Definitions and terminology

The correct place to begin any exposition of a major component in biospheric functioning is with precise definitions and crisp discrimination. This should be a relatively simple exercise but for the need to satisfy a consensus of understanding and usage. Particularly among the biological sciences, scientific knowledge is evolving rapidly and, as it does so, it often modifies and outgrows the constraints of the previously acceptable terminology. I recognised this problem for plankton science in an earlier monograph (Reynolds, 1984a). Since then, the difficulty has worsened and it impinges on many sections of the present book. The best means of dealing with it is to accept the issue as a symptom of the good health and dynamism of the science and to avoid constraining future philosophical development by a redundant terminological framework.

The need for definitions is not subverted, however, but it transforms to an insistence that those that are ventured are provisional and, thus, open to challenge and change. To be able to reveal something also of the historical context of the usage is to give some indication of the limitations of the terminology and of the areas of conjecture impinging upon it.

So it is with ‘plankton’. The general understanding of this term is that it refers to the collective of organisms that are adapted to spend part or all of their lives in apparent suspension in the open water of the sea, of lakes, ponds and rivers.

Introduction

The interaction of mycorrhizas and water in understanding plant water dynamics has been relevant since Frank (1885) first coined the term mykorhiza, a plant–fungus mutualism. He described an ectomycorrhiza as a ‘wet-nurse’ to the host in that water and nutrients must flow through the hyphae to the plant root tip. Stahl (1900) proposed that mycorrhizas increased water throughput, depositing greater amounts of nutrients in the roots resulting in the improved growth. We now know that carbon and nutrient exchange is an active process, regulated by both plant and fungal genes, and requiring substantial inputs of energy from the host and concentrating mechanisms in the fungus. However, water movement is a passive process. That is, it flows in response to energy gradients, without regard to active processes. Because it is a passive process, in mesic regions a large amount of water flows through a relatively saturated soil around the fungal hypha into the rather high area of root surface. This occurs at rates which would not be affected by the comparatively small surface area of the hypha–root interface. The focus of studies on mycorrhizas and water relations has been on whether mycorrhizas enhance plant water uptake with drought. This becomes rather critical in that past studies have often misinterpreted data of mycorrhizas and water flux, or designed studies measuring water fluxes in materials such as sand, or in limited potting volumes (relative to root length) that place unreasonable constraints on mycorrhizal response.

For over 50 years I have worked in the herbarium at Cambridge University on the British and European floras. I have collected about 30,000 numbers consisting of some 50,000 specimens from most parts of the British Isles and made many visits to Continental Europe. Particular attention has been given to most critical genera: Cerastium, Conyza, Crepis, Dactylorhiza, Euphrasia, Fumaria, Hieracium, Limonium, Pilosella, Prunus, Rhinanthus, Salicornia, Salix, Scleranthus, Sorbus and Ulmus; and in helping friends in various ways I have considered the taxonomy of Alchemilla, Batrachian Ranunculi, Chenopodium, Potamogeton, Rubus and Taraxacum. I have also spent much time studying ecotypic and geographical variation, in particular a comparison of those variants which occur on the coasts in dunes, shingle and salt-marsh with those growing as arable weeds, and those in mountains. Special attention has also been given to trees and shrubs.

It has long been my wish to publish this information in a critical flora of Great Britain and Ireland. In the 1970s a group of us tried to get a grant to carry this out, but we were unsuccessful. Clive Stace then started work on his New Flora of the British Isles, which was first published in 1991, with a second edition in 1997. In it he gives only abbreviated descriptions and omits most of the species in the large apomictic genera and many of the infraspecific variants.

It has been one of the continuing satisfactions of my academic career in Cambridge that the University Herbarium, of which I was Curator from 1948 to 1973, has provided an academic base for all my specialist interest in angiosperm taxonomy to develop. Indeed, I count myself doubly fortunate that, 12 years after my retirement from academic life, the Herbarium, with its staff and visitors, still provides such a base where scholarship can be pursued for its own sake. With great pleasure I welcome this volume, the first of a set of five promised to us by Peter Sell and Gina Murrell. My association with Peter goes back more than half a century: though I was ‘senior partner’ in our happy collaboration in the post-war Herbarium, ours was a symbiotic relationship from which we both greatly benefited, and I was delighted when Gina, who had been part of the team in the 1960s and 1970s, returned to the fold as Herbarium Technician in 1991.

As explained in the Preface, this project to write an entirely new critical flora of the British Isles comes to fruition some 20 years after an earlier scheme, in which the late Professor David Valentine took a leading part, had failed to find any financial support. Both Clive Stace to whose New Flora of the British Isles (1997) Peter pays tribute in the Preface, and Peter himself, were enthusiastic supporters of the Valentine project, and were prepared to play major parts in writing the Flora.

HISTORICAL BACKGROUND

The first real flora of these islands was John Ray's Catalogus Plantarum Angliae et Insularum Adjacentium in 1670. The first flora to use the Linnaean binomial system of nomenclature was William Hudson's Flora Anglica nearly a hundred years later in 1762. This was followed by William Withering's Botanical Arrangement of all the Vegetables naturally growing in Great Britain in 1776–92, the first of many floras written primarily for the amateur.

James Sowerby's English Botany, whose text was written by J. E. Smith, was first published between 1790 and 1820. It presented for the first time a complete set of coloured illustrations of our plants, illustrations which are still unsurpassed for line and colour. The third edition, published between 1863 and 1872, has inferior illustrations, but its text, rewritten by James Boswell Syme, is still important for its nomenclature and infraspecific taxa.

Three especially famous floras were produced in the nineteeth century. George Bentham's Handbook of the British Flora in 1858 was written as a before-breakfast relaxation. In it keys appeared for the first time in a British flora. It was revised by J. D. Hooker in 1886.

J. D. Hooker's Student's Flora of the British Islands, first published in 1870 and finally revised in 1884, had very clear and concise descriptions and was the main flora used by many generations of botanists up until the 1950s. It is also important in that Hooker was one of the first authors to make frequent use of the category of subspecies.

Perspective

A large part of this book, thus far, has dealt with the typical condition in stems of gymnosperms and dicotyledons. This chapter will present interesting and important information about stem growth in monocotyledons as well as development and patterns of organization in some plants usually characterized as having “anomalous” structure. Unlike gymnosperms and dicotyledons, monocotyledons, even the largest taxa among the palms, do not produce a typical vascular cambium. Although most are characterized solely by primary growth, some palms, some members of the Liliaceae and Agavaceae, and a few other monocotyledons increase in size by secondary growth. The tissues derived from the secondary meristem are strikingly different from the secondary xylem and phloem of the gymnosperms and other angiosperms.

Primary peripheral thickening meristem

As in other plants, the activity of apical meristems of monocotyledons results primarily in an increase in length of the stems. The diameter of a palm stem does not vary greatly from the base to the most distal leaf-bearing region; thus considerable diametric growth must occur in the internodes just beneath the apical meristem, and this is accomplished by activity of the primary peripheral thickening meristem. This meristem is a rather diffuse region located in the periphery of the broad region of the stem immediately below the apical meristem. Its longitudinal extent varies in different species.

Since my introduction to plant anatomy by William Strickland at the University of Richmond and my interaction with Arthur Eames and Harlan Banks at Cornell University during graduate study, I have been entranced by the elegant beauty of plant structure. At the University of Michigan I taught both paleobotany and plant anatomy for many years, and served as committee chair for graduate students, some of whom studied fossil plants and others of whom worked on the structure and development of extant taxa. During the past several decades during which the introduction of new techniques of study at the subcellular and molecular levels has resulted in a resurgence of research throughout the world, my interest in the development of plant structure has grown steadily.

Many books on plant structure, some highly technical, have appeared since the publication of the seminal textbooks of Katherine Esau during the 1950s and 1960s, but no single book that, in my opinion, incorporates both the basic knowledge of plant anatomy and contemporary information and ideas about the development of structure and form that could be used as an effective introductory textbook. Consequently, I have tried to meet the challenge of preparing such a book. In each chapter I have presented what I consider to be the fundamental knowledge essential for an understanding of basic plant structure and development and have integrated with this the results of some of the most significant recent research on plant development.

Perspective

The eukaryotic cell is composed, with a few exceptions, of both a living protoplast, the site of cellular metabolism, and an enclosing cellulosic wall of one or more layers (Fig. 3.1). While not alive as a structural unit, the wall is commonly traversed by living components, plasmodesmata, which connect adjacent protoplasts and, thus facilitate communication between, and the integration of, cells within a tissue. All plant cells possess a protoplast during development, and in many it persists throughout the life of the plant. Some cells, however, do not achieve their ultimate functional state until the protoplast dies as, for example, a specialized water-conducting cell such as a vessel member.

The protoplasts of all plant cells are basically similar, but may differ in relation to the function of the mature cells. For example, the protoplast of a parenchyma cell in the outer cortex or in a leaf will contain many chloroplasts since a major function of these cells is photosynthesis. In contrast, a cell of the pith (a storage region) in the center of the stem may lack chloroplasts but will contain unpigmented plastids in which starch is synthesized (amyloplasts). The protoplast of an immature vessel member, however, destined to die, may contain no plastids at all, or plastids of a highly modified type.