1.Describe in detail, how plants overcame the obstacles to living on land.

The fossil record indicates that nothing lived on the land surfaces of our planet until about 440 million years ago. For the first 3 billion years of life’s existence on Earth, life was confined to the sea. Scientists are not sure why it took so long for life to reach terrestrial habitats, but they suspect that intense solar radiation may have made the surfaces of land uninhabitable. With the advent of photosynthesis in Earth's oceans, oxygen gas began to accumulate in the atmosphere. Some of this oxygen gas, O₂, was converted to ozone, O₃, leading to the development of an ozone layer high in the atmosphere. Then, as it does today, the ozone layer shielded Earth’s surface from much of the harmful solar radiation.

Soon after the appearance of significant amounts of oxygen in Earth’s atmosphere, plants and fungi invaded the land. Both plants and fungi probably evolved from multicellular protists. Multicellularity enabled plants to develop the complex structures and association that have contributed to their success on land. Before the descendents of the earliest plants could thrive in terrestrial habitats, they had to overcome three obstacles: they had to be a able to conserve water; and they had to have a way to reproduce on land.

Mutualistic associations similar to mycorrhizae may have played a key role in the initial occupation of land. Mycorrhizae are symbiotic relationships between fungi and the roots of plants. The plants provide the fungi with carbohydrates and other organic molecules made during photosynthesis. The fungi absorb from the soil the phosphorus and other materials that are needed by plants. Although the first plants lacked roots, fungi have been seen within and among the root cells of many fossilized early plants. Thus, some botanists (scientists who study plants) think that mutualistic associations similar to mycorrhizae have enabled the first plants to absorb minerals from Earth’s rocky surface. Today, approximately 80% of all living plant species form mycorrhizae.

One of the key challenges to living on land is to avoid drying out. The first plants were very small and lives on the edges of oceans, where water was abundant. However, to occupy drier habitats, a means of conse4rving water was needed. For plants, the solution to this problem was the development of a watertight outer covering called a cuticle. Made of a waxy substance, the cuticle covers the aboveground parts of a plants and prevents these tissues from losing water to air. Like the wax on a shiny car, the cuticle is impermeable to water, but it is also impermeable to the gases required by plants for photosynthesis and cellular respiration.

Passages through the cuticle, in the for of specialized pores called stomata, developed and enabled plants to exchange gases. The word stomata means "mouth in Greek. Occurring on at least some portions of all plants except liverworts, stomata permit carbon dioxide gas to enter a plant body and permit water vapor and oxygen gas to exit. Because of the cuticle and stomata, water enters most plants primarily through their roots (which do not have a cuticle) and exists primarily through stomata. A pair of specialized cells called guard cells boarders each stomata and controls its size by expanding and contracting. The timing of the opening and closing of stomata is critical to preventing excessive water loss while admitting the carbon dioxide required for photosynthesis.

To reproduce sexually, and organism’s male and female gametes must be able to reach one another. The male gametes of aquatic algae are able to swim through eater to fertilize the female gametes. The gametes of plants that live on land, however, must be able to move in an environment where water is not abundant. Also, they must be protected from drying out while they are being transferred. The eggs of the first plants were surrounded by jackets of cells, and a film of water was required for a sperm to swim to an egg and fertilize it. Today, mosses, ferns, and several other groups of primitive plants still reproduce this way. In more advanced plants, the sperm are enclosed in multicellular structures (pollen grains) that keep them from drying out, Such structures enable the male gametes of more advanced plants to be transmitted to female gametes by wind or animals rather than water.

2. Describe the improvements made by each of the following groups as they became more complex in evolution.

1. Algae
2. Bryophytes
3. Seedless Vascular Plants
4. Gymnosperms
5. Angiosperms

A. Algae are a diverse group of primarily aquatic, mostly plantlike organisms that occur in such dissimilar forms as microscopic single cells, loose, filmy conglomerations, matted or branched colonies, or giant seaweed’s with rootlike holdfasts and structures resembling stems and leaves.

Most of the algae have characteristics in common with plants, in that they have cell walls, contain the green pigment chlorophyll, and manufacture their own food through the process of photosynthesis. The chlorophyll may be masked by other pigments, giving the various types of algae predominantly different colors. Some types, more animal-like, are motile (capable of moving about) and ingest organic food, although they may also contain chlorophyll and conduct photosynthesis. Soft, even gelatinous cell surfaces are usual, but some types form shells or scales, and others produce stony, coral-like, or calcareous, deposits.

Algae are worldwide in distribution, thriving in all bodies of water, rocky coastlines, and terrestrial environments with ample moisture. Some species are adapted to such extremes of temperature as hot springs or arctic snows. Others survive in sandy soils or deserts. The habitats of marine and coastal algae vary according to degree of wave action, height of tides, and the light intensity required for photosynthesis; the various algae types are found in distinct zones or layers in the oceans and on beaches and cliffs.

Methods of reproduction in algae may be vegetative by division of a single cell or fragmentation of a colony, asexual by production of motile spores (zoospores) or thick-walled nonmotile spores, or sexual by union of gametes (sex cells). The gametes may be identical (isogametes), differentiated into male and female (anisogametes), or markedly differentiated (heterogametes) into small, motile male cells and large, nonmotile female cells. Many species of algae reproduce by an alternation of generations, requiring separate asexual and sexual organisms to complete a life cycle.

Isogamy is the most common reproductive mode of the green algae and may have been present in the first plants that evolved. The isogametes, that is, sex cells that are not distinguishably male or female, shed their cell walls and slowly fuse their cytoplasm and nuclei, forming a single cell with two sets of genes. The zygote (the first stage of a new organism) develops a thick, protective wall and germinates when conditions are favorable, somewhat like a plant seed. The zygote divides to produce four new haploid cells (one set of genes in each cell), which are released into the surroundings. In some algae, three of the haploid cells fail to develop in the zygote. The haploid stages of the life cycle predominate, because the only diploid stage (two sets of genes in a cell) is the zygote itself. In other algae, notably the complex seaweed, the diploid generation is large with an extended phase, and the haploid generation is microscopic and brief. Many intermediate variations are found.

The last form of multicellular algal reproduction that we’ll consider is the complex cycle known as alternation of generations. This cycle is characterized by two distinct multicellular phases: a haploid, gamete-producing phase called the gametophyte, and a diploid, spore producing phaser called the sporophyte.

If you take a Ulva which is a diploid sporophyte. The sporophyte forms reproductive cells called sporangia that produce haploid zoospores by meiosis. These zoospores divide mitotically, forming more motile spores. The spores settle throughout the water, land on rocks, and grow into multicellular , haploid gametophytes. A gametophyte looks exactly like the sporophyte. The gametophyte produces gametangia and then produces plus and minus gametes that unite and form zygotes. The diploid zygote completes the cycle by dividing mitotically into a new diploid sporophyte.

It is of exceptional significance that this life cycle occurs in a green algae. Plants, which presumably evolved from green algae, also have an alteration of generations as their sexual cycle. The plant life cycle differs from that of Ulva in two respects. The sporophyte and the gametophyte do not look alike, and gametes are formed in multicellular rather then unicellular gametangia.

B. Lacking water-gathering roots and the kind of specialized tissues that transport water up the body of a vascular plant, the bryophytes must absorb moisture through aboveground structures. As a consequence, they grow most successfully in moist, shady places and bogs. Some of them, like sphagnum, are able to absorb and hold large amounts of water; in effect, they maintain a watery existence even on land. The majority of the bryophytes are tropical, but some species occur in temperate regions, and a few even reach the Arctic and Antarctic.

Most bryophytes are comparatively simple in their structures and are relatively small, usually less than 20 cm. in length. A single moss plant may sprawl; only to a keen observer. In the damp environments frequented by the bryophytes, individual cells can absorb water and nutrients directly from the air or by diffusion from nearby cells. Like the lichens, they are sensitive indicators of pollution.

Although bryophytes do not have true roots, they are generally attached to the substrate by means of rhizoids, which are elongate single cells or filaments of cells. Many bryophytes also have small lifelike structures in which photosynthesis takes place. These structures lack the specialized tissues of the "true" leaves of the vascular plants and are only one or a few cell layers thick. For these reasons, the lifelike structures of the bryophytes and the leaves if the vascular plants are believed to have evolved separately. As in other plants, the body of a bryophyte is specialized for support and food storage.

Bryophytes, like all plants, have a life cycle with alternation of generations. In contrast to the vascular plants, however, the bryophytes are characterized by a haploid gametophyte that is usually larger than the diploid sporophyte.

The life cycle of a moss begins when a haploid spore germinates to form a network of horizontal filaments known as protonemata. Individual gametophytes grow up like branches from this network. The multicellular antheridia and archegonia are borne on the gametophyte. When sufficient moisture is present, the sperm, which are biflagellate, are released from the antheridium and swim to the archegonium, to which they are attracted chemically. Without free water in which the sperm can swim, the life cycle can not be completed. Fusion of sperm and egg takes place within the archegonium. Inside the archegonium, the zygote develops into a sporophyte, which remains attached to the gametophyte and is nutritionally dependent upon it. Typically the sporophyte consists of a foot, a stalk, and a single, large sporangium, from which the spores are discharged.

Asexual reproduction, often by fragmentation, is also common. Many mosses and liverworts also produce minute bodies, known as gemmae, that can give rise to new plants.

The mosses include many species in which a central strand of specialized conducting cells distributes water and carbohydrates throughout the plant. These conducting strands make up what is called vascular tissue. Simple in design, the vascular tissue in mosses is composed of conducting cells that lack thickened walls.

Because their vascular tissue is so simple, mosses are still grouped with the liverworts and hornworts, and all three groups are considered to be nonvascular plants. The three phyla of nonvascular plants share an important similarity. Their life cycles, are dominated by the gametophyte generation. The archegonia and antheridia of mosses are produced on separate gametophytes. The moss sporophyte consists of a bare stalk that supports a spore capsule, or sporangium, in which haploid spores are produced by meiosis.

C. Seedless vascular plants such as the tree fern, Cyanthea, are the first plants to develop a vascular system. A vascular system enabled the development of a body differentiated into shoots and roots. Because they had conducting cells with reinforced walls, vascular plants were able to grow much larger than nonvascular plants. The development of a waxy covering called a cuticle and spores that were resistant to drying aided in the survival of the seedless vascular plants on land. A life cycle dominated by the diploid sporophyte generation evolved with the seedless vascular plants. Today, ferns are the only widely successful seedless vascular plants.

Fern spores, which are highly resistant to drying, are produced in sporangia that grow in clumps on the lower side of the fronds. These are drought-resistant spores. Ferns are most abundant in the tropics and prefer most habitats. A film of water is required for the motile sperm to swim to eggs so ferns are still tied to water. The reduced gametophyte is less than 1 cm across.

D. Seeds apparently arose only once among the vascular plants, as the plant life cycle continued to shift toward a more dominant sporophyte generation and a more reduced gametophyte generation. Of the five phyla of living seed plants, four are collectively called gymnosperms. The word gymnosperm comes from the Greek word gymnos, meaning "naked and sperma, meaning "seed", and refers to the fact that gymnosperm seeds do not develop within a fruit. First appearing about 380 million years ago, gymnosperms were the first seed plants. The flowering plants, or angiosperms evolved from gymnosperms and make up the fifth phylum of seed plants. The word angiosperm comes from the Greek word angeion, meaning "case" and sperma, meaning "seed," and refers to the fact that angiosperms seeds develop within a fruit. First appearing between 150 and 200 million years ago, angiosperms are the most recently evolved of all the plant phyla.

The gametophytes of seed plants have become highly reduced during the course of evolution. Developing from spores that are produce within the tissue of the sporpophyte individuals, the gametophytes of seed plants are entirely dependent upon those sporophyte individuals for nutrients and water. Seed plants produce two kinds of gametophytes: a very tiny male gametophyte, or microgametophyte, that produces sperm, and a relatively large female gametophyte, or megagametophyte, that produces eggs. Thus, the spores that produce the microgametophytes are called microspores, and those that produce the megagametophytes are called megaspores. A pollen grain, which consists of only a few haploid cells surrounded by a thick protective wall, is a mature microspore that contains a microgametophyte. Each megagametophyte develops from a megaspore within an ovule, a multicellular structure that is part of the sporophyte. If the egg inside of an ovule is fertilized, the ovule and its contents become a seed.

Wind, insects, and other animals transport pollen grains to the female reproductive structures that contain ovules. The transportation of pollen grains from a plant’s male reproductive structure to a female reproductive structure of a plant of the same species is called pollination. When a pollen grain reaches a female reproductive structure, the pollen grain cracks open. A pollen tube then grows from the pollen grain to an ovule and enables a sperm to pass directly to an egg. Thus, in seed plants there is no need for a film of water during the fertilization process.

Four plant classes constitute gymnosperms, according to the five-kingdom system of plant and animal classification: Cycads (Cycadinae), the Ginkgo (Ginkgoinae), gnetids (Gnetinae), and Conifers (Coniferinae). Some botanists classify gnetids as conifers. The earliest gymnosperms--seed ferns and fossil conifers--no longer exist. Cycads are evergreen, tropical shrubs and trees that have single, thick stems; large, leafy cones; and palmlike leaves. The nine surviving genera of cycads--the most primitive of gymnosperms--belong to the order Cycadales, three others being extinct. About 50 species of ginkgo existed 130 million years ago, of which only one, Ginkgo biloba, survives. This deciduous tree has fanlike leaves and rudimentary cones, the male cones resembling catkins and the female having two exposed ovules. Gnetids--of which no fossil record exists--comprise three highly diverse genera: joint firs, genus Ephedra, semiarid shrubs from which the drug ephedrine is derived; genus GNETUM, broad-leaved tropical trees and woody vines; and Welwitschia mirabilis, an African shrub having only two leathery leaves, which are never shed. Most conifers, which comprise about 50 genera, have branching stems and scalelike or needlelike leaves. They make up more than 30 percent of the world's forests and include such evergreens as pines, firs, and spruces as well as the deciduous larches, dawn redwood, and bald cypress. The pollen and seed cones are woody and in some species are carried on the same tree instead of on separate trees, as in the other classes.

The basic reproduction cycle of gymnosperms begins when male and female gametophytes develop from spores produced by the plants. Pollen is usually carried to the female cones by wind, and fertilization takes up to a year. The resulting embryos are scattered and develop into seedlings.

F. The most successful of all plants are angiosperms, seed plants that produce flowers. The remarkable evolutionary success of the angiosperms is the culmination of the plant’s kingdom’s adaptation to life on land. Ninety percent of all living plants – more than 250,000 species of trees, shrubs, herbs, fruits, vegetables, and grains – are angiosperms. In short, nearly all of the plants that you see every day are angiosperms. Virtually all of your food come directly or indirectly from angiosperms. In fact, more than half of the calories that humans consume come from just three species of angiosperms: rice, corn, and wheat.

The unique angiosperm flower probably evolved from a now extinct gymnosperm group that had insect-pollinated cones combining male and female reproductive parts. Living gymnosperms are mostly wind-pollinated, but among certain fossil and extant groups evidence of insect pollination exists. Although insects facilitate pollination, they also eat ovules, and it is believed that the development of the ovule-enclosing carpel of the angiosperm was an adaptation to protect the ovules and developing seeds from insect predation. The carpel also provided protection from other harmful environmental influences, such as dryness, and it allowed reduction in the size of the ovule, refinement of the process of pollination, and the development of other parts of the flower, all of which improved the chances of successful reproduction.

Among plants more advanced in evolutionary development than the ferns, the gametophyte does not occur as an independent plant. The sporophyte is the conspicuous generation, and the vestigial gametophytes are reduced to a few nuclei that can be seen only with a microscope. Among the flowering plants, the pollen grain is the microspore, within which are produced male gametophytes that contain the sperm. The egg sac, or female gametophyte, is produced by germination of a megaspore within the ovary or pistil of the flower. Microspores and megaspores are produced within the anther sacs of stamens and within the ovulary tissues of the pistil, respectively.

3. Describe significance of the parts found in the following structures. Discuss the diversity of these structures found in nature.

1. Flowers
2. Seeds
3. Fruits

A. The flower is the reproductive structure of angiosperms , or flowering plants. Compared to the reproductive structures of other plants, the flower is unique in several ways. It consists of four kinds of modified leaves, two of which (stamens and carpels, the latter sometimes called pistils) bear POLLEN and seeds. Several nonflowering plants also produce pollen and seeds on modified leaves, but in angiosperms the modified leaf called the carpel forms an ovary that completely encloses the ovule, which becomes the seed. In the gymnosperms, ovules are borne on open modified leaves, such as the scale of a pinecone. The term angiosperm, derived from the Greek, means "seed in a vessel." Gymnosperm means "naked seed." According to the fossil record, flowering plants appeared only about 140 million years ago, although some recently found fossil evidence suggests that they appeared 80 million years before that. (The earliest land plants, blue-green algae, appeared perhaps 1.2 billion years ago.) The angiosperms now dominate the world's vegetation. Only the gymnosperms offer any substantial competition. There may be more than 250,000 angiosperm species, compared to fewer than 1,000 gymnosperm species and fewer than about 40,000 other types of vascular plants (ferns and their relatives) and bryophytes (liverworts, mosses, hornworts). There are fewer than 15,000 species of algae, and perhaps more than 100,000 species of fungi and bacteria.

Four kinds of modified leaves make up a complete flower: carpels and stamens (primary reproductive structures) and petals and sepals (secondary structures). The carpel is the female reproductive structure. It has a stigma, where the pollen becomes attached and germinates; a style, through which the pollen tube grows; and an ovary with one or more ovules. The egg cell that will unite with the sperm cell (delivered by the pollen tube) forms in the ovule. The stamen is the male structure; its filament supports an anther, in which the pollen is formed. The often brightly colored petals are important in attracting pollinators, and the often lifelike sepals enclose the bud before the flower opens. The many species of flowering plants are usually distinguished from one another by the way these four basic flower parts are modified, although closely related species within a genus may have quite similar flowers.

Some flowers have only one carpel, others have two or a few, and still others have many. Several carpels in a single flower may be separate or fused together. If fused, they may be joined only at the ovaries or along their entire length. The ovary may contain one to many ovules, and these may be arranged in various ways. Frequently, the ovaries are attached to the receptacle (the end of the stem, or peduncle, that supports the flower parts) at the same level as the other flower parts, in which case the ovary is said to be hypogynous (or superior). In some cases the other flower parts are attached above the ovary, which is then said to be epigynous (inferior). In the rose family and some of its relatives, the stamens, petals, and sepals are attached around the ring of a cup with the ovaries at the bottom of the cup (perigynous).

Stamens also vary in several ways, although not as markedly as ovaries. Classification schemes often depend on the number of stamens in a given flower and whether they are attached oppositely or alternately with the petals.

The petals together form the corolla, with numerous and often beautiful forms. Besides the number of petals, two other important variations occur. First, petals may be separately attached to the receptacle, or they may be united along their edges to form a tube. Second, the corolla may be radially symmetrical, with petals radiating out in all directions from the center of the flower (as in a buttercup, geranium, lily, or rose), or some petals may have shapes different from others, so that the flower has dorsiventral symmetry--in which a vertical plane divides the flower into two equal, mirror-image halves (as in snapdragon, honeysuckle, or orchid).

Many flower petals have patterns of pigment that absorb only in the ultraviolet part of the spectrum. Insects, which have eyes that are sensitive to ultraviolet light, see patterns on the flower that are not visible to humans. These patterns frequently consist of radiating lines that lead the insect to the nectar. A few flowers (for example, clematis) have no true petals but do have colorful sepals.

If a flower lacks any of the four basic parts, it is called incomplete. If it lacks one of the essential reproductive parts (stamens or carpels), it is called imperfect. Thus, flowers that have both stamens and carpels but lack petals or sepals are perfect incomplete flowers. Imperfect flowers can be male or female. If male and female flowers occur on the same plant, the plant is called monoecious; if male and female flowers are on separate plants, it is dioecious. Maize (corn) is a monoecious plant, with its tassels (stamens) at the top and its ears (carpels) on the stem below. Cottonwoods are dioecious-- the male trees produce pollen, and female trees produce seeds.

In most angiosperms, pollen is transferred by insects. Insect- pollinated flowers often have rather showy corollas, which are often modified to ensure the dusting of pollen onto the insects as they penetrate the flowers in search of nectar. The dusted insects transfer the pollen to the stigma of the next flower they enter. Flowers pollinated by moths, hummingbirds, or bats may have specialized corollas that match the appropriate organs of the animals seeking the nectar.

In some major groups, pollen is transferred by the wind. Some species of wind-pollinated flowers are not at all showy, with the anthers suspended on long filaments so that the pollen dusts freely into the wind. The pollen grains may be winged, which allows them to be carried more easily on the breezes. Styles and stigmas may also extend some distance from the flower, to catch the blowing pollen. Sepals and petals may be either absent or quite small. Grasses, which are some of the most successful plants, are wind-pollinated, as are many trees- -for example, maples, oaks, and walnuts.

A few species, including such important crops as wheat, rice, barley, oats, and peas, are self-pollinated. The pollen is transferred directly from stamens to carpels. Such species naturally maintain their genetic purity. To produce new hybrids, cross-pollination must be carried out manually. Some flowers (dandelion, hawkweed, certain grasses) do not require pollination to produce seed. Certain cells in the ovule other than the egg cell develop into seeds in the process called apomixis.

A group of flowers on a plant is called an inflorescence. A great variety of inflorescences occur among the angiosperms. The simplest is a single, solitary flower at the end of a stem, with leaves at the base. It is rare for an entire plant to have a single flower, as is true of the tulip; but a solitary, terminal flower at the end of the main stem, with axillary flowers in the angles between leaves and stems, is common.

A number of flowers radiating along a single stem, usually with modified leaves (bracts) at the base of the peduncles, is a raceme. Most racemes are indeterminate, meaning that the younger flowers are at the tip of the stem in the center of the raceme. A spike occurs when the flowers in the raceme are attached closely to the main stem. For example, a head of wheat is spiked, as are virtually all grass flowers. A compound raceme with several branching stems, each forming a raceme, is called a panicle. In a small number of species, the oldest flowers may occur near the stem tips of a raceme or panicle; this determinate structure is a cyme. When all the peduncles of several flowers in an inflorescence radiate from the same point, they form a flattopped, or sometimes rounded, umbel.

Flowers densely packed together on short peduncles and a short main axis form a head; clover is an example of this formation. The most common flower heads occur in the large aster or sunflower (composite) family. In a sunflower or daisy, two kinds of flowers occur in the head: ray or strap flowers, which consist of one long petal with an ovary and sometimes stamens; and disk flowers, which consist of five greatly reduced, radially symmetrical petals at the tips of a corolla tube, plus an ovary and, usually, stamens. The sepals in a composite flower head may have been modified to form filaments, such as the parachute on a dandelion seed. Two other special inflorescences are the catkins, rather loose, hanging spikes of flowers occurring on birch and other trees; and the spadices, which are spikes of male flowers above female flowers surrounded by large, sometimes colored leaves called spathes, as on calla lily.

The products of the flower are the seed and the fruit. The seed is the mature ovule. It includes a minute embryo plant and, almost always, stored food that will supply the seedling when it begins to grow after sprouting, or germination. Important seeds that humans eat include the cereals, such as wheat, rice, maize; legumes, such as peas, beans, lentils, peanuts; and nuts. Many seeds are rich in fats (including oils), a concentrated form of energy, and are of great commercial importance--for example, soybeans, cottonseed, coconuts, peanuts, rapeseed, sunflower, and linseed (flax). The cereals store mostly carbohydrate, and many legumes store much protein along with carbohydrate and, often, fat.

In a restricted botanical sense, the fruit is the mature ovary wall, but often food is stored in accessory tissues besides the ovary wall.

B. By providing the offspring of plants with several survival advantages, seeds have had an enormous influence on the evolution of plants on land. A seed is a sporophyte plant embryo surrounded by a protective coat. The hard cover of a seed is called the seed coat. Formed from the sporophyte tissue of the parental plant, the seed coat protects the embryo and other tissues in the seed from drying out. In addition to their role in protecting a plant embryo, seeds have enabled plants to become better adapted to living on land in at least three other respects.

1. Dispersal- Seeds enable the offspring of plants, which are anchored in one place by their roots, to be dispersed to new locations. Many seeds have appendages, such as wings, that help wind, water, or animals carry them away from their parent plant. The dispersal of a plant’s offspring prevents the parent and offspring from competing with each other for water, nutrients, light, and living space. Seed dispersal also facilitates the migration of a plant species to new habitats.

Methods of Seed Dispersal

Some plants have Somara’s which make thew wind carry them to different distances through which they fall down. Seeds use wind to travel distances. Such seeds from dandelions have little parachutes which makes them go long distances with the help of the wind. Hawkweed, Pileword, Aster, Sow Thistle all use this parachute method. Some plants use berries which the birds eat. The birds do not digest the seeds and they get dispersed by means of the bird’s droppings. Firethorn, Pokeweed, Dogwood, Buckhorn, Spice bush, Grape, Honey suckle, Bittersweet, Viburnum, and Eponym all use this method. Some plants have the seeds so that squirrels and chipmunks pick them up and sometimes bury them into the ground. When they forget where they have planted them, a new plant is planted. A hickory tree is an example. Some seeds take advantage of the animal’s fur. The seed gets attached on the animal’s fur by little hooks which work on the same mechanism as Velcro and they are carried. When they are scratched of, they fall apart and the seeds get planted. Queen Anne’s Lace, and Enchanter’s Nightmare use these hooks. Cattails, genus Typha, are perennial reeds found in marshy areas throughout the temperate regions of the world. The common cattail, T. latifolia, of North America has long, straplike leaves and stalks with thickly flowered cylindrical spikes that become dark brown at maturity. Pollinated from male flowers on the upper end of the spike, the female flowers on the lower end may produce a million or more small, downy seeds, the "cat's tail." Cattail leaves are used for weaving rush chairseats, mats, and baskets. The young shoots and partly developed pollen spike may be cooked and eaten, and the starchy roots cooked as a vegetable or ground into a flour. Many airborne seeds may land in streams and also get carried to different areas. Jewelweed’s seeds explodes and it sends the seeds flying. The Blooming Witschale’s seed also splits open in it’s own time and then even the wind splits it and scatters the seeds. Some seeds just fall down like the Mullein, Toadlax, and Ciqueloil which tend to grow in patches for this reason.

2. Nourishment- Most kinds of seeds have abundant food stored in them. Playing a role similar to that of the yolk in an egg, this food supply is a ready source of energy for a plant embryo as it starts its growth. Thus, seeds offer a young plant nourishment during the critical period just after germination when the seedling must establish itself.
3. Dormancy- Once a seed has fallen to the ground, it may lie dormant for many years. When conditions are favorable, particularly when moisture is present, the seed will begin to grow into a young plant. By remaining dormant until conditions improve, seeds enable plants to postpone development during unfavorable conditions such as a drought or a cold-period. Thus, seeds aid in synchronizing the growth of a new plant with the season of the year.

C. Fruit is the ripened ovary of any flowering plant, or angiosperm, and usually contains one or more seeds. No fruit occurs in the other class of seed plants, gymnosperm, which includes the fern and the conifer.

By definition, fruit refers to such edibles as tomatoes, string beans, corn, peas, and mustard, as well as to nuts, acorns, oranges, peaches, and others. Tomatoes, string beans, and peaches, for example, are all fruits that are eaten whole; whereas peas, corn, and mustard are the seeds, or fertilized ovules, of fruits. Flour is ground from the fruit of the wheat plant, and coffee is made from the seeds of the coffee fruit, or bean.

Some fruits are partly derived from flower structures other than the ovary, and these are called accessory fruits. Most accessory fruits, such as bananas, cucumbers, and gooseberries, are fleshy throughout and are therefore called false berries. The apple and pear are accessory fruits called pomes; the edible portion is the fleshy exterior, and the true fruit forms the core.

Fruits promote seed dispersal and seed germination. Animals that eat fleshy fruits may spit out or expel undigested seeds with the feces and deposit them in a new location. Dry fruits, like nuts, may be carried about by animals such as the squirrel and left in some forgotten hiding place. Fruits with burrs, hooks, or wing blades may be scattered widely by the wind or, clinging to the pelt of a passing animal, be transported to other locations. Fruits that fall to the ground eventually decay, and this aids seed development by enriching the soil.

The nutritional value of fruits varies. Many have few calories because they are composed largely of water: a ripe tomato, for example, may be 97 percent water. Such fruits are valued in the human diet primarily for their vitamin contents and their distinctive tastes and textures. Soybeans and peanuts, on the other hand, have high protein and caloric contents, and valuable oils are obtained from olive and sunflower fruits and castor-oil seeds. Cereal grains are humankind's major food, contributing more than two-thirds of the world production of edible dry matter and half of the world's protein.

A simple fruit consists of a single ripened ovary and may be either dry or fleshy. With ripening, the walls of a simple dry fruit become leathery, papery, or woody. At maturity the walls may be dehiscent, opening to shed the seeds, or indehiscent, remaining closed and usually containing only one seed. Dehiscent fruits are further classified as follicles, legumes, or capsules. The follicle dehisces along one side only. Examples include milkweed and peony fruits. Such legumes as the pea dehisce along two sides.

The capsule, one of the commonest kinds of simple dry fruits, develops from a compound pistil, which is two or more carpels (inner flower parts) fused together. The poppy fruit is a capsule from which the seeds are released through a distal ring of pores. The large single seed of the horse-chestnut fruit, however, is released only when the thick, spiny, three-valved capsule falls apart at maturity.

Indehiscent dry fruits include the achene, grain, samara, and nut. The achene--for example, of the dandelion or buttercup--contains a single seed that almost fills the fruit cavity but is separable from the ovary wall, or pericarp. Because of their small size, achenes are frequently mistaken for seeds. The grain, or caryopsis, is the characteristic fruit of the grass family, including the cereals. It differs from the achene in that the thin seed coat is fused with the pericarp. The samara also is usually one-seeded and has a winglike outgrowth of the pericarp that facilitates its dispersal by wind. Familiar examples are the fruits of elm, sycamore, ash, and maple trees.

A nut is a drupe, which is a one-seeded fruit with a thickened pericarp that hardens upon ripening. Examples are the fruits of hazel, oak, beech, chestnut, and walnut. The term nut is popularly misused, often when referring to individual seeds. The so-called Brazil nut is a seed, one of 12 to 20 borne in a globular, thick-walled capsule. The peanut fruit is a legume containing edible seeds, or peanuts, and the edible parts of almond and walnuts are the seeds of drupes.

Fruits in which all or most of the fruit wall is fleshy at maturity are classified as simple fleshy fruits. They are further classified as berries, drupes, false berries, and pomes. The seeds escape as a result of the decomposition of the fleshy tissues. The entire ovary wall of the berry ripens into a fleshy, usually edible, pericarp. Berries include the fruits of the tomato, grape, date, aubergine, avocado, and red pepper. There may be a single seed, as in the date, or many, as in the tomato. Citrus fruits are modified berries in which the pericarp forms the peel and the edible part consists of saclike outgrowths of the carpel walls.

The pericarp of a drupe is divided into three parts: an outer exocarp, which is often a thin skin; the fleshy mesocarp; and the endocarp, which is a stone or pit enclosing the seed. Drupes include the olive, plum, cherry, and peach. In the coconut fruit the exocarp and mesocarp form the fibrous husk, while the familiar nut is a single seed enclosed in the woody endocarp.

Compound fruit is either classified as aggregate or multiple. An aggregate fruit is a cluster of ripened ovaries produced by a single flower. The individual fruits of raspberry, for example, are tiny drupes that separate as a unit from the receptacle. The strawberry, however, is both aggregate and accessory: the individual fruits are achenes, commonly called the seeds, while the fleshy edible part is the receptacle.

A multiple fruit is formed from a number of flowers grouped closely together as an inflorescence, rather than a single flower. Each flower produces a fruit, and the fruits remain together at maturity. The best example is the pineapple, which comprises fruits derived from several hundred individual flowers fused together. The fig, breadfruit, and mulberry are also multiple fruits.