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28 The Plant Kingdom: Seed Plants Magnolia fruit with protruding seeds. Magnolia (Magnolia grandiflora) is a flowering plant, and its seeds are enclosed within a fruit. M. F. Merlet /Science Photo Library/Photo Researchers, Inc. C hapter 27 focused on plants that reproduce by means of spores, haploid reproductive units that give rise to gameto- phytes. Although the most successful and widespread plants also produce spores, their primary means of reproduction and dispersal is by seeds, which represent an important adaptation for life on land (see photograph). Each seed consists of an embryonic sporophyte, nutritive tissue, and a protective coat. Seeds develop from the fertilized egg cell, the female gametophyte, and its associated tissues. The two groups of seed plants, gymnosperms and angiosperms (flowering plants), exhibit the greatest evolutionary complexity in the plant kingdom and are the dominant plants in most terrestrial environments. Seeds are reproductively superior to spores for three main rea- KEY C ON CEP TS sons. First, a seed contains a multicellular young plant with embry- Seed plants include gymnosperms and angiosperms. onic root, stem, and one or more leaves already formed, whereas Gymnosperms produce exposed seeds, usually in cones borne on the sporophytes. a spore is a single cell. Second, a seed contains an abundant food supply. After germination, food stored in the seed nourishes the Conifers are the most diverse and numerous of the four living gymnosperm phyla. plant embryo until it becomes self-sufficient. Because a spore is a Angiosperms produce ovules enclosed within carpels; following fertilization, seeds develop from the ovules, and the ovaries of carpels become fruits. a spore. Third, a seed is protected by a multicellular seed coat that Angiosperms, which compose a single phylum, dominate the land and exhibit great diversity in both vegetative and reproductive structures. metabolism and germinate when conditions become favorable. Gymnosperms and angiosperms evolved from ancestral seedless vascular plants. single cell, few food reserves exist for the plant that develops from is very thick and hard in some plants, as, for example, in lima beans. Like spores, seeds live for extended periods at reduced rates of Seeds and seed plants are intimately connected with the development of human civilization. From prehistoric times, early humans collected and used seeds for food. The food stored in seeds is a concentrated source of proteins, oils, carbohydrates, and vitamins, 600 which are nourishing for humans as well as for germinating plants. are stored as conveniently or for as long. Although flowering plants Seeds are easy to store (if kept dry), so humans can collect them produce most seeds that humans consume, the seeds of certain during times of plenty to save for times of need. Few other foods gymnosperms—the piñon pine, for example—are edible. ■ AN INTRODUCTION TO SEED PLANTS Learning Objective 1 Compare the features of gymnosperms and angiosperms. In Chapter 27, you learned that some seedless vascular plants are heterosporous. However, all seed plants are heterosporous and produce two types of spores: microspores and megaspores. In fact, heterospory is a requirement of seed production. Following fertilization in seed plants, an ovule, which is a megasporangium and its enclosed structures, develops into a seed. Seed plants also have integuments, layers of sporophyte tissue that surround and enclose the megasporangium. After fertilization takes place, the seed coat develops from the integuments. Botanists divide seed plants into two groups based on whether or not an ovary wall surrounds their ovules (an ovary is a structure that contains one or more ovules). The two groups of seed plants are the gymnosperms and the angiosperms (❚ Table 28-1). The word gymnosperm is derived from the Greek for “naked seed.” Gymnosperms produce seeds that are totally exposed or borne on the scales of cones. In other words, an ovary wall does not surround the ovules of gymnosperms. Pine, spruce, fir, phyte stage and part in the multicellular haploid gametophyte stage. The sporophyte generation is the dominant stage in each group, and the gametophyte generation is significantly reduced in size and entirely dependent on the sporophyte generation. Unlike the plants we have considered so far (bryophytes and ferns; see Chapter 27), gymnosperms and flowering plants do not have free-living gametophytes. Instead, the female gametophyte is attached to and nutritionally dependent on the sporophyte generation. Review ❚ ❚ GYMNOSPERMS Learning Objectives 2 that means “seed enclosed in a vessel or case.” Angiosperms are flowering plants that produce their seeds within a fruit (a mature ovary). Thus, the ovules of angiosperms are protected. Flowering plants, which are extremely diverse, include corn, oaks, water lilies, cacti, apples, grasses, palms, and buttercups. Both gymnosperms and flowering plants have vascular tissues: xylem, for conducting water and dissolved minerals (inorganic nutrients); and phloem, for conducting dissolved sugar. Both have life cycles with an alternation of generations, that is, they spend part of their lives in the multicellular diploid sporo- What is an ovule? How do gymnosperm and angiosperm seeds differ? 3 4 Trace the steps in the life cycle of a pine, and compare its sporophyte and gametophyte generations. Summarize the features that distinguish gymnosperms from bryophytes and ferns. Name and briefly describe the four phyla of gymnosperms. The gymnosperms include some of the most interesting members of the plant kingdom. For example, a giant sequoia (Sequoiadendron giganteum) known as the General Sherman Tree, in Sequoia National Park in California, is one of the world’s most massive organisms. It is 82 m (267 ft) tall and has a girth of 23.7 m (77 ft) measured 1.5 m (5 ft) above ground level. Another gymnosperm, a coast redwood (Sequoia sempervirens) known as the Mendocino TABLE 28-1 A Comparison of Gymnosperms and Angiosperms Characteristic Gymnosperms Angiosperms Growth habit Woody trees and shrubs Woody or herbaceous Conducting cells in xylem Tracheids Vessel elements and tracheids Reproductive structures Cones (usually) Flowers Pollen grain transfer Wind (usually) Animals or wind Fertilization Egg and sperm ¡ zygote; double fertilization in gnetophytes Double fertilization: egg and sperm ¡ zygote; two polar nuclei and sperm ¡ endosperm Seeds Exposed or borne on scales of cones Enclosed within fruit derived from ovary Number of species About 840 More than 300,000 Geographic distribution Worldwide Worldwide The Plant Kingdom: Seed Plants 601 Key Point Keith Kent /Science Photo Library/Photo Researchers, Inc. Seed plants include four gymnosperm phyla and one phylum of flowering plants (angiosperms). Figure 28-1 Bristlecone pine at sunrise Conifers are woody plants that produce seeds in cones The conifers (phylum Coniferophyta), which include pines, spruces, hemlocks, and firs, are the most familiar group of gymnosperms (❚ Fig. 28-3a). These woody trees or shrubs produce annual additions of secondary tissues (wood and bark; see Chapter 34); there are no herbaceous (nonwoody) conifers. The wood (secondary xylem) consists of tracheids, which are long, tapering cells with pits through which water and dissolved minerals move from one cell to another. Many conifers produce resin, a viscous, clear or translucent substance consisting of several organic compounds that may protect the plant from attack by fungi or insects. The resin collects in resin ducts, tubelike cavities that extend throughout the roots, stems, and leaves. Cells lining the resin ducts produce and secrete resin. Most conifers have leaves called needles that are commonly long and narrow, tough, and leathery (❚ Fig. 28-3b). Pines bear clusters of two to five needles, depending on the species. In a few conifers, such as American arborvitae, the leaves are scalelike and 602 Chapter 28 Angiosperms Evolution of flowering plants Bristlecone pines (Pinus aristata), found in mountainous parts of California, Nevada, and Utah, are the world’s longest-lived trees. tree, is among the world’s tallest trees, measuring 112 m (364 ft) in the year 2000. Botanists using tree-ring analysis determined that one of the oldest living trees, a bristlecone pine (Pinus aristata) in the White Mountains of California, is 4900 years old (❚ Fig. 28-1). Gymnosperms are usually classified into four phyla, which represent four different evolutionary lines (❚ Fig. 28-2). Numbering 630 species, the largest phylum of gymnosperms is Coniferophyta, commonly called conifers. Two phyla of gymnosperms, Ginkgophyta (the ginkgoes) and Cycadophyta (the cycads), are evolutionary remnants of groups that were more significant in the past. The fourth phylum, Gnetophyta (gnetophytes), is a collection of some unusual plants that share certain traits not found in other gymnosperms. Gnetophytes Conifers Ginkgoes Cycads Gymnosperms Evolution of seeds Figure 28-2 Gymnosperm and angiosperm evolution This cladogram shows one hypothesis of phylogenetic relationships among living seed plants, based on structural evidence and molecular comparisons. The arrangement of the phyla shown here may change as future analyses help clarify relationships. cover the stem (❚ Fig. 28-3c). Most conifers are evergreen and bear their leaves throughout the year. Only a few, such as the dawn redwood, larch, and bald cypress, are deciduous and shed their needles at the end of each growing season. Most conifers are monoecious: they have separate male and female reproductive parts in different locations on the same plant. These reproductive parts are generally borne in strobili (commonly called cones), hence the name conifer, which means “cone-bearing.” Conifers occupy extensive areas, ranging from the Arctic to the tropics, and are the dominant vegetation in the forested regions of Alaska, Canada, northern Europe, and Siberia. In addition, they are important in the Southern Hemisphere, particularly in wet, mountainous areas of temperate and tropical regions in South America, Australia, New Zealand, and Malaysia. Southwestern China, with more than 60 species of conifers, has the greatest regional diversity of conifer species in the world. California, New Caledonia (an island east of Australia), southeastern China, and Japan also have considerable diversity of conifer species. Ecologically, conifers contribute food and shelter to animals and other organisms, and their roots hold the soil in place and help prevent soil erosion. Humans use conifers for their wood (for building materials as well as paper products), medicinal www.thomsonedu.com/biology/solomon Angiosperms Gnetophytes Conifers Ginkgoes Cycads Gymnosperms Michael P. Godomski /Photo Researchers, Inc. (b) (a) Figure 28-3 Conifers (a) Colorado blue spruce (Picea pungens ) is a coniferous evergreen tree native to Colorado, Wyoming, Utah, and New Mexico. Spruces are important ornamental plants, as shown in this New Jersey garden. value (such as the anticancer drug Taxol from the Pacific yew), turpentine, and resins. Because of their attractive appearance, conifers such as firs, spruces, pines, and cedars are grown for landscape design and decorative holiday trees and wreaths. Pines represent a typical conifer life cycle The genus Pinus, by far the largest genus in the conifers, consists 1 , a pine tree is of about 100 species. As shown in ❚ Figure 28-4 ● a mature sporophyte. Pine is heterosporous and therefore produces microspores and megaspores in separate cones.1 Male cones, usually 1 cm or less in length, are smaller than female cones and are generally produced on the lower branches each spring (❚ Fig. 28-5). The more familiar, woody female cones, which are on the tree year-round, are usually found on the upper branches of the tree and bear seeds after reproduction. Female cones vary considerably in size. The sugar pine (P. lambertiana) that grows in California produces the world’s longest female cones, which reach lengths of 60 cm (2 ft). Each male cone, also called a pollen cone, consists of sporophylls, leaflike scales that bear sporangia on the underside. At the base of each sporophyll are two microsporangia, which contain numerous microsporocytes, also called microspore mother cells. 1 (c) It may be helpful to review alternation of generations in Chapter 27, including Figure 27-16, which depicts a heterosporous life cycle, before studying the pine life cycle. (b, c) Leaf variation in conifers. (b) Needles of white pine (Pinus strobus). (c) Small, scalelike leaves of American arborvitae (Thuja occidentalis). 2 , each microsporocyte undergoes meiosis to In Figure 28-4 ● form four haploid microspores. Microspores then develop into extremely reduced male gametophytes. Each immature male gametophyte, also called a pollen grain, consists of four cells, two of which — a generative cell and a tube cell — are involved in reproduction. The other two cells soon degenerate. Two large air sacs on each pollen grain provide buoyancy for wind dissemination. 3 , male cones shed pollen grains in great numbers, and wind In ● currents carry some to the immature female cones. Many botanists think that the female cones (also called 4 , each seed cones) are modified branch systems. As shown in ● cone scale bears two ovules, or megasporangia, on its upper surface. Within each megasporangium, meiosis of a megasporocyte, or megaspore mother cell, produces four haploid megaspores. One of these divides mitotically, developing into the female gametophyte, which produces an egg within each of several archegonia. The other three megaspores are nonfunctional and soon degenerate. When the ovule is ready to receive pollen, it produces a sticky droplet at the opening where the pollen grains land. Pollination, the transfer of pollen to the female cones, occurs in the spring for a week or 10 days, after which the pollen cones wither and drop off the tree. One of the many pollen grains that adhere to the sticky female cone grows a pollen tube, an outgrowth that digests its way through the megasporangium to the egg within the archegonium. The germinated pollen grain with its pollen tube is the mature male gametophyte. The tube cell, which is involved The Plant Kingdom: Seed Plants 603 David Cavagnaro John D. Cunningham / Visuals Unlimited Angiosperms Gnetophytes Conifers Cycads Ginkgoes Gymnosperms (a) The leaves of Gnetum gnemon resemble those of flowering plants. Note the exposed seeds. Gnetophytes over the counter in weight-control medications and herbal energy boosters; several deaths have been reported from chronic use or overdose of products containing ephedrine. The third gnetophyte genus, Welwitschia, contains a single species found in deserts of southwestern Africa (❚ Fig. 28-8c). Most of Welwitschia’s body — a long taproot — grows underground. Its short, wide stem forms a shallow disc, up to 0.9 m (3 ft) in diameter, from which two ribbonlike leaves extend. These two leaves continue to grow from the stem throughout the plant’s life, but their ends are usually broken and torn by the wind, giving the appearance of numerous leaves. Each leaf grows to about 2 m (6.5 ft) in length. When Welwitschia reproduces, cones form around the edge of its disclike stem. Review ❚ ❚ ❚ ❚ What is the dominant generation in the pine life cycle? How does pollination occur in gymnosperms? What features distinguish gymnosperms from other plants? What are the four groups of gymnosperms? What features distinguish cycads from ginkgo? From gnetophytes? FLOWERING PLANTS Learning Objectives 5 6 7 8 Summarize the features that distinguish flowering plants from other plants. Briefly explain the life cycle of a flowering plant, and describe double fertilization. Contrast eudicots and monocots, the two largest classes of flowering plants. Discuss the evolutionary adaptations of flowering plants. Robert and Linda Mitchell Figure 28-8 (b) A male joint fir (Ephedra) has pollen cones clustered at the nodes. In the 19th century, European pioneers used species native to the American Southwest to make a beverage, Mormon tea. (c) Welwitschia mirabilis is native to deserts in southwestern Africa. It survives on moisture-laden fogs that drift inland from the ocean. Photographed in the Namib Desert, Namibia. Flowering plants, or angiosperms (phylum Anthophyta), are the most successful plants today, surpassing even the gymnosperms in importance. They have adapted to almost every habitat and, with at least 300,000 species, are Earth’s dominant plants. Flowering plants come in a wide variety of sizes and forms, from herbaceous violets to massive eucalyptus trees. Some flowering plants — tulips and roses, for example —have large, conspicuous flowers; others, such as grasses and oaks, produce small, inconspicuous flowers. Flowering plants are vascular plants that reproduce sexually by forming flowers and, after a unique double fertilization process (discussed later), seeds within fruits. The fruit protects the developing seeds and often aids in their dispersal (see Chapter 36). Flowering plants have efficient water-conducting cells called vesThe Plant Kingdom: Seed Plants 607 sel elements in their xylem, and efficient sugar-conducting cells called sieve tube elements in their phloem (see Chapter 32). Flowering plants are extremely important to humans because our survival as a species literally depends on them. All our major food crops are flowering plants, including cereal crops such as rice, wheat, corn, and barley. Woody flowering plants such as oak, cherry, and walnut provide valuable lumber. Flowering plants give us fibers such as cotton and linen and medicines such as digitalis and codeine. Products as diverse as rubber, tobacco, coffee, chocolate, and aromatic oils for perfumes come from flowering plants. Economic botany is the subdiscipline of botany that deals with plants of economic importance. Monocots and eudicots are the two largest classes of flowering plants Phylum Anthophyta is divided into several classes with only a few members each and two very large classes: the monocots (class Monocotyledones) and the eudicots (class Eudicotyledones) (❚ Fig. 28-9). The smaller classes will be discussed later in the chapter in the context of their evolutionary significance; for now, we restrict our discussion of flowering plants to the monocots and eudicots, which collectively represent about 97% of all flowering plant species. Eudicots are more diverse and include many more species (at least 200,000) than the monocots (at least 90,000). ❚ Table 28-2 provides a comparison of some of the general features of the two classes. Monocots include palms, grasses, orchids, irises, onions, and lilies. Monocots are mostly herbaceous plants with long, narrow leaves that have parallel veins (the main leaf veins run parallel to one another). The parts of monocot flowers usually occur in threes. For example, a flower may have three sepals, three petals, six stamens, and a compound pistil consisting of three fused carpels (these flower parts are discussed shortly). Monocot seeds have a single cotyledon, or embryonic seed leaf; endosperm, a nutritive tissue, is usually present in the mature seed. Eudicots include oaks, roses, mustards, cacti, blueberries, and sunflowers. Eudicots are either herbaceous (such as a tomato plant) or woody (such as a hickory tree). Their leaves vary in shape but usually are broader than monocot leaves, with netted veins (branched veins resembling a net). Flower parts usually occur in fours or fives or multiples thereof. Two cotyledons are present in eudicot seeds, and endosperm is usually absent in the mature seed, having been absorbed by the two cotyledons during seed development. Flowers are involved in sexual reproduction Flowers are reproductive shoots usually composed of four parts — sepals, petals, stamens, and carpels — arranged in whorls (circles) on the end of a flower stalk, or peduncle (❚ Fig. 28-10). The peduncle may terminate in a single flower or a cluster of flowers known as an inflorescence. The tip of the flower stalk that bears the flower parts is known as the receptacle. All four floral parts are important in the reproductive process, but only the stamens (the “male” organs) and carpels (the “female” organs) produce gametes. A flower that has all four parts is complete, whereas an incomplete flower lacks one or more of these four parts. A flower with both stamens and carpels is perfect, whereas an imperfect flower has stamens or carpels, but not both. Angiosperms Richard H. Gross Gnetophytes Flowering plants John Gerlach / Tom Stack & Associates Figure 28-9 Conifers Cycads Ginkgoes Gymnosperms (a) Monocot. Trillium erectum, like most monocots, has floral parts in threes. Note the three green sepals, three red petals, six stamens, and three stigmas (the compound pistil consists of three fused carpels). 608 Chapter 28 (b) Eudicot. Most eudicots, such as this Tacitus, have floral parts in fours or fives. Note the five petals, 10 stamens, and five separate pistils. Five sepals are also present but barely visible against the background. www.thomsonedu.com/biology/solomon S U M M ARY WI T H K EY TERMS Learning Objectives 1 Compare the features of gymnosperms and angiosperms (page 601). 6 ❚ The two groups of seed plants are the gymnosperms and the angiosperms. Gymnosperms produce seeds that are totally exposed or borne on the scales of cones; an ovary wall does not surround the ovules of gymnosperms. Angiosperms are flowering plants that produce their seeds within a fruit (a mature ovary). 2 ❚ The sporophyte generation is dominant in flowering plants; gametophytes are extremely reduced in size and nutritionally dependent on the sporophyte generation. Flowering plants are heterosporous and produce microspores and megaspores within the flower. ❚ Each microspore develops into a pollen grain (immature male gametophyte). One of each four megaspores produced by meiosis develops into an embryo sac (female gametophyte). The embryo sac contains seven cells with eight nuclei; the egg cell and the central cell with two polar nuclei participate in fertilization. Trace the steps in the life cycle of a pine, and compare its sporophyte and gametophyte generations (page 601). ❚ A pine tree is a mature sporophyte; pine gametophytes are extremely small and nutritionally dependent on the sporophyte generation. Pine is heterosporous and produces microspores and megaspores in separate cones. ❚ Double fertilization, which results in the formation of a diploid zygote and triploid endosperm, is characteristic of flowering plants. ❚ Male cones produce microspores that develop into pollen grains (immature male gametophytes) that are carried by air currents to female cones. ❚ Female cones produce megaspores. One of each four megaspores produced by meiosis develops into a female gametophyte within an ovule (megasporangium). ❚ After pollination, the transfer of pollen to the female cones, a pollen tube grows through the megasporangium to the egg within the archegonium. After fertilization, the zygote develops into an embryo encased inside a seed adapted for wind dispersal. 3 4 Explore plant life cycles by clicking on the figures in ThomsonNOW. 7 ❚ Eudicots (class Eudicotyledones) usually have floral parts in fours or fives or multiples thereof, and their seeds each contain two cotyledons. The nutritive organs in their mature seeds are usually the cotyledons, which have absorbed the nutrients in the endosperm. 8 Name and briefly describe the four phyla of gymnosperms (page 601). ❚ Ginkgo biloba, the only surviving species in phylum Ginkgophyta, is a deciduous, dioecious tree. The female ginkgo produces fleshy seeds directly on branches. ❚ Gnetophytes (phylum Gnetophyta) share a number of traits with angiosperms. 5 Summarize the features that distinguish flowering plants from other plants (page 607). ❚ Flowering plants, or angiosperms (phylum Anthophyta), constitute the phylum of vascular plants that produce flowers and seeds enclosed within a fruit. They are the most diverse and most successful group of plants. ❚ The flower, which may contain sepals, petals, stamens, and carpels, functions in sexual reproduction. Unlike those of gymnosperms, the ovules of flowering plants are enclosed within an ovary. After fertilization, the ovules become seeds, and the ovary develops into a fruit. Discuss the evolutionary adaptations of flowering plants (page 607). ❚ Flowering plants reproduce sexually by forming flowers. After double fertilization, seeds form within fruits. Flowering plants have efficient water-conducting vessel elements in their xylem and efficient carbohydrateconducting sieve tube elements in their phloem. Wind, water, insects, or other animals transfer pollen grains in various flowering plants. ❚ Conifers (phylum Coniferophyta), the largest phylum of gymnosperms, are woody plants that bear needles (leaves that are usually evergreen) and produce seeds in cones. Most conifers are monoecious and have male and female reproductive parts in separate cones on the same plant. ❚ Cycads (phylum Cycadophyta) are palmlike or fernlike in appearance. They are dioecious—they have male and female reproductive structures on separate plants—but reproduce with pollen and seeds in conelike structures. Contrast eudicots and monocots, the two largest classes of flowering plants (page 607). ❚ Most monocots (class Monocotyledones) have floral parts in threes, and their seeds each contain one cotyledon. The nutritive tissue in their mature seeds is endosperm. Summarize the features that distinguish gymnosperms from bryophytes and ferns (page 601). ❚ Unlike bryophytes, gymnosperms are vascular plants. Unlike bryophytes and ferns, gymnosperms produce seeds. Gymnosperms also produce wind-borne pollen grains, a feature that ferns and other seedless vascular plants lack. Briefly explain the life cycle of a flowering plant, and describe double fertilization (page 607). Learn more about flower structure by clicking on the figure in ThomsonNOW. 9 Summarize the evolution of gymnosperms from seedless vascular plants, and trace the evolution of flowering plants from gymnosperms (page 614). ❚ Seed plants arose from seedless vascular plants. Progymnosperms were seedless vascular plants that had megaphylls and “modern” woody tissue. Progymnosperms probably gave rise to conifers as well as to seed ferns, which in turn likely gave rise to cycads and possibly ginkgo. ❚ The evolution of the gnetophytes, particularly their relationship to flowering plants, is unclear. ❚ Flowering plants probably descended from ancient gymnosperms that had specialized features, such as leaves with broad, expanded blades and closed carpels. Flowering plants likely arose only once. The Plant Kingdom: Seed Plants 617 T E S T Y O U R U N DE R S TAND ING 1. Seed plants lack which of the following structure(s)? (a) ovules surrounded by integuments (b) microspores and megaspores (c) vascular tissues (d) a large, nutritionally independent sporophyte (e) a large, nutritionally independent gametophyte 2. Conifers, cycads, ginkgo, and gnetophytes are collectively called (a) club mosses (b) gymnosperms (c) angiosperms (d) eudicots (e) seedless vascular plants 3. Most conifers are , having male and female reproductive parts at different locations on the same plant. (a) incomplete (b) imperfect (c) monoecious (d) dioecious (e) perfect 4. The immature male gametophytes of pine are called (a) ovules (b) stamens (c) seed cones (d) pollen grains (e) polar nuclei 5. The transfer of pollen grains from the male to the female reproductive structure is known as (a) pollination (b) fertilization (c) embryo sac development (d) seed development (e) fruit development 6. Motile sperm cells are found as vestiges in these two gymnosperm groups: (a) monocots, eudicots (b) gnetophytes, conifers (c) gnetophytes, flowering plants (d) cycads, conifers (e) cycads, ginkgo 7. There are at least species of flowering plants. (a) 235 (b) 3000 (c) 30,000 (d) 300,000 (e) 3,000,000 8. This class of flowering plants includes the palms, grasses, and orchids. (a) eudicots (b) gnetophytes (c) cycads (d) monocots (e) conifers 9. The pistil has three sections: (a) stigma, style, and anther (b) anther, filament, and ovule (c) stigma, style, and ovary (d) ovary, ovule, and sepal (e) corolla, stamen, and sepal 10. A simple pistil consists of a single (a) calyx (b) carpel (c) ovule (d) filament (e) petal 11. A flower that lacks stamens is both and . (a) complete; imperfect (b) incomplete; perfect (c) complete; perfect (d) incomplete; imperfect 12. After fertilization, the develop(s) into a fruit and the develop(s) into a seed. (a) ovary; ovule (b) polar nuclei; ovule (c) ovary; endosperm (d) ovule; ovary (e) ovule; polar nuclei 13. The female gametophyte in flowering plants is also called the (a) polar nuclei (b) anther (c) embryo sac (d) endosperm (e) sporophyll 14. This flowering plant may be the nearest living relative to the ancestor of all flowering plants. (a) Amborella (b) Archaeopteris (c) Gnetum (d) water lily (e) Archaeanthus 15. This cross section through an ovary reveals that the pistil is (a) simple, with one carpel (b) compound, with two fused carpels (c) compound, with three fused carpels (d) compound, with six separate carpels (e) compound, with six fused carpels C R I TI C AL TH I N KI N G 1. How are cones and flowers alike? How are they different? (Hint: Your answer should consider microspores /megaspores and seeds.) 5. Analyzing Data. According to the cladogram in Figure 28-19, which plant(s) is /are the outgroup? Which feature does the outgroup lack that all other angiosperms possess? 2. How do the life cycles of seedless plants (see Chapter 27) and seed plants differ? In what fundamental way are they alike? 3. Evolution Link. Most flowers contain both male and female reproductive structures, in contrast to the cones of gymnosperms, which are either male or female. Explain how bisexual flowers might be an advantageous evolutionary adaptation to the flowering plants that possess them. Additional questions are available in ThomsonNOW at www.thomsonedu.com/ login 4. Evolution Link. Contrast the algae, mosses, ferns, gymnosperms, and angiosperms with respect to their dependence on water as a transport medium for reproductive cells. Suggest a hypothesis to explain how the differences might be adaptive to living on land. 618 Chapter 28 www.thomsonedu.com/biology/solomon