MADE BY:-

GUIDED BY:-

DEEPAK YADAVMaster of science-m.scA.U. PRF.D R MISHRA

PRF, DK CHAUHAN

TOPIC –SEED SCALE COMPLEX

SEWARD’s hypotheses -Perhaps the Lycopsida form a gymnosperm because l.s. of Selaginela megasporangium it shown megaspore 3 abortive , ligule, sporophyll and megasporangia.Sporophyll-bract scaleLigules- ovuleferous scaleMegasporangiophyll-coneThey are analogous partsAs for as leaf is concerned –Lycopodium. clavatum –they are microsporophyll’s as that of conifers Lycopsida- It originate coniferFilicopsida- It originated Cycas and Pteridosperm

FLORIN SEWARd

Florin’s hypotheses (SWEDEN, 1894-1965)Florin 1951 –ovuliferous scale is compound structure and not simple as

proposed by seward.Lebachia - Ernetiodendron –Voltiza – Pseudovolzia – OlmanniaDuring carboniferous and permian these plant appeared and source of coalFLORIN called is “samen schoppen komplex” which means Seed scale

complex .

Lebachia, voltzia, psudovoltzia

Voltziales and the origin of the ovuliferous scales

Although the evidence from organography, comparative anatony, and ontology supports the view that ovulate cones in the conifers is a compound strobilous,the phylogenetic origin of the ovuliferous scales remains to be explained. The scale is similar to sporophyll in that it bears ovules, but its axillary position with reference to a bract represents a puzziling situation from an evilutionary point of view, of all the conflicting and involved theories that have been proposed during the past century,the most plausible and best supported view was advanced by Florin:

Florin termed the fertile shoot in these and other conifers “seed scale complexes” and belived they support the view that the compound megasporangiate strobilus is the primary form in the coniferales, with the exception of the taxales (taxaceae). The great man regarded the taxales as having the separate evolutanory history because of they lack definable seed cones: this view

has been questioned in recent years (Miller,1977).

In summary, the main trends in seed cone & seed scale evolutoin have been towards:-- (1)the elimination of all but a few sterile scales, which became fused into the so-called ovuliferous scale,(2)the recurvation of ovules and suppression of their stalks,(3)their final incorporation with the lower adaxial side of the ovuliferous scales in derived conifers. On the basis of the ground plan-divergence method of cladistics,Miller(1982) have proposed

a phylogeny of the voltziales and modern-day families of the coniferales based upon fourteen

characters of the bract, seed scale complex.

Mature female Pinus coulteri cone An Aleppo Pine cone

Conifer cone possesing seed scale complex

A cone (in formal botanical usage: strobilus, plural strobili) is an organ on plants in the division Pinophyta (conifers) that contains the reproductive structures. The familiar woody cone is the female cone, which produces seeds. The male cones, which produce pollen, are usually herbaceous and much less conspicuous even at full maturity. The name "cone" derives from the fact that the shape in some species resembles a geometric cone. The individual plates of a cone are known as scales.The male cone (microstrobilus or pollen cone) is structurally similar across all conifers, differing only in small ways (mostly in scale arrangement) from species to species. Extending out from a central axis are microsporophylls (modified leaves). Under each microsporophyll is one or several microsporangia (pollen sacs).The female cone (megastrobilus, seed cone, or ovulate cone) contains ovules which, when fertilized by pollen, become seeds. The female cone structure varies more markedly between the different conifer families, and is often crucial for the identification of many species of conifers.

Female cones of the conifer families

Pinaceae cones

Intact and disintegrated fir conesYoung cones of a Colorado Blue Spruce

The members of the pine family (pines, spruces, firs, cedars, larches, etc.) have cones that are imbricate (that is, with scales overlapping each other like fish scales). These are the "archetypal" cones. The scales are spirally arranged in fibonacci number ratios.The female cone has two types of scale: the bract scales, derived from a modified leaf, and the seed scales (or ovuliferous scales), one subtended by each bract scale, derived from a highly modified branchlet. On the upper-side base of …..

each seed scale are two ovules that develop into seeds after fertilization by pollen grains. The bract scales develop first, and are conspicuous at the time of pollination; the seed scales develop later to enclose and protect the seeds, with the bract scales often not growing further. The scales open temporarily to receive gametophytes, then close during fertilization and maturation, and then re-open again at maturity to allow the seed to escape. Maturation takes 6–8 months from pollination in most Pinaceae genera, but 12 months in cedars and 18–24 months (rarely more) in most pines. The cones open either by the seed scales flexing back when they dry out, or (in firs, cedars and golden larch) by the cones disintegrating with the seed scales falling off. The cones are conic, cylindrical or ovoid (egg-shaped), and small to very large, from 2–60 cm long and 1–20 cm broad.

Araucariaceae conesMembers of the Araucariaceae (Araucaria, Agathis, Wollemia) have the bract and seed scales fully fused, and have only one ovule on each scale. The cones are spherical or nearly so, and large to very large, 5–30 cm diameter, and mature in 18 months; at maturity, they disintegrate to release the seeds. In Agathis, the seeds are winged and separate readily from the seed scale, but in the other two genera, the seed is wingless and fused to the scale.

Podocarpaceae cones

Berry-like Podocarpus cone

The cones of the Podocarpaceae are similar in function, though not in development, to those of the Taxaceae (q.v. below), being berry-like with the scales highly modified, evolved to attract birds into dispersing the seeds. In most of the genera, two to ten or more scales are fused together into a usually swollen, brightly coloured, soft, edible fleshy aril. Usually only one or two scales at the apex of the cone are fertile, each bearing a single wingless seed, but in Saxegothaea several scales may be fertile. The fleshy scale complex is 0.5–3 cm long, and the seeds 4–10 mm long. In some genera (e.g. Prumnopitys), the scales are minute and not fleshy, but the seed coat develops a fleshy layer instead, the cone having the appearance of one to three small plums on a central stem. The seeds have a hard coat evolved to resist digestion in the bird's stomach, and are passed in the bird's droppings.

Cupressaceae cones

Juniper "berries", which are used to flavor gin, are actually modified cones.

Giant Sequoia cones

Members of the cypress family (cypresses, arborvitae, junipers, redwoods, etc.) differ in that the bract and seed scales are fully fused, with the bract visible as no more than a small lump or spine on the scale. The botanical term galbulus (plural galbuli; from the Latin for a cypress cone) is sometimes used instead of strobilus for members of this family. The female cones have one to 20 ovules on each scale. They often have peltate scales, as opposed to the imbricate cones described above, though some have imbricate scales. The cones are usually small, 0.3–6 cm long, and often spherical or nearly so, like those of Nootka Cypress, while others, such as Western Redcedar, are narrow. The scales are arranged either spirally, or in decussate whorls of two (opposite pairs) or three, rarely four. The genera with spiral scale arrangement were often treated in a separate family (Taxodiaceae) in the past. In most of the genera, the cones are woody and the seeds have two narrow wings (one along each side of the seed), but in three genera (Platycladus, Microbiota and Juniperus), the seeds are wingless, and in Juniperus, the cones are fleshy and berry-like.

Tetraclinis cones

Sciadopityaceae conesThe cones and seeds of Sciadopitys (the only member of the family) are similar to those of some Cupressaceae, but larger, 6–11 cm long; the scales are imbricate and spirally arranged, and have 5-9 ovules on each scale.

Taxaceae and Cephalotaxaceae cones

Berry-like yew cone

Members of the yew family and the closely related Cephalotaxaceae have the most highly modified cones of any conifer. There is only one scale in the female cone, with a single poisonous ovule. The scale develops into a soft, brightly coloured sweet, juicy, berry-like aril which partly encloses the deadly seed. The seed alone is poisonous. The whole 'berry' with the seed is eaten by birds, which digest the sugar-rich scale and pass the hard seed undamaged in their droppings, so dispersing the seed far from the parent plant.

Cycadaceae conesThis group of cone-bearing plants retains some types of 'primitive' characteristics. Its leaves unfurl, much like ferns. There are three extant families of Cycads of about 305 species. It reproduces with large cones, and is related to the other conifers in that regard, but it does not have a woody trunk like most cone-bearing families.

Welwitschiaceae cones

A unique cone-bearing plant in the Order Welwitschiales, Welwitschia mirabilis is often called a living fossil and is the only species in its genus, which is the only genus in its family, which is the only family in its Order. The male cones are on male plants, and female cones on female plants. After emergence of the two cotyledons, it sets only two more leaves. Those two leaves then continue to grow longer from their base, much like fingernails. This allows it great drought tolerance, which is likely why it has survived in the desert of Namibia, while all other representatives from its order are now extinct.

REFERENCE:-

MORPHOLOGY AND EVOLUTION OF VASCULAR PLANTS;E M GIFFORD; A S FOSTER

GOOGLE;WIKIPEDIA, CONIFER CONE

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