Chapter 9b-Stems and Material Transport Woody plants produce wood tissue and bark through the activity of secondary meristems: The secondary meristem result in growth in a lateral direction, such as the increase in girth of a tree. Woody plants include: Trees have 1 or only a few main stems, whereas shrubs have several to many main stems.
Vascular cambium The vascular cambium develops from meristematic cells between xylem and phloem. Fascicular Interfascicular
Vascular cambium The mature vascular cambium takes the form of a cylinder. The vascular cambium produces lignin-rich secondary xylem tissue to the inside (wood) and secondary phloem to the outside (inner bark). Two types of cells in the vascular cambium: Division of fusiform initials generate: secondary xylem secondary phloem Division of ray initials generate: -ray parenchyma cells -ray tracheids form the vascular rays In contrast to the xylem, only one year s production of secondary phloem (the innermost bark) is active in sugar transport.
Cork cambium As young woody stems enlarge, the epidermis ruptures and is replaced by the cork. The cork, cork cambium, and parenchyma cells make up the periderm. As a plant grows older, a series of additional periderms may form until remnants of several are visible in the outer bark. The periderm(s) can take on different appearances The walls of the cork cells are well-equipped to protect the stems from pathogens and other damages. They contain secondary compounds such as: Suberin is composed of: Beech Hackberry Birch -phenolic compounds to prevent microbial attack -waxes to prevent water loss
Cork tissues also contain: The bark often includes openings called lenticels that allow gas exchange for the respiration of the cells of the bark. Humans use stems in many ways Paper Papyrus is made from thick stems of the papyrus plant, Cyperus papyrus. Ancient Egyptians used papyrus to make: Today, most paper is made from wood pulp generated from trees grown in plantations. Genetic engineers have succeeded in producing normally structured aspen trees with: During the pulping process, lignin by-products generate dioxin and other toxic compounds. Cork Quercus suber (cork oak) Commercial cork is obtained by stripping the outer bark when the tree is 20-25 years old. After the cork is stripped, new cork develops from underlying periderm layers. Cork is widely used for: Wood Modern humans use wood from many types of trees for:
Study outline from Chapter 9b-Stems and Material Transport What are the two secondary meristems that produce wood tissue and bark? Define secondary growth. What is the difference between a tree, a shrub and a vine? What is the vascular cambium? How does the vascular cambium develop? What is the fascicular cambium? What is the interfascicular cambium? Name the secondary vascular tissues that are produced by the vascular cambium? Name the two types of cells in the vascular cambium? The division of the fusiform initials generate and (secondary xylem) toward the inside of the cell, and (secondary phloem) toward the surface of the stem. The division of the ray initials generate and to form the. During each growing season, the produces new cylinders of (annual growth ring), but only a thin layer of (innermost bark) is responsible for sugar transport in a tree. -------------------------------------------------------------------------------------- Use the following diagram to explain secondary growth in woody stems. How does this process result in growth rings? Label the figure using the following terms: secondary xylem secondary phloem (innermost bark) vascular cambium vascular ray
Study outline from Chapter 9b-Stems and Material Transport What is the cork cambium? What is the periderm? Which components make up the periderm? What is the inner bark? What is the function of inner bark? What is the outer bark? What is the function of outer bark? The walls of the cork cells contain the secondary compounds and. What is suberin? What is lignin? What are lenticels? What is the function of lenticels? What are three human uses of stems? What is papyrus? What were some uses of papyrus? What is cork? What are some uses for cork? Label the figure using the following terms: periderm layers innermost periderm outer bark secondary xylem (wood) secondary phloem (inner bark) vascular cambium