irregular, yellow flowers. Sepals 3 or 5, one forming a wide-mouthed
spur. Petals 5, four of which are united in pairs. Stamens 5. Fruit a
capsule with five elastic valves. (The Balsam Family.)
22. OXALIDACEÆ.--Low herbs, with radical, generally trifoliate leaves;
and axillary, regular flowers. Sepals 5. Petals 5, united at the base.
Stamens 10. Ovary five-celled, with many ovules. (The Wood Sorrel
Family.)
* * * * *
23. CELASTRACEÆ.--Trees or shrubs, with opposite leaves; and small,
regular flowers in axillary cymes. Sepals and petals usually 4. Stamens
usually 4, alternating with the petals. Carpels 4. Fruit a fleshy
capsule. (Spindle Tree.)
24. RHAMNACEÆ.--Shrubs with simple leaves; small, greenish flowers; and
berry-like fruit. Sepals, petals, and stamens 4 or 5. Stamens opposite
the petals. Ovary superior, three-celled, with one ovule in each cell.
(The Buckthorn Family.)
25. LEGUMINOSÆ.--Herbs or shrubs with alternate, stipuled leaves,
generally pinnate or ternate, often tendrilled; and papilionaceous
(butterfly-like) flowers. Sepals 5, combined. Petals 5, irregular.
Stamens generally 10, all, or nine of them united. Ovary superior. Fruit
a pod. (The Pea Family.)
26. ROSACEÆ.--Trees, shrubs, or herbs with alternate, stipuled leaves;
and conspicuous, regular flowers. Sepals 4 or 5. Petals 4 or 5. Stamens
many. Carpels 1, 2, 5, or many. (The Rose Family.)
27. ONAGRACEÆ.--Herbs with mostly entire, simple, exstipulate leaves;
and conspicuous, regular flowers. Sepals 2 to 4. Petals 2 to 4, twisted
in the bud, or absent. Stamens 2 to 4, or 8. Ovary inferior, with
carpels 1 to 6 (usually 4), many-seeded. (The Willow-herb Family.)
28. HALORAGIACEÆ.--Aquatic herbs with whorled leaves and minute flowers.
Sepals 2 to 4 or absent. Petals 2 to 4 or absent. Stamens 1, 2, 4, or 8.
Ovary inferior. Carpels 1 to 4. (The Mare's-tail Family.)
29. LYTHRACEÆ.--Herbs with opposite or whorled, entire leaves; and
conspicuous, regular flowers. Sepals, and petals 3 to 6. Stamens
generally twice as many as petals. Ovary superior. Carpels 2 to 6. Fruit
a many-seeded capsule. (The Loosestrife Family.)
30. TAMARISCACEÆ.--Shrub with minute, scale-like leaves; and lateral
spikes of small, regular flowers. Sepals and petals 4 or 5. Stamens 4 to
10, on the disc. Styles 3. (The Tamarisk.)
31. CUCURBITACEÆ.--Rough, climbing herb, with tendrilled,
palmately-lobed leaves; greenish, dioecious flowers in axillary
racemes; and scarlet berries. Sepals and petals 5, united. Stamens 3.
Ovary inferior. Carpels 3. (The White Bryony.)
32. SAXIFRAGACEÆ.--Shrubs and herbs with regular flowers. Sepals and
petals 4 or 5. Stamens 4 or 10. Carpels 2 or 4, united. (The Saxifrage
Family.)
33. CRASSULACEÆ.--Succulent herbs with simple leaves; and small,
regular, starry flowers. Sepals, petals, and carpels 3 to 20, usually 5.
Stamens twice as many as the petals. Carpels superior, forming
follicles. (The Stonecrop Family.)
34. ARALIACEÆ.--Climbing shrub with clinging rootlets, evergreen leaves,
umbels of yellowish flowers, and black berries. Sepals, petals, stamens,
carpels, and seeds 5 each. Ovary inferior. (The Ivy.)
35. CORNACEÆ.--Herbs and shrubs with opposite leaves, small flowers, and
berry-like fruits. Sepals, petals, and stamens 4 or 5. Ovary inferior.
Carpels 2, each with one ovule. (The Dogwood Family.)
36. UMBELLIFERÆ.--Herbs with mostly compound, pinnate leaves, sheathing
at the base; and compound umbels of small, white flowers. Sepals,
petals, and stamens 5. Ovary inferior. Fruit of two adhering carpels.
(The Parsley Family.)
* * * * *
37. CAPRIFOLIACEÆ.--Shrubs and herbs with opposite leaves, and
conspicuous (sometimes irregular) flowers. Sepals and petals 3 to 5.
Stamens 4 to 10. Fruit a berry. (The Honeysuckle Family.)
38. RUBIACEÆ.--Herbs with whorled leaves; and small, regular flowers.
Sepals, petals, and stamens 4 to 6. Carpels 2. (The Bedstraw Family.)
39. VALERIANACEÆ.--Herbs with opposite leaves and small (sometimes
irregular) flowers. Sepals 3 to 5, often downy. Petals 3 to 5. Stamens 1
or 3. Ovary of three carpels, one-celled. (The Valerian Family.)
40. DIPSACEÆ.--Herbs with opposite leaves; and heads of small flowers,
mostly blue. Calyx enclosed in a whorl of scaly bracts. Petals 4 or 5.
Stamens 4, free. Ovary one-celled and one-seeded. (The Teasel Family.)
41. COMPOSITÆ.--Herbs with heads of small flowers with tubular or
strap-shaped corollas. Calyx absent or represented by a whorl of silky
hairs (pappus). Stamens 4 or 5, anthers generally united. (The Daisy
Family.)
* * * * *
42. CAMPANULACEÆ.--Herbs with milky sap; alternate, entire, scattered
leaves; and usually conspicuous, blue, regular flowers. Sepals, petals,
and stamens 5. Ovary of 2 to 8 carpels. (The Bellflower Family.)
43. VACCINIACEÆ.--Low (mostly mountainous) shrubs, with scattered,
simple, alternate leaves; small drooping, reddish or pink, regular
flowers; and edible berries. Sepals, petals, and carpels 4 or 5. Stamens
8 or 10. (The Cranberry Family.)
* * * * *
44. ERICACEÆ.--Shrubs or herbs with opposite or whorled, evergreen
leaves; and small conspicuous, regular, flowers. Sepals, petals, and
carpels 4 or 5. Stamens 5 to 10. (The Heath Family.)
* * * * *
45. AQUIFOLIACEÆ.--Shrub with evergreen, spiny leaves; and small,
greenish, regular flowers. Sepals, petals, stamens, and carpels 4 or 5.
Fruit berry-like, with one-seeded stones. (The Holly.)
46. OLEACEÆ.--Trees or shrubs with opposite leaves; and small, regular
flowers. Sepals and petals 4, sometimes absent. Stamens 2. Fruit a berry
or a samara. (The Olive Family.)
47. APOCYNACEÆ.--Slender, prostrate shrubs, with milky sap; opposite,
evergreen, entire leaves; and conspicuous, regular, purple flowers.
Sepals, petals, and stamens 5. Corolla salver-shaped. (The Periwinkle
Family.)
48. GENTIANACEÆ.--Bitter herbs with opposite, simple, entire leaves; and
regular, conspicuous flowers. Sepals, petals, and stamens 4 to 10.
Carpels 2. Fruit a capsule. (The Gentian Family.)
49. CONVOLVULACEÆ.--Herbs, generally twining, with alternate, simple
leaves (sometimes absent); and mostly conspicuous, regular flowers.
Sepals, petals, and stamens 4 or 5. Ovary two-or four-celled. Fruit a
four-seeded capsule. (The Bindweed Family.)
50. SOLANACEÆ.--Herbs or shrubs with alternate leaves, and axillary
cymes of regular flowers. Sepals, petals, and stamens 5. Ovary
two-celled. Fruit berry-like or a capsule, many seeded. (The Nightshade
Family.)
51. SCROPHULARIACEÆ.--Herbs with mostly irregular, lipped flowers.
Sepals and petals 4 or 5. Stamens 2, or 4, two longer than the others.
Carpels 2. Fruit a many-seeded capsule. (The Figwort Family.)
52. OROBANCHACEÆ.--Fleshy, brown, parasitic plants, with scattered
scale-leaves; and mostly brownish, irregular flowers. Sepals 4 or 5.
Petals 5, lipped. Stamens 4, two longer than the others. Carpels 2.
Fruit a one-chambered, many-seeded capsule. (The Broom-rape Family.)
53. VERBENACEÆ.--An erect, branched herb, with opposite leaves; and a
compound spike of small, irregular flowers. Sepals and petals 5. Corolla
lipped. Stamens 4, two longer than the others. Ovary four-celled. Fruit
of 4 nutlets. (The Vervain.)
54. LABIATÆ.--Herbs, mostly aromatic, with square stems, opposite
leaves, and whorls or cymes of irregular flowers. Sepals and petals 5.
Corolla usually lipped. Stamens 4 (rarely 2), two longer than the
others. Fruit of 4 one-seeded nutlets. (The Dead Nettle Family.)
55. BORAGINACEÆ.--Herbs, mostly rough, with alternate, simple leaves;
and spikes of conspicuous, regular flowers. Sepals, petals, and stamens
5. Carpels 2. Fruit of 4 one-seeded nutlets. (The Borage Family.)
56. LENTIBULARIACEÆ.--Insectivorous, marsh herbs, with radical, entire
leaves, or much-divided floating leaves with bladders; and conspicuous,
irregular flowers. Sepals and petals 5. Corolla usually lipped. Stamens
2. Fruit a one-chambered, many-seeded capsule. (The Butterwort Family.)
57. PRIMULACEÆ.--Herbs, mostly with radical leaves; and conspicuous,
regular flowers. Sepals, petals, and stamens 4 to 9. Stamens opposite
the petals. Ovary one-celled, with free central placenta. Fruit a
many-seeded capsule. (The Primrose Family.)
58. PLUMBAGINACEÆ.--Herbs, mostly maritime, with radical or alternate
leaves; and mostly blue, regular flowers. Sepals, petals, and stamens 5.
Stamens opposite the petals, and usually free. Carpels 3 to 5. Ovary
one-celled and one-seeded. (The Thrift Family.)
59. PLANTAGINACEÆ.--Herbs with (generally) simple, entire, radical
leaves; and spikes of greenish flowers. Sepals, petals, and stamens 4.
Corolla scaly. Carpels usually 2 or 4. Fruit a one-to four-chambered
capsule. (The Plantain Family.)
_Note._--_Plants in which calyx or corolla are, or appear to be, absent
occur in orders_ 1, 6, 14, 26, 27, 28, 29, and 32.
* * * * *
60. AMARANTHACEÆ.--A smooth, prostrate herb, with scattered, stalked,
exstipulate, simple leaves; and small, axillary, green, monoecious
flowers. Sepals and stamens 3 to 5. (The Amaranth.)
61. CHENOPODIACEÆ.--Herbs with simple, exstipulate leaves, or leafless,
jointed stems; and small green flowers. Sepals 3 to 5, persistent.
Stamens 1 to 5, opposite the sepals. Fruit indehiscent. (The Goosefoot
Family.)
62. POLYGONACEÆ.--Herbs with sheathing stipules; alternate, simple
leaves; and small flowers. Sepals 3 to 6, green or coloured, usually
persistent. Stamens 5 to 8. Fruit indehiscent. (The Dock Family.)
63. ELEAGNACEÆ.--A shrub with silvery scales; alternate, entire,
exstipulate leaves; and inconspicuous, dioecious flowers. Sepals 2 to
4, persistent. Stamens 4. Fruit berry-like. (The Sea Buckthorn.)
64. THYMELACEÆ.--Shrubs with tough inner bark; simple, entire,
exstipulate leaves; and conspicuous, perfect, sweet-scented flowers.
Sepals 4. Stamens 8. Fruit berry-like. (The Spurge Laurel Family.)
* * * * *
65. LORANTHACEÆ.--A green, parasitic, much branched shrub, with
opposite, simple, entire leaves; inconspicuous, dioecious flowers; and
whitish viscid berries. Sepals and stamens 4. Ovary one-chambered. Berry
one-seeded. (The Mistletoe.)
66. ARISTOLOCHIACEÆ.--Herbs and climbing shrubs, with alternate leaves
and perfect flowers. Sepals 2 or 3, sometimes coloured, sometimes
lipped. Ovary with 4 to 6 chambers, containing many ovules. (The
Birthwort Family.)
67. SANTALACEÆ.--A slender, prostrate, root-parasite, with alternate,
linear leaves; and inconspicuous, perfect flowers. Sepals and stamens 4
or 5. Ovary one-celled. Fruit dry, one-seeded. (The Bastard Toad-flax.)
* * * * *
68. EMPETRACEÆ.--A mountain, evergreen, resinous shrub, with alternate,
narrow leaves; and inconspicuous, dioecious flowers. Perianth of 6
scales. Stamens 3. Ovary of 3 to 9 cells, with one ovule in each cell.
(The Crowberry.)
69. EUPHORBIACEÆ.--Trees, shrubs, or herbs, generally with a milky sap;
simple, entire leaves; and small, inconspicuous flowers, sometimes
enclosed in calyx-like bracts. Perianth of 3 or 4 parts, or absent.
Stamens 1 or many. Fruit separating into 2 or 3 carpels elastically.
(The Spurge Family.)
70. URTICACEÆ.--Herbs, often with simple, stinging leaves; and small,
green, clustered, unisexual flowers. Stamens 4 or 5, opposite the
sepals. Ovary superior, one-celled. Fruit indehiscent. (The Nettle
Family.)
71. ULMACEÆ.--Trees with alternate, distichous leaves, and perfect
flowers. Perianth of 4 or 5 parts, bell-shaped. Stamens 4 or 5. Ovary
superior, with one or two cells. Fruit a thin, one-seeded samara. (The
Elm Family.)
* * * * *
72. CUPULIFERÆ.--Trees or shrubs with alternate, stipuled, simple
leaves; and small, green flowers. Perianth of 5 or 6 parts. Stamens 5 to
20. Fruit a nut, enclosed in a tough cupule. (The Oak Family.)
73. BETULACEÆ.--Trees or shrubs with alternate leaves and small flowers.
Stamens 1 or more. Fruit small, indehiscent, winged, not enclosed in a
cup. (The Birch Family.)
74. SALICACEÆ.--Trees with alternate, simple leaves; and flowers which
generally appear before the leaves. Stamens one or more to each scale.
Fruit many-seeded, not enclosed in a cup. (The Willow Family.)
75. MYRICACEÆ.--A small aromatic shrub, with alternate, simple leaves;
and inconspicuous flowers. Stamens 4 to 8. Fruit a drupe. (The Bog
Myrtle.)
76. CONIFERÆ.[1]--Shrubs or trees with rigid evergreen, linear leaves;
and resinous juices. Male flowers in catkins. Female flowers generally
in cones. Seeds not enclosed in an ovary. (The Pine Family.)
[1] The members of the Pine family do not really belong to the
Dicotyledons, although their stems increase in thickness in the same way
as those of our other trees and shrubs. They belong to the _Gymnosperms_
(naked-seeded group), in which the seeds are not produced in ovaries;
but it is more convenient, for our present purpose, to place them near
our other forest trees.
* * * * *
77. ORCHIDACEÆ.--Herbs mostly with tuberous roots, and conspicuous,
irregular, perfect flowers in spikes or racemes. Sepals, petals, and
carpels 3. Stamens 1 or 2, united to the style. (The Orchid Family.)
78. IRIDACEÆ.--Herbs with fleshy, underground stems; narrow leaves; and
handsome, irregular, perfect flowers. Perianth of 6 parts. Stamens and
carpels 3. Ovary 3-celled. Fruit a many-seeded capsule with three
valves. (The Iris Family.)
79. AMARYLLIDACEÆ.--Herbs with bulbs, narrow leaves, and handsome,
regular, perfect flowers. Perianth of 6 parts. Stamens 6. Ovary
3-celled. Fruit a 3-valved capsule. (The Narcissus Family.)
80. HYDROCHARIDACEÆ.--Aquatic herbs, with floating or submerged leaves;
and conspicuous, regular, dioecious flowers. Sepals and petals 3.
Stamens 3 to 12. Carpels 3 or 6. Fruit a berry. (The Frog-bit Family.)
* * * * *
81. DIOSCORIACEÆ.--A climbing herb, with broad, glossy leaves; and
small, monoecious flowers. Sepals, petals, and carpels 3. Stamens 6.
Ovary 3-celled. Fruit a berry. Seeds 6. (The Black Bryony.)
* * * * *
82. LILIACEÆ.--Herbs with mostly narrow leaves, and conspicuous,
regular, perfect flowers. Perianth of 6 parts, Stamens 6. Ovary
3-celled. Fruit a berry or capsule. (The Lily Family.)
83. ALISMACEÆ.--Aquatic plants with radical, net-veined leaves; and
conspicuous, white, perfect flowers. Perianth of 6 parts. Stamens 6 or
more. Carpels numerous, and distinct or nearly so. (The Water-plantain
Family.)
84. NAIDACEÆ.--Aquatic plants with mostly floating or submerged leaves;
and inconspicuous flowers. Perianth of 4 to 6 scales, or absent. Stamens
and carpels 1 to 6. (The Pond-weed Family.)
85. LEMNACEÆ.--Minute floating plants, with green, cellular fronds,
rarely flowering. Flowers very small, enclosed in a bract. Stamen 1.
Ovary one-celled. Ovules 1 to 7. (The Duckweed Family.)
86. ARACEÆ.--Herbs with net-veined, radical leaves; and small flowers on
a fleshy spadix enclosed in a leafy sheath. Perianth of 6 parts, or
absent. Stamens 1 to 6. Ovary of one to three cells. Fruit berry-like.
(The Cuckoo Pint Family.)
87. TYPHACEÆ.--Erect marsh plants, with long, narrow leaves; and small
monoecious flowers in conspicuous spikes or heads. Perianth absent.
Stamens many. Fruit a one-seeded drupe. (The Reed-mace Family.)
88. JUNCACEÆ.--Rush-like herbs, with cylindrical or narrow leaves, and
small, brown flowers. Perianth membranous, of 6 parts. Stamens 6.
Carpels 3. Fruit a 3-valved capsule. (The Rush Family.)
* * * * *
89. CYPERACEÆ.--Grassy herbs, with usually solid, triangular stems; and
linear leaves, with tubular sheaths. Flowers in spikelets, unisexual or
perfect. Stamens 1 to 3. Carpels and stigmas 2 or 3. (The Sedge Family.)
90. GRAMINEÆ.--Grassy herbs, with hollow stems; and linear leaves, with
split sheaths. Flowers usually perfect. Stamens usually 3. Stigmas 1 or
2. (The Grass Family.)
II
THE POLLINATION AND FERTILISATION OF FLOWERS
Since flowers are the reproductive organs of the plant it seems only
natural to suppose that the wonderful variety of colour and form which
they exhibit might have some connexion with the processes concerned in
the propagation of their respective species, and the more we study the
nature of the flowers and observe the methods by which pollen is
transferred from stamens to stigmas, the stronger becomes our conviction
that the diversities mentioned are all more or less connected with the
one great function of reproduction.
This being the case, we propose to devote a short chapter to a simple
account of the uses of the parts of a flower, and to the various
contrivances on the part of the plant to secure the surest and best
means of perpetuating the species.
It has already been stated that the stamens produce pollen cells, and
that the ovary contains one or more ovules. As soon as the anthers are
mature, they open and set free the pollen cells they contained. A stigma
is said to be mature when it exposes a sticky surface to which pollen
cells may adhere, and on which these cells will grow. When a pollen cell
has been transferred to such a stigma, it is nourished by the fluid
secreted by the latter, and sends out a slender, hollow filament (the
pollen tube) which immediately begins to descend through the stigma, and
through the style, if any, till it reaches the ovary.
[Illustration: POLLEN CELLS THROWING OUT THEIR TUBES]
Should the reader desire to watch the growth of the pollen tubes, he can
easily do so by shaking some pollen cells (preferably large ones, such
as those of some lilies) on to a solution of sugar, and watching them at
intervals with the aid of a lens. In the course of a few hours the
pollen tubes will be seen to protrude, and these eventually grow to a
considerable length.
In order that the ovules of a flower may develop into seeds, it is
necessary that they become impregnated by pollen from the anthers of the
same species, and this is brought about in the following manner: The
pollen cells having been transferred by some means to the mature stigma,
they adhere to the surface of the latter, and, deriving their
nourishment from the secretion of the stigmatic cells, as above
described, proceed to throw out their tubes. These tubes force their way
between the cells of the stigma and style, and enter the ovary. Each
tube then finds its way to one of the ovules, which it enters by means
of a minute opening in its double coat called the micropyle, penetrates
the embryo-sac, and reaches the ovum or egg-cell. The ovule is now
impregnated or fertilised, and the result is that the ovum divides and
subdivides into more and more cells till at last an embryo plant is
built up. The ovule has thus become a seed, and its further development
into a mature plant depends on its being transferred to a suitable soil,
with proper conditions as to heat and moisture.
If the flower concerned is a perfect one, and the ovules are impregnated
by pollen from its own anthers, it is said to be self-fertilised; but if
the pollen cells that fertilise the ovules have been transferred from a
distinct flower, it is said to be cross-fertilised.
Now, it has been observed that although self-fertilisation will give
rise to satisfactory results in some instances, producing seeds which
develop into strong offspring, cross-fertilisation will, as a rule,
produce better seeds. In fact, self-fertilisation is not at all common
among flowers, and the pollen has frequently no effect unless it has
been transferred from another flower. In a few cases it has been found
that the pollen even acts as a poison when it is deposited on the stigma
of the same flower, causing it to shrivel up and die. In many instances
the structure and growth of the flower is such that self-pollination is
absolutely impossible; and where it is possible the seedlings resulting
from the process are often very weak.
It has already been hinted that the wonderful variety of form and colour
exhibited by flowers has some connexion with this important matter of
the transfer of pollen, and the reader who is really interested in the
investigation of the significance of this great diversity will find it a
most charming study to search into the advantages (to the flower) of
the different peculiarities presented, especially if he endeavours to
confirm his conclusions by direct observations of the methods by which
the pollen cells are distributed to the stigmas.
Pollen cells are usually distributed either by the agency of the wind or
by insects; and it is generally easy to determine, by the nature of the
flower itself, which is the method peculiar to its species.
A wind-pollinated flower is generally very inconspicuous. It produces no
nectar, which forms the food of such a large number of insects, and has
no gaudy perianth, nor does it emit any odour such as would be likely to
attract these winged creatures. Its anthers generally shed an abundance
of pollen, to compensate for the enormous loss naturally entailed in the
wasteful process of wind-distribution, and the pollen is so loosely
attached that it is carried away by the lightest breeze. Further, the
anthers are never protected from the wind, but protrude well out of the
flower; and the stigma or stigmas, which are also exposed, have a
comparatively large area of sticky surface, and are often hairy or
plumed in such a manner that they form effectual traps for the capture
of the floating pollen cells.
An insect-pollinated flower, on the other hand, has glands (_nectaries_)
for the production of nectar, and its perianth is usually of such a
conspicuous nature that it serves as a signal to attract the insects to
the feast. (In some instances the individual flowers are very small, but
these are generally produced in such clusters that they become
conspicuous through their number.) Often it emits a scent which assists
in guiding the insects to their food. Its stamens are generally so well
protected by the perianth that the pollen is not likely to be removed
except by the insects that enter the flower; and the supply of pollen is
usually not so abundant as in the wind-pollinated species, for the
insects, travelling direct from flower to flower, convey the cells with
greater economy. The stigmas, too, are generally smaller, and are
situated in such a position that, when mature, they are rubbed by that
portion of the insect's body which is already dusted with pollen.
As we watch the nectar-feeding insects at work, we not only observe that
the flowers they visit possess the general characters given above as
common to the insect-pollinated species, but also that, in many
instances, the structure of the flower is such that the transfer of
pollen from anthers to stigma could only be accomplished by the
particular kind of insect which it feeds. Various contrivances are also
adopted by many flowers to attract the insects which are most useful to
them, and to exclude those species which would deprive them of nectar
and pollen without aiding in the work of pollination. Thus, some flowers
are best pollinated by the aid of certain nocturnal insects, which they
attract at night by the expansion of their pale-coloured corollas and by
the emission of fragrant perfumes. These close their petals by day in
order to economise their stores and protect their parts from injury
while their helpers are at rest. Others require the help of day-flying
insects: these are expanded while their fertilisers are on the wing, and
sleep throughout the night.
We do not propose to give detailed accounts of the various stratagems by
which flowers secure the aid of insects in this short chapter. Several
examples are given in connexion with the descriptions of flowers in
subsequent pages, but a few typical instances, briefly outlined here,
will give the reader some idea of features which should be observed as
flowers are being examined.