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Tree stems are black boxes. When mature, they can be very

difficult to study in situ. They may be very tall (100 meters)

and have large diameters (several meters). Their internal struc-

ture is complex, ranging from fairly homogeneous wood com-

prised largely of dead xylem elements in the conifers, to

anastomosing primary vascular bundles embedded in a matrix

of parenchyma in the monocotyledons, to heterogeneous wood

with a variety of living and dead xylem elements in the dicoty-

ledons. A stem changes structure and function with distance

from its center (e.g., in woody stems: heartwood, sapwood,

lateral meristems, phloem, and outer bark). The outer bark is

viewed primarily as a protective sheath for the stem; it also acts

as an efficient cloaking device to prevent easy access by

researchers to the internal functions of the stem. All stem

functions must integrate to support the rest of the tree. Stemsare tied to leaves at stem tops and roots at stem bases. Water

and nutrients in the stem destined for leaves enter through

roots; photosynthate destined for roots is produced in the

leaves. So, it is difficult to investigate excised stems and infer

normal function from the results. Most tree stems are not

disposable (as are most leaves and fine roots and the stems of

many shrubs); destructive research on tree stems usually

means sacrificing the entire tree. Nonetheless, understanding

stem biology is critical to better ecological modeling, agricul-

ture, wildlife management, lumber production, and other natu-

ral resource management. As understanding and techniques

and technology improve, the limitations that have faced the

biologists and engineers are gradually being overcome.The improvements in stem research are clearly seen in

ecology. Ecology is a synthetic field that is based upon the

integration of various other fields to understand how organ-

isms relate to their environments. Historically, ecosystem

modelers treated whole trees as black boxes, with the uptake

and release of energy, water, nutrients, and carbon described

with little consideration for the internal processes that influ-

enced fluxes. At the same time, plant physiologists emphasized

processes affecting photosynthesis, because the conversion of

light and carbon to food is basic to life on earth. Physiologists

also studied respiration and water relations which are integral

to determining net carbon gain. The easily accessible leaves

and somewhat less accessible fine roots were the site of mostresearch. New knowledge from this research was incorporated

into the ecological models, but then the tree stems, rather than

the whole tree, were treated as black boxes. As understanding

of the physiological ecology of trees improved over the last ten

years and ecologists became aware of the critical role of tree

stems, ecologists have begun to collaborate with taxonomists,

morphologists, anatomists, physiologists, and engineers to in-

vestigate tree stems in their own right and to incorporate the

new data into ecosystem models (e.g., the dynamics of stem

water storage). Interactions with pathologists and zoologists,

including entomologists, are elaborating and expanding the

concepts of stem functions to include interactions with and

internal responses to other taxa.

Plant Stems: Physiology and Functional Morphology is a

collection of comprehensive review papers by leading re-

searchers on what is known and what is not known about

stems, with an emphasis on tree stems. The product of a

workshop held recently in Oregon, it is also a call for the

integration of research on stems from different fields. It is the

first attempt to synthesize knowledge from diverse fields into

a coherent concept of an integrated stem. Gartner, the editor,

carefully organized the material into five sections: stem archi-

tecture in plant performance, stems in the transport and storage

of water, live stem cells in plant performance, stems in prevent-

ing or reacting to plant injury, and synthesis. The topics cov-

ered in various chapters include an impressive array ofresearch areas: structural support; short- and long-distance

transport; water, nutrient, and metabolite storage; stem photo-

synthesis; epiflora and epifauna; development; and defense

against and reaction to disturbances such as fire, pollution, and

pathogens. Authors frequently cross-reference other chapters.

From necessity, some of the discussions are speculative and

many examples are from herbaceous plants. Although much of

the reported research is from the North American and Euro-

pean temperate zones, African and Asian species and tropical

and boreal species are mentioned (e.g., palms and tree ferns).

In this context, trees are woody plants (including shrubs) or

other arborescent vascular plants. Frequently, investigating

organisms that operate at environmental extremes or that oc-cupy morphologically, anatomically, or functionally fringe po-

sitions, gives insight into typical organisms. The authors cite

such examples often, clearly indicating the features that distin-

guish the example from typical plants. As a result, readers

develop an appreciation for the breadth of solutions to func-

tional problems. The approach challenges readers to think

about the tradeoffs inherent in various solutions. Readers may

disagree with some of the assertions, but Plant Stems will

have challenged them to view stems in a more integrated way.

The editor and authors have produced a good and timely

synthesis on the function of tree stems. Most of my criticisms

are minor. It is not possible to cover all aspects of stem

physiology in such a volume. I especially missed more discus-sion on stem gas exchange and internal aeration. There is a

chapter on stems and air pollution, although the book does not

discuss the effects of groundwater pollution on stems. But

given the wide structural and functional variation in stems, it

is remarkable that this book has so comprehensively covered

their functions and interactions.

Some chapters are very clear and easy to follow, others leave

the reader to fill in gaps. Not all of the authors are clear about

when they speculate. Terminology from several research fields

is used in the text, but many terms are not defined. Defining

more of the terminology would ease reading across disciplines.

Plant Stems: Physiology and Functional Morphology

BARBARA L. GARTNER, Editor

Academic Press, 525 B Street, Suite 1900, San Diego, CA 92101-4495; 1995,440 pages, hardcover, $89.95 US, ISBN 0-12-276460-9

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The chapters by Gartner, Givinish, Holbrook, Nilsen, Pate and

Jeschke, and Weber and Grulke are especially well written and

clear. Some authors clearly state where the most important

areas for future research are, and some emphasize the impor-

tance of more research in terms of real-world applications.

As I read the review chapters, I looked forward to a summary

chapter that pulled all of stem biology together, but an entire

second volume would be required to develop a synthesis of the

preceding chapters with one voice. Hinckley and Schultes

summary chapter reiterates some of the important concepts

developed in the book, such as redundancy and modularity of

construction, the incorporation of life history into the annual

rings and structure of stems of individual trees, the energy

costs of building disposable and nondisposable stems, re-

sponding to environmental signals and communication among

plant organs, difficulties in research on tree stems, interactions

among stem functions and processes, and trade-offs among

and optimization of functional strategies.

The books index limits its usefulness for reference. Not all

occurrences of some terms used within the text are listed (e.g.,

integrated physiological unit), and I couldnt find index entries

for monocotyledons, palms, primary xylem, or vascular bun-

dles----all of which are discussed in various places throughout

the volume. Also, inclusion of taxa in the index, or in a separate

index, would have been very useful.

This book deserves a wide readership. Researchers, gradu-

ate students, and advanced undergraduates in any field con-

cerned with plant growth or function will find the book

informative and thought provoking. College teachers and labo-ratory instructors will be able to glean ideas for student pro-

jects from the many suggestions for proposed research.

Referring to the wide diversity of perspectives in this vol-

ume, Hinckley and Schulte write, ...we tend to study our small

piece of the stem, but if we are to understand it as an entire

structure we must take this broader view. The next steps are

for botanists, ecologists, and other scientists to read this book,

do the research, and integrate the results among their fields.

Clearly, the black box is being uncloaked----the time for inte-

gration and synthesis has arrived!

Ann M. Lewis, Department of Forestry and Wildlife Manage-

ment, Holdsworth Hall, University of Massachusetts, Amherst,

MA 01003-4210, USA.

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TREE PHYSIOLOGY VOLUME 17, 1997