Low temperature represents, together with drought and salt stress, one of the most important environmental constraints limiting the pro­ ductivity and the distribution of plants on the Earth. Winter survival, in particular, is a highly complex phenomenon, with regards to both stress factors and stress responses. The danger from winter cold is the result not only of its primary effect, i. e. the formation of ice in plant tissues; additional threats are presented by the freezing of water in and on the ground and by the load and duration ofthe snow cover. In recent years, a number of books and reviews on the subject of chilling and frost resistance in plants have appeared: all of these publications, however, concentrate principally on the mechanisms of injury and resistance to freezing at the cellular or molecular level. We are convinced that analysis of the ultrastructural and biochemical alterations in the cell and particularly in the plasma membrane during freezing is the key to understanding the limits of frost resistance and the mechanisms of cold acclimation. This is undoubtedly the immediate task facing those of us engaged in resistance research. It is nevertheless our opinion that, in addition to understanding the basic physiological events, we should be careful not to overlook the importance of the comparative aspects of the freezing processes, the components of stress avoidance and tolerance and the specific levels of resistance.

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1. Low Temperature and Frost as Environmental Factors.- 1.1 Low Temperature Hazards.- 1.2 Cold, Frost, and Snow.- 1.3 The Occurrence of Cold, Frost, and Snow.- 1.4 Frost and Snow in the Plant's Environment.- 1.5 Time of Onset, Severity and Duration of Frost: The Freezing Risk.- 1.6 Temperature Fluctuations in Wintering Trees.- 2. The Freezing Process in Plants.- 2.1 Freezing of Water and Aqueous Solutions.- 2.1.1 Ice Nucleation.- 2.1.2 Freezing of Solutions.- 2.1.3 Sequence of Events in the Freezing of Liquids.- 2.1.4 Vitrification of Water and Solutes.- 2.2 Freezing of Plant Cells.- 2.2.1 Extracellular Freezing.- 2.2.2 Intracellular Freezing.- 2.2.3 Freezing of Intact Tissues.- 2.2.4 Threshold Freezing Temperature and Supercooling of Plant Tissues.- 2.2.5 Initiation and Progress of Freezing in the Whole Plant.- 3. Freezing Injuries in Plants.- 3.1 Typology of Freezing Mechanisms.- 3.2 Causes of Death by Freezing.- 3.3 Phenomenology of Frost Damage.- 3.3.1 Symptoms of Injury.- 3.3.2 Freezing Damage Peculiar to Trees.- 3.4 Results of Freezing Injury and Chances of Recovery.- 4. Mechanisms of Frost Survival.- 4.1 Components of Frost Survival.- 4.1.1 Frost Mitigation.- 4.1.2 Frost Exclusion.- 4.1.3 Components of Frost Resistance.- 4.2 Supercooling as a Survival Mechanism.- 4.2.1 Persistent Supercooling of Leaves.- 4.2.2 Deep Supercooling of Xylem Ray Parenchyma Cells.- 4.3 Extraorgan and Extratissue Freezing.- 4.3.1 Deep Supercooling and Extraorgan Freezing of Hydrated Seeds.- 4.3.2 Deep Supercooling and Extraorgan Freezing of Floral Primordia of Woody Angiosperms.- 4.3.3 Extraorgan Freezing of Conifer Buds.- 4.4 Comparison and Classification of Frost Survival Mechanisms.- 4.5 Survival at Ultralow Temperatures.- 4.5.1 Desiccated Plant Tissues.- 4.5.2 Hydrated Plant Tissues.- 5. Cold Acclimation in Plants.- 5.1 The Annual Course of Frost Resistance.- 5.2 The Seasonal Cold Acclimation Process.- 5.2.1 Seasonality Timing.- 5.2.2 Induction of Cold Acclimation and the First Stage of the Hardening Process.- 5.2.3 The Second Stage of Frost Hardening.- 5.3 Environmental Control of the Level of Frost Resistance.- 5.3.1 Fluctuation of Frost Resistance During Winter.- 5.3.2 Water Content of the Plant and Frost Resistance.- 5.4 Biochemical and Structural Changes During Cold Acclimation.- 5.4.1 Metabolic Pathway Shifts from the Growing State to the Dormant State.- 5.4.2 Sugars and Related Compounds.- 5.4.3 Amino Acids.- 5.4.4 Nucleic Acids and Proteins.- 5.4.5 Lipid Changes.- 5.4.6 Abscisic Acid.- 5.4.7 Cytological Changes During Cold Acclimation.- 6. Frost Resistance in Plants.- 6.1 Genetic Variation in Frost Resistance.- 6.1.1 Differences in Frost Resistance Between Plant Taxa.- 6.1.2 Differences in Frost Resistance Within Populations.- 6.1.3 Inheritance of Frost Resistance.- 6.2 Differences in Frost Resistance of Various Plant Organs and Tissues.- 6.2.1 Vegetative Organs.- 6.2.2 Reproductive Organs.- 6.3 Ontogenetic Variation in Frost Resistance.- 6.3.1 Variation of Frost Resistance During the Cell Cycle.- 6.3.2 Frost Resistance of Seeds.- 6.3.3 Frost Susceptibility During Germination and at the Early Seedling Stage.- 6.3.4 Frost Resistance During Establishment and Ageing.- 7. Regional Distribution of Plants and Their Adaptive Responses to Low Temperatures.- 7.1 Woody Plants Within the Tropics.- 7.1.1 Mangroves.- 7.1.2 Palms.- 7.2 Evergreen Broad-Leaved Trees and Shrubs.- 7.2.1 Temperate Rain Forest Species.- 7.2.2 Mediterranean Sclerophylls.- 7.3 Transition from an Evergreen to a Deciduous Flora and Its Consequences for Frost Survival.- 7.3.1 Woody Plants.- 7.3.2 Ferns.- 7.4 Conifers.- 7.4.1 The Freezing Resistance of Various Conifer Families and Its Connection with Their Distribution Range.- 7.4.2 Characteristics of Freezing Resistance of Conifers.- 7.5 Mountain Plants.- 7.5.1 Dwarf Shrubs and Herbs of Temperate Mountains.- 7.5.2 Caulescent Giant Rosette Plants of Tropical High Mountains.- 7.6 Trends of Adaptive Improvement of Low Temperature Resistance in Vascular Plants.- 8. Winter Damage as the Result of a Complexity of Constraint.- 8.1 Winter Desiccation.- 8.2 Damage Due to Ice Encasement and Compact Snow.- 8.3 Harmful Effects of Heavy and Long-Lasting Snow Cover.- 8.4 Winter Survival: A Complex Response.- Determination of Frost Resistance for Comparative Studies.- Field Survival.- Artificial Freezing Tests.- Analysis of the Freezing Process.- Frost Treatment of the Samples.- Identification of Frost Injuries.- Quantification of Frost Resistance.- References.- Terminology and Definitions.- Taxonomic Index.