Inflorescence and fruit

The peduncle and inflorescence develop from the apical meristem, the diameter of which is suddenly increased until the initiation of the peduncle (Kerns et al., 1936). The stage of inflorescence emergence is called 'red heart' because of the five to seven reddish peduncle bracts at its base. These bracts

Fig. 2.3. 1. Diagram of a transverse section of a 'Smooth Cayenne' leaf showing: a.c., aerating canal; f.s., fibre strand; e, epidermis; v.b., vascular bundle; m, mesophyll; ws.t., water-storage tissue. 2. Outer epidermis showing: cu, cuticle; s.b., silica body; u.w., undulating wall. 3. Aerating canal showing: c.a.c., central aerating canal; s.c., stellate cell; chl, chloroplast. 4. Lower boundary of water-storage tissue showing: ch, chlorenchyma; chl, chloroplast; p.c., palisade cells of water-storage tissue. 5. Lower epidermis showing: ss.r., substomatal ring; s.a.c., secondary aerating canal; l.a.c., lateral accessory cell; g.c., guard cell; ss.c., substomatal chamber; s.b., silica body; p, pore. 6. Hypodermis and mesophyll (trichomes not shown) showing: ch, chlorenchyma; chl, chloroplast; fi, fibres; hy, hypodermis. 7. Vascular bundle (mesophyll without chloroplasts) showing: ph, phloem; xy, xylem. (After Py et al., 1987, with permission.)

X 200

X 200

Inflorescence Pineapple Red Heart

Fig. 2.3. 1. Diagram of a transverse section of a 'Smooth Cayenne' leaf showing: a.c., aerating canal; f.s., fibre strand; e, epidermis; v.b., vascular bundle; m, mesophyll; ws.t., water-storage tissue. 2. Outer epidermis showing: cu, cuticle; s.b., silica body; u.w., undulating wall. 3. Aerating canal showing: c.a.c., central aerating canal; s.c., stellate cell; chl, chloroplast. 4. Lower boundary of water-storage tissue showing: ch, chlorenchyma; chl, chloroplast; p.c., palisade cells of water-storage tissue. 5. Lower epidermis showing: ss.r., substomatal ring; s.a.c., secondary aerating canal; l.a.c., lateral accessory cell; g.c., guard cell; ss.c., substomatal chamber; s.b., silica body; p, pore. 6. Hypodermis and mesophyll (trichomes not shown) showing: ch, chlorenchyma; chl, chloroplast; fi, fibres; hy, hypodermis. 7. Vascular bundle (mesophyll without chloroplasts) showing: ph, phloem; xy, xylem. (After Py et al., 1987, with permission.)

are shorter and narrower than the ordinary leaves. The peduncle elongates after flower formation. Its length varies widely with the botanical varieties or even cultivars. In addition to its bracts, it bears, in many cultivars, a variable number of slips (up to a dozen or more), which can be positioned more or less regularly between the stem and the fruit, at the axis of the peduncle bracts, or grouped just beneath the fruit. These slips can be considered as dwarfish 'aborted' fruits with a relatively large crown (Collins, 1960). They may constitute an appreciable source of planting material in extensive cultivation systems.

The inflorescence consists of fewer than 50 (in some wild clones) to more than 200 (in some cultivars) individual flowers; it is capped by a crown, composed of numerous short leaves (up to 150) on a short stem. The flowers or individual fruits are disposed around the central axis according to an 8/21 phyllotaxy in large-fruited cultivated pineapples (M.B. Linford, cited by Kerns et al., 1936) and a 5/13 phyllotaxy for small-fruited wild pineapples or for young cultivated pineapples flowering prematurely (Kerns et al., 1936). The fibrous axis containing the many vascular bundles that supply

Fig. 2.4. Transverse section of a mature root of 'Smooth Cayenne' pineapple showing: e, epidermis; ex, exodermis; oc, outer cortex with raphide cells (rc), whose transverse walls are collapsed to form air passages; ic, outer portion of inner cortex; t, tracheids; ph, phloem; p, pith; v, vessel; pc, pericycle; en, endodermis; l, large lacunae formed by collapse of many cells of inner cortex; rh, root hairs. (After Krauss, 1949b. © The University of Chicago, all rights reserved.)

Fig. 2.4. Transverse section of a mature root of 'Smooth Cayenne' pineapple showing: e, epidermis; ex, exodermis; oc, outer cortex with raphide cells (rc), whose transverse walls are collapsed to form air passages; ic, outer portion of inner cortex; t, tracheids; ph, phloem; p, pith; v, vessel; pc, pericycle; en, endodermis; l, large lacunae formed by collapse of many cells of inner cortex; rh, root hairs. (After Krauss, 1949b. © The University of Chicago, all rights reserved.)

the flowers is continuous with the peduncle and with the short stem of the crown (Fig. 2.5). Between the uppermost flower and the crown is a transition region with bracts but no flowers. The edible part of the fruit consists chiefly of the ovaries, the bases of sepals and bracts and the cortex of the axis. The fruit shell is composed chiefly of sepal and bract tissues and the apices of the ovaries (Okimoto, 1948). Anthesis normally takes place within a day. Flowering lasts 10-15 days and occurs in a more or less acropetal succession along the inflorescence axis, but some cultivars flower in a very disorderly manner.

Flowers are hermaphroditic and trimer-ous, with three sepals, three petals, six stamens in two whorls of three and one tricarpellate pistil (Fig. 2.6). The anthers are bilobed, introrse and dorsifixed. The hollow, trilobed and trifid style is almost as long as the petals and equal to or longer than the stamens. At anthesis, each stylar canal is an unobstructed open channel from the stigma to the locule directly above the placenta. Petals are ligulate and free, each bearing at its base two slender funnelform scales or, more rarely, lateral folds that overlap the filaments. Petals are white at their base to violet-blue at their tip. They are so close together at their outer end that only small insects can enter the flower. This narrow tubular flower and the abundant nectar production are particularly adapted to hummingbird pollination. Indeed, the three large nectary glands are so productive that nectar often fills the corolla and seeps out. The sepals are deltoid and appear similar to the bracts in colour and texture. Each flower is surrounded and subtended at its base by a pulpous and thick

Inflorescence Pineapple Fruit
Fig. 2.5. The morphology of a 'Smooth Cayenne' pineapple fruit. (After Okimoto, 1949. © The University of Chicago, all rights reserved.)

bract, covered by trichomes, which becomes pointed and papyraceous at its tip. Parts of three other bracts complete the enclosure of the flower. Bract spininess is correlated with leaf spininess.

In the syncarpic inflorescence resulting from the fusion of the basal part of the flowers and their axis, ovaries of adjacent flowers are separated by the parenchymatous tissue of the calyx and bract bases. The ovary is inferior, tricarpellate and trilocular, with the three septa forming an inverted Y when seen in tangential section of the inflorescence. The placentae and ovules are located in the upper part of three deep cavities, called locules, which are separated by the nectary glands. The ovules are caudate and arranged in two single or double rows. The number of ovules per flower varies with the cultivars, from 16 to 71 (Coppens d'Eeckenbrugge et al., 1993). The occurrence of two types of ovules (unitegmic orthotropous and bitegmic anatropous) within the same ovary is common and orthotropous ovules are fertilized (Okimoto, 1948; Rao and Wee, 1979; F. Van Miegroet, 1993, personal communica tion). Orthotropous ovules are much less frequent than anatropous ovules and their presence and numbers are a varietal characteristic (M.F. Duval and G. Coppens d'Eeckenbrugge, unpublished results). Pollen grains are prolate and spheroidal, biconvex, isopolar and bilaterally symmetrical and diaperturate, with circular to slightly elongated apertures situated at the poles. The equatorial (36-51 ^m) and polar (46-59 ^m) dimensions are variable. The exine is reticulate, and the polar areas show finer reticulation than the rest of the surface (Wee and Rao, 1979). Male and female gametogen-esis and embryogenesis are revised by Chan et al. (Chapter 3, this volume).

There is no floral abscission, and, except for the withering of the style, stamens and petals, the entire blossom develops parthenocarpically into a berry-like fruitlet. In the cultivated pineapple, growth from blossoming inflorescence to mature fruit results in a 20-fold increase in weight. The enlargement of the calyx results from continued growth by cellular division, in stages up to flowering, and cell enlargement, in the

Bracts Pineapple

Fig. 2.6. Pineapple flower. A. Floral diagram. B. Flower and subtending bract. C. Cross-section of ovary at placenta level. D. Longitudinal section. E. Petal with scales and opposite stamen. BR, subtending bract; DU, nectary duct; GL, septal gland; LO, locule; O, ovary limit; P, petal; PL, placenta; S, sepal; ST, stamen; STY, style. (After Okimoto, 1949. © The University of Chicago, all rights reserved.)

Fig. 2.6. Pineapple flower. A. Floral diagram. B. Flower and subtending bract. C. Cross-section of ovary at placenta level. D. Longitudinal section. E. Petal with scales and opposite stamen. BR, subtending bract; DU, nectary duct; GL, septal gland; LO, locule; O, ovary limit; P, petal; PL, placenta; S, sepal; ST, stamen; STY, style. (After Okimoto, 1949. © The University of Chicago, all rights reserved.)

later stages. During this size increase, cell walls get thinner. The bract, sepal and ovary tissues are prominent structures in the mature fruit. The large, conspicuous bract is fleshy and widened at its base and bends over the flattened calyx surface, covering half of the fruitlet. Its papery tip dries during maturation. Internally, the locules get longer but relatively narrower and less conspicuous in the developed fruit because of the expansion of adjacent tissues, especially of the septa. Placentas show some enlargement but far less than the septal tissues, unless they bear mature seeds. The seeds are approximately 3-5 mm long and 1-2 mm wide, flat on one side and curved on the other, with a pointed end. They contain a hard flinty endosperm and a minute embryo enclosed in a brown to black coat, extremely tough and leathery and roughened by numerous longitudinal ridges (Miles Thomas and Holmes, 1930). In the mature fruit, the stylar canals get completely closed, first by a mucilaginous plug, soon after anthesis, and a week or two later by cellular occlusion.

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  • Demsas
    Which inflorosence is in pinapple?
    10 months ago

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