Various - "The Good Housekeeping Marriage Book"

Ben Field - "Exciting Adventures of Mister Robert Robin"

Franklin Beech - "The Dyeing of Woollen Fabrics"

Richard F. Burton - "The Book of the Thousand Nights and a Night, Volume 7"

Annual Bibliography of Commonwealth Literature 2007
This paper argues that discourses of love in Ghanaian market literature for youth offer a view into complex negotiations of agency and empowerment. Drawing on Deborah Durham's notion of youth as "social `shifters'" and Francis Nyamnjoh's conception of the "interconnectedness" of agency, I take Ghanaian market literature as one specific case of how African literature for youth foregrounds questions of continuity and change as African societies enter into increasingly complex global relations. In this literature for youth, received notions of love, often constructed out of impressions from American pop and hip hop music, carry new notions of agency that compete with existing "domesticated" forms. Authors like Ike Tandoh and Evelyn Tay employ discourses of love to offer youth alternative avenues for empowerment in a context of socio-economic disenfranchizement. In a creative process of "straddling", this writing both reveals and reproduces the contradictions that obtain in youth configurations of agency.

Elements of Structural and Systematic Botany

D >> Douglas Houghton Campbell >> Elements of Structural and Systematic Botany







CHAPTER XIX.

CLASSIFICATION OF DICOTYLEDONS (_Continued_).


DIVISION II.--_Sympetalae_.

The _Sympetalae_ or _Gamopetalae_ are at once distinguished from the
_Choripetalae_ by having the petals more or less united, so that the
corolla is to some extent tubular. In the last order of the
_Choripetalae_ we found a few examples (_Mimosaceae_) where the same
thing is true, and these form a transition from the _Choripetalae_ to
the _Sympetalae_.

There are two great divisions, _Isocarpae_ and _Anisocarpae_. In the
first the carpels are of the same number as the petals and sepals; in
the second fewer. In both cases the carpels are completely united,
forming a single, compound pistil. In the _Isocarpae_ there are usually
twice as many stamens as petals, occasionally the same number.

There are three orders of the _Isocarpae_, viz., _Bicornes_,
_Primulinae_, and _Diospyrinae_. The first is a large order with six
families, including many very beautiful plants, and a few of some
economic value. Of the six families, all but one (_Epacrideae_) are
represented in the United States. Of these the _Pyrolaceae_ includes
the pretty little pyrolas and prince's-pine (_Chimaphila_) (Fig. 116,
_J_); the _Monotropeae_ has as its commonest examples, the curious
Indian-pipe (_Monotropa uniflora_), and pine-sap (_M. hypopitys_)
(Fig. 116, _L_). These grow on decaying vegetable matter, and are
quite devoid of chlorophyll, the former species being pure white
throughout (hence a popular name, "ghost flower"); the latter is
yellowish. The magnificent rhododendrons and azaleas (Fig. 116, _F_),
and the mountain laurel (_Kalmia_) (Fig. 116, _I_), belong to the
_Rhodoraceae_. The heath family (_Ericaceae_), besides the true heaths
(_Erica_, _Calluna_), includes the pretty trailing-arbutus or
may-flower (_Epigaea_), _Andromeda_, _Oxydendrum_ (Fig. 116, _E_),
wintergreen (_Gaultheria_), etc. The last family is represented by the
cranberry (_Vaccinium_) and huckleberry (_Gaylussacia_).

[Illustration: FIG. 116.--Types of _Isocarpous sympetalae_
(_Bicornes_). _A_, flowers, fruit, and leaves of huckleberry,
_Gaylussacia_ (_Vaccinieae_), x 1. _B_, vertical section of the flower,
x 3. _C_, a stamen: i, from in front; ii, from the side, x 4. _D_,
cross-section of the young fruit, x 2. _E_, flower of sorrel-tree,
_Oxydendrum_ (_Ericaceae_), x 2. _F_, flower of azalea (_Rhododendron_),
x 1/2. _G_, cross-section of the ovary, x 3. _H_, diagram of the flower.
_I_, flower of mountain laurel (_Kalmia_), x 1. _J_, prince's-pine,
_Chimaphila_ (_Pyrolaceae_), x 1/2. _K_, a single flower, x 1. _L_, plant
of pine-sap, _Monotropa_, (_Monotropeae_), x 1/2. _M_, section of a
flower, x 1.]

The second order, the primroses (_Primulinae_), is principally
represented in the cooler parts of the world by the true primrose
family (_Primulaceae_), of which several familiar plants may be
mentioned. The genus _Primula_ includes the European primrose and
cowslip, as well as two or three small American species, and the
commonly cultivated Chinese primrose. Other genera are _Dodecatheon_,
of which the beautiful shooting-star (_D. Meadia_) (Fig. 117, _A_) is
the best known. Something like this is _Cyclamen_, sometimes
cultivated as a house plant. The moneywort (_Lysimachia nummularia_)
(Fig. 117, _D_), as well as other species, also belongs here.

[Illustration: FIG. 117.--_Isocarpous sympetalae_ (_Primulinae_,
_Diospyrinae_). _A_, shooting-star, _Dodecatheon_ (_Primulaceae_), x 1/2.
_B_, section of a flower, x 1. _C_, diagram of the flower. _D_,
Moneywort, _Lysimachia_ (_Primulaceae_), x 1/2. _E_, a perfect flower of
the persimmon, _Diospyros_ (_Ebenaceae_), x 1. _F_, the same, laid open:
section of the young fruit, x 2. _H_, longitudinal section of a ripe
seed, x 1. _em._ the embryo. _I_, fruit, x 1/2.]

The sea-rosemary (_Statice_) and one or two cultivated species of
plumbago are the only members of the plumbago family (_Plumbagineae_)
likely to be met with. The remaining families of the _Primulinae_ are
not represented by any common plants.

The third and last order of the _Isocarpous sympetalae_ has but a
single common representative in the United States; viz., the persimmon
(_Diospyros_) (Fig. 117, _E_). This belongs to the family _Ebenaceae_,
to which also belongs the ebony a member of the same genus as the
persimmon, and found in Africa and Asia.

The second division of the _Sympetalae_ (the _Anisocarpae_) has usually
but two or three carpels, never as many as the petals. The stamens are
also never more than five, and very often one or more are abortive.

[Illustration: FIG. 118.--Types of _Anisocarpous sympetalae_
(_Tubiflorae_). _A_, flower and leaves of wild phlox (_Polemoniaceae_),
x 1/2. _B_, section of a flower, x 1. _C_, fruit, x 1. _D_, flower of
blue valerian (_Polemonium_), x 1. _E_, flowers and leaf of
water-leaf, _Hydrophyllum_ (_Hydrophyllaceae_), x 1/2. _F_, section of a
flower, x 1. _G_, flower of wild morning-glory, _Convolvulus_
(_Convolvulaceae_), x 1/2. One of the bracts surrounding the calyx and
part of the corolla are cut away. _H_, diagram of the flower. _I_, the
fruit of a garden morning-glory, from which the outer wall has fallen,
leaving only the inner membranous partitions, x 1. _J_, a seed, x 1.
_K_, cross-section of a nearly ripe seed, showing the crumpled embryo,
x 2. _L_, an embryo removed from a nearly ripe seed, and spread out;
one of the cotyledons has been partially removed, x 1.]

The first order (_Tubiflorae_) has, as the name indicates, tubular
flowers which show usually perfect, radial symmetry (_Actinomorphism_).
There are five families, all represented by familiar plants. The first
(_Convolvulaceae_) has as its type the morning-glory (_Convolvulus_)
(Fig. 118, _G_), and the nearly related _Ipomoeas_ of the gardens. The
curious dodder (_Cuscuta_), whose leafless, yellow stems are sometimes
very conspicuous, twining over various plants, is a member of this
family which has lost its chlorophyll through parasitic habits. The
sweet potato (_Batatas_) is also a member of the morning-glory family.
The numerous species, wild and cultivated, of phlox (Fig. 118, _A_),
and the blue valerian (_Polemonium_) (Fig. 118, _D_), are examples of
the family _Polemoniaceae_.

[Illustration: FIG. 119.--_Anisocarpous sympetalae_ (_Tubiflorae_). _A_,
inflorescence of hound's-tongue, _Cynoglossum_ (_Borragineae_), x 1/2.
_B_, section of a flower, x 2. _C_, nearly ripe fruit, x 1. _D_,
flowering branch of nightshade, _Solanum_ (_Solaneae_), x 1/2. _E_, a
single flower, x 1. _F_, section of the flower, x 2. _G_, young fruit,
x 1. _H_, flower of _Petunia_ (_Solaneae_), x 1/2. _I_, diagram of the
flower.]

The third family (_Hydrophyllaceae_) includes several species of
water-leaf (_Hydrophyllum_) (Fig. 118, _E_) and _Phacelia_, among our
wild flowers, and species of _Nemophila_, _Whitlavia_ and others from
the western states, but now common in gardens.

The Borage family (_Borragineae_) includes the forget-me-not
(_Myosotis_) and a few pretty wild flowers, _e.g._ the orange-flowered
puccoons (_Lithospermum_); but it also embraces a number of the most
troublesome weeds, among which are the hound's-tongue (_Cynoglossum_)
(Fig. 119, _A_), and the "beggar's-ticks" (_Echinospermum_), whose
prickly fruits (Fig. 119, _C_) become detached on the slightest
provocation, and adhere to whatever they touch with great tenacity.
The flowers in this family are arranged in one-sided inflorescences
which are coiled up at first and straighten as the flowers expand.

The last family (_Solaneae_) includes the nightshades (_Solanum_)
(Fig. 119, _D_), to which genus the potato (_S. tuberosum_) and the
egg-plant (_S. Melongena_) also belong. Many of the family contain a
poisonous principle, _e.g._ the deadly nightshade (_Atropa_), tobacco
(_Nicotiana_), stramonium (_Datura_), and others. Of the cultivated
plants, besides those already mentioned, the tomato (_Lycopersicum_),
and various species of _Petunia_ (Fig. 119, _H_), _Solanum_, and
_Datura_ are the commonest.

The second order of the _Anisocarpae_ consists of plants whose flowers
usually exhibit very marked, bilateral symmetry (_Zygomorphism_). From
the flower often being two-lipped (see Fig. 120), the name of the
order (_Labiatiflorae_) is derived.

Of the nine families constituting the order, all but one are
represented within our limits, but the great majority belong to two
families, the mints (_Labiatae_) and the figworts (_Scrophularineae_).
The mints are very common and easily recognizable on account of their
square stems, opposite leaves, strongly bilabiate flowers, and the
ovary splitting into four seed-like fruits (Fig. 120, _D_, _F_).

The great majority of them, too, have the surface covered with
glandular hairs secreting a strong-scented volatile oil, giving the
peculiar odor to these plants. The dead nettle (_Lamium_) (Fig. 120,
_A_) is a thoroughly typical example. The sage, mints, catnip,
thyme, lavender, etc., will recall the peculiarities of the family.

The stamens are usually four in number through the abortion of one of
them, but sometimes only two perfect stamens are present.

[Illustration: FIG. 120.--_Anisocarpous sympetalae_ (_Labiatiflorae_).
_A_, dead nettle, _Lamium_, (_Labiatae_), x 1/2. _B_, a single flower,
x 1. _C_, the stamens and pistil, x 1. _D_, cross-section of the
ovary, x 2. _E_, diagram of the flower; the position of the absent
stamen is indicated by the small circle. _F_, fruit of the common
sage, _Salvia_ (_Labiatae_), x 1. Part of the persistent calyx has been
removed to show the four seed-like fruits, or nutlets. _G_, section of
a nutlet, x 3. The embryo fills the seed completely. _H_, part of an
inflorescence of figwort, _Scrophularia_ (_Scrophularineae_), x 1. _I_,
cross-section of the young fruit, x 2. _J_, flower of speedwell,
_Veronica_ (_Scrophularineae_), x 2. _K_, fruit of _Veronica_, x 2.
_L_, cross-section of _K_. _M_, flower of moth-mullein, _Verbascum_
(_Scrophularineae_), x 1/2. _N_, flower of toad-flax, _Linaria_
(_Scrophularineae_), x 1. _O_, leaf of bladder-weed, _Utricularia_
(_Lentibulariaceae_), x 1. _x_, one of the "traps." _P_, a single trap,
x 5.]

The _Scrophularineae_ differ mainly from the _Labiatae_ in having round
stems, and the ovary not splitting into separate one-seeded fruits.
The leaves are also sometimes alternate. There are generally four
stamens, two long and two short, as in the labiates, but in the
mullein (_Verbascum_) (Fig. 120, _M_), where the flower is only
slightly zygomorphic, there is a fifth rudimentary stamen, while in
others (_e.g._ _Veronica_) (Fig. 120, _J_) there are but two stamens.
Many have large, showy flowers, as in the cultivated foxglove
(_Digitalis_), and the native species of _Gerardia_, mullein,
_Mimulus_, etc., while a few like the figwort, _Scrophularia_
(Fig. 120, _H_), and speedwells (_Veronica_) have duller-colored or
smaller flowers.

[Illustration: FIG. 121.--_Anisocarpous sympetalae_ (_Labiatiflorae_).
_A_, flowering branch of trumpet-creeper, _Tecoma_ (_Bignoniaceae_),
x 1/4. _B_, a single flower, divided lengthwise, x 1/2. _C_, cross-section
of the ovary, x 2. _D_, diagram of the flower. _E_, flower of vervain,
_Verbena_ (_Verbenae_), x 2: i, from the side; ii, from in front; iii,
the corolla laid open. _F_, nearly ripe fruit of the same, x 2. _G_,
part of a spike of flowers of the common plantain, _Plantago_
(_Plantagineae_), x 1; The upper flowers have the pistils mature, but
the stamens are not yet ripe. _H_, a flower from the upper (younger)
part of the spike. _I_, an older expanded flower, with ripe stamens,
x 3.]

The curious bladder-weed (_Utricularia_) is the type of the family
_Lentibulariaceae_, aquatic or semi-aquatic plants which possess
special contrivances for capturing insects or small water animals.
These in the bladder-weed are little sacs (Fig. 120, _P_) which act as
traps from which the animals cannot escape after being captured. There
does not appear to be here any actual digestion, but simply an
absorption of the products of decomposition, as in the pitcher-plant.
In the nearly related land form, _Pinguicula_, however, there is much
the same arrangement as in the sundew.

The family _Gesneraceae_ is mainly a tropical one, represented in the
greenhouses by the magnificent _Gloxinia_ and _Achimenes_, but of
native plants there are only a few parasitic forms destitute of
chlorophyll and with small, inconspicuous flowers. The commonest of
these is _Epiphegus_, a much-branched, brownish plant, common in
autumn about the roots of beech-trees upon which it is parasitic, and
whence it derives its common name, "beech-drops."

The bignonia family (_Bignoniaceae_) is mainly tropical, but in our
southern states is represented by the showy trumpet-creeper (_Tecoma_)
(Fig. 121, _A_), the catalpa, and _Martynia_.

The other plants likely to be met with by the student belong either to
the _Verbenaceae_, represented by the showy verbenas of the gardens,
and our much less showy wild vervains, also belonging to the genus
_Verbena_ (Fig. 121, _E_); or to the plantain family (_Plantagineae_),
of which the various species of plantain (_Plantago_) are familiar to
every one (Fig. 121, _G_, _I_). The latter seem to be forms in which
the flowers have become inconspicuous, and are wind fertilized, while
probably all of its showy-flowered relatives are dependent on insects
for fertilization.

The third order (_Contortae_) of the _Anisocarpae_ includes five
families, all represented by familiar forms. The first, the olive
family (_Oleaceae_), besides the olive, contains the lilac and jasmine
among cultivated plants, and the various species of ash (_Fraxinus_),
and the pretty fringe-tree (_Chionanthus_) (Fig. 122, _A_), often
cultivated for its abundant white flowers. The other families are the
_Gentianaceae_ including the true gentians (_Gentiana_) (Fig. 122,
_F_), the buck-bean (_Menyanthes_), the centauries (_Erythraea_ and
_Sabbatia_), and several other less familiar genera; _Loganiaceae_,
with the pink-root (_Spigelia_) (Fig. 122, _D_), as the best-known
example; _Apocynaceae_ including the dog-bane (_Apocynum_) (Fig. 122,
_H_), and in the gardens the oleander and periwinkle (_Vinca_).

[Illustration: FIG. 122.--_Anisocarpous sympetalae_ (_Contortae_). _A_,
flower of fringe-tree, _Chionanthus_ (_Oleaceae_), x 1. _B_, base of
the flower, with part of the calyx and corolla removed, x 2. _C_,
fruit of white ash, _Fraxinus_ (_Oleaceae_), x 1. _D_, flower of
pink-root, _Spigelia_ (_Loganiaceae_), x 1/2. _E_, cross-section of the
ovary, x 3. _F_, flower of fringed gentian, _Gentiana_ (_Gentianaceae_),
x 1/2. _G_, diagram of the flower. _H_, flowering branch of dog-bane,
_Apocynum_ (_Apocynaceae_), x 1/2. _I_, vertical section of a flower,
x 2. _J_, bud. _K_, flower of milk-weed, _Asclepias_ (_Asclepiadaceae_),
x 1. _L_, vertical section through the upper part of the flower, x 2.
_gy._ pistil. _p_, pollen masses. _an._ stamen. _M_, a pair of pollen
masses, x 6. _N_, a nearly ripe seed, x 1.]

The last family is the milk-weeds (_Asclepiadaceae_), which have
extremely complicated flowers. Our numerous milk-weeds (Fig. 122, _K_)
are familiar representatives, and exhibit perfectly the peculiarities
of the family. Like the dog-banes, the plants contain a milky juice
which is often poisonous. Besides the true milk-weeds (_Asclepias_),
there are several other genera within the United States, but mostly
southern in their distribution. Many of them are twining plants and
occasionally cultivated for their showy flowers. Of the cultivated
forms, the wax-plant (_Hoya_), and _Physianthus_ are the commonest.

[Illustration: FIG. 123.--_Anisocarpous sympetalae_ (_Campanulinae_).
_A_, vertical section of the bud of American bell-flower, _Campanula_
(_Campanulaceae_), x 2. _B_, an expanded flower, x 1. The stamens have
discharged their pollen, and the stigma has opened. _C_, cross-section
of the ovary, x 3. _D_, flower of the Carpathian bell-flower
(_Campanula Carpatica_), x 1. _E_, flower of cardinal-flower,
_Lobelia_ (_Lobeliaceae_), x 1. _F_, the same, with the corolla and
sepals removed. _an._ the united anthers. _gy._ the tip of the pistil.
_G_, the tip of the pistil, x 2, showing the circle of hairs
surrounding the stigma. _H_, cross-section of the ovary, x 3. _I_, tip
of a branch of cucumber, _Cucurbita_ (_Cucurbitaceae_), with an
expanded female flower ([Female]). _J_, androecium of a male flower,
showing the peculiar convoluted anthers (_an._), x 2. _K_,
cross-section of the ovary, x 2.]

The fourth order (_Campanulinae_) also embraces five families, but of
these only three are represented among our wild plants. The
bell-flowers (_Campanula_) (Fig. 123, _A_, _D_) are examples of the
family _Campanulaceae_, and numerous species are common, both wild and
cultivated.

[Illustration: FIG. 124.--_Anisocarpous sympetalae_ (_Aggregatae_). _A_,
flowering branch of _Houstonia purpurea_, x 1 (_Rubiaceae_). _B_,
vertical section of a flower, x 2. _C_, fruit of bluets (_Houstonia
coerulea_), x 1. _D_, cross-section of the same. _E_, bedstraw,
_Galium_ (_Rubiaceae_), x 1/2. _F_, a single flower, x 2. _G_, flower of
arrow-wood, _Viburnum_ (_Caprifoliaceae_), x 2. _H_, the same, divided
vertically. _I_, flowering branch of trumpet honeysuckle, _Lonicera_
(_Caprifoliaceae_), x 1/2. _J_, a single flower, the upper part laid
open, x 1. _K_, diagram of the flower. _L_, part of the inflorescence
of valerian, _Valeriana_, (_Valerianeae_), x 1. _M_, young; _N_, older
flower, x 2. _O_, cross-section of the young fruit; one division of
the three contains a perfect seed, the others are crowded to one side
by its growth. _P_, inflorescence of teasel, _Dipsacus_ (_Dipsaceae_),
x 1/4. _fl._ flowers. _Q_, a single flower, x 1. _R_, the same, with the
corolla laid open.]

The various species of _Lobelia_, of which the splendid
cardinal-flower (_L. Cardinalis_) (Fig. 123, _E_) is one of the most
beautiful, represent the very characteristic family _Lobeliaceae_.
Their milky juice contains more or less marked poisonous properties.
The last family of the order is the gourd family (_Cucurbitaceae_),
represented by a few wild species, but best known by the many
cultivated varieties of melons, cucumbers, squashes, etc. They are
climbing or running plants, and provided with tendrils. The flowers
are usually unisexual, sometimes dioecious, but oftener monoecious
(Fig. 123, _I_).

[Illustration: FIG. 125.--_Anisocarpous sympetalae_ (_Aggregatae_).
Types of _Compositae_. _A_, inflorescence of Canada thistle
(_Cirsium_), x 1. _B_, vertical section of _A_. _r_, the receptacle or
enlarged end of the stem, to which the separate flowers are attached.
_C_, a single flower, x 2. _o_, the ovary. _p_, the "pappus" (calyx
lobes). _an._ the united anthers. _D_, the upper part of the stamens
and pistil, x 3: i, from a young flower; ii, from an older one. _an._
anthers. _gy._ pistil. _E_, ripe fruit, x 1. _F_, inflorescence of
may-weed (_Maruta_). The central part (disc) is occupied by perfect
tubular flowers (_G_), the flowers about the edge (rays) are sterile,
with the corolla much enlarged and white, x 2. _G_, a single flower
from the disc, x 3. _H_, inflorescence of dandelion (_Taraxacum_), the
flowers all alike, with strap-shaped corollas, x 1. _I_, a single
flower, x 2. _c_, the split, strap-shaped corolla. _J_, two ripe
fruits, still attached to the receptacle (_r_). The pappus is raised
on a long stalk, x 1. _K_, a single fruit, x 2.]

The last and highest order of the _Sympetalae_, and hence of the
dicotyledons, is known as _Aggregatae_, from the tendency to have the
flowers densely crowded into a head, which not infrequently is closely
surrounded by bracts so that the whole inflorescence resembles a
single flower. There are six families, five of which have common
representatives, but the last family (_Calycereae_) has no members
within our limits.

The lower members of the order, _e.g._ various _Rubiaceae_ (Fig. 124,
_A_, _E_), have the flowers in loose inflorescences, but as we examine
the higher families, the tendency for the flowers to become crowded
becomes more and more evident, and in the highest of our native forms
_Dipsaceae_ (Fig. 124, _P_) and _Compositae_ (Fig. 125) this is very
marked indeed. In the latter family, which is by far the largest of
all the angiosperms, including about ten thousand species, the
differentiation is carried still further. Among our native _Compositae_
there are three well-marked types. The first of these may be
represented by the thistles (Fig. 125, _A_). The so-called flower of
the thistle is in reality a close head of small, tubular flowers
(Fig. 125, _C_), each perfect in all respects, having an inferior
one-celled ovary, five stamens with the anthers united, and a
five-parted corolla. The sepals (here called the "pappus") (_p_) have
the form of fine hairs. These little flowers are attached to the
enlarged upper end of the flower stalk (receptacle, _r_), and are
surrounded by closely overlapping bracts or scale leaves which look
like a calyx; the flowers, on superficial examination, appear as
single petals. In other forms like the daisy and may-weed (Fig. 125,
_F_), only the central flowers are perfect, and the edge of the
inflorescence is composed of flowers whose corollas are split and
flattened out, but the stamens and sometimes the pistils are wanting
in these so-called "ray-flowers." In the third group, of which the
dandelion (Fig. 125, _H_), chicory, lettuce, etc., are examples, all
of the flowers have strap-shaped, split corollas, and contain both
stamens and pistils.

The families of the _Aggregatae_ are the following: I. _Rubiaceae_ of
which _Houstonia_ (Fig. 124, _A_), _Galium_ (_E_), _Cephalanthus_
(button-bush), and _Mitchella_ (partridge-berry) are examples;
II. _Caprifoliaceae_, containing the honeysuckles (_Lonicera_)
(Fig. 124, _I_), _Viburnum_ (_G_), snowberry (_Symphoricarpus_), and
elder (_Sambucus_); III. _Valerianeae_, represented by the common
valerian (_Valeriana_) (Fig. 124, _L_); IV. _Dipsaceae_, of which the
teasel (_Dipsacus_) (Fig. 124, _P_), is the type, and also species of
scabious (_Scabiosa_); V. _Compositae_ to which the innumerable,
so-called compound flowers, asters, golden-rods, daisies, sunflowers,
etc. belong; VI. _Calycereae_.

[Illustration: FIG. 126.--_Aristolochiaceae_. _A_, plant of wild ginger
(_Asarum_), x 1/3. _B_, vertical section of the flower, x 1. _C_,
diagram of the flower.]

Besides the groups already mentioned, there are several families of
dicotyledons whose affinities are very doubtful. They are largely
parasitic, _e.g._ mistletoe; or water plants, as the horned pond-weed
(_Ceratophyllum_). One family, the _Aristolochiaceae_, represented by
the curious "Dutchman's pipe" (_Aristolochia sipho_), a woody twiner
with very large leaves, and the common wild ginger (_Asarum_)
(Fig. 126), do not appear to be in any wise parasitic, but the
structure of their curious flowers differs widely from any other group
of plants.




CHAPTER XX.

FERTILIZATION OF FLOWERS.


If we compare the flowers of different plants, we shall find almost
infinite variety in structure, and this variation at first appears to
follow no fixed laws; but as we study the matter more thoroughly, we
find that these variations have a deep significance, and almost
without exception have to do with the fertilization of the flower.

In the simpler flowers, such as those of a grass, sedge, or rush among
the monocotyledons, or an oak, hazel, or plantain, among dicotyledons,
the flowers are extremely inconspicuous and often reduced to the
simplest form. In such plants, the pollen is conveyed from the male
flowers to the female by the wind, and to this end the former are
usually placed above the latter so that these are dusted with the
pollen whenever the plant is shaken by the wind. In these plants, the
male flowers often outnumber the female enormously, and the pollen is
produced in great quantities, and the stigmas are long and often
feathery, so as to catch the pollen readily. This is very beautifully
shown in many grasses.

If, however, we examine the higher groups of flowering plants, we see
that the outer leaves of the flower become more conspicuous, and that
this is often correlated with the development of a sweet fluid
(nectar) in certain parts of the flower, while the wind-fertilized
flowers are destitute of this as well as of odor.

If we watch any bright-colored or sweet-scented flower for any length
of time, we shall hardly fail to observe the visits of insects to it,
in search of pollen or honey, and attracted to the flower by its
bright color or sweet perfume. In its visits from flower to flower,
the insect is almost certain to transfer part of the pollen carried
off from one flower to the stigma of another of the same kind, thus
effecting pollination.

That the fertilization of a flower by pollen from another is
beneficial has been shown by many careful experiments which show that
nearly always--at least in flowers where there are special
contrivances for cross-fertilization--the number of seeds is greater
and the quality better where cross-fertilization has taken place, than
where the flower is fertilized by its own pollen. From these
experiments, as well as from very numerous studies on the structure of
the flower with reference to insect aid in fertilization, we are
justified in the conclusion that all bright-colored flowers are, to a
great extent, dependent upon insect aid for transferring the pollen
from one flower to another, and that many, especially those with
tubular or zygomorphic (bilateral) flowers are perfectly incapable of
self-fertilization. In a few cases snails have been known to be the
conveyers of pollen, and the humming-birds are known in some cases, as
for instance the trumpet-creeper (Fig. 121, _A_), to take the place of
insects.[14]

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