CHAPTER XVIII

THE FLOWER--ITS PARTS AND FORMS

The function of the flower is to _produce seed_. It is probable that all its varied forms and colors contribute to this supreme end. These forms and colors please the human fancy and add to the joy of living, but the flower exists for the good of the plant, not for the good of man. The parts of the flower are of two general kinds--those that are directly concerned in the _production of seeds_, and those that act as _covering and protecting organs_. The former parts are known as the =essential organs=; the latter as the =floral envelopes=.

=Envelopes.=--The floral envelopes usually bear a close resemblance to leaves. These envelopes are very commonly of two series or kinds--the _outer_ and the _inner_. The outer series, known as the =calyx=, is usually smaller and green. It usually comprises the outer cover of the flower bud. The calyx is the lowest whorl in Fig. 173.

[Illustration: FIG. 173.--FLOWER OF A BUTTERCUP IN SECTION.]

The inner series, known as the =corolla=, is usually colored and more special or irregular in shape than the calyx. It is the showy part of the flower, as a rule. The corolla is the second or large whorl in Fig. 173.

The _calyx_ may be composed of several leaves. Each leaf is a =sepal=. If it is of one piece, it may be lobed or divided, in which case the divisions are called =calyx-lobes=.

In like manner, the corolla may be composed of =petals=, or it may be of one piece and variously lobed. A calyx of one piece, no matter how deeply lobed, is =gamosepalous=. A corolla of one piece is =gamopetalous=. When these series are of separate pieces, as in Fig. 173, the flower is said to be =polysepalous= and =polypetalous=. Sometimes both series are of separate parts, and sometimes only one of them is so formed.

_The floral envelopes are homologous with leaves._ Sepals and petals, at least when more than three or five, are in more than one whorl, and one whorl stands below another so that the parts overlap. They are borne on the expanded or thickened end of the flower stalk; this end is the =torus=. In Fig. 173 all the parts are seen as attached to the torus. This part is sometimes called the _receptacle_, but this word is a common-language term of several meanings, whereas torus has no other meaning. Sometimes one part is attached to another part, as in the fuchsia (Fig. 174), in which the petals are borne on the calyx-tube.

[Illustration: FIG. 174.--FLOWER OF FUCHSIA IN SECTION.]

=Subtending Parts.=--Sometimes there are _leaf-like parts just below the calyx_, looking like a second calyx. Such parts accompany the carnation flower. These parts are =bracts= (bracts are small specialized leaves); and they form an =involucre=. We must be careful that we do not mistake them for true flower parts. Sometimes the bracts are large and petal-like, as in the great white blooms of the flowering dogwood: here the real flowers are several, small and greenish, forming a small cluster in the center.

=Essential Organs.=--The essential organs are of two series. The outer series is composed of the =stamens=. The inner series is composed of the =pistils=.

_Stamens_ bear the =pollen=, which is made up of grains or spores, each spore usually being a single plant cell. The stamen is of two parts, as is readily seen in Figs. 173, 174,--the enlarged terminal part or =anther=, and the stalk or =filament=. The filament is often so short as to seem to be absent, and the anther is then said to be _sessile_. The anther bears the pollen spores. It is made up of two or four parts (known as sporangia or spore-cases), which burst and discharge the pollen. _When the pollen is shed, the stamen dies._

The _pistil has three parts_: the lowest, or seed-bearing part, which is the =ovary=; the =stigma= at the upper extremity, which is a flattened or expanded surface, and usually roughened or sticky; the stalk-like part or =style=, connecting the ovary and stigma. Sometimes the style is apparently wanting, and the stigma is said to be sessile on the ovary. These parts are shown in the fuchsia (Fig. 174). The ovary or seed vessel is at _a_. A long style, bearing a large stigma, projects from the flower. See also Figs. 175 and 176.

[Illustration: FIG. 175.--THE STRUCTURE OF A PLUM BLOSSOM.

_se_, sepals; _p_, petals; _sta_, stamens; _o_, ovary; _s_, style; _st_, stigma. The pistil consists of the ovary, style, and stigma. It contains the seed part. The stamens are tipped with anthers, in which the pollen is borne. The ovary, _o_, ripens into the fruit.]

Stamens and pistils probably are homologous with leaves. A pistil is sometimes conceived to represent anciently a leaf as if rolled into a tube; and an anther, a leaf of which the edges may have been turned in on the midrib.

[Illustration: FIG. 176.--SIMPLE PISTILS OF BUTTERCUP, one in longitudinal section.]

The pistil may be of _one part or compartment, or of many parts_. The different units or parts of which it is composed are =carpels=. Each carpel is homologous with a leaf. Each carpel bears one or more seeds. A pistil of one carpel is =simple=; of two or more carpels, =compound=. Usually the structure of the pistil may be determined by cutting horizontally across the lower or seed-bearing part, as Figs. 177, 178 explain. A flower may contain a simple pistil (one carpel), as the pea (Fig. 177); _several simple pistils_ (several separate carpels), as the buttercup (Fig. 176); or a _compound pistil_ with carpels united, as the Saint John’s wort (Fig. 178) and apple. How many carpels in an apple? A peach? An okra pod? A bean pod? The seed cavity in each carpel is called a =locule= (Latin _locus_, a place). In these locules _the seeds are borne_.

[Illustration: FIG. 177.--PISTIL OF GARDEN PEA, the stamens being pulled down in order to disclose it; also a section showing the single compartment (compare Fig. 188).]

[Illustration: FIG. 178.--COMPOUND PISTIL OF A ST. JOHN’S WORT. It has 5 carpels.]

=Conformation of the Flower.=--A flower that has calyx, corolla, stamens, and pistils is said to be =complete= (Fig. 173); all others are =incomplete=. In some flowers both the floral envelopes are wanting: such are =naked=. When one of the floral envelope series is wanting, the remaining series is said to be calyx, and the flower is therefore =apetalous= (without petals). The knotweed (Fig. 179), smartweed, buckwheat, elm are examples.

[Illustration: FIG. 179.--KNOTWEED, a very common but inconspicuous plant along hard walks and roads. Two flowers, enlarged, are shown at the right. These flowers are very small and borne in the axils of the leaves.]

Some flowers lack the pistils: these are =staminate=, whether the envelopes are missing or not. Others lack the stamens: these are =pistillate=. Others have neither stamens nor pistils: these are =sterile= (snowball and hydrangea). Those that have both stamens and pistils are =perfect=, whether or not the envelopes are missing. Those that lack either stamens or pistils are =imperfect= or =diclinous=. Staminate and pistillate flowers are imperfect or diclinous.

[Illustration: FIG. 180.--STAMINATE CATKINS OF OAK. The pistillate flowers are in the leaf axils, and not shown in this picture.]

[Illustration: FIG. 181.--BEGONIA FLOWERS.

Staminate at _A_; pistillate below, with the winged ovary at _B_.]

When staminate and pistillate flowers are borne on the same plant, _e.g._ oak (Fig. 180), corn, beech, chestnut, hazel, walnut, hickory, pine, begonia (Fig. 181), watermelon, gourd, pumpkin, the plant is =monœcious= (“in one house”). When they are on different plants, _e.g._ poplar, cottonwood, bois d’arc, willow (Fig. 182), the plant is =diœcious= (“in two houses”). Some varieties of strawberry, grape, and mulberry are partly diœcious. Is the rose either monœcious or diœcious?

[Illustration: FIG. 182.--CATKINS OF A WILLOW.

A staminate flower is shown at _s_, and a pistillate flower at _p_. The staminate and pistillate are on different plants.]

[Illustration: FIG. 183.--FLOWER OF GARDEN NASTURTIUM.

Separate petal at _a_. The calyx is produced into a spur.]

[Illustration: FIG. 184.--THE FIVE PETALS OF THE PANSY, detached to show the form.]

[Illustration: FIG. 185.--FLOWER OF CATNIP.]

Flowers in which the parts of each series are alike are said to be =regular= (as in Figs. 173, 174, 175). Those in which some parts are unlike other parts of the same series are =irregular=. Their regularity may be in calyx, as in nasturtium (Fig. 183); in corolla (Figs. 184, 185); in the stamens (compare nasturtium, catnip, Fig. 185, sage); in the pistils. Irregularity is most frequent in the corolla.

=Various Forms of Corolla.=--The corolla often assumes very definite or distinct forms, especially when gamopetalous. It may have a long tube with a wide-flaring limb, when it is said to be =funnelform=, as in morning-glory and pumpkin. If the tube is very narrow and the limb stands at right angles to it, the corolla is =salverform=, as in phlox. If the tube is very short and the limb wide-spreading and nearly circular in outline, the corolla is =rotate= or =wheel-shaped=, as in potato.

A gamopetalous corolla or gamosepalous calyx is often cleft in such way as to make two prominent parts. Such parts are said to be =lipped= or =labiate=. Each of the lips or lobes may be notched or toothed. In 5-membered flowers, the lower lip is usually 3-lobed and the upper one 2-lobed. Labiate flowers are characteristic of the mint family (Fig. 185), and the family therefore is called the Labiatæ. (Literally, labiate means merely “lipped,” without specifying the number of lips or lobes; but it is commonly used to designate 2-lipped flowers.) Strongly 2-parted polypetalous flowers may be said to be labiate; but the term is oftenest used for gamopetalous corollas.

Labiate gamopetalous flowers that are closed in the throat (or entrance to the tube) are said to be grinning or =personate= (personate means _masked_, or _person-like_). Snap-dragon is a typical example; also toadflax or butter-and-eggs (Fig. 186), and many related plants. Personate flowers usually have definite relations to insect pollination. Observe how an insect forces his head into the closed throat of the toadflax.

[Illustration: FIG. 186.--PERSONATE FLOWER OF TOADFLAX.]

The peculiar flowers of the pea tribes are explained in Figs. 187, 188.

[Illustration: FIG. 187.--FLOWERS OF THE COMMON BEAN, with one flower opened (_a_) to show the structure.]

[Illustration: FIG. 188.--DIAGRAM OF ALFALFA FLOWER IN SECTION:

_C_, calyx; _D_, standard; _W_, wing; _K_, keel; _T_, stamen-tube; _F_, filament of tenth stamen; _X_, stigma; _Y_, style; _O_, ovary; the dotted lines at _E_ show position of stamen tube, when pushed upward by insects. Enlarged.]

=Spathe Flowers.=--In many plants, very simple (often naked) flowers are borne in dense, more or less fleshy spikes, and the spike is inclosed in or attended by a leaf, sometimes corolla-like, known as a =spathe=. The spike of flowers is technically known as a =spadix=. This type of flower is characteristic of the great arum family, which is chiefly tropical. The commonest wild representatives in the North are Jack-in-the-pulpit, or Indian turnip, and skunk cabbage. In the former the flowers are all diclinous and naked. In the skunk cabbage all the flowers are perfect and have four sepals. The common calla is a good example of this type of inflorescence.

[Illustration: FIG. 189.--HEAD OF SUNFLOWER.]

=Compositous Flowers.=--The head (anthodium) or so-called “flower” of sunflower (Fig. 189), thistle, aster, dandelion, daisy, chrysanthemum, goldenrod, _is composed of several or many little flowers, or_ =florets=. These florets are inclosed in a more or less dense and usually green _involucre_. In the thistle (Fig. 190) this involucre is prickly. A longitudinal section discloses the florets, all attached at bottom to a common torus, and densely packed in the involucre. The pink tips of these florets constitute the showy part of the head.

[Illustration: FIG. 190.--LONGITUDINAL SECTION OF THISTLE HEAD; also a FLORET OF THISTLE.]

Each floret of the thistle (Fig. 190) is a complete flower. At _a_ is the ovary. At _b_ is a much-divided plumy calyx, known as the =pappus=. The corolla is long-tubed, rising above the pappus, and is enlarged and 5-lobed at the top, _c_. The style projects at _e_. The five anthers are united about the style in a ring at _d_. Such anthers are said to be =syngenesious=. These are the various parts of the florets of the Compositæ. In some cases the pappus is in the form of barbs, bristles, or scales, and sometimes it is wanting. The pappus, as we shall see later, assists in distributing the seed. Often the florets are not all alike. The corolla of those in the outer circles may be developed into a _long, straplike, or tubular part_, and the head then has the appearance of being one flower with a border of petals. Of such is the sunflower (Fig. 189), aster, bachelor’s button or cornflower, and field daisy (Fig. 211). These long corolla-limbs are called rays. In some cultivated composites, all the florets may develop =rays=, as in the dahlia and chrysanthemum. In some species, as dandelion, all the florets naturally have rays. Syngenesious arrangement of anthers is the most characteristic single feature of the composites.

[Illustration: FIG. 191.--PETALS ARISING FROM THE STAMINAL COLUMN OF HOLLYHOCK, and accessory petals in the corolla-whorl.]

=Double Flowers.=--Under the stimulus of cultivation and increased food supply, flowers tend to become double. True doubling arises in two ways, morphologically: (1) _stamens or pistils may produce petals_ (Fig. 191); (2) _adventitious or accessory petals may arise in the circle of petals_. Both of these categories may be present in the same flower. In the full double hollyhock the petals derived from the staminal column are shorter and make a rosette in the center of the flower. In Fig. 192 is shown the doubling of a daffodil by the modification of stamens. Other modifications of flowers are sometimes known as doubling. For example, double dahlias, chrysanthemums, and sunflowers are forms in which the disk flowers have developed rays. The snowball is another case. In the wild snowball the external flowers of the cluster are large and sterile. In the cultivated plant all the flowers have become large and sterile. Hydrangea is a similar case.

[Illustration: FIG. 192.--NARCISSUS OR DAFFODIL. Single flower at the right.]

SUGGESTIONS.--=145.= If the pupil has been skillfully conducted through this chapter _by means of careful study of specimens_ rather than as a mere memorizing process, he will be in mood to challenge any flower that he sees and to make an effort to understand it. Flowers are endlessly modified in form; but they can be understood if the pupil looks first for the anthers and ovaries. How may anthers and ovaries always be distinguished? =146.= It is excellent practice to find the flowers in plants that are commonly known by name, and to determine the main points in their structure. What are the flowers in Indian corn? pumpkin or squash? celery? cabbage? potato? pea? tomato? okra? cotton? rhubarb? chestnut? wheat? oats? =147.= Do all forest trees have flowers? Explain. =148.= Name all the monœcious plants you know. Diœcious. =149.= What plants do you know that bloom before the leaves appear? Do any bloom after the leaves fall? =150.= Explain the flowers of marigold, hyacinth, lettuce, clover, asparagus, garden calla, aster, locust, onion, burdock, lily-of-the-valley, crocus, Golden Glow rudbeckia, cowpea. =151.= Define a _flower_.

NOTE TO THE TEACHER.--It cannot be urged too often that _the specimens themselves_ be studied. If this chapter becomes a mere recitation on names and definitions, the exercise will be worse than useless. Properly taught by means of the flowers themselves, the names become merely incidental and a part of the pupil’s language, and the subject has living interest.