The Vascular Cambium

The cambium has been variously defined as follows: "The actively dividing layer of cells that lies between, and gives rise to, secondary xylem and phloem (vascular cambium)" (IAWA 1964); "A meristem with products of periclinal divisions commonly contributed in two directions and arranged in radial files. Term pre ferably applied only to the two lateral meristems, the vascular cambium and cork cambium, or phellogen" (Esau 1977); and, "Lateral meristem in vascular plants which produces secondary xylem, secondary phloem, and parenchyma, usually in radial rows; it consists of one layer of initials and their undifferentiated deriva tives" (Little and Jones 1980). Clearly, the cambium is a diverse and extensive meristem, and no one defini tion will encompass all manifestations of what anatomists consider cambium. Its diversity and extent are further exemplified by a single plant, such as a temperate zone tree, in which procambium is initiated in the embryo and perpetuated throughout every lateral, primary meristem before giving rise to cambium in the secondary body. The cambium thereafter performs its meristematic task of producing daughter cells that differentiate to specialized tissue systems. The cam bium, however, does not remain static. Its derivatives vary either in form, or TImc tion, or rate of production at different positions on the tree, with age of the tree, and with season of the year. Moreover, the cambium responds both to internal sig nals and to external stimuli such as environment or wounding.

Texte du rabat

The increase in girth and diameter of woody dicotyledons and gymnosperms is due to secondary vascular tissues produced by the vascular cambium, a pervasive meristem that is present in almost every plant part that persists for more than one year. Consequently, knowledge of the structure and function of the vascular cambium is fundamental to understanding the growth and development of woody plants. The book begins with an historical account of events leading to our present understanding of the cellular tissues comprising the vascular cambium. Subsequent chapters discuss specific characteristics of the cambium with special emphasis on modes of cell division and the products of these divisions. The vascular cambium consists of two cell types, fusiform and ray cell initials, and these cells divide both anticlially and periclinally. The manifold consequences of these two modes of cambial cell division are thoroughly explored and analyzed in this exceptionally detailed and richly illustrated text.

Contenu
1 Introduction.- 2 Fossil Evidence.- 3 Historical.- 3.1 Derivation of the Word Cambium.- 3.2 The Concept of Cambium as a Tissue.- 4 Defining the Cambium.- 4.1Cambial Cell Theories.- 4.2 Special Criteria.- 4.3 Reconciliation.- 4.4 Terminology.- 4.5 Special Features.- 5 Cambial Cell Characteristics.- 5.1 Cell Shape.- 5.2 Fusiform Initial Size.- 5.3 Ultrastructure.- 5.4 Cytochemistry.- 5.5 Cambial Cell Division.- 5.6 Cambial Aging.- 6 Anticlinal Cambial Divisions.- 6.1 Pseudotransverse and Transverse Divisions.- 6.2 Radial Anticlinal Divisions.- 6.3 Fates of Initial Cells.- 6.4 Tangential Increase of Cambium.- 6.5 Frequency of Anticlinal Divisions.- 6.6 Aberrant Anticlinal Divisions.- 6.7 Mechanism of Cell Elongation.- 7 Periclinal Cambial Divisions.- 7.1 Nonstoried Cambia.- 7.2 Storied Cambia.- 7.3 Anomalous Cambia.- 8 Rays.- 8.1 Medullary Rays - Historical.- 8.2 Classification of Rays.- 8.3 Ray Dynamics.- 8.4 Selected Examples.- 8.5 Radial Plates and Erect Cells.- 8.6 Effect of Eccentricity.- 8.7 Miscellaneous Features.- 9 Intercellular Spaces.- 9.1 Nonsecretory.- 9.2 Secretory.- 10 Cambial Wounding.- 10.1 Introduction.- 10.2 Barrier Zone.- 10.3 Mechanical Wounds.- 10.4 Ionizing Radiation.- 10.5 Biological Wounds.- 10.6 Environmental Factors.- 10.7 Cambial Marking.- 10.8 Cambial Electrical Resistance.- 10.9 Reconciliation.- 11 Cambial Zone Characteristics.- 11.1 Cambial Zonation.- 11.2 Radial Cell Wall Thickness.- 11.3 Number of Cambial Zone Cells.- 11.4 Cambial Reactivation.- 11.5 Alternation of Cambial Divisions.- 11.6 Mid-Season Growth Pause.- 11.7 Cambial Growth Cessation.- 11.8 Discontinuous and Missing Growth Rings.- 11.9 Complete Maturation of the Cambium.- References.