Fig. 326. Simple pistil of Podophyllum, cut across, showing ovules borne on placenta.
Fig. 327. Pistil of a Saxifrage, of two simple carpels or pistil-leaves, united at the base only, cut across both above and below.
Fig. 328. Compound 3-carpellary pistil of common St. John's-wort, cut across: the three styles separate.
Fig. 329. The same of shrubby St. John's-wort; the three styles as well as ovaries here united into one.
Fig. 330. Compound 3-carpellary pistil of Tradescantia or Spiderwort; the three stigmas as well as styles and ovary completely coalescent into one.
309. A Compound Pistil is a combination of two, three, or a greater number of pistil-leaves or carpels in a circle, united into one body, at least by their ovaries. The annexed figures should make it clear. A series of Saxifrages might be selected the gynœcium of which would show every gradation between two simple pistils, or separate carpels, and their complete coalescence into one compound and two-celled ovary. Even when the constituent styles and stigmas are completely coalescent into one, the nature of the combination is usually revealed by some external lines or grooves, or (as in Fig. 328-330) by the internal partitions, or the number of the placentæ. The simplest case of compound pistil is that
310. With two or more Cells and Axile Placentæ, namely, with as many cells as there are carpels, that have united to compose the organ. Such a pistil is just what would be formed if the simple pistils (two, three, or five in a circle, as the case may be), like those of a Pæony or Stonecrop (Fig. 224, 225), pressed together in the centre of the flower, were to cohere by their contiguous parts. In such a case the placentæ are naturally axile, or all brought together in the axis or centre; and the ovary has as many Dissepiments, or internal Partitions, as there are carpels in its composition. For these are the contiguous and coalescent walls or sides of the component carpels. When such pistils ripen into pods, they often separate along these lines into their elementary carpels.
Fig. 331, 332. Pistil of a Sandwort, with vertical and transverse section of the ovary: free central placenta.
311. One-celled, with free Central Placenta. The commoner case is that of Purslane (Fig. 272) and of the Pink and Chickweed families (Fig. 331, 332). This is explained by supposing that the partitions (such as those of Fig. 329) have early vanished or have been suppressed. Indeed, traces of them may often be detected in Pinks. On the other hand, it is equally supposable that in the Primula family the free central is derived from parietal placentation by the carpels bearing ovules only at base, and forming a consolidated common placenta in the axis. Mitella and Dionæa help out this conception.
Fig. 333. Plan of a one-celled ovary of three carpel-leaves, with parietal placentæ, cut across below, where it is complete; the upper part showing the top of the three leaves it is composed of, approaching, but not united.
Fig. 334. Cross section of the ovary of Frost weed (Helianthemum), with three parietal placentæ, bearing ovules.
Fig. 335. Cross section of an ovary of Hypericum graveolens, the three large placentæ meeting in the centre, so as to form a three-celled ovary. 336. Same in fruit, the placentæ now separate and rounded.
312. One-celled, with Parietal Placentæ. In this not uncommon case it is conceived that the two or three or more carpel-leaves of such a compound pistil coalesce by their adjacent edges, just as sepal-leaves do to form a gamosepalous calyx, or petals to form a gamopetalous corolla, and as is shown in the diagram, Fig. 333, and in an actual cross-section, Fig. 334. Here each carpel is an open leaf, or with some introflexion, bearing ovules along its margins; and each placenta consists of the contiguous margins of two pistil-leaves grown together. There is every gradation between this and the three-celled ovary with the placentæ in the axis, even in the same genus, sometimes even in different stages in the same pistil (Fig. 335, 336).
§ 2. GYMNOSPERMOUS GYNŒCIUM.
313. The ordinary pistil has a closed ovary, and accordingly the pollen can act upon the contained ovules only indirectly, through the stigma. This is expressed in a term of Greek derivation, viz.:—
Angiospermous, meaning that the seeds are borne in a sac or closed vessel. The counterpart term is
Gymnospermous, meaning naked-seeded. This kind of pistil, or gynœcium, the simplest of all, yet the most peculiar, characterizes the Pine family and its relatives.
Fig. 337. A pistil, that is, a scale of the cone, of a Larch, at the time of flowering; inside view, showing its pair of naked ovules.
Fig. 338. Branchlet of the American Arbor-Vitæ, considerably larger than in nature, terminated by its pistillate flowers, each consisting of a single scale (an open pistil), together forming a small cone.
Fig. 339. One of the scales or carpels of the last, removed and more enlarged, the inside exposed to view, showing a pair of ovules on its base.
314. While the ordinary simple pistil is conceived by the botanist to be a leaf rolled together into a closed pod (306), those of the Pine, Larch (Fig. 337), Cedar, and Arbor-Vitæ (Fig. 338, 339) are open leaves, in the form of scales, each bearing two or more ovules on the inner face, next the base. At the time of blossoming, these pistil-leaves of the young cone diverge, and the pollen, so abundantly shed from the staminate blossoms, falls directly upon the exposed ovules. Afterward the scales close over each other until the seeds are ripe. Then they separate that the seeds may be shed. As the pollen acts directly on the ovules, such pistil (or organ acting as pistil) has no stigma.
315. In the Yew, and in Torreya and Gingko, the gynœcium is reduced to extremest simplicity, that is, to a naked ovule, without any visible carpel.
316. In Cycas the large naked ovules are borne on the margins or lobes of an obvious open leaf. All Gymnospermous plants have other peculiarities, also distinguishing them, as a class, from Angiospermous plants.
Section XI. OVULES.
317. Ovule (from the Latin, meaning a little egg) is the technical name of that which in the flower answers to and becomes the seed.
318. Ovules are naked in gymnospermous plants (as just described), in all others they are enclosed in the ovary. They may be produced along the whole length of the cell or cells of the ovary, and then they are apt to be numerous, or only from some part of it, generally the top or the bottom. In this case they are usually few or single (solitary, as in Fig. 341-343). They may be sessile, i. e. without stalk, or they may be attached by a distinct stalk, the Funicle or Funiculus (Fig. 340).
Fig. 341. Section of the ovary of a Buttercup, lengthwise, showing its ascending ovule.
Fig. 342. Section of the ovary of Buckwheat, showing the erect ovule.
Fig. 343. Section of the ovary of Anemone, showing its suspended ovule.
319. Considered as to then position and direction in the ovary, they are
Horizontal, when they are neither turned upward nor downward, as in Podophyllum (Fig. 326),
Ascending, when rising obliquely upwards, usually from the side of the cell, not from its very base, as in the Buttercup (Fig. 341), and the Purslane (Fig. 272),
Erect, when rising upright from the very base of the cell, as in the Buckwheat (Fig. 342),
Pendulous, when hanging from the side or from near the top, as in the Flax (Fig. 270), and
Suspended, when hanging perpendicularly from the very summit of the cell, as in the Anemone (Fig. 343). All these terms equally apply to seeds.
320. In structure an ovule is a pulpy mass of tissue, usually with one or two coats or coverings. The following parts are to be noted, viz.—
Kernel or Nucleus, the body of the ovule. In the Mistletoe and some related plants, there is only this nucleus, the coats being wanting.
Teguments, or coats, sometimes only one, more commonly two. When two, one has been called Primine, the other Secundine. It will serve all purposes to call them simply outer and inner ovule coats.
Orifice, or Foramen, an opening through the coats at the organic apex of the ovule. In the seed it is Micropyle.
Chalaza, the place where the coats and the kernel of the ovule blend.
Hilum, the place of junction of the funiculus with the body of the ovule.
Fig. 344. Orthotropous ovule of Buckwheat: c, hilum and chalaza; f, orifice.
Fig. 345. Campylotropous ovule of a Chickweed: c, hilum and chalaza; f, orifice.
Fig. 346. Amphitropous ovule of Mallow: f, orifice; h, hilum; r, rhaphe; c, chalaza.
Fig. 347. Anatropous ovule of a Violet, the parts lettered as in the last.
321. The Kinds of Ovules. The ovules in their growth develop in three or four different ways and thereby are distinguished into
Orthotropous or Straight, those which develop without curving or turning, as in Fig. 344. The chalaza is at the insertion or base, the foramen or orifice is at the apex. This is the simplest, but the least common kind of ovule.
Campylotropous or Incurved, in which, by the greater growth of one side, the ovule curves into a kidney-shaped outline, so bringing the orifice down close to the base or chalaza; as in Fig. 345.
Amphitropous or Half Inverted, Fig. 346. Here the forming ovule, instead of curving perceptibly, keeps its axis nearly straight, and, as it grows, turns round upon its base so far as to become transverse to its funiculus, and adnate to its upper part for some distance. Therefore in this case the attachment of the funiculus or stalk is about the middle, the chalaza is at one end, the orifice at the other.
Fig. 348-350. Three early stages in the growth of ovule of a Magnolia, showing the forming outer and inner coats which even in the later figure have not yet completely enclosed the nucleus; 351, further advanced, and 352, completely anatropous ovule.
Fig. 353. Longitudinal section, and 354, transverse section of 352.
Fig. 355. Same as 353, enlarged showing the parts in section: a, outer coat; b, inner coat; c, nucleus; d, rhaphe.
Anatropous or Inverted, as in Fig. 347, the commonest kind, so called because in its growth it has as it were turned over upon its stalk, to which it has continued adnate. The organic base, or chalaza, thus becomes the apparent summit, and the orifice is at the base, by the side of the hilum or place of attachment. The adnate portion of the funiculus, which appears as a ridge or cord extending from the hilum to the chalaza, and which distinguishes this kind of ovule, is called the Rhaphe. The amphitropous ovule (Fig. 346) has a short or incomplete rhaphe.
322. Fig. 348-352 show the stages through which an ovule becomes anatropous in the course of its growth. The annexed two figures are sections of such an ovule at maturity; and Fig. 355 is Fig. 353 enlarged, with the parts lettered.
Section XII. MODIFICATIONS OF THE RECEPTACLE.
Fig. 356. Longitudinal section of flower of Silene Pennsylvanica, showing stipe between calyx and corolla.
Fig. 357. Flower of a Cleome of the section Gynandropsis, showing broadened receptacle to bear petals, lengthened stipe below the stamens, and another between these and pistil.
Fig. 358. Pistil of Geranium or Cranesbill.
Fig. 359. The same, ripe, with the five carpels splitting away from the long beak (carpophore), and hanging from its top by their recurving styles.
323. The Torus or Receptacle of the flower (237, Fig. 223) is the portion which belongs to the stem or axis. In all preceding illustrations it is small and short. But it sometimes lengthens, sometimes thickens or variously enlarges, and takes on various forms. Some of these have received special names, very few of which are in common use. A lengthened portion of the receptacle is called
A Stipe. This name, which means simply a trunk or stalk, is used in botany for various stalks, even for the leaf-stalk in Ferns. It is also applied to the stalk or petiole of a carpel, in the rare cases when there is any, as in Goldthread. Then it is technically distinguished as a Thecaphore. When there is a stalk, or lengthened internode of receptacle, directly under a compound pistil, as in Stanleya and some other Cruciferæ, it is called a Gynophore. When the stalk is developed below the stamens, as in most species of Silene (Fig. 356), it has been called an Anthophore or Gonophore. In Fig. 357 the torus is dilated above the calyx where it bears the petals, then there is a long internode (gonophore) between it and the stamens; then a shorter one (gynophore) between these and the pistil.
324. A Carpophore is a prolongation of receptacle or axis between the carpels and bearing them. Umbelliferous plants and Geranium (Fig. 358, 359) afford characteristic examples.
Fig. 360. Longitudinal section of a young strawberry, enlarged.
Fig. 361. Similar section of a young Rose-hip.
Fig. 362. Enlarged and top-shaped receptacle of Nelumbium, at maturity.
325. Flowers with very numerous simple pistils generally have the receptacle enlarged so as to give them room; sometimes becoming broad and flat, as in the Flowering Raspberry, sometimes elongated, as in the Blackberry, the Magnolia, etc. It is the receptacle in the Strawberry (Fig. 360), much enlarged and pulpy when ripe, which forms the eatable part of the fruit, and bears the small seed-like pistils on its surface. In the Rose (Fig. 361), instead of being convex or conical, the receptacle is deeply concave, or urn-shaped. Indeed, a Rose-hip may be likened to a strawberry turned inside out, like the finger of a glove reversed, and the whole covered by the adherent tube of the calyx. The calyx remains beneath in the strawberry.
326. In Nelumbium, of the Water-Lily family, the singular and greatly enlarged receptacle is shaped like a top, and bears the small pistils immersed in separate cavities of its flat upper surface (Fig. 362).
327. A Disk is an enlarged low receptacle or an outgrowth from it, hypogynous when underneath the pistil, as in Rue and the Orange (Fig. 363), and perigynous when adnate to calyx-tube (as in Buckthorn, Fig. 364, 365), and Cherry (Fig. 271), or to both calyx-tube and ovary, as in Hawthorn (Fig. 273). A flattened hypogynous disk, underlying the ovary or ovaries, and from which they fall away at maturity, is sometimes called a Gynobase, as in the Rue family. In some Borragineous flowers, such as Houndstongue, the gynobase runs up in the centre between the carpels into a carpophore. The so-called epigynous disk (or Stylopodium) crowning the summit of the ovary in flowers of Umbelliferæ, etc., cannot be said to belong to the receptacle.
Fig. 364. Flower of a Buckthorn showing a conspicuous perigynous disk.
Fig. 365. Vertical section of same flower.
Section XIII. FERTILIZATION.
328. The end of the flower is attained when the ovules become seeds. A flower remains for a certain time (longer or shorter according to the species) in anthesis, that is, in the proper state for the fulfilment of this end. During anthesis, the ovules have to be fertilized by the pollen; or at least some pollen has to reach the stigma, or in gymnospermy the ovule itself, and to set up the peculiar growth upon its moist and permeable tissue, which has for result the production of an embryo in the ovules. By this the ovules are said to be fertilized. The first step is pollination, or, so to say, the sowing of the proper pollen upon the stigma, where it is to germinate.
§ 1. ADAPTATIONS FOR POLLINATION OF THE STIGMA.
329. These various and ever-interesting adaptations and processes are illustrated in the "Botanical Text Book, Structural Botany," chap. VI. sect. iv., also in a brief and simple way in "Botany for Young People, How Plants Behave." So mere outlines only are given here.
330. Sometimes the application of pollen to the stigma is left to chance, as in diœcious wind-fertilized flowers; sometimes it is rendered very sure, as in flowers that are fertilized in the bud; sometimes the pollen is prevented from reaching the stigma of the same flower, although placed very near to it, but then there are always arrangements for its transference to the stigma of some other blossom of the kind. It is among these last that the most exquisite adaptations are met with.
331. Accordingly, some flowers are particularly adapted to close or self-fertilization; others to cross fertilization; some for either, according to circumstances.
Close Fertilization occurs when the pollen reaches and acts upon a stigma of the very same flower (this is also called self-fertilization), or, less closely, upon other blossoms of the same cluster or the same individual plant.
Cross Fertilization occurs when ovules are fertilized by pollen of other individuals of the same species.
Hybridization occurs when ovules are fertilized by pollen of some other (necessarily some nearly related) species.
332. Close Fertilization would seem to be the natural result in ordinary hermaphrodite flowers; but it is by no means so in all of them. More commonly the arrangements are such that it takes place only after some opportunity for cross fertilization has been afforded. But close fertilization is inevitable in what are called
Cleistogamous Flowers, that is, in those which are fertilized in the flower-bud, while still unopened. Most flowers of this kind, indeed, never open at all; but the closed floral coverings are forced off by the growth of the precociously fertilized pistil. Common examples of this are found in the earlier blossoms of Specularia perfoliata, in the later ones of most Violets, especially the stemless species, in our wild Jewel weeds or Impatiens, in the subterranean shoots of Amphicarpæa. Every plant which produces these cleistogamous or bud-fertilized flowers bears also more conspicuous and open flowers, usually of bright colors. The latter very commonly fail to set seed, but the former are prolific.
333. Cross Fertilization is naturally provided for in diœcious plants (249), is much favored in monœcious plants (249), and hardly less so in dichogamous and in heterogonous flowers (338). Cross fertilization depends upon the transportation of pollen; and the two principal agents of conveyance are winds and insects. Most flowers are in their whole structure adapted either to the one or to the other.
334. Wind-fertilizable or Anemophilous flowers are more commonly diœcious or monœcious, as in Pines and all coniferous trees, Oaks, and Birches, and Sedges; yet sometimes hermaphrodite, as in Plantains and most Grasses; they produce a superabundance of very light pollen, adapted to be wind-borne; and they offer neither nectar to feed winged insects, nor fragrance nor bright colors to attract them.
335. Insect-fertilizable or Entomophilous flowers are those which are sought by insects, for pollen or for nectar, or for both. Through their visits pollen is conveyed from one flower and from one plant to another. Insects are attracted to such blossoms by their bright colors, or their fragrance, or by the nectar (the material of honey) there provided for them. While supplying their own needs, they carry pollen from anthers to stigmas and from plant to plant, thus bringing about a certain amount of cross fertilization. Willows and some other diœcious flowers are so fertilized, chiefly by bees. But most insect-visited flowers have the stamens and pistils associated either in the same or in contiguous blossoms. Even when in the same blossom, anthers and stigmas are very commonly so situated that under insect-visitation, some pollen is more likely to be deposited upon other than upon own stigmas, so giving a chance for cross as well as for close fertilization. On the other hand, numerous flowers, of very various kinds, have their parts so arranged that they must almost necessarily be cross-fertilized or be barren, and are therefore dependent upon the aid of insects. This aid is secured by different exquisite adaptations and contrivances, which would need a volume for full illustration. Indeed, there is a good number of volumes devoted to this subject.[1]
336. Some of the adaptations which favor or ensure cross fertilization are peculiar to the particular kind of blossom. Orchids, Milkweeds, Kalmia, Iris, and papilionaceous flowers each have their own special contrivances, quite different for each.
337. Irregular flowers (253) and especially irregular corollas are usually adaptations to insect-visitation. So are all Nectaries, whether hollow spurs, sacs, or other concavities in which nectar is secreted, and all nectariferous glands.
338. Moreover, there are two arrangements for cross fertilization common to hermaphrodite flowers in various different families of plants, which have received special names, Dichogamy and Heterogony.
339. Dichogamy is the commoner case. Flowers are dichogamous when the anthers discharge their pollen either before or after the stigmas of that flower are in a condition to receive it. Such flowers are
Proterandrous, when the anthers are earlier than the stigmas, as in Gentians, Campanula, Epilobium, etc.
Proterogynous, when the stigmas are mature and moistened for the reception of pollen, before the anthers of that blossom are ready to supply it, and are withered before that pollen can be supplied. Plantains or Ribworts (mostly wind-fertilized) are strikingly proterogynous: so is Amorpha, our Papaws, Scrophularia, and in a less degree the blossom of Pears, Hawthorns, and Horse-chestnut.
340. In Sabbatia, the large-flowered species of Epilobium, and strikingly in Clerodendron, the dichogamy is supplemented and perfected by movements of the stamens and style, one or both, adjusted to make sure of cross fertilization.
341. Heterogony. This is the case in which hermaphrodite and fertile flowers of two sorts are produced on different individuals of the same species; one sort having higher anthers and lower stigmas, the other having higher stigmas and lower anthers. Thus reciprocally disposed, a visiting insect carries pollen from the high anthers of the one to the high stigma of the other, and from the low anthers of the one to the low stigma of the other. These plants are practically as if diœcious, with the advantage that both kinds are fruitful. Houstonia and Mitchella, or Partridge-berry, are excellent and familiar examples. These are cases of
Heterogone Dimorphism, the relative lengths being only short and long reciprocally.
Heterogone Trimorphism, in which there is a mid-length as well as a long and a short set of stamens and style; occurs in Lythrum Salicaria and some species of Oxalis.
342. There must be some essential advantage in cross fertilization or cross breeding. Otherwise all these various, elaborate, and exquisitely adjusted adaptations would be aimless. Doubtless the advantage is the same as that which is realized in all the higher animals by the distinction of sexes.
§ 2. ACTION OF POLLEN, AND FORMATION OF THE EMBRYO.
343. Pollen-growth. A grain of pollen may be justly likened to one of the simple bodies (spores) which answer for seeds in Cryptogamous plants. Like one of these, it is capable of germination. When deposited upon the moist surface of the stigma (or in some cases even when at a certain distance) it grows from some point, its living inner coat breaking through the inert outer coat, and protruding in the form of a delicate tube. This as it lengthens penetrates the loose tissue of the stigma and of a loose conducting tissue in the style, feeds upon the nourishing liquid matter there provided, reaches the cavity of the ovary, enters the orifice of an ovule, and attaches its extremity to a sac, or the lining of a definite cavity, in the ovule, called the Embryo-Sac.
344. Origination of the Embryo. A globule of living matter in the embryo-sac is formed, and is in some way placed in close proximity to the apex of the pollen tube; it probably absorbs the contents of the latter; it then sets up a special growth, and the Embryo (8-10) or rudimentary plantlet in the seed is the result.
FOOTNOTES:
[1] Beginning with one by C. C. Sprengel in 1793, and again in our day with Darwin, "On the Various Contrivances by which Orchids are fertilized by Insects," and in succeeding works.
Section XIV. THE FRUIT.
345. Its Nature. The ovary matures into the Fruit. In the strictest sense the fruit is the seed-vessel, technically named the Pericarp. But practically it may include other parts organically connected with the pericarp. Especially the calyx, or a part of it, is often incorporated with the ovary, so as to be undistinguishably a portion of the pericarp, and it even forms along with the receptacle the whole bulk of such edible fruits as apples and pears. The receptacle is an obvious part in blackberries, and is the whole edible portion in the strawberry.
346. Also a cluster of distinct carpels may, in ripening, be consolidated or compacted, so as practically to be taken for one fruit. Such are raspberries, blackberries, the Magnolia fruit, etc. Moreover, the ripened product of many flowers may be compacted or grown together so as to form a single compound fruit.
347. Its kinds have therefore to be distinguished. Also various names of common use in descriptive botany have to be mentioned and defined.
348. In respect to composition, accordingly, fruits may be classified into
Simple, those which result from the ripening of a single pistil, and consist only of the matured ovary, either by itself, as in a cherry, or with calyx-tube completely incorporated with it, as in a gooseberry or cranberry.
Aggregate, when a cluster of carpels of the same flower are crowded into a mass; as in raspberries and blackberries.
Fig. 366. Forming fruit (capsule) of Gaultheria, with calyx thickening around its base. 367. Section of same mature, the berry-like calyx nearly enclosing the capsule.
Fig. 368. Section of a part of a strawberry. Compare with Fig. 360.
Fig. 369. Similar section of part of a blackberry. 370. One of its component simple fruits (drupe) in section, showing the pulp, stone, and contained seed; more enlarged. Compare with Fig. 375.
Accessory or Anthocarpous, when the surroundings or supports of the pistil make up a part of the mass; as does the loose calyx changed into a fleshy and berry-like envelope of our Wintergreen (Gaultheria, Fig. 366, 367) and Buffalo-berry, which are otherwise simple fruits. In an aggregate fruit such as the strawberry the great mass is receptacle (Fig. 360, 368); and in the blackberry (Fig. 369) the juicy receptacle forms the central part of the savory mass.
Multiple or Collective, when formed from several flowers consolidated into one mass, of which the common receptacle or axis of inflorescence, the floral envelopes, and even the bracts, etc., make a part. A mulberry (Fig. 408, which superficially much resembles a blackberry) is of this multiple sort. A pine-apple is another example.
349. In respect to texture or consistence, fruits may be distinguished into three kinds, viz.—
Fleshy Fruits, those which are more or less soft and juicy throughout;
Stone Fruits, or Drupaceous, the outer part fleshy like a berry, the inner hard or stony, like a nut; and
Dry Fruits, those which have no flesh or pulp.
350. In reference to the way of disseminating the contained seed, fruits are said to be
Indehiscent when they do not open at maturity. Fleshy fruits and stone fruits are of course indehiscent. The seed becomes free only through decay or by being fed upon by animals. Those which escape digestion are thus disseminated by the latter. Of dry fruits many are indehiscent; and these are variously arranged to be transported by animals. Some burst irregularly; many are
Dehiscent, that is, they split open regularly along certain lines, and discharge the seeds. A dehiscent fruit almost always contains many or several seeds, or at least more than one seed.
Fig. 371. Leafy shoot and berry (cut across) of the larger Cranberry, Vaccinium macrocarpon.
Fig. 372, 373. Pepo of Gourd, in section. 373. One carpel of same in diagram.
Fig. 374. Longitudinal and transverse sections of a pear (pome).
351. The principal kinds of fruit which have received substantive names and are of common use in descriptive botany are the following. Of fleshy fruits the leading kind is
352. The Berry, such as the gooseberry and currant, the blueberry and cranberry (Fig. 371), the tomato, and the grape. Here the whole flesh is soft throughout. The orange is a berry with a leathery rind.
353. The Pepo, or Gourd-fruit, is a hard-rinded berry, belonging to the Gourd family, such as the pumpkin, squash, cucumber, and melon, Fig. 372, 373.
354. The Pome is a name applied to the apple, pear (Fig. 374), and quince; fleshy fruits, like a berry, but the principal thickness is calyx, only the papery pods arranged like a star in the core really belonging to the carpels. The fruit of the Hawthorn is a drupaceous pome, something between pome and drupe.
355. Of fruits which are externally fleshy and internally hard the leading kind is
356. The Drupe, or Stone-fruit; of which the cherry, plum, and peach (Fig. 375) are familiar examples. In this the outer part of the thickness of the pericarp becomes fleshy, or softens like a berry, while the inner hardens, like a nut. From the way in which the pistil is constructed, it is evident that the fleshy part here answers to the lower, and the stone to the upper face of the component leaf. The layers or concentric portions of a drupe, or of any pericarp which is thus separable, are named, when thus distinguishable into three portions,—
Epicarp, the external layer, often the mere skin of the fruit,
Mesocarp, the middle layer, which is commonly the fleshy part, and
Endocarp, the innermost layer, the stone. But more commonly only two portions of a drupe are distinguished, and are named, the outer one
Sarcocarp or Exocarp, for the flesh, the first name referring to the fleshy character, the second to its being an external layer; and
Putamen or Endocarp, the Stone, within.
357. The typical or true drupe is of a single carpel. But, not to multiply technical names, this name is extended to all such fruits when fleshy without and stony within, although of compound pistil,—even to those having several or separable stones, such as the fruit of Holly. These stones in such drupes, or drupaceous fruits, are called Pyrenæ, or Nucules, or simply Nutlets of the drupe.
358. Of Dry fruits, there is a greater diversity of kinds having distinct names. The indehiscent sorts are commonly one-seeded.
Fig. 376. Akene of a Buttercup. 377. The same, divided lengthwise, to show the contained seed.
Fig. 378. Akene of Virgin's-bower, retaining the feathered style, which aids in dissemination.
359. The Akene or Achenium is a small, dry and indehiscent one-seeded fruit, often so seed-like in appearance that it is popularly taken for a naked seed. The fruit of the Buttercup or Crowfoot is a good example, Fig. 376, 377. Its nature, as a ripened pistil (in this case a simple carpel), is apparent by its bearing the remains of a style or stigma, or a scar from which this has fallen. It may retain the style and use it in various ways for dissemination (Fig. 378).
360. The fruit of Compositæ (though not of a single carpel) is also an akene. In this case the pericarp is invested by an adherent calyx-tube; the limb of which, when it has any, is called the Pappus. This name was first given to the down like that of the Thistle, but is applied to all forms under which the limb of the calyx of the "compound flower" appears. In Lettuce, Dandelion (Fig. 384), and the like, the achenium as it matures tapers upwards into a slender beak, like a stalk to the pappus.