The second family, the fumitories (Fumariaceæ) are delicate, smooth plants, with curious flowers and compound leaves. The garden bleeding-heart (Dicentra spectabilis) and the pretty, wild Dicentras (Fig. 103, F) are familiar to nearly every one.

Other examples are the mountain fringe (Adlumia), a climbing species, and several species of Corydalis, differing mainly from Dicentra in having the corolla one-sided.

The mustard family (Cruciferæ) comprises by far the greater part of the order. The shepherd’s-purse, already studied, belongs here, and may be taken as a type of the family. There is great uniformity in all as regards the flowers, so that the classification is based mainly on differences in the fruit and seeds. Many of the most valuable garden vegetables, as well as a few more or less valuable wild plants, are members of the family, which, however, includes some troublesome weeds. Cabbages, turnips, radishes, with all their varieties, belong here, as well as numerous species of wild cresses. A few like the wall-flower (Cheiranthus) and stock (Matthiola) are cultivated for ornament.

The last family is the caper family (Capparideæ), represented by only a few not common plants. The type of the order is Capparis, whose pickled flower-buds constitute capers.

The fourth order (Cistifloræ) of the Aphanocyclæ is a very large one, but the majority of the sixteen families included in it are not represented within our limits. The flowers have the sepals and petals in fives, the stamens either the same or more numerous.

Among the commoner members of the order are the mignonettes (Resedaceæ) and the violets (Violaceæ), of which the various wild and cultivated species are familiar plants (Fig. 104, A, M). The sundews (Droseraceæ) are most extraordinary plants, growing in boggy land over pretty much the whole world. They are represented in the United States by several species of sundew (Drosera), and the still more curious Venus’s-flytrap (Dionæa) of North Carolina. The leaves of the latter are sensitive, and composed of two parts which snap together like a steel trap. If an insect lights upon the leaf, and touches certain hairs upon its upper surface, the two parts snap together, holding the insect tightly. A digestive fluid is secreted by glands upon the inner surface of the leaf, and in a short time the captured insect is actually digested and absorbed by the leaves. The same process takes place in the sundew (Fig. 104, N) where, however, the mechanism is somewhat different. Here the tentacles, with which the leaf is studded, secrete a sticky fluid which holds any small insect that may light upon it. The tentacles now slowly bend inward and finally the edges of the leaf as well, until the captured insect is firmly held, when a digestive process, similar to that in Dionœa, takes place. This curious habit is probably to be explained from the position where the plant grows, the roots being in water where there does not seem to be a sufficient supply of nitrogenous matter for the wants of the plant, which supplements the supply from the bodies of the captured insects.

Similar in their habits, but differing much in appearance from the sundews, are the pitcher-plants (Sarraceniaceæ), of which one species (Sarracenia purpurea) is very common in peat bogs throughout the northern United States. In this species (Fig. 105, A, B), the leaves form a rosette, from the centre of which arises in early summer a tall stalk bearing a single, large, nodding, dark-reddish flower with a curious umbrella-shaped pistil. The leaf stalk is hollow and swollen, with a broad wing on one side, and the blade of the leaf forms a sort of hood at the top. The interior of the pitcher is covered above with stiff, downward-pointing hairs, while below it is very smooth. Insects readily enter the pitcher, but on attempting to get out, the smooth, slippery wall at the bottom, and the stiff, downward-directed hairs above, prevent their escape, and they fall into the fluid which fills the bottom of the cup and are drowned, the leaf absorbing the nitrogenous compounds given off during the process of decomposition. There are other species common in the southern states, and a California pitcher-plant (Darlingtonia) has a colored appendage at the mouth of the pitcher which serves to lure insects into the trap.

Two other families of the order contain familiar native plants, the rock-rose family (Cistaceæ), and the St. John’s-worts (Hypericaceæ). The latter particularly are common plants, with numerous showy yellow flowers, the petals usually marked with black specks, and the leaves having clear dots scattered through them. The stamens are numerous, and often in several distinct groups (Fig. 105, C, D).

The last order of the Aphanocyclæ (the Columniferæ) has three families, of which two, the mallows (Malvaceæ), and the lindens (Tiliaceæ), include well-known species. Of the former, the various species of mallows (Fig. 106, A) belonging to the genus Malva are common, as well as some species of Hibiscus, including the showy swamp Hibiscus or rose-mallow (H. moscheutos), common in salt marshes and in the fresh-water marshes of the great lake region. The hollyhock and shrubby Althæa are familiar cultivated plants of this order, and the cotton-plant (Gossypium) also belongs here. In all of these the stamens are much branched, and united into a tube enclosing the style. Most of them are characterized also by the development of great quantities of a mucilaginous matter within their tissues.

The common basswood (Tilia) is the commonest representative of the family Tiliaceæ (Fig. 106, G). The nearly related European linden, or lime-tree, is sometimes planted. Its leaves are ordinarily somewhat smaller than our native species, which it, however, closely resembles.

The first order (Gruinales) includes six families, consisting for the most part of plants with conspicuous flowers. Here belong the geraniums (Fig. 107, A), represented by the wild geraniums and crane’s-bill, and the very showy geraniums (Pelargonium) of the gardens. The nasturtiums (Tropæolum) represent another family, mostly tropical, and the wood-sorrels (Oxalis) (Fig. 107, I) are common, both wild and cultivated. The most useful member of the order is unquestionably the common flax (Linum), of which there are also several native species (Fig. 107, F). These are types of the flax family (Linaceæ). Linen is the product of the tough, fibrous inner bark of L. usitatissimum, which has been cultivated for its fibre from time immemorial. The last family is the balsam family (Balsamineæ). The jewel-weed or touch-me-not (Impatiens), so called from the sensitive pods which spring open on being touched, is very common in moist ground everywhere (Fig. 107, L–P). The garden balsam, or lady’s slipper, is a related species (I. balsamina).

The third order of the Eucyclæ, the Æsculinæ, embraces six families, of which three, the horsechestnuts, etc. (Sapindaceæ), the maples (Aceraceæ), and the milkworts (Polygalaceæ), have several representatives in the northern United States. Of the first the buckeye (Æsculus) (Fig. 108, J) and the bladder-nut (Staphylea) (Fig. 108, G) are the commonest native genera, while the horsechestnut (Æsculus hippocastanum) is everywhere planted.

The various species of maple (Acer) are familiar examples of the Aceraceæ (see Fig. 106, A, F).

The fourth and last order of the Eucyclæ, the Frangulinæ, is composed mainly of plants with inconspicuous flowers, the stamens as many as the petals. Not infrequently they are diœcious, or in some, like the grape, some of the flowers may be unisexual while others are hermaphrodite (i.e. have both stamens and pistil). Among the commoner plants of the order may be mentioned the spindle-tree, or burning-bush, as it is sometimes called (Euonymus) (Fig. 109, A), and the climbing bitter-sweet (Celastrus) (Fig. 109, D), belonging to the family Celastraceæ; the holly and black alder, species of Ilex, are examples of the family Aquifoliaceæ; the various species of grape (Vitis), the Virginia creeper (Ampelopsis quinquefolia), and one or two other cultivated species of the latter, represent the vine family (Vitaceæ or Ampelidæ), and the buckthorn (Rhamnus) is the type of the Rhamnaceæ.

The fifth group of the Choripetalæ is a small one, comprising but a single order (Tricoccæ). The flowers are small and inconspicuous, though sometimes, as in some Euphorbias and the showy Poinsettia of the greenhouses, the leaves or bracts surrounding the inflorescence are conspicuously colored, giving the whole the appearance of a large, showy, single flower. In northern countries the plants are mostly small weeds, of which the various spurges or Euphorbias are the most familiar. These plants (Fig. 109, K) have the small flowers surrounded by a cup-shaped involucre (L, M) so that the whole inflorescence looks like a single flower. In the spurges, as in the other members of the order, the flowers are very simple, being often reduced to a single stamen or pistil (Fig. 109, M, N). The plants generally abound in a milky juice which is often poisonous. This juice in a number of tropical genera is the source of India-rubber. Some genera like the castor-bean (Ricinus) and Croton are cultivated for their large, showy leaves.

The water starworts (Callitriche), not uncommon in stagnant water, represent the family Callitrichaceæ, and the box (Buxus) is the type of the Buxaceæ.

The last and highest group of the Choripetalæ, the Calycifloræ, embraces a very large assemblage of familiar plants, divided into eight orders and thirty-two families. With few exceptions, the floral axis grows up around the ovary, carrying the outer floral leaves above it, and the ovary appears at the bottom of a cup around whose edge the other parts of the flower are arranged. Sometimes, as in the fuchsia, the ovary is grown to the base of the cup or tube, and thus looks as if it were outside the flower. Such an ovary is said to be “inferior” in distinction from one that is entirely free from the tube, and thus is evidently within the flower. The latter is the so-called “superior” ovary. The carpels are usually united into a compound pistil, but may be separate, as in the stonecrop (Fig. 111, E), or strawberry (Fig. 114, C).

The first order of the Calycifloræ (Umbellifloræ) has the flowers small, and usually arranged in umbels, i.e. several stalked flowers growing from a common point. The ovary is inferior, and there is a nectar-secreting disc between the styles and the stamens. Of the three families, the umbel-worts or Umbelliferæ is the commonest. The flowers are much alike in all (Fig. 110, A, B), and nearly all have large, compound leaves with broad, sheathing bases. The stems are generally hollow. So great is the uniformity of the flowers and plant, that the fruit (Fig. 110, D) is generally necessary before the plant can be certainly recognized. This is two-seeded in all, but differs very much in shape and in the development of oil channels, which secrete the peculiar oil that gives the characteristic taste to the fruits of such forms as caraway, coriander, etc. Some of them, like the wild parsnip, poison hemlock, etc., are violent poisons, while others like the carrot are perfectly wholesome.

The wild spikenard (Aralia) (Fig. 110, F), ginseng, and the true ivy (Hedera) are examples of the Araliaceæ, and the various species of dogwood (Cornus) (Fig. 110, J–N) represent the dogwood family (Corneæ).

The second order (Saxifraginæ) contains eight families, including a number of common wild and cultivated plants. The true saxifrages are represented by several wild and cultivated species of Saxifraga, the little bishop’s cap or mitre-wort (Mitella) (Fig. 111, D), and others. The wild hydrangea (Fig. 111, F) and the showy garden species represent the family Hydrangeæ. In these some of the flowers are large and showy, but with neither stamens nor pistils (neutral), while the small, inconspicuous flowers of the central part of the inflorescence are perfect. In the garden varieties, all of the flowers are changed, by selection, into the showy, neutral ones. The syringa or mock orange (Philadelphus) (Fig. 111, I), the gooseberry, and currants (Ribes) (Fig. 111, A), and the stonecrop (Sedum) (Fig. 111, E) are types of the families Philadelpheæ, Ribesieæ, and Crassulaceæ.

The third order (Opuntieæ) has but a single family, the cacti (Cactaceæ). These are strictly American in their distribution, and inhabit especially the dry plains of the southwest, where they reach an extraordinary development. They are nearly or quite leafless, and the fleshy, cylindrical, or flattened stems are usually beset with stout spines. The flowers (Fig. 112, A) are often very showy, so that many species are cultivated for ornament and are familiar to every one. The beautiful night-blooming cereus, of which there are several species, is one of these. A few species of prickly-pear (Opuntia) occur as far north as New York, but most are confined to the hot, dry plains of the south and southwest.

The fourth order (Passiflorinæ) are almost without exception tropical plants, only a very few extending into the southern United States. The type of the order is the passion-flower (Passiflora) (Fig. 112, B), whose numerous species are mostly inhabitants of tropical America, but a few reach into the United States. The only other members of the order likely to be met with by the student are the begonias, of which a great many are commonly cultivated as house plants on account of their fine foliage and flowers. The leaves are always one-sided, and the flowers monœcious.[13] Whether the begonias properly belong with the Passiflorinæ has been questioned.

The fifth order (Myrtifloræ) have regular four-parted flowers with usually eight stamens, but sometimes, through branching of the stamens, these appear very numerous. The myrtle family, the members of which are all tropical or sub-tropical, gives name to the order. The true myrtle (Myrtus) is sometimes cultivated for its pretty glossy green leaves and white flowers, as is also the pomegranate whose brilliant, scarlet flowers are extremely ornamental. Cloves are the dried flower-buds of an East-Indian myrtaceous tree (Caryophyllus). In Australia the order includes the giant gum-trees (Eucalyptus), the largest of all known trees, exceeding in size even the giant trees of California.

Among the commoner Myrtifloræ, the majority belong to the two families Onagraceæ and Lythraceæ. The former includes the evening primroses (Œnothera), willow-herb (Epilobium) (Fig. 113, D), and fuchsia; the latter, the purple loosestrife (Lythrum) and swamp loosestrife (Nesæa). The water-milfoil (Myriophyllum) (Fig. 113, J) is an example of the family Haloragidaceæ, and the Rhexias of the eastern United States represent with us the family Melastomaceæ.

The sixth order of the Calycifloræ is a small one (Thymelinæ), represented in the United States by very few species. The flowers are four-parted, the calyx resembling a corolla, which is usually absent. The commonest member of the order is the moosewood (Dirca) (Fig. 113, A), belonging to the first of the three families (Thymelæaceæ). Of the second family (Elæagnaceæ), the commonest example is Shepherdia, a low shrub having the leaves covered with curious, scurfy hairs that give them a silvery appearance. The third family (Proteaceæ) has no familiar representatives.

The seventh order (Rosifloræ) includes many well-known plants, all of which may be united in one family (Rosaceæ), with several sub-families. The flowers are usually five-parted with from five to thirty stamens, and usually numerous, distinct carpels. In the apple and pear (Fig. 114, I), however, the carpels are more or less grown together; and in the cherry, peach, etc., there is but a single carpel giving rise to a single-seeded stone-fruit (drupe) (Fig. 114, E, H). In the strawberry (Fig. 114, A), rose (G), cinquefoil (Potentilla), etc., there are numerous distinct, one-seeded carpels, and in Spiræa (Fig. 114, F) there are five several-seeded carpels, forming as many dry pods when ripe. The so-called “berry” of the strawberry is really the much enlarged flower axis, or “receptacle,” in which the little one-seeded fruits are embedded, the latter being what are ordinarily called the seeds.

The last order of the Calycifloræ and the highest of the Choripetalæ is the order Leguminosæ, of which the bean, pea, clover, and many other common plants are examples. In most of our common forms the flowers are peculiar in shape, one of the petals being larger than the others, and covering them in the bud. This petal is known as the standard. The two lateral petals are known as the wings, and the two lower and inner are generally grown together forming what is called the “keel” (Fig. 115, A, B). The stamens, ten in number, are sometimes all grown together into a tube, but generally the upper one is free from the others (Fig. 115, C). There is but one carpel which forms a pod with two valves when ripe (Fig. 115, D). The seeds are large, and the embryo fills the seed completely. From the peculiar form of the flower, they are known as Papilionaceæ (papilio, a butterfly). Many of the Papilionaceæ are climbers, either having twining stems, as in the common beans, or else with part of the leaf changed into a tendril as in the pea (Fig. 115, A), vetch, etc. The leaves are usually compound.

Of the second family (Cæsalpineæ), mainly tropical, the honey locust (Gleditschia) and red-bud (Cercis) (Fig. 115, G) are the commonest examples. The flowers differ mainly from the Papilionaceæ in being less perfectly papilionaceous, and the stamens are almost entirely distinct (Fig. 115, H). The last family (Mimosaceæ) is also mainly tropical. The acacias, sensitive-plant (Mimosa), and the sensitive-brier of the southern United States (Schrankia) (Fig. 115, I) represent this family. The flowers are quite different from the others of the order, being tubular and the petals united, thus resembling the flowers of the Sympetalæ. The leaves of Mimosa and Schrankia are extraordinarily sensitive, folding up if irritated.

CHAPTER XIX.
CLASSIFICATION OF DICOTYLEDONS (Continued).
Division II.—Sympetalæ.

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).

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.

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 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.