A top priority in climate research is obtaining broad-extent and long-term data to support analyses of historical patterns and trends, and for model development and evaluation. Along with directly measured climate data from the present and recent past, it is important to obtain estimates of long past climate variations spanning multiple centuries and millennia. These longer time perspectives are needed for assessing the unusualness of recent climate changes, as well as for providing insight on the range, variation and overall dynamics of the climate system over time spans exceeding available records from instruments, such as rain gauges and thermometers. Tree rings have become increasingly valuable in providing this long-term information because extensive data networks have been developed in temperate and boreal zones of the Earth, and quantitative methods for analyzing these data have advanced. Tree rings are among the most useful paleoclimate information sources available because they provide a high degree of chronological accuracy, high replication, and extensive spatial coverage spanning recent centuries. With the expansion and extension of tree-ring data and analytical capacity new climatic insights from tree rings are being used in a variety of applications, including for interpretation of past changes in ecosystems and human societies. This volume presents an overview of the current state of dendroclimatology, its contributions over the last 30 years, and its future potential. The material included is useful not only to those who generate tree-ring records of past climate-dendroclimatologists, but also to users of their results-climatologists, hydrologists, ecologists and archeologists. 'With the pressing climatic questions of the 21st century demanding a deeper understanding of the climate system and our impact upon it, this thoughtful volume comes at critical moment. It will be of fundamental importance in not only guiding researchers, but in educating scientists and the interested lay person on the both incredible power and potential pitfalls of reconstructing climate using tree-ring analysis.', Glen M. MacDonald, UCLA Institute of the Environment, CA, USA 'This is an up-to-date treatment of all branches of tree-ring science, by the world's experts in the field, reminding us that tree rings are the most important source of proxy data on climate change. Should be read by all budding dendrochronology scientists.', Alan Robock, Rutgers University, NJ, USA

Forests comprise the greatest storage of carbon on land, provide fuel for millions, are the habitat for most terrestrial biodiversity, and are critical to the economies of many countries. Yet changes in the extent and dynamics of forests are inherently difficult to detect and quantify. Remote sensing technologies may facilitate the measurement of some key forest properties which, when combined with other information contained in various computer models, may allow for the quantification of critical forest functions. This book explores how remote sensing and computer modeling can be combined to estimate changes in the carbon storage, or productivity, of forests - from the level of the leaf to the level of the globe. Land managers, researchers, policy makers and students will all find stimulating discussions among an international set of experts at the cutting edge of the interface between science, technology and management.

The subject of fruit ripening is one of vital interest and importance to the massive international fruit growing and fruit trade industries. This book is the definitive handbook on the subject, bringing together a vast wealth of important information from an experienced team of international contributors.

Comprising 26 chapters, this volume deals with the genetic transformation of medicinal plants. It describes methods to obtain plants resistant to insects, diseases, herbicides, and plants with an increased production of compounds of medicinal and pharmaceutical importance. The plant species included are "Ajuga reptans," "Anthemis nobilis," "Astragalus" spp., "Atropa" "belladonna," "Catharanthus roseus," "Datura" spp., "Duboisia" species, "Fagopyrum" spp., "Glycyrrhiza" "uralensis," "Lobelia" spp., "Papaver" "somniferum," "Panax" "ginseng," "Peganum" "harmala," "Perezia" spp., "Pimpinella" "anisum," "Phyllanthus" "niruri," "Salvia" "miltiorrhiza," "Scoparia dulcis," "Scutellaria" "baicalesis," "Serratula" "tinctoria," "Solanum aculeatissimum," "Solanum " "commersonii," "Swainsona galegifolia," tobacco, and "Vinca minor."
This book is of special interest to advanced students, teachers, and researchers in the field of pharmacy, plant tissue culture, phytochemistry, molecular biology, biomedical engineering, and plant biotechnology in general.

Recent advances in our understanding of the fundamental role of bioactive lipids in normal and abnormal physiology was the theme of the XVlth International Spring Sympo- 6-9, 1996 at the George Washington University School sium on Health Sciences held on May of Medicine in Washington, D.C. Over 250 participants shared their latest findings on fundamental mechanisms in lipid metabolism, transport, and signal transduction. Most of the papers presented at the plenary sessions have been collected in this volume, which is divided into seven parts. The focus of Part I is on the new roles that fatty acids and esters play in cellular function. These activities include regulation of gene expression, control of eicosanoid-me- diated responses, and intracellular calcium sequestration. Most biological effects of fatty acids, esters, and phospholipids are transmitted via the interaction of these lipid molecules with specific lipid binding proteins. The chapters in Part II detail the involvement of these in the transport of fatty acids, fatty acyl CoA esters, and phospholipids, and in the proteins modulation of the fatty acid-induced activation of the peroxisome proliferator-activated receptors. The study of arachidonic acid metabolism continues to be the subject of intense interest and research. A number of studies in Part III deal with the substantial differences between the constitutive prostaglandin H synthase isozyme (PGHS-l or COX-I) and the inducible form PGHS-2 (COX-2) regarding compartmentation, control, and expression.

This is an extended version of lectures that were held at the summer workshop Atmosphiirische Umweltforschung im Spannungsfeld zwischen Technik und Natur (At mospheric Environmental Research between Technology and Nature) at the Techni 16, 1996. We were very happy to have Paul J. Crutzen, cal University in Cottbus on July winner of the Nobel Prize for chemistry in 1995, presenting the key lecture on glo bally changing chemistry in the atmosphere. Over the last decades, atmospheric chem istry has been established step by step, not just as an applied discipline of chemistry, but also as a key discipline for our understanding of air pollution, biogeochemical cycling, and climactic processes as well. In fact, the new definition of meteorology as the science of physics and chemistry of the atmosphere expresses this development very well. The chemistry of the atmosphere is strongly influenced by anthropogenic emissions, even on a global scale. As a result of emissions and chemical reactions, the chemical composition of the atmosphere influences the ecosystems directly via depo sition of trace substances, and indirectly by changing the physical climate. Therefore, in this book we combined state-of-the-art lectures describing the physical and chemi cal status of the atmosphere and selected issues representing the interface between atmosphere, technology and nature. Oxidising capacity, heterogeneous processes and acidity still remain as key issues in atmospheric chemistry, even in regions where efficient air control measures have been adopted resulting in reduction of primary atmospheric pollutants."

For the last two decades the loss of, in particular, tropical rainforest has alarmed the public in the developed parts of the world. The debate has been characterised by a lack of understand ing of the causes and effects of the process, leading to the prevailing reaction being unquali fied condemnation. Such attitude has even been observed among scientists, claiming suprem acy to biodiversity conservation. Many scientific analyses are available, but the basis for so ber debates and appropriate actions is still highly insufficient. Two recent international initia tives! will hopefully lead to improved knowledge of deforestation and forest degradation as they recognise the need for studies to critically investigate those issues. This book will pro vide useful input to the initiatives. In my opinion, the scientific analyses have not sufficiently promoted the understanding that the fate of tropical forests is first and foremost a concern of the governments of the countries in which the forests are situated. Tropical forests may be important to the global environment and their rich biodiversity may be a human heritage. But their main importance is their poten tial contribution to improving livelihood in the countries in question.

Biological nitrogen fixation (BNF) - the conversion of molecular nitrogen into ammonia - is one of the most important reactions in ecology and agriculture. It is performed exclusively by microbes (prokaryotes) that live in symbiosis with plants. This book summarizes the latest research on this reaction, the participating microbes and the genetics of how their relevant genes could be transferred into the plants. In the light of a more sustainable and less ecologically damaging agriculture, this is becoming an increasingly pressing issue.

etween 1772 and 1799, Dominique Chaix wrote 170 letters to Dominique Villars. B None of the letters that Vtllars wrote in response have survived, and there is evidence to indicate that Chaix simply did not retain incoming letters once they had served their informative purpose. Villars, blessed with more ample facilities, kept incoming letters; and those from Chaix are now preserved in the Bibliotheque Municipale de Grenoble in three volumes under the number RI0073. A transcription of them for public use was made earlier in this century under the supervision of Georges de Manteyer [Georges-Barthelemy-Marie Pinet de Manteyer] when he was archivist of the Department of Hautes-Alpes. I am gready indebted to Mme Marie-Fran~ise Bois-Delatte, Conservateur des Fonds Dauphinoise at the Bibliotheque Municipale d'Etude et d'lnformation in Grenoble, not merely for making these letters available to me, but for her eagerness to see someone take an interest in Dauphinois botanists. I met a similar friendly interest at the Archives du Departement des Hautes-Alpes in Gap. I thank M. Pierre-Yves Playoust, Directeur des Services, and members of his archival staff for the cordial assistance in my search for materials documenting the career of the abbe Chaix. I am also obligated to the Hunt Institute for Botanical Documentation at Carnegie Mellon University in Pittsburgh for providing me photocopies of Villars' letters in their Allioni collection. They relate to the composition of a flora for Dauphine and are revealing of Villars' character.

This book contains the majority of the presentations of the Second International Symposium on the Biology of Root Formation and Development that was hcld in Jerusa lem, Israel, June 23---28, 1996. Following the First Symposium on the Biology of Adventi tious Root Formation, held in Dallas. USA, 1993, we perceived the need to include all kinds of roots, not only the shoot-borne ones. The endogenous signals that control root formation. and the subsequent growth and development processes, are very much alike, re gardless of the sites and sources of origin of the roots. Therefore, we included in the Sec ond Symposium contributions on both shoot-borne (i.e., adventitious) roots and root-borne (i.e., lateral) roots. Plant roots have remained an exciting and an intriguing field of sciencc. During thc years that followed the first symposium, an exceptional proliferation of interest in root biology has developed, associated with the intensive research activity in this field and the contemporary developments in the understanding of root function and development. New methods have been applied, and old ideas and interprctations werc rccxamined. Alto gether, it became necessary to update our viewpoints and to expand them.

This proceedings is based on a joint meeting of the two IUFRO (International Union of Forestry Research Organizations) Working Parties, Somatic Cell Genetics (S2.04-07) and Molecular Genetics (S2.04-06) held in Gent, Belgium, 26-30 September, 1995. Although a joint meeting of the two Working Parties had been discussed in the past, this was the first such meeting that became a successful reality. In fact this meeting provided an excellent forum for discussions and interactions in forest bioteclUlology that encouraged the participants to vote for a next joint meeting. In the past decade rapid progress has been made in the somatic cell genetics and molecular genetics of forest trees. In order to cover recent developments in the broad area of biotechnology, the scientific program of the meeting was divided into several sessions. These included somatic embryogenesis, regeneration, transformation, gene expression, molecular markers, genome mapping, and biotic and abiotic stresses. The regeneration of plants, produced by organogenesis or somatic embryogenesis, is necessary not only for mass cloning of forest trees, but also for its application in genetic transformation and molecular biology. Although micropropagation has been achieved from juvenile tissues in a number of forest tree species, in vitro regeneration from mature trees remains a challenging problem in most hardwoods and conifers. The mechanisms involved in the transition from juvenile to mature phase in woody plants are poorly understood. This transition can now be investigated at the molecular level.

Morphometrical differentiation 63 Prediction of breeding origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Body mass 69 Primary moult 69 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 The taxonomy of the Eurasian Golden Plover 69 The existence of a partial breast-feather moult during breeding 69 Morphometrical differentiation between both sexes . . . . . . . . . . . . . . . . . . . . . . . . 70 The occurrence of primary moult on the breeding grounds 70 Summary 70 6 Grey Plover - Pluvialis squatarola 71 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Morphometrical differentiation 77 Prediction of breeding origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Accuracy 81 Exclusivity 81 Contact zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Body mass 85 Primary moult 85 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 The taxonomy of the Grey Plover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Small size at northern latitudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Morphometrical variation in the Palearctic 87 Summary 87 7 Red Knot - Calidris canutus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Morphometrical differentiation 93 Prediction of breeding origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Accuracy 99 Exclusivity 101 Contact zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Body mass 102 Primary moult 103 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 of the Knot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 The taxonomy Is the knot breeding in Yakutia? 106 Different degrees of geographical variation in the d'd' and !f!f 106 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 8 Sanderling - Calidris alba 109 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Morphometrical differentiation 111 Prediction of breeding origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Accuracy 116 Exclusivity 118 Contact zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Body mass 118 Primary moult 118 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 The taxonomy of the Sanderling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Sexing Sanderlings 119 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 VI 9 Curlew Sandpiper - Calidris ferruginea 121 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Morphometrical differentiation 123 Prediction of a bird's sex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Accuracy 127 Exclusivity 127 Body mass 127 Primary moult 127 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 The taxonomy of the Curlew Sandpiper 127 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fantasies and dreams have their rightful place in science, and sometimes they turn into reality. Regeneration of hybrid plants through protoplast fusion is one such dream come true. In the early 1970s I shared the pioneering excitement in the field of protoplast technology at the Second International Congress of Plant Tissue Culture held in Strasbourg, France. Subsequently, I participated in three international conferences devoted to plant protoplasts, in Salamanca, Spain (1972), Versailles, France (1972), and Nottingham, England (1975). At Versailles Dr. P.S. Carlson presented his work on the successful regeneration of somatic hybrids between Nicotiana glauca and Nicotiana langsdorfii. The enthusi- asm shown by the participants was sufficient indication of the bright future of somatic hybridization. On my return from Versailles, I gathered my thoughts and prepared a concept paper on Potentials of Protoplast Culture Work in Agriculture which was published in Euphytica (Bajaj 1974). The studies on protoplast fusion and somatic hybridization then gained momentum and active work started in many laboratories. Very significant work was done by Melchers et al. (1978) who obtained a somatic hybrid between potato and tomato, calling it "Pomato".

Since 1993 a major research programme, "Stochastic Decision Analysis in Forest Management" has been running at Department of Economics and Natural Resources, The Royal Veterinary and Agricultural University (KVL), Copenhagen, in collaboration with Institute of Mathematical Statistics, University of Copenhagen (KU). The research is funded by the two Universities; The Danish Agricultural and Veterinary Research Council; The Danish Research Academy; The National Forest and Nature Agency; and Danish Informatics Network in the Agricultural Sciepces (DINA). A first international workshop in the research programme was held 5 - 8 August, 1996 at Eldrupgaard, Denmark, within the frameworkofacollaborationagreementbetween University of California at Berkeley (UCB) and the Danish Universities, and funded by The Danish Research Academy and the L0venholm Foundation. Having participated in the workshop, Professor Peter Berck (UCB) suggested that the papers be published along with selected papers in the same scientific field, i.e. mainly cointegration analysis of time series in forestry. The editors express their sincere appreciations to the many persons who have contributed to the realisation of the present book: participants in the research programme and the workshop, in particular Professors S0ren Johansen (KU) and Peter Berck (UCB); authors outside the programme/workshop; reviewers of the papers not previously published, in particuler Associate Professors Niels Haldrup (Aarhus University) and Henrik Hansen (KVL); and finally Mrs Mette Riis and Lizzie Rohde who did the tedious work of giving the papers a uniform style. Copenhagen, October 1998.

The quality of human life has been maintained and enhanced for generations by the use of trees and their products. In recent years, ever rising human population growth has put tremendous pressure on trees and tree products; growing awareness of the potential of previously un exploited tree resources and environmental pollution have both accelerated development of new technologies for tree propagation, breeding and improvement. Biotechnology of trees may be the answer to solve the problems which cannot be solved by conventional breeding methods. The combination of biotechnology and conventional methods such as plant propagation and breeding may be a novel approach to improving and multiplying in large number the trees and woody plants. So far, plant tissue culture technology has largely been exploited in the propagation of ornamental plants, especially foliage house plants, by com- mercial companies. Generally, tissue culture of woody plants has been recal- citrant. However, limited success has been achieved in tissue culture of angiosperm and gymnosperm woody plants. A number of recent reports on somatic embryogenesis in woody plants such as Norway spruce (Picea abies), Loblolly pine (Pinus taeda), Sandalwood (Santalum album), Citrus, Mango (Mangifera indica), etc. offer a ray of hope of: (a) inexpensive clonal propa- gation for large-scale production of plants or "emblings" or "somatic embryo plants"; (b) protoplast work; (c) cryopreservation; (d) genetic transforma- tion; and (e) artificial or manufactured seed production.

With one volume each year, this series keeps scientists and advanced students informed of the latest developments and results in all areas of the plant sciences.
The present volume includes reviews on genetics, cell biology, physiology, comparative morphology, systematics, ecology, and vegetation science.

Elms occur, both naturally and cultivated, throughout much of the temperate world. Because of their high tolerance to extreme growing conditions and their widespread distribution, elms have been widely planted in cities, towns and rural areas throughout North America and northern Europe. As such, their current demise due to several pandemics of Dutch elm disease has spurred a huge body of research on breeding for disease resistance, conservation and systematics. The Elms: Breeding, Conservation and Disease Management provides the current state of knowledge in these areas and is an important reference work for pathologists, breeders, taxonomists, and arborists.

27 chapters cover the distribution, economic importance, conventional propagation, micropropagation, tissue culture studies, and in vitro production of important medicinal and other pharmaceutical compounds in various species of Anchusa, Brucea, Catharanthus, Chrysanthemum, Coleus, Corydalis, Coreopsis, Emilia, Ginkgo, Gloriosa, Hypericum, Inonotus, Leucosceptrum, Lilium, Linum, Mosses, Nandina, Penstemon, Prunus, Pteridium, Quassia, Ribes, Senecio, Taraxacum, Thermopsis, Vanilla, and Vitiveria. Like the previous five volumes on medicinal and aromatic plants (Volumes 4, 7, 15, 21, and 24), this book contains a wealth of useful information for advanced students and researchers in the field of plant biotechnology and chemical engineering, pharmacy, botany and tissue culture.

The research that has culminated in the pUblication being introduced . worldwide) save by one or two of this Manual was in the first place undertaken private conifer enthusiasts. My own efforts at 1 for a new edition of the book Manual of Cultivated recording data at Devizes made possible the Conifers by P. den Ouden and Dr B. K. Boom appearance in 1979 of a larger book: Manual of (both now deceased), published in 1965. Dwarf Conifers. That book was clearly in effect The claim in that book to have included every a partial up-dating of the den Ouden and Boom cultivar published since 1753 was not entirely book under revision, so the decision was made realised, and the stated objective, i. e. that the book to produce an entirely new work, with the present should serve as a basis for the international register title and with the following objectives. that was even at that date under consideration required a lot of space to be devoted to quite 1. To bring the taxonomy into line with current archaic information. practice. Each of the authors of the Manual of Cultivated 2. To extend the species descriptions and make them (by the use of side headings) more easy Conifers was well qualified for the task. P. den Ouden had been systematically collecting conifer to use. 3. To supply some form of 'keys'.

With one volume each year, this series keeps scientists and advanced students informed of the latest developments and results in all areas of the plant sciences.
The present volume includes reviews on genetics, cell biology, physiology, comparative morphology, systematics, ecology, and vegetation science.

At the end of the 1970s, when signs of destabilization of forests became visible in Eu rope on a large scale, it soon became obvious that the syndrome called "forest de cline" was caused by a network of interrelated factors of abiotic and biotic origin. All attempts to explain the wide-spread syndrome by a single cause, and there were many of them, failed or can only be regarded as a single mosaic stone in the network of caus es behind the phenomenon. Forest ecosystems are highly complex natural or quasi natural systems, which exhibit different structures and functions and as a conse quence different resilience to internal or external stresses. Moreover, forest ecosys tems have a long history, which means that former impacts may act as predisposing factors for other stresses. The complexity and the different history of forest ecosys tems are two reasons that make it difficult to assess the actual state and future devel opment of forests. But there are two other reasons: one is the large time scale in which forests react, the other is the idiosyncrasy of the reactions on different sites. Due to the slow reaction and the regional complexity of the abiotic environment of forest ecosys tems, a profound analysis of each site and region is necessary to identify the underly ing causes and driving forces when attempting to overcome the destruction of forest ecosystems.

The quality of human life has been maintained and enhanced for generations by the use of trees and their products. In recent years, ever rising human population growth has put tremendous pressure on trees and tree products; growing awareness of the potential of previously unexploited tree resources and environmental pollution have both accelerated development of new technologies for tree propagation, breeding and improvement. Biotechnology of trees may be the answer to solve the problems which cannot be solved by conventional breeding methods. The combination of biotechnology and conventional methods such as plant propagation and breeding may be a novel approach to improving and multiplying in large number the trees and woody plants. So far, plant tissue culture technology has largely been exploited in the propagation of ornamental plants, especially foliage house plants, by com mercial companies. Generally, tissue culture of woody plants has been recal citrant. However, limited success has been achieved in tissue culture of angiosperm and gymnosperm woody plants. A number of recent reports on somatic embryogenesis in woody plants such as Norway spruce (Picea abies), Loblolly pine (Pinus taeda), Sandalwood (Santalurn album), Citrus, Mango (Mangifera indica), etc., offer a ray of hope of: a) inexpensive clonal propa gation for large-scale production of plants or "emblings" or "somatic embryo plants," b) protoplast work, c) cryopreservation, d) genetic transformation, and e) artificial or manufactured seed production."

Chromosomes. being well-defined structures that are easily vis ible under the optical microscope. readily lend themselves to in tense physical and biochemical study. The understanding of the structure and function of this most critical genetic material has progressed through a number of interesting stages. Often connected with the development of new techniques in staining and photography. using the standard microscope and the electron microscope. It is interesting to look back at the history of cytogenetics. I would like especially to emphasize the work of Karl Sax and many of his students. Work with Tradescantia became feasible after Edgar Anderson straightened out the ecology and Sax took advantage of the small number of chromosomes easily visible under the microscope. As a matter of fact. this development is seen as the foundation for the quantitative analysis of radiation effects on chromosomes. During the 50 years since then.- more refined studies have been initiated. The study of cytogenetic mechanisms has become an important tool for the recognition of the effects of environmental factors on all liv ing systems and has made SCE studies possible. One of the most important stages in chromosome research was the development, in radiation biology, of radiolabeling the chromosome with tritiated thymidine. This technique. published in 1957 by Dr.

However, the transition from primitive to 'advanced' cultivars has had the effect of narrowing the genetic base. This has happened in two distinct ways: (1) selection for relative uniformity, resulting in 'pure' lines, multi lines, single or double hybrids, etc.; and (2) selection for closely defined objectives. Both of these processes have resulted in a marked reduction in genetic variation. At the same time, there has been a tendency to restrict the gene pool from which parental material has been drawn. This is a result of the high level of productivity achieved when breeding within a restricted but well-adapted gene pool, and of breeding methods which have made it possible to introduce specifically desired improvements, such as disease resistance and quality characteristics, into breeding stocks with a minimum of disturbance to genotypic structure. Developments in agriculture, such as intensive mechanization, the widespread application of fertilizers and the use of herbicides, fungicides and pesticides, have created a situation whereby a few, selected high yielding cultivars may be grown over large parts of the earth, so further contributing to a decline in crop genetic diversity. This process is under way in all countries, both developed and developing, and unfortunately in cludes some of the richest primary and secondary gene centres of several important food crops."