35.1 Meristems elaborate the plant body plan after germination.
Meristems
• Meristematic tissues are masses of small cells containing dense cytoplasm and proportionately large nuclei. (p. 730)
• Apical meristems are located at the tips of roots and shoots, and produce primary tissue by dividing and continually adding more cells to the tips of the seedling's body. (p. 730)
• Root apical meristem is protected by a root cap. (p. 730)
• Apical meristem gives rise to three primary meristems: protoderm, procambium, and ground meristem. (pp. 730-731)
• Most woody plants possess active lateral meristems that produce secondary growth and increase a plant's girth with secondary tissues. (p. 731)
Organization of the Plant Body
• A vascular plant consists of a root system for anchoring the plant and a shoot system composed of stems and leaves that serve as the main photosynthetic sites and hold the reproductive organs, such as flowers, fruits, and seeds. (p. 732)
• Three basic tissue types are ground tissue, dermal tissue, and vascular tissue. (p. 732)
Primary and Secondary Growth
• Primary growth plays an important role in establishing the organism's basic body plan. (p. 733)
• Evolution of secondary growth allowed the development of thick trunks and wide, treelike organisms. (p. 733)
35.2 Plants have three basic tissues, each composed of several cell types.
Dermal Tissue
• Epidermal cells arise from the protoderm and cover all primary plant parts. (p. 734)
• Guard cells, trichomes, and root hairs are all specialized epidermal cells that function in absorption or protection. (pp. 734-735)
Ground Tissue
• Parenchyma cells are the most abundant type of plant cells, are relatively unspecialized, and perform a wide variety of functions. (p. 736)
• Collenchyma cells are relatively flexible and provide support for plant organs. (p. 736)
• Sclerenchyma cells have tough, thick walls and are divided into long, slender fibers and variable-sized, branched sclereids. (p. 736)
Vascular Tissue
• Xylem is the main water-conducting tissue. Composed of vessels and tracheids, xylem carries water to the shoots and leaves, and helps drive transpiration. (p. 737)
• Primary xylem is derived from procambium, and secondary xylem is formed by vascular cambium. (p. 737)
• Phloem is the principal food-conducting tissue in vascular plants. (p. 738)
• Food conduction is carried out through sieve cells and sieve-tube members. (p. 738)
35.3 Root cells differentiate as they become distanced from the dividing root apical meristem.
Root Structure
• The four major regions in the root are the root cap, which protects delicate tissues as the roots elongate, and help perceive gravity; the zone of cell division, where the cells multiply; the zone of elongation, where roots lengthen as the cells produced by the primary meristem become several times longer than wide; and the zone of maturation, where cells differentiate into specific cell types. (pp. 739-741)
Modified Roots
• Most plants produce either a taproot system or a fibrous root system, although other root types, such as aerial roots, pneumatophores, contractile roots, parasitic roots, food storage roots, water storage roots, and buttress roots, can also exist. (p. 743)
35.4 Stems are the backbone of the shoot, transporting nutrients and supporting the aerial plant organs.
Stem Structure
• Leaves may be arranged alternately, oppositely, or whorled on the stem. (p. 744)
• Stems are divided into nodes and internodes, while leaves are divided into a blade and often a petiole and stipules. (p. 744)
• Axillary meristems, which are produced in the angle between a petiole and the stem, frequently develop into branches or into flowers. (p. 744)
• In primary meristems, the protoderm gives rise to the epidermis, the ground meristem produces parenchyma cells, and procambium produces primary xylem and primary phloem. (p. 745)
Modified Stems
• Bulbs, corms, rhizomes, runners and stolons, tubers, tendrils, and cladophylls are all modified stems that perform special functions, such as food storage, plant support, or vegetative propagation. (p. 747)
35.5 Leaves are adapted to support basic plant functions.
Leaf External Structure
• Leaves are initiated as primordia by the apical meristems and are the principal sites of photosynthesis on land. (p. 748)
• Leaves are either simple, with undivided blades, or compound, with the blade divided into leaflets. (p. 749)
Leaf Internal Structure
• Leaves are divided into a waxy cuticle, an upper epidermis, palisade mesophyll, spongy mesophyll, and lower epidermis. (p. 750)
Modified Leaves
• Leaves have evolved a variety of adaptations, including floral leaves, spines, reproductive leaves, window leaves, shade leaves, and insectivorous leaves. (p. 751)