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After a brief introduction, this chapter discusses, in general, the origin and development of stems. Items such as the apical meristem and the tissues derived from it, leaf gaps, cambia, secondary tissues, and lenticels are included. This general discussion is followed by notes on the distinctions between herbaceous and woody dicot stems and monocot stems. This section covers annual rings, rays, heartwood and sapwood, resin canals, bark, laticifers, and vascular bundles.

Next, there is a survey of specialized stems (rhizomes, stolons, tubers, bulbs, corms, cladophylls, and others). The chapter concludes with a discussion of the economic importance of wood and stems.

Some Learning Goals

Know the tissues that develop from shoot apices and the meristems from which each tissue is derived. Distinguish between primary tissues and secondary tissues.

Learn and give the function of each of the following: vascular cambium, cork cambium, stomata, lenticels.

Contrast the stems of herbaceous and woody dicots with the stems of monocots.

Understand the composition of wood and its annual rings, sapwood, heartwood, and bark. Explain how a log is sawed for commercial use.

Distinguish among rhizomes, stolons, tubers, bulbs, corms, cladophylls, and tendrils.

Learn at least 10 human uses of wood and stems in general.

brief check of furnishings and tools around the

A house and garage—or even the house itself— soon reveals that, with the exception of appliances and the family car, much of what we use daily and take for granted, from pencils and pianos to newspapers and brooms, has some wood content. Most of that wood directly or indirectly involves plant stems. In fact, stems have been an integral part of human life ever since cave dwellers first used wooden clubs to kill for food.

Grafting, which usually involves artificially uniting stems or parts of stems of different but related varieties of plants, has been practiced by humans for hundreds of years. The careful matching of certain tissues is critical to its success, as is seen in the discussion of grafting in Chapter 14. To understand how and why grafts may or may not be successful and to identify which parts of stems are useful, we first need to examine the structure of stems and learn the basic functions of the various tissues.

Unlike animals, some plants have indeterminate growth (i.e., they can grow indefinitely), with the meristems at their tips increasing their length and other meristems increasing their girth for hundreds or even thousands of years. In stems, the cells produced by the meristems usually become the familiar, erect, aerial shoot system with branches and leaves. In certain plants, such as ferns or perennial grasses, this shoot system may develop horizontally beneath or at the surface of the ground; in other plants, the stem may be so short and inconspicuous as to appear nonexistent. In a number of plants, stems are modified in ways that allow specialized functions, such as climbing or the storage of food or water.

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