CLASSIFICATION OF DICOTYLEDONS (_Continued_).
DIVISION II.--_Sympetalæ_.
The _Sympetalæ_ or _Gamopetalæ_ are at once distinguished from the
_Choripetalæ_ by having the petals more or less united, so that the
corolla is to some extent tubular. In the last order of the
_Choripetalæ_ we found a few examples (_Mimosaceæ_) where the same
thing is true, and these form a transition from the _Choripetalæ_ to
the _Sympetalæ_.
There are two great divisions, _Isocarpæ_ and _Anisocarpæ_. 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 _Isocarpæ_ there are usually
twice as many stamens as petals, occasionally the same number.
There are three orders of the _Isocarpæ_, viz., _Bicornes_,
_Primulinæ_, and _Diospyrinæ_. 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 (_Epacrideæ_) are
represented in the United States. Of these the _Pyrolaceæ_ includes
the pretty little pyrolas and prince's-pine (_Chimaphila_) (Fig. 116,
_J_); the _Monotropeæ_ 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
_Rhodoraceæ_. The heath family (_Ericaceæ_), besides the true heaths
(_Erica_, _Calluna_), includes the pretty trailing-arbutus or
may-flower (_Epigæa_), _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 sympetalæ_
(_Bicornes_). _A_, flowers, fruit, and leaves of huckleberry,
_Gaylussacia_ (_Vaccinieæ_), × 1. _B_, vertical section of the flower,
× 3. _C_, a stamen: i, from in front; ii, from the side, × 4. _D_,
cross-section of the young fruit, × 2. _E_, flower of sorrel-tree,
_Oxydendrum_ (_Ericaceæ_), × 2. _F_, flower of azalea (_Rhododendron_),
× ½. _G_, cross-section of the ovary, × 3. _H_, diagram of the flower.
_I_, flower of mountain laurel (_Kalmia_), × 1. _J_, prince's-pine,
_Chimaphila_ (_Pyrolaceæ_), × ½. _K_, a single flower, × 1. _L_, plant
of pine-sap, _Monotropa_, (_Monotropeæ_), × ½. _M_, section of a
flower, × 1.]
The second order, the primroses (_Primulinæ_), is principally
represented in the cooler parts of the world by the true primrose
family (_Primulaceæ_), 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 sympetalæ_ (_Primulinæ_,
_Diospyrinæ_). _A_, shooting-star, _Dodecatheon_ (_Primulaceæ_), × ½.
_B_, section of a flower, × 1. _C_, diagram of the flower. _D_,
Moneywort, _Lysimachia_ (_Primulaceæ_), × ½. _E_, a perfect flower of
the persimmon, _Diospyros_ (_Ebenaceæ_), × 1. _F_, the same, laid open:
section of the young fruit, × 2. _H_, longitudinal section of a ripe
seed, × 1. _em._ the embryo. _I_, fruit, × ½.]
The sea-rosemary (_Statice_) and one or two cultivated species of
plumbago are the only members of the plumbago family (_Plumbagineæ_)
likely to be met with. The remaining families of the _Primulinæ_ are
not represented by any common plants.
The third and last order of the _Isocarpous sympetalæ_ has but a
single common representative in the United States; viz., the persimmon
(_Diospyros_) (Fig. 117, _E_). This belongs to the family _Ebenaceæ_,
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 _Sympetalæ_ (the _Anisocarpæ_) 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 sympetalæ_
(_Tubifloræ_). _A_, flower and leaves of wild phlox (_Polemoniaceæ_),
× ½. _B_, section of a flower, × 1. _C_, fruit, × 1. _D_, flower of
blue valerian (_Polemonium_), × 1. _E_, flowers and leaf of
water-leaf, _Hydrophyllum_ (_Hydrophyllaceæ_), × ½. _F_, section of a
flower, × 1. _G_, flower of wild morning-glory, _Convolvulus_
(_Convolvulaceæ_), × ½. 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, × 1. _J_, a seed, × 1.
_K_, cross-section of a nearly ripe seed, showing the crumpled embryo,
× 2. _L_, an embryo removed from a nearly ripe seed, and spread out;
one of the cotyledons has been partially removed, × 1.]
The first order (_Tubifloræ_) 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
(_Convolvulaceæ_) has as its type the morning-glory (_Convolvulus_)
(Fig. 118, _G_), and the nearly related _Ipomœas_ 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 _Polemoniaceæ_.
[Illustration: FIG. 119.--_Anisocarpous sympetalæ_ (_Tubifloræ_). _A_,
inflorescence of hound's-tongue, _Cynoglossum_ (_Borragineæ_), × ½.
_B_, section of a flower, × 2. _C_, nearly ripe fruit, × 1. _D_,
flowering branch of nightshade, _Solanum_ (_Solaneæ_), × ½. _E_, a
single flower, × 1. _F_, section of the flower, × 2. _G_, young fruit,
× 1. _H_, flower of _Petunia_ (_Solaneæ_), × ½. _I_, diagram of the
flower.]
The third family (_Hydrophyllaceæ_) 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 (_Borragineæ_) 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 (_Solaneæ_) 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 _Anisocarpæ_ 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 (_Labiatifloræ_) 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 (_Labiatæ_) and the figworts (_Scrophularineæ_).
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 sympetalæ_ (_Labiatifloræ_).
_A_, dead nettle, _Lamium_, (_Labiatæ_), × ½. _B_, a single flower,
× 1. _C_, the stamens and pistil, × 1. _D_, cross-section of the
ovary, × 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_ (_Labiatæ_), × 1. Part of the persistent calyx has been
removed to show the four seed-like fruits, or nutlets. _G_, section of
a nutlet, × 3. The embryo fills the seed completely. _H_, part of an
inflorescence of figwort, _Scrophularia_ (_Scrophularineæ_), × 1. _I_,
cross-section of the young fruit, × 2. _J_, flower of speedwell,
_Veronica_ (_Scrophularineæ_), × 2. _K_, fruit of _Veronica_, × 2.
_L_, cross-section of _K_. _M_, flower of moth-mullein, _Verbascum_
(_Scrophularineæ_), × ½. _N_, flower of toad-flax, _Linaria_
(_Scrophularineæ_), × 1. _O_, leaf of bladder-weed, _Utricularia_
(_Lentibulariaceæ_), × 1. _x_, one of the "traps." _P_, a single trap,
× 5.]
The _Scrophularineæ_ differ mainly from the _Labiatæ_ 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 sympetalæ_ (_Labiatifloræ_).
_A_, flowering branch of trumpet-creeper, _Tecoma_ (_Bignoniaceæ_),
× ¼. _B_, a single flower, divided lengthwise, × ½. _C_, cross-section
of the ovary, × 2. _D_, diagram of the flower. _E_, flower of vervain,
_Verbena_ (_Verbenæ_), × 2: i, from the side; ii, from in front; iii,
the corolla laid open. _F_, nearly ripe fruit of the same, × 2. _G_,
part of a spike of flowers of the common plantain, _Plantago_
(_Plantagineæ_), × 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,
× 3.]
The curious bladder-weed (_Utricularia_) is the type of the family
_Lentibulariaceæ_, 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 _Gesneraceæ_ 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 (_Bignoniaceæ_) 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 _Verbenaceæ_, 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 (_Plantagineæ_),
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 (_Contortæ_) of the _Anisocarpæ_ includes five
families, all represented by familiar forms. The first, the olive
family (_Oleaceæ_), 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
_Gentianaceæ_ including the true gentians (_Gentiana_) (Fig. 122,
_F_), the buck-bean (_Menyanthes_), the centauries (_Erythræa_ and
_Sabbatia_), and several other less familiar genera; _Loganiaceæ_,
with the pink-root (_Spigelia_) (Fig. 122, _D_), as the best-known
example; _Apocynaceæ_ including the dog-bane (_Apocynum_) (Fig. 122,
_H_), and in the gardens the oleander and periwinkle (_Vinca_).
[Illustration: FIG. 122.--_Anisocarpous sympetalæ_ (_Contortæ_). _A_,
flower of fringe-tree, _Chionanthus_ (_Oleaceæ_), × 1. _B_, base of
the flower, with part of the calyx and corolla removed, × 2. _C_,
fruit of white ash, _Fraxinus_ (_Oleaceæ_), × 1. _D_, flower of
pink-root, _Spigelia_ (_Loganiaceæ_), × ½. _E_, cross-section of the
ovary, × 3. _F_, flower of fringed gentian, _Gentiana_ (_Gentianaceæ_),
× ½. _G_, diagram of the flower. _H_, flowering branch of dog-bane,
_Apocynum_ (_Apocynaceæ_), × ½. _I_, vertical section of a flower,
× 2. _J_, bud. _K_, flower of milk-weed, _Asclepias_ (_Asclepiadaceæ_),
× 1. _L_, vertical section through the upper part of the flower, × 2.
_gy._ pistil. _p_, pollen masses. _an._ stamen. _M_, a pair of pollen
masses, × 6. _N_, a nearly ripe seed, × 1.]
The last family is the milk-weeds (_Asclepiadaceæ_), 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 sympetalæ_ (_Campanulinæ_).
_A_, vertical section of the bud of American bell-flower, _Campanula_
(_Campanulaceæ_), × 2. _B_, an expanded flower, × 1. The stamens have
discharged their pollen, and the stigma has opened. _C_, cross-section
of the ovary, × 3. _D_, flower of the Carpathian bell-flower
(_Campanula Carpatica_), × 1. _E_, flower of cardinal-flower,
_Lobelia_ (_Lobeliaceæ_), × 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, × 2, showing the circle of hairs
surrounding the stigma. _H_, cross-section of the ovary, × 3. _I_, tip
of a branch of cucumber, _Cucurbita_ (_Cucurbitaceæ_), with an
expanded female flower (♀). _J_, andrœcium of a male flower, showing
the peculiar convoluted anthers (_an._), × 2. _K_, cross-section of
the ovary, × 2.]
The fourth order (_Campanulinæ_) 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 _Campanulaceæ_, and numerous species are common, both wild and
cultivated.
[Illustration: FIG. 124.--_Anisocarpous sympetalæ_ (_Aggregatæ_). _A_,
flowering branch of _Houstonia purpurea_, × 1 (_Rubiaceæ_). _B_,
vertical section of a flower, × 2. _C_, fruit of bluets (_Houstonia
cœrulea_), × 1. _D_, cross-section of the same. _E_, bedstraw,
_Galium_ (_Rubiaceæ_), × ½. _F_, a single flower, × 2. _G_, flower of
arrow-wood, _Viburnum_ (_Caprifoliaceæ_), × 2. _H_, the same, divided
vertically. _I_, flowering branch of trumpet honeysuckle, _Lonicera_
(_Caprifoliaceæ_), × ½. _J_, a single flower, the upper part laid
open, × 1. _K_, diagram of the flower. _L_, part of the inflorescence
of valerian, _Valeriana_, (_Valerianeæ_), × 1. _M_, young; _N_, older
flower, × 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_ (_Dipsaceæ_),
× ¼. _fl._ flowers. _Q_, a single flower, × 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 _Lobeliaceæ_.
Their milky juice contains more or less marked poisonous properties.
The last family of the order is the gourd family (_Cucurbitaceæ_),
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 diœcious, but oftener monœcious
(Fig. 123, _I_).
[Illustration: FIG. 125.--_Anisocarpous sympetalæ_ (_Aggregatæ_).
Types of _Compositæ_. _A_, inflorescence of Canada thistle
(_Cirsium_), × 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, × 2. _o_, the ovary. _p_, the "pappus" (calyx
lobes). _an._ the united anthers. _D_, the upper part of the stamens
and pistil, × 3: i, from a young flower; ii, from an older one. _an._
anthers. _gy._ pistil. _E_, ripe fruit, × 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, × 2. _G_, a single flower
from the disc, × 3. _H_, inflorescence of dandelion (_Taraxacum_), the
flowers all alike, with strap-shaped corollas, × 1. _I_, a single
flower, × 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, × 1. _K_, a single fruit, × 2.]
The last and highest order of the _Sympetalæ_, and hence of the
dicotyledons, is known as _Aggregatæ_, 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 (_Calycereæ_) has no members
within our limits.
The lower members of the order, _e.g._ various _Rubiaceæ_ (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
_Dipsaceæ_ (Fig. 124, _P_) and _Compositæ_ (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 _Compositæ_
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 _Aggregatæ_ are the following: I. _Rubiaceæ_ of
which _Houstonia_ (Fig. 124, _A_), _Galium_ (_E_), _Cephalanthus_
(button-bush), and _Mitchella_ (partridge-berry) are examples;
II. _Caprifoliaceæ_, containing the honeysuckles (_Lonicera_)
(Fig. 124, _I_), _Viburnum_ (_G_), snowberry (_Symphoricarpus_), and
elder (_Sambucus_); III. _Valerianeæ_, represented by the common
valerian (_Valeriana_) (Fig. 124, _L_); IV. _Dipsaceæ_, of which the
teasel (_Dipsacus_) (Fig. 124, _P_), is the type, and also species of
scabious (_Scabiosa_); V. _Compositæ_ to which the innumerable,
so-called compound flowers, asters, golden-rods, daisies, sunflowers,
etc. belong; VI. _Calycereæ_.
[Illustration: FIG. 126.--_Aristolochiaceæ_. _A_, plant of wild ginger
(_Asarum_), × ⅓. _B_, vertical section of the flower, × 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 _Aristolochiaceæ_, 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.