Summary

Concept 24.1: The Plant Body Is Organized and Constructed in a Distinctive Way

• The vegetative organs of flowering plants are roots, which form a root system, and stems and leaves, which (together with flowers, which are sexual organs) form a shoot system. Review Figure 24.1
• Plant development is influenced by three unique properties of plants (compared with animals): meristems, the presence of cell walls, and the totipotency of most plant cells.
• During embryogenesis, the apical–basal axis and the radial axis of the plant body are established, as are the shoot apical meristem and the root apical meristem. Review Figures 24.4 and 24.5
• Three tissue systems, arranged concentrically, extend throughout the plant body: the dermal tissue system, ground tissue system, and vascular tissue system. Review Figure 24.6
• The vascular tissue system includes xylem, which conducts water and mineral ions absorbed by the roots to the shoot, and phloem, which conducts the products of photosynthesis throughout the plant body.

Concept 24.2: Apical Meristems Build the Primary Plant Body

• Primary growth is characterized by the lengthening of roots and shoots and by the proliferation of new roots and shoots through branching. Some plants also undergo secondary growth, by which they increase in thickness.
• Apical meristems generate primary growth, and lateral meristems generate secondary growth. Review Figure 24.7
• Apical meristems at the tips of shoots and roots give rise to three primary meristems (protoderm, ground meristem, and procambium), which in turn produce the three tissue systems of the plant body.
• The root apical meristem gives rise to the root cap and the three primary meristems. The cells in the root tip are arranged in three zones that grade into one another: the zone of cell division, zone of cell elongation, and zone of cell maturation. Review Figure 24.8
• The vascular tissue of roots is contained within the stele. It is arranged differently in eudicot and monocot roots. Review Figure 24.9 and ACTIVITIES 24.1 and 24.2
• The root system of eudicots typically consists of a taproot and lateral roots. Monocots typically have a fibrous root system made up of adventitious roots. Review Figure 24.10
• In stems, the vascular tissue is divided into vascular bundles, each containing both xylem and phloem. Review Figure 24.11 and ACTIVITIES 24.3 and 24.4
• Eudicot leaves have two zones of photosynthetic mesophyll cells that are supplied by veins with water and minerals. Review Figure 24.12 and ACTIVITY 24.5
• The organs of the primary plant body may be modified to perform specialized functions. Review Figure 24.13

Concept 24.3: Many Eudicot Stems and Roots Undergo Secondary Growth

• Two lateral meristems, the vascular cambium and cork cambium, are responsible for secondary growth. The vascular cambium produces secondary xylem (wood) and secondary phloem (inner bark). The cork cambium produces a protective tissue called cork. Review Figures 24.14 and 24.15 and ANIMATED TUTORIAL 24.1

Concept 24.4: Domestication Has Altered Plant Form

• Although the plant body plan is simple, it can be changed dramatically by minor genetic differences, as evidenced by the natural diversity of wild plants.
• Crop domestication involves artificial selection of certain desirable traits found in wild populations. As a result of artificial selection over many generations, the body forms of crop plants are very different from those of their wild relatives. Review Figure 24.16