only that
they are constantly tending to become so, just as
water always tends to find its own level.

But, however this may be, if my main argument is
correct, it opens out a very wide and interesting field
of study, for every one of the almost infinite forms of
leaves must have some cause and explanation.

THE END.

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