Plant Cell Biology

531 Pages·2009·21.65 MB·English

Preface
This book is in essence the lectures I give in my plant Recognizing the basic similarities between all living
cell biology course at Cornell University. Heretofore, the eukaryotic cells (Quekett, 1852, 1854; Huxley, 1893), I
lecture notes have gone by various titles, including “Cell discuss both animal and plant cells in my course. Although
La Vie,” “The Book Formerly Known as Cell La Vie,” the examples are biased toward plants (as they should be in
“Molecular Theology of the Cell,” “Know Thy Cell” (with a plant cell biology course), I try to present the best exam-
apologies to Socrates), “Cell This Book” (with apolo- ple to illustrate a process and sometimes the best examples
gies to Abbie Hoffman), and “Impressionistic Plant Cell are from animal cells. I take the approach used by August
Biology.” I would like to take this opportunity to describe Krogh (1929); that is, there are many organisms in the
this course. It is a semester-long course for undergradu- treasure house of nature and if one respects this treasure,
ate and graduate students. Since the undergraduate biol- one can find an organism created to best illuminate each
ogy majors are required to take genetics, biochemistry, and principle! I try to present my course in a balanced manner,
evolution as well as 1 year each of mathematics and phys- covering all aspects of plant cell biology without empha-
ics, and 2 years of chemistry, I have done my best to inte- sizing any one plant, organelle, molecule, or technique.
grate these disciplines into my teaching. Moreover, many I realize, however, that the majority of papers in plant
of the students also take plant anatomy, plant physiology, cell biology today are using a few model organisms and
plant growth and development, plant taxonomy, plant bio- “-omic” techniques. My students can learn about the suc-
chemistry, plant molecular biology, and a variety of courses cesses gained though this approach in a multitude of other
that end with the suffix “-omics”; I have tried to show the courses. I teach them that there are other approaches.
connections between these courses and plant cell biology. Pythagoras believed in the power of numbers, and I
Nonbotanists can find a good introduction to plant biology believe that the power of numbers is useful for under-
in Mauseth (2009) and Taiz and Zeiger (2006). standing the nature of the cell. In my class, I apply the
Much of the content has grown over the past 20 years power of numbers to help relate quantities that one wishes
from the questions and insights of the students and teaching to know to things that can be easily measured (Hobson,
assistants who have participated in the class. The students’ 1923; Whitehead, 1925; Hardy, 1940; Synge, 1951, 1970;
interest has been sparked by the imaginative and insight- Feynman, 1965; Schrödinger, 1996). For example, the area of
ful studies done by the worldwide community of cell biolo- a rectangle is difficult to measure. However, if one knows its
gists, which I had the honor of presenting. length and width, and the relation that area is the product of
I have taken the approach that real divisions do not length and width, the area can be calculated from the easily
exist between subject areas taught in a university, but only measurable quantities. Likewise, the circumference or area
in the state of mind of the teachers and researchers. With of a circle is relatively difficult to measure. However, if one
this approach, I hope that my students do not see plant cell measures the diameter and multiplies it by π, or the square of
biology as an isolated subject area, but as an entrée into the diameter by π/4, one can easily obtain the circumference
every aspect of human endeavor. One of the goals of my and area, respectively. In the same way, one can easily esti-
course is to try to reestablish the connections that once mate the height of a tree from easily measurable quantities if
existed between mathematics, astronomy, physics, chemis- one understands trigonometry and the definition of tangent.
try, geology, philosophy, and biology. It is my own personal My teaching was greatly influenced by a story that
attempt, and it is an ongoing process. Consequently, it is Hans Bethe told at a meeting at Cornell University com-
far from complete. Even so, I try to provide the motivation memorating the 50th anniversary of the chain reaction pro-
and resources for my students to weave together the threads duced by Enrico Fermi. Bethe spoke about the difference
of these disciplines to create their own personal tapestry of between his graduate adviser, Arnold Sommerfeld, and
the cell from the various lines of research. his postdoctoral adviser, Enrico Fermi. He said that, in the
Plant Cell Biology
Copyright © 22000099, Elsevier, Inc. All rights of reproduction in any form reserved. xiii
xiv Preface
field of atomic physics, Sommerfeld was a genius at cre- each term. Some specialized terms are essential for pre-
ating a mathematical theory to describe the available data. cise communication in science just as it is in describ-
Sommerfeld’s skill, however, depended on the presence of ing love and beauty. However, some terms are created
data. Fermi, on the other hand, could come up with theories to hide our ignorance, and consequently prevent further
even if the relevant data were not apparent. He would make inquiry, because something with an official-sounding name
estimates of the data from first principles. For example, he seems well understood (Locke, 1824; Hayakawa, 1941;
estimated the force of the first atomic bomb by measuring Rapoport, 1975). In Goethe’s (1808) “Faust Part One,”
the distance small pieces of paper flew as they fell to the Mephistopheles says: “For at the point where concepts fail.
ground during the blast in Alamogordo. Knowing that the At the right time a word is thrust in there. With words we
force of the blast diminished with the square of the distance fitly can our foes assail.” Francis Bacon (1620) referred to
from the bomb, Fermi estimated the force of the bomb rela- this problem as the “Idols of the Marketplace.” Often we
tive to the force of gravity. Within seconds of the blast, he think we are great thinkers when we answer a question
calculated the force of the bomb to be approximately 20 with a Greek or Latin word. For example, if I am asked,
kilotons, similar to which the expensive machines recorded “Why are leaves green?” I quickly retort, “Because they
(Fermi, 1954; Lamont, 1965). have chlorophyll.” The questioner is satisfied, and says
In order to train his students to estimate things that they “Oh.” The conversation ends. However, chlorophyll is just
did not know, Fermi would ask them, “How many piano the Greek word for green leaf. Thus, I really answered the
tuners are there in Los Angeles?” After they looked befud- question with a tautology. I really said “Leaves are green
dled, he would say, “You can estimate the number of piano because leaves are green” and did not answer the question
tuners from first principles! For example, how many peo- at all. It was as if I was reciting a sentence from scripture,
ple are there in Los Angeles? One million? What percent- which I had committed to memory without giving it much
age has pianos? Five percent? Then there are 50,000 pianos thought. However, I gave the answer in Greek, and with
in Los Angeles. How often does a piano need to be tuned? authority … so it was a scientific answer.
About once a year? Then 50,000 pianos need to be tuned in In “An Essay Concerning Human Understanding,” John
a year. How many pianos can a piano tuner tune in a day? Locke (1824) admonished that words are often used in a
Three? Then one tuner must spend 16,667 days a year tun- nonintellectual manner. He wrote,
ing pianos. But since there are not that many days in a year,
and he or she probably only works 250 days a year, then … he would not be much better than the Indian before-
there must be around 67 piano tuners in Los Angeles.” mentioned, who, saying that the world was supported by
My students apply the power of numbers to the study a great elephant, was asked what the elephant rested on;
of cellular processes, including membrane transport, pho- to which his answer was, a great tortoise. But being again
tosynthesis, and respiration, in order to get a feel for these pressed to know what gave support to the broad-backed tor-
toise, replied, something he knew not what. And thus here, as
processes and the interconversions that occur during these
in all other cases where we use words without having clear
processes between different forms of energy. My students
and distinct ideas, we talk like children; who being questioned
apply the power of numbers to the study of cell growth,
what such a thing is, which they know not, readily give the
chromosome motion, and membrane trafficking in order to
satisfactory answer, that it is something; which in truth signi-
be able to postulate and evaluate the potential mechanisms
fies no more, when so used either by children or men, but that
involved in these processes, and the relationships between they know not what; and that the thing that they pretend to
these processes and the bioenergetic events that power know and talk of is what they have no distinct idea of at all,
them. Becoming facile with numbers allows the students to and so are perfectly ignorant of it, and in the dark.
understand, develop, and critique theories. “As the Greek
origin of the word [theory] implies, the Theory is the true Sometimes terms are created to become the shibbo-
seeing of things—the insight that should come with healthy leths of a field, and sometimes they are created for political
sight” (Adams and Whicher, 1949). reasons, financial reasons, or to transfer credit from some-
Using the power of numbers to relate seemingly unre- one who discovers something to someone who renames it
lated processes, my students are able to try to analyze all (Agre et al., 1995). Joseph Fruton (1992) recounted (and
their conclusions in terms of first principles. They also learn translated) a story of a conversation with a famous chemist
to make predictions based on first principles. The students in Honoré de Balzac’s La Peau de Chagrin:
must be explicit in terms of what they are considering to
be facts, what they are considering to be the relationship
“Well, my old friend,” said Planchette upon seeing Japhet
between facts, and where they are making assumptions. This
seated in an armchair and examining a precipitate, “How
provides a good entrée into research, because the facts must goes it in chemistry?”
be refined and the assumptions must be tested (East, 1923). “It is asleep. Nothing new. The Académie has in the mean-
I do not try to introduce any more terminology in my time recognized the existence of salicine. But salicine, aspar-
class than is necessary, and I try to explain the origin of agine, vauqueline, digitaline are not new discoveries.”
Preface xv
“If one is unable to produce new things,” said Raphael, “it present concepts are only the last approximation in a long
seems that you are reduced to inventing new names.” series of similar attempts which, of course, is not ended.”
“That is indeed true, young man.” I teach my students that it is important to be skeptical
when considering old as well as new ideas. According to
I teach plant cell biology with a historical approach and
Thomas Gold (1989),
teach “not only of the fruits but also of the trees which have
borne them, and of those who planted these trees” (Lenard, New ideas in science are not always right just because they
1906). This approach also allows them to understand the are new. Nor are the old ideas always wrong just because
origins and meanings of terms; to capture the excitement they are old. A critical attitude is clearly required of every
of the moment of discovery; to elucidate how we, as a sci- scientist. But what is required is to be equally critical to the
entific community, know what we know; and it empha- old ideas as to the new. Whenever the established ideas are
accepted uncritically, but conflicting new evidence is brushed
sizes the unity and continuity of human thought (Haldane,
aside and not reported because it does not fit, then that par-
1985). I want my students to become familiar with the great
ticular science is in deep trouble—and it has happened quite
innovators in science and to learn their way of doing sci-
often in the historical past.
ence (Wayne and Staves, 1998, 2008). I want my students
to learn how the scientists we learn about choose and pose To emphasize the problem of scientists unquestioningly
questions, and how they go about solving them. I do not accepting the conventional wisdom, Conrad H. Waddington
want my students to know just the results and regurgitate (1977) proposed the acronym COWDUNG to signify the
those results on a test (Szent-Györgyi, 1964; Farber, 1969). Conventional Wisdom of the Dominant Group.
I do not want my students to become scientists who merely In teaching in a historical manner, I recognize the impor-
repeat on another organism the work of others. I want my tance of Thomas H. Huxley’s (1853) warnings that “Truth
students to become like the citizens of Athens, who accord- often has more than one Avatar, and whatever the forgetful-
ing to Pericles “do not imitate—but are a model to others.” ness of men, history should be just, and not allow those who
Whether or not my students become professional cell biolo- had the misfortune to be before their time to pass for that
gists, I hope they forever remain amateurs and dilettantes in reason into oblivion” and “The world, always too happy to
terms of cell biology. That is, I hope that I have helped them join in toadying the rich, and taking away the ‘one ewe lamb’
become “one who loves cell biology” and “one who delights from the poor.” Indeed, it is often difficult to determine who
in cell biology” (Chargaff, 1986)—not someone who can- makes a discovery (Djerassi and Hoffmann, 2001). I try to
not recognize the difference between a pile of bricks and an the best of my ability to give a fair and accurate account of
edifice (Forscher, 1963), not someone who sells “buyology” the historical aspects of cell biology.
(Wayne and Staves, 2008), and not someone who sells his or My course includes a laboratory section and my stu-
her academic freedom (Rabounski, 2006; Apostol, 2007). dents perform experiments to acquire personal experience
Often people think that a science course should teach in understanding the living cell and how it works (Hume,
what is new, but I answer this with an amusing anec- 1748; Wilson, 1952; Ramón y Cajal, 1999). Justus von
dote told by Erwin Chargaff (1986): “Kaiser Wilhelm I Liebig (1840) described the importance of the experimen-
of Germany, Bismark’s old emperor, visited the Bonn tal approach this way:
Observatory and asked the director: ‘Well, dear Argelander,
what’s new in the starry sky?’ The director answered Nature speaks to us in a peculiar language, in the language of
promptly: ‘Does your Majesty already know the old?’ phenomena; she answers at all times the questions which are
The emperor reportedly shook with laughter every time he put to her; and such questions are experiments. An experiment
is the expression of a thought: we are near the truth when the
retold the story.”
phenomenon, elicited by the experiment, corresponds to the
According to R. John Ellis (1996),
thought; while the opposite result shows that the question was
falsely stated, and that the conception was erroneous.
It is useful to consider the origins of a new subject for two
reasons. First, it can be instructive; the history of science pro-
My students cannot wait to get into the laboratory. In
vides sobering take-home messages about the importance of
fact, they often come in on nights and weekends to use the
not ignoring observations that do not fit the prevailing con-
microscopes to take photomicrographs. At the end of the
ceptual paradigm, and about the value of thinking laterally, in
semester, the students come over to my house for dinner
case apparently unrelated phenomena conceal common prin-
(I worked my way through college as a cook) and bring
ciples. Second, once a new idea has become accepted there
is often a tendency to believe that it was obvious all along— their best photomicrographs. After dinner, they vote on the
hindsight is a wonderful thing, but the problem is that it is twelve best, and those are incorporated into a class cal-
never around when you need it! endar. The calendars are beautiful and the students often
make extra to give as gifts.
The historical approach is necessary, in the words of In 1952, Edgar Bright Wilson Jr. wrote in An
George Palade (1963), “to indicate that recent findings and Introduction to Scientific Research, “There is no excuse for
xvi Preface
doing a given job in an expensive way when it can be car- the people who they consider to be the best scientists. This
ried through equally effectively with less expenditure.” is a shame. They read the work of others … but not the best.
Today, with an emphasis on research that can garner sig- Interestingly, they usually are well read when it comes to
nificant money for a college or university through indirect reading the best writers (e.g., Shakespeare, Faulkner, etc.).
costs, there is an emphasis on the first use of expensive Typically, the people on my students’ lists of best scien-
techniques to answer cell biological questions and often tists have written books for the layperson or an autobiogra-
questions that have already been answered. However, the phy (Wayne and Staves, 1998). Even Isaac Newton wrote
very expense of the techniques often prevents one from a book for the layperson! I give my class these references
performing the preliminary experiments necessary to learn and encourage them to become familiar with their favorite
how to do the experiment so that meaningful and valuable scientists first hand. The goal of my lectures and this book
data and not just lists are generated. Unfortunately, the lists is to facilitate my students’ personal and continual journey
generated with expensive techniques often require statisti- in the study of life.
cians and computer programmers, who are far removed My goal in teaching plant cell biology is not only to
from experiencing the living cells through observation and help my students understand the mechanisms of the cell
measurement, to tell the scientist which entries on the list and its organelles in converting energy and material mat-
are meaningful. Thus, there is a potential for the distinction ter into a living organism that performs all the functions
between meaningful science and meaningless science to we ascribe to life. I also hope to deepen my students’ ideas
become a blur. I use John Synge’s (1951) essay on vicious of the meaning, beauty, and value of life and the value in
circles to help my students realize that there is a need to searching for meaning and understanding in all processes
distinguish for themselves what is fundamental and what is involved in living.
derived. I thank Mark Staves and my family, Michelle, Katherine,
By contrast, this book emphasizes the importance of the Zack, Beth, Scott, my mother and father, and aunts and
scientists who have made the great discoveries in cell biol- uncles, for their support over the years. I also thank my col-
ogy using relatively low-tech quantitative and observational leagues at Cornell University and teachers at the Universities
methods. But—and this is a big but—these scientists also of Massachusetts, Georgia, and California at Los Angeles,
treated their brains, eyes, and hands as highly developed sci- and especially Peter Hepler and Masashi Tazawa, who taught
entific instruments. I want my students to have the ability to me how to see the universe in a living cell.
get to know these great scientists. I ask them to name who
they think are the 10 best scientists who ever lived. Then I Randy Wayne,
ask if they have ever read any of their original work. In the Department of Plant Biology, Cornell University
majority of the cases, they have never read a single work by
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Library of Congress Cataloging-in-Publication Data
Wayne, Randy.
  Plant cell biology / Randy Wayne.
    p. cm.
  Includes bibliographical references and index.
  ISBN 978-0-12-374233-9 (hardback : alk. paper)  1.  Plants—Cytology.  I. Title. 
  QK725.W39 2009
  571.6’2—dc22
  2009018976
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ISBN: 978-0-12-374233-9
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Printed in the United States of America
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for inspiring my generation to be courageous in the pursuit of science
Chapter 1
On the Nature of Cells
The world globes itself in a drop of dew. The microscope cannot
find the animalcule which is less perfect for being little. Eyes,
ears, taste, smell, motion, resistance, appetite, and organs of
reproduction that take hold on eternity—all find room to consist
in the small creature. So do we put our life into every act. The
true doctrine of omnipresence is that God reappears with all His
parts in every moss and cobweb.
— Ralph Waldo Emerson, “Compensation”
. IntroductIon: what Is a cell?
In the introduction to his book, Grundzüge der Botanik,
Matthias Schleiden (1842), often considered the cofounder
FIgure .  Cells of cork. (Source: From Hooke, 1665.)
of the cell theory, admonished, “Anyone who has an idea of
learning botany from the present book, may just as well put
it at once aside unread; for from books botany is not learnt”
(quoted in Goebel, 1926). Likewise, I would like to stress that
an understanding of plant cell biology, and what a plant cell
is, comes from direct experience. I hope that this book helps
facilitate your own personal journey into the world of the cell.
Exploring the world made accessible by the invention of
the microscope, Robert Hooke (1665) discovered a regular,
repeating structure in cork that he called a cell. The word
cell comes from the Latin celle, which in Hooke’s time
meant “a small apartment, esp. one of several such in the
same building, used e.g. for a store-closet, slave’s room,
prison cell; also cell of a honeycomb; … also a monk’s or
hermit’s cell” (Oxford English Dictionary, 1933). Hooke
used the word cell to denote the stark appearance of the
air-filled pores he saw in the honeycomb-like pattern in
the cork that he viewed with his microscope (Figure 1.1). FIgure .2  The cortical cells of a small root of asparagus. (Source:
From Grew, 1682.)
Hooke’s perspective of the emptiness of cells was propa-
gated by Nehemiah Grew (1682), who compared the cells of
the pith of asparagus to the froth of beer (Figure 1.2), and is of wood or piths, as the valves in the heart, veins and other
still implied in words with the prefix cytos, which in Greek passages of animals, that open and give passage to the con-
tained fluid juices one way, and shut themselves, and impede
means “hollow place”. Hooke, however, did realize that
the passage of such liquors back again, yet have I not hitherto
there might be more to a cell than he could see. He wrote,
been able to say anything positive in it; … but … some dili-
Now, though I have with great diligence endeavoured to find gent observer, if helped with better microscopes, may in time,
whether there be any such thing in those microscopical pores detect [them].
Plant Cell Biology
Copyright © 22000099, Elsevier, Inc. All rights of reproduction in any form reserved. 
2 Plant Cell Biology
FIgure .3  Stellate cells from the petiole of a banana. (Source: From
von Mohl, 1852.)
FIgure .5  Photomicrograph of a swimming Dunaliella cell taken
with Nomarski differential interference contrast optics.
To further emphasize the vitality of cells, von Mohl also
stressed that cells were endowed with the ability to perform
all kinds of movements.
In the world of the living cell, the only thing that is certain
is change—movement occurs at all levels, from the molecular
to the whole cell. While I was taught that plants, unlike ani-
mals, do not move, some plants can constantly change their
position. Get a drop of pond water and look at it under the
microscope. Watch a single-celled alga like Dunaliella under
the microscope (Figure 1.5). See it swim? These plant cells
are Olympic-class swimmers: they swim about 50 m/s—
FIgure .4  Spiral vessels, sap tubes, and cells of Marantha lutea.
equivalent to five body lengths per second. Not only can the
(Source: From deCandolle and Sprengel, 1821.)
cells swim, but they can also change their motile behavior
in response to external stimuli. When a bright flash of light
Hugo von Mohl (1852) pointed out in Principles of the (from the sun or a photographic flash) strikes swimming
Anatomy and Physiology of the Vegetable Cell, the first Dunaliella cells, like synchronous swimmers, they all swim
textbook devoted to plant cell biology, that indeed plant backward for about a half second. From this observation,
cells are not vacuous when viewed with optically corrected even a casual observer will conclude that individual cells have
microscopes, but contain a nucleus and “an opake, viscid well-developed sensory systems that can sense and respond to
fluid of a white colour, having granules intermingled in external stimuli (Wayne et al., 1991).
it, which fluid I call protoplasm.” Von Mohl, echoing the In contrast to Dunaliella, some cells, particularly those
conclusions of Henri Dutrochet (1824) and John Queckett of higher plants, remain static within an immobile cell wall.
(1852), further revealed through his developmental stud- Yet, if you look inside the cell, you are again faced with
ies that cells have a variety of shapes (Figure 1.3) and give movement. You see that the protoplasm dramatically flows
rise to all structures in the plant including the phloem and throughout a plant cell, a phenomenon known as cytoplas-
xylem. This was contrary to the earlier opinions of deCan- mic streaming (Kamiya, 1959). Look at the giant internodal
dolle and Sprengel (1821), who believed that there were cell of Chara (Figure 1.6). The cytoplasm rotates around
three elementary forms in plants—dodecahedral-shaped the cell at about 100 m/s. If you electrically stimulate the
cells, noncellular tubes, and noncellular spirals (Figure 1.4). cell, the cytoplasmic streaming ceases instantly. As the
By focusing on mature plants, deCandolle and Sprengel neurobiologists say, the cell is excitable and responds to
had not realized that the tubelike vessels and the spiral-like external stimuli. In fact, action potentials were observed in
protoxylem developed from dodecahedral-shaped cells. characean internodal cells before they were observed in the
chapter |   On the Nature of Cells 3
FIgure .8  Bright-field photomicrograph of the streaming cytoplasm
of the slime mold Physarum polycephalum.
FIgure .6  Photomicrograph of a portion of a giant internodal cell of
Chara showing several nuclei being carried by cytoplasmic streaming.
The velocity in one direction is slightly greater than the
velocity in the opposite direction. This causes the cell to
migrate in the direction of the more rapid streaming. Since
the plasmodium migrates toward food, the velocity of cyto-
plasmic streaming in each direction is probably affected by
the gradient of nutrients. Nobody knows how this cell per-
ceives the direction of food and how this signal is converted
into directions for migration. Will you find out?
While looking at Physarum, notice that the protoplasm
is not homogeneous, but is full of relatively large round
bodies rushing through the cell (Figure 1.8). Is what you
see the true nature of protoplasm, or are there smaller enti-
ties, which are invisible in a light microscope, that are also
important in the understanding of cells? Edmund B. Wilson
(1923) describes the power and the limitations of the light
microscope in studying protoplasm:
When viewed under a relatively low magnification … only the
larger bodies are seen; but as ... we increase the magnification
FIgure .7  Dark-field photomicrograph of the slime mold Physarum … we see smaller and smaller bodies coming into view, at every
polycephalum.
stage graduating down to the limit of vision … which in round
numbers is not less than 200 submicrons. … Such an order of
magnitude seems to be far greater than that of the molecules
nerve cells of animals (Cole and Curtis, 1938, 1939). The
of proteins and other inorganic substances. … Therefore an
events that occur between electrical stimulation and the immense gap remains between the smallest bodies visible with
cessation of streaming are relatively well understood, and the microscope and the molecules of even the most complex
I discuss these throughout the book. organic substances. For these reasons alone ... we should be
Lastly, take a look at the large single-celled plasmodium certain that below the horizon of our present high-power micro-
of the slime mold Physarum (Figure 1.7; Coman, 1940; scopes there exists an invisible realm peopled by a multitude of
Kamiya, 1959; Carlisle, 1970; Konijn and Koevenig, 1971; suspended or dispersed particles, and one that is perhaps quite
as complex as the visible region of the system with which the
Ueda et al., 1975; Durham and Ridgway, 1976; Chet et al.,
cytologist is directly occupied.
1977; Kincaid and Mansour, 1978a,b; Hato, 1979; Dove and
We have now arrived at a borderland, where the cytologist
Rusch, 1980; Sauer, 1982; Dove et al., 1986; Bailey, 1997;
and the colloidal chemist are almost within hailing distance of
Bozzone and Martin, 1998). Its cytoplasm streams at about
each other—a region, it must be added, where both are tread-
2000 m/s. The force exerted by the streaming causes the
ing on dangerous ground. Some of our friends seem disposed
plasmodium to migrate about 0.1 m/s. Why does it move to think that the cytologist should halt at the artificial bound-
so slowly when streaming is so rapid? Notice that the cyto- ary set by the existing limits of microscopical vision and hand
plasmic streaming changes direction in a rhythmic manner. over his inquiry to the biochemist and biophysicist with a