acute. In their direction they are erect or reflexed (with their apices downwards), spreading outwards (divergent or patulous), or arched inwards (connivent). They are usually of a greenish colour (herbaceous); but sometimes they are coloured or petaloid, as in the fuchsia, tropāeolum, globe-flower and pomegranate. Whatever be its colour, the external envelope of the flower is considered as the calyx. The vascular bundles sometimes form a prominent rib, which indicates the middle of the sepal; at other times they form several ribs. The venation is useful as pointing out the number of leaves which constitute a gamosepalous calyx. In a polysepalous calyx the number of the parts is indicated by Greek numerals prefixed; thus, a calyx which has three sepals is trisepalous; one with five sepals is pentasepalous. The sepals occasionally are of different forms and sizes. In Aconite one of them is shaped like a helmet (galeate). In a gamosepalous calyx the sepals are united in various ways, sometimes very slightly, and their number is marked by the divisions at the apex. These divisions either are simple projections in the form of acute or obtuse teeth (fig. 49); or they extend down the calyx as fissures about half-way, the calyx being trifid (three-cleft), quinquefid (five-cleft), &c., according to their number; or they reach to near the base in the form of partitions, the calyx being tripartite, quadripartite, quinquepartite, &c. The union of the parts may be complete, and the calyx may be quite entire or truncate, as in some Correas, the venation being the chief indication of the different parts. The cohesion is sometimes irregular, some parts uniting to a greater extent than others; thus a two-lipped or labiate calyx is formed. The upper lip is often composed of three parts, which are thus posterior or next the axis, while the lower has two, which are anterior. The part formed by the union of the sepals is called the tube of the calyx; the portion where the sepals are free is the limb.
 |
 |
 |
| |||||
| Fig. 49. | Fig. 50. | |||||||
 | ||||||||
| Fig. 51. | Fig. 52. | Fig. 53. | ||||||
|
Fig. 49.—Gamosepalous five-toothed calyx of Campion (Lychnis). | ||||||||
|
Fig. 50.—Obsolete calyx (c) of Madder (Rubia) adherent to the pistil, in the form of a rim. | ||||||||
|
Fig. 51.—Feathery pappus attached to the fruit of Groundsel (Senecio vulgaris). | ||||||||
|
Fig. 52.—Caducous calyx (c) of Poppy. There are two sepals which fall off before the petals expand. | ||||||||
|
Fig. 53.—Fruit of Physalis Alkekengi, consisting of the persistent calyx (s), surrounding the berry (fr), derived from the ovary. (After Duchartre.) | ||||||||
Occasionally, certain parts of the sepals undergo marked enlargement. In the violet the calycine segments are prolonged downwards beyond their insertions, and in the Indian cress (Tropaeolum) this prolongation is in the form of a spur (calcar), formed by three sepals; in Delphinium it is formed by one. In Pelargonium the spur from one of the sepals is adherent to the flower-stalk. In Potentilla and allied genera an epicalyx is formed by the development of stipules from the sepals, which form an apparent outer calyx, the parts of which alternate with the true sepals. In Malvaceae an epicalyx is formed by the bracteoles. Degenerations take place in the calyx, so that it becomes dry, scaly and glumaceous (like the glumes of grasses), as in the rushes (Juncaceae); hairy, as in Compositae; or a mere rim, as in some Umbelliferae and Acanthaceae, and in Madder (Rubia tinctorum, fig. 50), when it is called obsolete or marginate. In Compositae, Dipsacaceae and Valerianaceae the calyx is attached to the pistil, and its limb is developed in the form of hairs called pappus (fig. 51). This pappus is either simple (pilose) or feathery (plumose). In Valeriana the superior calyx is at first an obsolete rim, but as the fruit ripens it is shown to consist of hairs rolled inwards, which expand so as to waft the fruit. The calyx sometimes falls off before the flower expands, as in poppies, and is caducous (fig. 52); or along with the corolla, as in Ranunculus, and is deciduous; or it remains after flowering (persistent) as in Labiatae, Scrophulariaceae, and Boraginaceae; or its base only is persistent, as in Datura Stramonium. In Eschscholtzia and Eucalyptus the sepals remain united at the upper part, and become disarticulated at the base or middle, so as to come off in the form of a lid or funnel. Such a calyx is operculate or calyptrate. The existence or non-existence of an articulation determines the deciduous or persistent nature of the calyx.
The receptacle bearing the calyx is sometimes united to the pistil, and enlarges so as to form a part of the fruit, as in the apple, pear, &c. In these fruits the withered calyx is seen at the apex. Sometimes a persistent calyx increases much after flowering, and encloses the fruit without being incorporated with it, becoming accrescent, as in various species of Physalis (fig. 53); at other times it remains in a withered or marcescent form, as in Erica; sometimes it becomes inflated or vesicular, as in sea campion (Silene maritima).
The corolla is the more or less coloured attractive inner floral envelope; generally the most conspicuous whorl. It is present in the greater number of Dicotyledons. Petals differ more from ordinary leaves than sepals do, and are Corolla. much more nearly allied to the staminal whorl. In some cases, however, they are transformed into leaves, like the calyx, and occasionally leaf-buds are developed in their axil They are seldom green, although occasionally that colour is met with, as in some species of Cobaea, Hoya viridiflora, Gonolobus viridiflorus and Pentatropis spiralis. As a rule they are highly coloured, the colouring matter being contained in the cell-sap, as in blue or red flowers, or in plastids (chromoplasts), as generally in yellow flowers, or in both forms, as in many orange-coloured or reddish flowers. The attractiveness of the petal is often due wholly or in part to surface markings; thus the cuticle of the petal of a pelargonium, when viewed with a ½ or ¼-in. object-glass, shows beautiful hexagons, the boundaries of which are ornamented with several inflected loops in the sides of the cells.
Petals are generally glabrous or smooth; but, in some instances, hairs are produced on their surface. Petaline hairs, though sparse and scattered, present occasionally the same arrangement as those which occur on the leaves; thus, in Bombaceae they are stellate. Coloured hairs are seen on the petals of Menyanthes, and on the segments of the perianth of Iris. They serve various purposes in the economy of the flower, often closing the way to the honey-secreting part of the flower to small insects, whose visits would be useless for purposes of pollination. Although petals are usually very thin and delicate in their texture, they occasionally become thick and fleshy, as in Stapelia and Rafflesia; or dry, as in heaths; or hard and stiff, as in Xylopia. A petal often consists of two portions—the lower narrow, resembling the petiole of a leaf, and called the unguis or claw; the upper broader, like the blade of a leaf, and called the lamina or limb. These parts are seen in the petals of the wallflower (fig. 54). The claw is often wanting, as in the crowfoot (fig. 55) and the poppy, and the petals are then sessile. According to the development of veins and the growth of cellular tissue, petals present varieties similar to those of leaves. Thus the margin is either entire or divided into lobes or teeth. These teeth sometimes form a regular fringe round the margin, and the
