Julius Sachs.

Lectures on the physiology of plants online

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FELLOW OF Christ's college, Cambridge, and professor of botany in






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After the fourth edition of my 'Text-Book of Botany' (1874) had nearly
passed out of print, I received from the publishers, as well as from botanical friends,
repeated invitations to prepare a fifth edition. It is, however, an old experience
that while one works up with pleasure a second and even a third edition of a
comprehensive work, frequent repetition eventually becomes inconvenient or even
painful to the author. Having experienced this sufficiently with the fourth edition,
I was unable to make up my mind to a fifth. Apart from other circumstances,
I was driven to this to an important extent by the progressive development of
my scientific convictions. My mode of comprehending important questions of the
Physiology of Plants had undergone changes in various directions, particularly in
consequence of my compilation of the 'History of Botany'; like others, more or
less subject to the prevailing opinions of the present, I had held as important
matters which I was gradually impelled to recognise as insignificant and tran-
sitory; higher stand-points and freer prospects opened out to me in the course of
time, and the form of my text-book would no longer adapt itself to the advanced
view. The artist may touch up his composition here and there with a few
strokes of the pencil, or even make greater alterations ; but that is not sufficient
when the composition itself has ceased to be the expression of his idea. This is
the position in which I find myself with respect to my text-book, since the chief
thing in it to me is the composition, the form of the exposition as a whole.

Moreover for several years past the wish had been taking a more and more
definite form in my mind, to set forth the most important results of the physiology of
plants in such a manner that not only students, but also wider circles, should be
interested in them. That object, however, is only to be attained by a freer form
of exposition, and I believe I have found it in the choice of lectures. It is not
only the right but also the duty of any one who lectures, however, to place in
the foreground his own mode of viewing the matter ; the audience wish to know
and should know how the science as a whole shapes itself in the mind of the
lecturer, and it is comparatively unimportant whether others think the same or

I would have the present book criticised from this point of view. It is
intended to introduce students and cultivated readers generally to the study of


the Physiology of Plants, free from the trammels of learned descriptions of appa-
ratus which of course could not be dispensed with in a text-book or hand-book
for specialists.

Perhaps no other branch of Natural Science is so unknown to the educated
public as the Physiology of Plants ; because, in spite of the important progress
which has been made in it during the last twenty years, and in spite of the uses to
which it may be applied, no one has undertaken to publish its established results
in a convenient and intelligible form. This really serious want in our literature
I wish to supply by means of my ' Lectures,' and this is of course only possible by
the contents being strictly scientific ; only the form of the exposition is to differ from
that hitherto customary, in running in phrases which are universally intelligible.
The object indicated, ho\\ever, requires also that much which is apparently self-
evident to the specialist must here be expressly brought forward and explained, so
that a certain prolixity of description is often unavoidable, while, on the other
hand, some questions of the day important to the Botanist are entirely passed
over or can only be briefly touched upon. Again, having regard to the super-
abundance of material, a suitable selection must be made, for, as is well known,
the secret of being tedious lies in trying to say all one knows.

The notes on the literature attached to the separate lectures are only intended
for those readers who may be by any chance stimulated by my book to wish for
further direction along the untrodden grounds of our literature.

The publishers were of opinion that a new edition of the systematic part of
my ' Text-book ' might conveniently be attached to my ' Lectures.' Since I have
myself neither the time nor the inclination to undertake such a new working-up
of this domain of Botany, I have made arrangements with Professor Goebel, and
he is to compile the systematic portion of my Text-book independently, and
according to his own judgment, and publish it as a separate Book, which the
reader may employ as a supplement to my ' Lectures.'

Dr. J. v. SACHS.

Würzburg, /?/w^ 27///, 18S2.


The work of translating Professor Sachs' 'Vorlesungen über Pflanzen-physio-
logie ' has been carried on during intervals between scientific duties of other kinds,
and some delay has resulted from the pressure of certain of these duties of late.

To put the graphic language of the original into English, which should be
as widely read in this country as the German lectures have been on the Continent,
has been a distinct wish and aim on my part ; but it is well known that difficulties
often arise in the attempt to render a German scientific sentence into simple English
intelligible to the general reader, and that the force of many expressions may be
readily injured or destroyed by displaying too much fear of their foreign form. That
it has not always been possible to reproduce the living ideas of the author with their
full force in the new language, I am only too well aware, but it is hoped that
the faults are venial : they would have been more numerous but for the kindness
of Dr. S. H. Vines, F.R.S., of Christ's College, Cambridge, who has been so good as
to look over the proofs before I finally revised them for the press, I am also
indebted to the courtesy of Mr. W. T. Thiselton Dyer, F.R.S., C.IVI.G., the Director
of the Royal Gardens, Kew, and to Dr. Bayley Balfour, F.R.S., Professor of Botany
in the University of Oxford, for several suggestions.

The index is the only real departure from the original: this I have greatly
extended, in the hope that it will be correspondingly useful to students and teachers.
With regard to the bibliography, I have not added to the notes selected by Professor
Sachs ; but it may be pointed out that further references to the literature connected
with special points are available in the English editions of De Bary's ' Comparative
Anatomy of the Ferns and Phanerogams,' by Professor Bower and Dr. Scott ;
Goebel's ' Outlines of the Classification and Special Morphology of Plants,' by
Professor Bayley Balfour and the Rev. H. E. F. Garnsey ; De Bary's ' Comparative
Morphology and Biology of the Fungi, INIycetozoa and Bacteria,' by the same ; and in
the ' Lectures on the Physiology of Plants,' by Dr. S. H. Vines.

Forestry School,

Cooper's Hill.


PART I. — Organography.


Lecture I. — Introductory Remarks on the Physiological Organography of the

Vegetative Organs i

Shoot and Root. — Typical, Rudimentary, and Reduced Forms. — Substance and
Form of Organs.

Lecture II.— The Typical Roots of Vascular Plants tl

Branching of Roots of Seedlings. — Place of Origin of Roots. — Development of
Roots. — Entrance of Roots into Soil. — Importance of Root-hairs. — Shortening of
Roots. — Conversion of Roots into Shoots.

Lecture III. — Roots, continued. Metamorphosed and Reduced Roots of Vascular

Cryptogams ; Rudimentary Roots of Mosses and Thallophytes ... 23
Lignified and Napiform Roots. — Roots of Parasites. — Roots of Muscinese. — Roots
of Liverworts. — Roots of Algse. — Roots of Fungi.

Lecture IV. — Typical Forms of Shoot of the Vascular Plants .... 36
Typical Shoots. — Continuity of Shoot-axis and Leaf. — Crowding of Leaves at the
Growing-point. — Buds. — Vascular bundles of Shoots. — Segmentation of Leaves. —
Venation of Leaves.

Lecture V. — Metamorphosed and Reduced Shoots of Vascular Plants. Shoots of

Mosses, Algae, and Fungi ........... 54

Succulent Shoots. — Cladodes. — Twining Shoots. — Tendrils.— Thorns. — Rimners,
Tubers, Bulbs. — Subterranean Shoots. — Root-like Shoots. — Shoots of Parasites. —
Relation of Chlorophyll to the Forms of Shoots. — Shoots of Mosses. — Shoots
of Liverworts. — Shoots of Algas. — Concluding remarks.

Lecture VI. — The Cellular Structure of Plants. Protoplasm, Nucleus, Cell-
Wall 73

Original meaning of the word ' Cell.' — Isolation of Cells. — Cell-wall and Cell-
contents. — Chemical nature of Protoplasm. — Protoplasm. — Movements of Proto-
plasm. — Chlorophyll-corpuscles. — Nucleus. — Cell-wall. — Deliquescence of cell- walls.
— Stratification, Striation, Pits. — Structure of Cell-wall.

Lecture VII. — Development of Cells 94

Growth and Cell-division. — Formation of Chambers in Mother-cells.— Development
of Reproductive Cells. — Uniformity of Cell-formation. — Behaviour of Nucleus
during division. — Origin of the New Septum. — Abnormal Nuclear division. — Non-
cellular Plants.

Lecture VIII. — Forms and Systems of Tissue : Epidermal Tissue and Vascular

Bimdles no

Common Wall of Tissue-cells. — Systems of Tissue. — Epidermis. — Cuticle. — Waxy
Coverings. — Stomata. — Epidermis of Moss. — Hairs. — Physiological significance of
Hairs. — Structure of Hairs. — Vascular Bundles (Strands). — Structure of Vascular
Bundles. — Xylem and Phloem of the Strand. — Arrangement of Xylem and Phloem.
— Vessels. — Sieve-tubes.



Lecture IX. — Systems of Tissue, continued. Fundamental Tissue. Rudimentary
Differentiations of Tissue ...........

Fundamental Tissue. — Hypoderm. — Sheaths. — Sclerenchyma. — Assimilatory Paren-
chyma. — Tissue-systems of Mosses. — Differentiations of Tissues in Algse. — Differ-
entiations of Tissues in Fungi.

Lecture X. — Secondary Growth in Thickness of Shoot- Axes and Roots . . 155

Correlation between Growth in Thickness and extent of Foliage. — Cambium-ring. —
Products of Cambium. — Wood. — Heart-wood and Alburnum. — Cork, Periderm. —
Bark. — Lenticels. — Secondary Growth in Thickness of Monocotyledons.

Lecture XL — Laticiferous Vessels and Receptacles for Secretions . . . 171

Latex-tubes. — Variety of Secretions. — Calcium Oxalate.— Calcium Carbonate. —
Secretion-vesicles. — Resin- and Gum-canals. — Internal Glands. — Epidermal Glands.

PART II. — The External Conditions of Vegetable-life, and the
Properties of Plants.

Lecture XI L— The General External Conditions of Plant-Life .... 189
Organic Structure and External Influences. — Cardinal Points of Temperature
suitable for Vegetation.- — Representation of the Dependence by Curves. — General
Law of Dependence. — Dependence on Light. — Daily Periodicity. — Influence of
Gravitation, Light, Electricity. — Dependence on Habitat. — Dependence on Animals.

Lecture XI 1 1. — The Molecular Structure of Plants and its Physiological Im-
portance 205

Molecules, Molecular Complexes. — Swelling. — Diosmosis. — Turgescence. — Artificial
Cells. — Tissue-tensions. — Rigidity due to Tissue- tensions. — Elasticity, &c. due to
Lignified Sclerenchyma.

PART III.— Nutrition.

Lecture XIV. — The Ascent of Water in Transpiring Land-Plants . . .225

Importance of the Water-current in Nutrition. — Transpiration from Leaves. —
Ascending Current in the Wood. — Sclerenchyma conducts water. — Distribution of
the Water-current in the Leaves. — Rapidity of the Upward Flow. — Filtration
through Wood. — Condemnation of the Capillarity Theory. — Calculation of the
Cubic Contents of the Wood-cavities. — Specific Properties of Wood. — Suction in
Cut Branches.

Lecture XV. — Conditions of Transpiration — Absorption of Water and Nutritive

Matters by the Roots of Land-Plants 246

Regulation of Transpiration. — Mechanics of Stomata. — Stomata as the Regulators of
Transpiration. — Transport of Nutritive Salts in Wood. — Absorption of Water and
Salts by Leaves. — Water contained in the Soil. — Absorption of Water by Root-
hairs. — Absorption of Substances held in the Soil. — Attachment of Root-hairs to
Particles of Soil. — Corrosion of Minerals by Roots.

Lecture XVI.— Excretion of Water in the Liquid State 266

Mobility under Pressure of the Water in Wood. — Water-currents in the Wood due
to Changes of Temperature. — Weeping of Root-stock. — Periodic variations in the
Excretion of Water. — Mechanics of the Weeping of Root-stocks. — Relation of Root-
pressure to Transpiration. — Excretion of Drops from Leaves. — Excretion of Drops
by Non-cellular Plants.



Lecture XVII.— The Nutritive Materials of Plants 282

Artificial Nutrition of Plants. — Influence of Iron. — Chlorosis. — Quantitative Selection.
— Importance of Silica. — Quantity of Ash in Plants. — Source of Nitrogen. — Source
of Carbon. — Action of Light in Assimilation.

Lecture XVIII. — The Production of the Organic Substance of Plants — Assimila-
tion 296

Evolution of Oxygen. — Chlorophyll the Instrument of Assimilation. — Influence of
Light on the Development of Chlorophyll. — Assimilation in the various parts of the
Solar Spectrum. — Assimilation not effected by the so-called Chemical Rays. —
Dependence on the Length of Waves of Light. — The first visible product of Assimi-

Lecture XIX. — Origin of Starch in the Chlorophyll, and in the Starch-forming

Corpuscles, Further Behaviour and Fate of the Chlorophyll .... 309
Starch in Chlorophyll. — Energy of Assimilation. — Visible Processes in the Chloro-
phyll. — Starch-forming Corpuscles. — Cheinical Processes in Chlorophyll. — Emptying
of Leaves in Autumn. — Colouring Matter of Chlorophyll.

Lecture XX. — Chemical Metamorphoses of the Products of Assimilation. Phy-
siological Classification of the Products of Metabolism 323

Origin of Proteids. — Employment of Reserve-materials. — Biological Significance of
products of Metabolism. — Reservoirs of Reserve-materials. — Forms of Reserv^e-
materials. — Aleurone-grains and Crystalloids. — Inulin. — Starch-grains. — Granulöse
and Cellulose of Starch-grains.

Lecture XXL— Renewal of Activity of Reserve-Materials. Ferments. Dormant

Periods 341

Ferments. — Growing Organs produce Ferments. — Peptones. — Asparagin. — Fats. —
Naegeli's distinction between Ferment-action and Fermentation. — Resting Periods
of Vegetation.

Lecture XXII. — Passage of the Plastic-Materials through the Tissues . . . 353
Transport of Constructive Materials over large Distances. — Employment of the
Constructive Materials in Growing Organs. — Movement and Consumption of the
Constructive Materials. — Mechanics of the Movements.— Movement in Latex-tubes.
— Movements induced by Growth.

Lecture XXIII. — The Absorption of Organic Nutritive Materials. Parasites.

Saprophytes. Insectivorous Plants 366

Nutrition of Parasites. — Action of Parasites on their Hosts. — Connection of Parasites
with their Hosts. — Sources of the Plastic Substances of Parasites. — Comparison with
Seedlings. — Diotiaa vmscipida. — Drosera. — Nepenthes and other Insectivorous

Lecture XXIV. — Lecture xxiii, continued. — Nutrition of Fungi. Lichens . . 380
Various effects of Fungi on their Substratum. — Nutritive Materials of Fungi. —
Nutritive and Non-nutritive Organic Substances. — Formation of Fat. — Fennentation
of Yeast. — Bacteria. — Putrefaction. — Tree-killing Fungi. — Ferment-action and Fer-
mentation of Fungi.— Parasitism of Lichen-fungi. — Configuration of Lichens con-
ditioned by Chlorophyll.

Lecture XXV. — The Respiration of Plants. Spontaneous Evolution of Heat.

Phosphorescence 395

Absorption of Oxygen and Evolution of Carbon Dioxide. — Quantity of Carbon
Dioxide respired. — Destruction of Organic Substance by Respiration. — Intra-
molecular Respiration. — Purpose of Respiration. — Measurement of Spontaneous
Heat. — Production of Light by Respiration.


PART IV.— Growth.

Lecture XXVI. — The Distribution of the Phases of Growth in Space and Time . 41 1
The Growth of Plants compared with that of Crystals. — The Three Phases of
Gro\vth. — Embryonic Conditions of Organs. — Elongation of Organs. — The Com-
pletion of Internal Differention in Organs. — Distribution of Growth in Non-Cellular
Plants. — Growth of Fungi. — Growth of Algse and Myxomycetes.

Lecture XXVIL — Relations between Growth and Cell-division in the Embryonic

Tissues 431

Dependence of Divisions on the Form of the Mother-cell. — The Arrangement of
Cells Independent of the Morphological and Physiological Nature of the Organ. —
Net-works of Cell-walls. — Periclines, Anticlines, Trajectories. — Arrangement of Cells
in an Elliptical Disc. — Examples agreeing with the Diagram. — Sequence of Anti-
clines and Periclines immaterial. — Displacement of Division-walls by Growth. —
Anticlines and Periclines in an Ellipsoidal body. — Anticlines and Periclines in
Growing-points. — The Apex of the Growing-point grows most slowly. — Confocal
and Co-axial Arrangement of Cells. — Apical Cells. — Transverse Segments of Apical
Cells. — Tetrahedral Apical Cells. — Significance of the Apical Cell.
Lecture XXVIIL — Formation of Organs at the Growing-point. Branching . 460
Forms of Growing-points. — Depressed Growing-points. — Metamorphosis of Growing-
point into an Organ. — Progressive Development of Organs at the Growing-point. —
Development of Leaves. — Development of Intemodes. — Shoots with and without
Branches. — Dichotomy or Bifurcation. — Apparently Endogenous Inception of Shoots.
Adventitious Growing-points.

Lecture XXIX. — Axis of Growth. Polarity. Laterality. Relations of Position 481
Axis of Growth. — Polarity in the Growing Axis. — Radial, Bilateral, Dorsi-ventral. —
Extension of the idea of Radial Structure. — Dorsi-ventral, Bilateral. — Dorsi-
ventrality. — Dorsi-ventral Shoots. — Laterality and Phyllotaxis. — Rejection of the
Spiral-theory. — Parastichies. — Divergences.

Lecture XXX. — Causal Relations of Growth of the different Organs of the Plant

one to another (Correlations) 502

Conception of the Form of Plants. — Influence of Growing Shoots on other Shoots. —
Bud-scales are suppressed Foliage-leaves. — Organs of like kind as Competitors
for the same Formative Substances. — Assimilatory Tissue forms thin Lamellae. —
Assimilating Surfaces influence the Formation of Wood and Roots. — The Activity
of the Roots affects the Functions of Leaves.

Lecture XXXI.— Influences of the Environment on the Processes of Configura-
tion in the Plant 515

Inherited Disposition and External Influences. — Influence of Gravitation on the
Origin of Growing-points. — Influence of Gravitation on the Orientation of Growing-
points. — Movement of Shoot-forming and Root-forming Substances. — Development
of Roots on the side turned away from Light. — Dorsiventral Structure induced by
Illumination.. — Influence of Light and Gravitation on Post-embryonic Growth. —
Influence of Gravitation on Post-embryonic Growth. — Influence of Light on Post-
embryonic Growth. — Etiolation. — Flower-forming Reserve Substance in Bulbs,
Tubers, &c. — Influence of Light on Post-embryonic Growth. — Gall-formations. —

Lecture XXXII. — The Course of Growth during Elongation. Periodic Varia-
tions 539

The Grand Period of Growth. — Distribution of Growth in the Growing Region. —
Length of the Growing Region. — Passive Motion of the Apices of Buds and Roots.
—Nutations due to Unequal Growth. Torsions due to Growth. — Growth by Day
and by Night. — Auxanometer. — Daily periods of Growth. — Daily periods in con-
tinued darkness. — Apparatus for Auxanometrical observation.


Lecture XXXIII. — Mechanical Causes and Effects of the Growth of Cells and

Organs 563

Turgescence as a Cause of Growth. — Cause of Turgescence. — Drooping.— Plas-
molysis retards Growth. — Tissue-tensions during Growth. — Transverse Tension in
Tissues. — Behaviour of an Isolated Prism of Pith. — Cortical Pressure. — Tissue-
tension in roots. — Effect of Pressures in Tissues on the form and size of Cells. —
Changes in Wood during alterations of Cortical Pressure. — Growth in Thickness of
the Branches of Trees. — Tyloses ; Callus. — Internal and External Work by means
of Growth.

PART v.— IrritabiUty.

Lecture XXXIV. — General Considerations on Irritability 587

Disproportionality between Stimulus and Effect. — Stimuli, Stimulation, Irritable
Structure. — Stimulation in Crystals. — Rigor of Irritable Organs. — Propagation and
after-effect of a Stimulus. — Propagation of a Stimulus compared with Physical
Processes. — Spontaneous Periodic Movements, — Specific Energy of Irritable Organs.

Lecture XXXV. — Irritability and Mobility of Protoplasmic Structures . . . 603
Swarm-spores and Antherozoids. — Velocity of Swarm-spores. — Rotation. — Influence
of Temperature on the Movement of Swarm-spores. — Emulsion-figures. — Action of
Light on Swarm-spores. — Influence of the Colour and Intensity of the Light. —
Amoebje, Plasmodia.— Circulation of Protoplasm in the Cell. — Circulation and
Rotation of Protoplasm. — Movements of Chlorophyll.— Causes of the Move-

Lecture XXXVI. — Periodic Movements of Foliage-Leaves and Flowers (Sleep-
Movements) 623

Variations in Illumination induce Movements. — Combination of different causes of
Movement. — Phototonus and Paratonic Light-stimuli. — Structure of Motile Organs.
— Tissue-tension in Motile Organs. — Histology of Motile Organs. — Changes in the
Water-contents due to alterations in the Light. — Description of the Daily
Periodicity. — Colours of Light. — Mechanics of the Movement. — Lever Action. —
Leaves without special Motile Organs. — Opening and Closing of Flowers. — Use
of Sleep-movements.

Lecture XXXVI I.— The Irritability of Mimosa and other Plants . . . -644
Description of the Phenomena of Irritability. — Escape of Water on Stimulation.—
The Irritable Movement is the consequence of the Expulsion of Water. — Irritable
Stamens of the Cynarese. — Cause of the Expulsion of Water from Stimulated Organs.
The Movement results from Changes in the Protoplasm and Cell-wall. — The
Irritability of Mimosa as means of protection.

Lecture XXXVI 1 1.— The Revolving of Tendrils and Twining Plants . . -657
Organography of Tendrils. — The Coiling of Tendrils. — Mechanics of the Coiling. —
Irritability. — Thick and thin Tendrils. — Advantageous properties of Tendrils. —
Nutation previous to Coiling. — Behaviour of Revolving Shoots on Supports. —
Twining without Supports. — Klinostat-movement of Free-shoots. — Feeble Shoots.
— Comparison of Twining-shoots and Tendrils. — Geotropism.

Lecture XXXIX. — Geotropism and Heliotropism 677

Geotropism. — Positive and Negative Geotropism. — Nature of the Geotropic Sti-
mulus. — Centrifugal Force. — Klinostat. — Form of Geotropic Curvature depends on
the Distribution of Growth. — Changes in Form of Shoot-axes during Erection. —
Geotropic Curvature of the Nodes of Grasses. — Motile Organs of Leaves. — Down-
ward curvatures. — Changes during Geotropic Downward curvatures. — Heliotropism.
Demonstration of Heliotropism. — Theory of Heliotropism. — Action of Colours of

Online LibraryJulius SachsLectures on the physiology of plants → online text (page 1 of 103)