INTRODUCTION. Internal Organization of the Plant Body. Summary of Types of Cells and Tissues. General References. DEVELOPMENT OF THE SEED PLANT. The Embryo. From embryo to the Adult Plant. Apical Meristems and Their Derivatives. Differentiation, Specialization, and Morphogenesis. References. THE CELL. Cytoplasm. Nucleus. Plastids. Mitochondria. Microbodies. Vacuoles. Paramural Bodies. Ribosomes. Dictyosomes. Endoplasmic Reticulum. Lipid Globules. Microtubules. Ergastic Substances. References. CELL WALL. Macromolecular Components and Their Organization in the Wall. Cell Wall Layers. Intercellular Spaces. Pits, Primary Pit--Fields, and Plasmodesmata. Origin of Cell Wall During Cell Division. Growth of Cell Wall. References. PARENCHYMA AND COLLENCHYMA. Parenchyma. Collenchyma. References. SCLERENCHYMA. Sclereids. Fibers. Development of Sclereids and Fibers. References. EPIDERMIS. Composition. Developmental Aspects. Cell Wall. Stomata. Trichomes. References. XYLEM: GENERAL STRUCTURE AND CELL TYPES. Gross Structure of Secondary Xylem. Cell Types in the Secondary Xylem. Primary Xylem. Differentiation of Tracheary Elements. References. XYLEM: VARIATION IN WOOD STRUCTURE. Conifer Wood. Dicotyledon Wood. Some Factors in Development of Secondary Xylem. Identification of Wood. References. VASCULAR CAMBIUM. Organization of Cambium. Developmental Changes in the Initial Layer. Patterns and Causal Relations in Cambial Activity. References. PHLOEM. Cell Types. Primary Phloem. Secondary Phloem. References. PERIDERM. Structure of Periderm and Related Tissues. Development of Periderm. Outer Aspect of Bark in Relation to Structure. Lenticels. References. SECRETORY STRUCTURES. External Secretory Structures. Internal Secretory Structures. References. THE ROOT: PRIMARY STATE OF GROWTH. Types of Roots. Primary Structure. Development. References. THE ROOT: SECONDARY STATE OF GROWTH AND ADVENTITIOUS ROOTS. Common Types of Secondary Growth. Variations in Secondary Growths. Physiologic Aspects of Secondary Growth in Roots. Adventitious Roots. References. THE STEM: PRIMARY STATE OF GROWTH. External Morphology. Primary Structure. Development. References. THE STEM: SECONDARY GROWTH AND STRUCTURAL TYPES. Secondary Growth. Types of Stems. References. THE LEAF: BASIC STRUCTURE AND DEVELOPMENT. Morphology. Histology of Angiosperm Leaf. Development. Abscission. References. THE LEAF: VARIATIONS IN STRUCTURE. Leaf Structure and Environment. Dicotyledon Leaves. Monocotyledon Leaves. Gymnosperm Leaves. References. THE FLOWER: STRUCTURE AND DEVELOPMENT. Concept. Structure. Development. References. THE FLOWER: REPRODUCTIVE CYCLE. Microsporogenesis. Pollen. Male Gametophyte. Megasporogenesis. Female Gametophyte. Fertilization. References. THE FRUIT. Concept and Classification. The Fruit Wall. Fruit Types. Fruit Growths. Fruit Abscission. References. THE SEED. Concept and Morphology. Seed Development. Seed Coat. Nutrient Storage Tissues. References. EMBRYO AND SEEDLING. Mature Embryo. Development of Embryo. Classification of Embryos. Seedling. References. Glossary. Index.

Anatomy of Seed Plants

Ruminants select nutritious diets from a diverse array of plant species that vary in kinds and concentrations of nutrients and toxins, and meet their nutritional requirements that vary with age, physiological state. and environmental conditions. Thus, ruminants possess a degree of nutritional wisdom in the sense that they generally select foods that meet nutritional needs and avoid foods that cause toxicosis. There is little reason to believe that nutritional wisdom occurs because animals can directly taste or smell either nutrients or toxins in foods. Instead, there is increasing evidence that neurally mediated interactions between the senses (i.e., taste and smell) and the viscera enable ruminants to sense the consequences of food ingestion, and these interactions operate in subtle but profound ways to affect food selection and intake, as well as the hedonic value of food. The sensation of being satisfied to the full (i.e., satiety) occurs when animals ingest adequate kinds and amounts of nutritious foods, and animals acquire preferences (mild to strong) for foods that cause satiety. Unpleasant feelings of physical discomfort (i.e., malaise) are caused by excesses of nutrients and toxins and by nutrient deficits, and animals acquire aversions (mild to strong) to foods that cause malaise. What constitutes excesses and deficits depends on each animal's morphology, physiology, and nutritional requirements. This does not mean that ruminants must maximize (optimize) intake of any particular nutrient or mix of nutrients within each meal or even on a daily basis, given that they can withstand departures from the normal average intake of nutrients (i.e., energy-rich substances, nitrogen, various minerals, and vitamins). Rather, hemostatic regulation needs only some increasing tendency, as a result of a gradually worsening deficit of some nutrient or of an excess of toxins or nutrients, to generate behavior to correct the disorder. Extreme states should cause herbivores to increase diet breadth and to acquire preferences for foods that rectify maladies. From an evolutionary standpoint, mechanisms that enable animals to experience feedback, sensations such as satiety and malaise, should be highly correlated with nutritional well being, toxicosis, and nutritional deficiencies, which are directly related with survival and reproduction.

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Postingestive Feedback as an Elementary Determinant of Food Preference and Intake in Ruminants

Characteristics of higher plant terpenoids that result in mediation of numerous kinds of ecological interactions are discussed as a framework for this Symposium on Chemical Ecology of Terpenoids. However, the role of terpenoid mixtures, either constitutive or induced, their intraspecific qualitative and quantitative compositional variation, and their dosage-dependent effects are emphasized in subsequent discussions. It is suggested that little previous attention to these characteristics may have contributed to terpenoids having been misrepresented in some chemical defense theories. Selected phytocentric examples of terpenoid interactions are presented: (1) defense against generalist and specialist insect and mammalian herbivores, (2) defense against insect-vectored fungi and potentially pathogenic endophytic fungi, (3) attraction of entomophages and pollinators, (4) allelopathic effects that inhibit seed germination and soil bacteria, and (5) interaction with reactive troposphere gases. The results are integrated by discussing how these terpenoids may be contributing factors in determining some properties of terrestrial plant communities and ecosystems. A terrestrial phytocentric approach is necessitated due to the magnitude and scope of terpenoid interactions. This presentation has a more broadly based ecological perspective than the several excellent recent reviews of the ecological chemistry of terpenoids.

Higher plant terpenoids:a phytocentric overview of their ecological roles

Linking herbivore experience, varied diets, and plant biochemical diversity

The net value of any plant trait can be assessed by measuring the costs and benefits associated with that trait. While the other contributors to this issue examine the possible benefits of terpenoids to plants, this article explores the metabolic costs of terpenoid accumulation in plants in the light of recent advances in terpenoid biochemistry. Terpenoids are more expensive to manufacture per gram than most other primary and secondary metabolites due to their extensive chemical reduction. The enzyme costs of making terpenoids are also high since terpenoid biosynthetic enzymes are apparently not shared with other metabolic pathways. In fact, plant cells may even possess more than one set of enzymes for catalyzing the basic steps of terpenoid formation. Terpenoids are usually sequestered in complex, multicellular secretory structures, and so storage costs for these substances are also likely to be substantial. However, not all of the processes involved in terpenoid accumulation require large investments of resources. For instance, the maintenance of terpenoid pools is probably inexpensive because there is no evidence that substantial quantities of terpenes are lost as a result of metabolic turnover, volatilization, or leaching. Moreover, plants may reduce their net terpenoid costs by employing individual compounds in more than one role or by catabolizing substances that are no longer needed, although it is still unclear if such practices are widespread. These findings (and other facets of terpenoid biochemistry and physiology) are discussed in relation to the assumptions and predictions of several current theories of plant defense, including the carbonnutrient balance hypothesis, the growth-differentiation balance hypothesis, and the resource availability hypothesis.

Metabolic costs of terpenoid accumulation in higher plants.

It has been hypothesized that herbivores instinctively avoid tannin-containing plant parts in response to the adverse effects of tannins on forage digestion. However, we found that goats learned to avoid condensed tannins (CTs) from blackbrush current season's growth by associating the flavor of foods containing CTs with aversive postingestive consequences. The aversive consequences experienced by goats apparently are not related to digestion inhibition and may depend on the structure of CTs and on how CTs are bound with other cell constituents. These observations suggest several areas of inquiry related to the interaction between CTs and herbivores. A better understanding of the physiological effects of CTs and how herbivores perceive these effects is essential to our knowledge of chemically mediated interactions between plants and mammalian herbivores. With few exceptions, the effects of food flavor have not been separated from those associated with postingestive consequences, even though our data show ...

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Conditioned Flavor Aversion: A Mechanism for Goats to Avoid Condensed Tannins in Blackbrush

A diverse array of secondary metabolites deters feeding by mammals on woody plants. However, not all secondary metabolites are equally deterrent and the potencies of these substances as antifeedants is related to their structures. Although the physiological reason underlying deterrence by secondary metabolites is not well understood, the available evidence indicates that toxicity is more important than digestion inhibition. Resource limitation influences the production of secondary metabolites by woody plants. Species that are adapted to unproductive habitats are more chemically defended than species that are adapted to productive habitats. Resource limitation also affects the phenotypic expression of chemical defense with nutrient stress favoring increased production of carbon-based secondary metabolites and reduced production of nitrogen-containing secondary metabolites. Light stress has the opposite effects on the production of these substances. Herbivory by mammals also affects the chemical defenses of woody plants. In some cases browsing results in increased defense and in others decreased defense. Three circumstances under which browsing by mammals can change the chemical defenses of woody plants are discussed.

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Thomas P. Clausen

Papers

Conditioned Flavor Aversion: A Mechanism for Goats to Avoid Condensed Tannins in Blackbrush

Chemically mediated interactions between woody plants and browsing mammals.

Woody Plant–Mammal Interactions

2′-Cinnamoylsalicortin, a phenolic glycoside from Salix sericea