CONCLUSION
In the stupendous pageant of living things which moves through creation,
the plants have a place unique and vitally important. Yet so quietly and
so slowly do they live and move that we in our hasty motion often forget
that they, equally with ourselves, belong to the living and evolving
organisms. When we look at the relative structures of plants divided by
long intervals of time we can recognize the progress they make; and this
is what we do in the study of fossil botany. We can place the salient
features of the flora of Palæozoic and Mesozoic eras in a few pages of
print, and the contrast becomes surprising. But the actual distance in
time between these two types of plants is immense, and must have extended
over several million years; indeed to speak of years becomes meaningless,
for the duration of the periods must have been so vast that they pass
beyond our mental grasp. In these periods we find a contrast in the
characters of the plants as striking as that in the characters of the
animals. Whole families died out, and new ones arose of more complex and
advanced organization. But in height and girth there is little difference
between the earliest and the latest trees; there seems a limit to the
possible size of plants on this planet, as there is to that of animals,
the height of mountains, or the depth of the sea. The “higher plants” are
often less massive and less in height than the lower—Man is less in
stature than was the Dinosaur—and though by no legitimate stretch of the
imagination can we speak of brain in plants, there is an unconscious
superiority of adaptation by which the more highly organized plants
capture the soil they dominate.
It has been noted in the previous chapters that so far back as the Coal
Measure period the vegetative parts of plants were in many respects
similar to those of the present, it was in the reproductive organs that
the essential differences lay. Naturally, when a race (as all races do)
depends for its very existence on the chain of individuals leading from
generation to generation, the most important items in the plant
structures must be those mechanisms concerned with reproduction. It is
here that we see the most fundamental differences between living and
fossil plants, between the higher and the lower of those now living,
between the forest trees of the present and the forest trees of the past.
The wood of the palæozoic Lycopods was in the quality and extent and
origin of its secondary growth comparable with that of higher plants
still living to-day—yet in the fruiting organs how vast is the contrast!
The Lycopods, with simple cones composed of scales in whose huge
sporangia were simple single-celled spores; the flowering plants, with
male and female sharply contrasted yet growing in the same cone (one can
legitimately compare a flower with a cone), surrounded by specially
coloured and protective scales, and with the “spore” in the tissue of the
young seed so modified and changed that it is only in a technical sense
that comparison with the Lycopod spore is possible.
To study the minute details of fossil plants it is necessary to have an
elaborate training in the structure of living ones. In the preceding
chapters only the salient features have been considered, so that from
them we can only glean a knowledge similar to the picture of a house by a
Japanese artist—a thing of few lines.
Even from the facts brought together in these short chapters, however, it
cannot fail to be evident how large a field fossil botany covers, and
with how many subjects it comes in touch. From the minute details of
plant anatomy and evolution pure and simple to the climate of departed
continents, and from the determination of the geological age of a piece
of rock by means of a blackened fern impression on it to the chemical
questions of the preservative properties of sea water, all is a part of
the study of “fossil botany”.
To bring together the main results of the study in a graphic form is not
an easy task, but it is possible to construct a rough diagram giving some
indication of the distribution of the chief groups of plants in the main
periods of time (see fig. 122).
Such a diagram can only represent the present state of our imperfect
knowledge; any day discoveries may extend the line of any group up or
down in the series, or may connect the groups together.
It becomes evident that so early as the Palæozoic there are nearly as
many types represented as in the present day, and that in fact
everything, up to the higher Gymnosperms, was well developed (for it is
hard indeed to prove that _Cordaites_ is less highly organized than some
of the present Gymnosperm types), but flowering plants and also the true
cycads are wanting, as well as the intermediate Mesozoic Bennettitales.
The peculiar groups of the period were the Pteridosperm series,
connecting links between fern and cycad, and the Sphenophyllums,
connecting in some measure the Lycopods and Calamites. With them some of
the still living groups of ferns, Lycopods, and Equisetaceæ were
flourishing, though all the species differed from those now extant. This
shows us how very far from the beginning our earliest information is, for
already in the Palæozoic we have a flora as diversified as that now
living, though with more primitive characters.
[Illustration: Fig. 122.—Diagram showing the relative distribution of
the main groups of plants through the geological eras. The dotted lines
connecting the groups and those in the pre-Carboniferous are entirely
theoretical, and merely indicate the conclusions reached at present.
The size of the surface of each group roughly indicates the part it
played in the flora of each period. Those with dotted surface bore
seeds, the others spores.]
In Mesozoic times the most striking group is that of the Cycads and
Bennettitales, the latter branch suggesting a direct connection between
the fern-cycad series and the flowering plants. This view, so recently
published and upheld by various eminent botanists, is fast gaining
ground. Indeed, so popular has it become among the specialists that there
is a danger of overlooking the real difficulties of the case. The
morphological leap from the leaves and stems of cycads to those of the
flowering plants seems a much more serious matter to presuppose than is
at present recognized.
As is indicated in the diagram, the groups do not appear isolated by
great unbridged gaps, as they did even twenty years ago. By means of the
fossils either direct connections or probable lines of connection are
discovered which link up the series of families. At present the greatest
gap now lies hedging in the Moss family, and, as was mentioned (p. 163),
fossil botany cannot as yet throw much light on that problem owing to the
lack of fossil mosses.
This glimpse into the past suggests a prophecy for the future. Evolution
having proceeded steadily for such vast periods is not likely to stop at
the stage reached by the plants of to-day. What will be the main line of
advance of the plants of the future, and how will they differ from those
of the present?
We have seen in the past how the differentiation of size in the spores
resulted in sex, and in the higher plants in the modifications along
widely different lines of the male and female; how the large spore
(female) became enclosed in protecting tissues, which finally led up to
true seeds (see p. 75), while the male being so temporary had no such
elaboration. As the seed advances it becomes more and more complex, and
when we reach still higher plants further surrounding tissues are pressed
into its service and it becomes enclosed in the carpel of the highest
flowering plants. After that the seed itself has fewer general duties,
and instead of those of the Gymnosperms with large endosperms collecting
food before the embryo appears, small ovules suffice, which only develop
after fertilization is assured. The various families of flowering plants
have gone further, and the whole complex series of bracts and fertile
parts which make up a flower is adapted to ensure the crossing of male
and female of different individuals. The complex mechanisms which seem
adapted for “cross fertilization” are innumerable, and are found in the
highest groups of the flowering plants. But some have gone beyond the
stage when the individual flowers had each its device, and accomplished
its seed-bearing independently of the other flowers on the same branch.
These have a combination of many flowers crowded together into one
community, in which there is specialization of different flowers for
different duties. In such a composite flower, the Daisy for example, some
are large petalled and brightly coloured to attract the pollen-carrying
insects, some bear the male organs only, and others the female or
seed-producing. Here, then, in the most advanced type of flowering plant
we get back again to the separation of the sexes in separate flowers; but
these flowers are combined in an organized community much more complex
than the cones of the Gymnosperms, for example, where the sexes are
separate on a lower plane of development.
It seems possible that an important group, if not the dominant group, of
flowering plants in the future will be so organized that the individual
flowers are very simple, with fewer parts than those of to-day, but that
they will be combined in communities of highly specialized individuals in
each flower head or cluster.
As well as this, in other species the minute structure of the vital
organs may show a development in a direction contrary to what has
hitherto seemed advance. Until recently flowers and their organs have
appeared to us to be specialized in the more advanced groups on such
lines as encourage “cross fertilization”. In “cross fertilization”, in
fact, has appeared to lie the secret of the strength and advance of the
races of plants. But modern cytologists have found that many of the
plants long believed to depend on cross fertilization are either
self-fertilized or not fertilized at all! They have passed through the
period when their complex structures for ensuring cross fertilization
were used, and though they retain these external structures they have
taken to a simpler method of seed production, and in some cases have even
dispensed with fertilization of the egg cell altogether. The female
vitality increased, the male becomes superfluous. It is simpler and more
direct to breed with only one sex, or to use the pollen of the same
individual. Many flowers are doing this which until recently had not been
suspected of it. We cannot yet tell whether it will work successfully for
centuries to come or is an indication of “race senility”.
Whether in the epochs to come flowering plants will continue to hold the
dominant position which they now do is an interesting theoretical
problem. Flowers were evolved in correlation with insect pollination. One
can conceive of a future, when all the earth is under dominion of man, in
which fruits will be sterilized for man’s use, as the banana is now, and
seed formation largely replaced by gardeners’ “cuttings”.
In those plants which are now living where the complex mechanisms for
cross-fertilization have been superseded by simple self-fertilization,
the external parts of the more elaborate method are still produced,
though they are apparently futile. In the future these vestigial organs
will be discarded, or developed in a more rudimentary form (for it is
remarkable how organs that were once used by the race reappear in members
of it that have long outgrown their use), and the morphology of the
flower will be greatly simplified.
Thus we can foresee on both sides much simplified individual flowers—in
the one group the reduced individuals associating together in communities
the members of which are highly specialized, and in the other the
solitary flowers becoming less elaborate and conspicuous, as they no
longer need the assistance of insects (the cleistogamic flowers of the
Violet, for example, even in the present day bend toward the earth, and
lack all the bright attractiveness of ordinary flowers), and perhaps
finally developing underground, where the seeds could directly germinate.
In the vegetative organs less change is to be expected, the examples from
the past lead us to foresee no great difference in size or general
organization of the essential parts, though the internal anatomy has
varied, and probably will vary, greatly with the whole evolution of the
plant.
But one more point and we must have done. Why do plants evolve at all?
Why did they do so through the geological ages of the past, and why
should we expect them to do so in the future? The answer to this question
must be less assured than it might have been even twenty years ago, when
the magnetism of Darwin’s discoveries and elucidations seemed to obsess
his disciples. “Response to environment” is undoubtedly a potent factor
in the course of evolution, but it is not the cause of it. There seems to
be something inherent in life, something apparently (though that may be
due to our incomplete powers of observation) apart from observable
factors of environment which causes slight spontaneous changes,
_mutations_, and some individuals of a species will suddenly develop in a
new direction in one or other of their parts. If, then, this places them
in a superior position as regards their environment or neighbours, it
persists, but if not, those individuals die out. The work of a special
branch of modern botany seems clearly to indicate the great importance of
this seemingly inexplicable spontaneity of life. In environment alone the
thoughtful student of the present cannot find incentive enough for the
great changes and advances made by organisms in the course of the world’s
history. The climate and purely physical conditions of the Coal Measure
period were probably but little different from those in some parts of the
world to-day, but the plants themselves have fundamentally changed. True,
their effect upon each other must be taken into account, but this is a
less active factor with plants than with men, for we can imagine nothing
equivalent to citizenship, society, and education in the plant
communities, which are so vital in human development.
It seems to have been proved that plants and animals may, at certain
unknown intervals, “mutate”; and mutation is a fine word to express our
recent view of one of the essential factors in evolution. But it is a
cloak for an ignorance avowedly less mitigated than when we thought to
have found a complete explanation of the causes of evolution in
“environment”.
In a sketch such as the present, outlines alone are possible, detail
cannot be elaborated. If it has suggested enough of atmosphere to show
the vastness of the landscape spreading out before our eyes back into the
past and on into the future, the task has been accomplished. There are
many detailed volumes which follow out one or other special line of
enquiry along the highroads and by-ways of this long traverse in
creation. If the bird’s-eye view of the country given in this book
entices some to foot it yard by yard under the guidance of specialists
for each district, it will have done its part. While to those who will
make no intimate acquaintance with so far off a land it presents a short
account by a traveller, so that they may know something of the main
features and a little of the romance of the fossil world.
APPENDIX I
LIST OF REQUIREMENTS FOR A COLLECTING EXPEDITION
In order to obtain the best possible results from an expedition, it is
well to go fossil hunting in a party of two, four, or six persons. Large
parties tend to split up into detachments, or to waste time in trying to
keep together.
Each individual should have strong suitable clothes, with as many pockets
arranged in them as possible. The weight of the stones can thus be
distributed over the body, and is not felt so much as if they were all
carried in a knapsack. Each collector should also provide himself with—
A satchel or knapsack, preferably of leather or strong canvas, but not
of large size, for when the space is limited selection of the specimens
is likely to be made carefully.
One or two hammers. If only one is carried, it should be of a fair size
with a square head and strong straight edge.
One chisel, entirely of metal, and with a strong straight cutting edge.
Soft paper to wrap up the more delicate fossils, in order to prevent
them from scraping each other’s surfaces; and one or two small
cardboard boxes for very fragile specimens.
A map of the district (preferably geologically coloured). Localities
should be noted in pencil on this, indicating the exact spot of finds.
For general work the one-inch survey map suffices, but for detailed
work it is necessary to have the six-inch maps of important districts.
A small notebook. Few notes are needed, but those few _must_ be taken
on the spot to be reliable.
A pencil or fountain pen, preferably both.
A penknife, which, among other things, will be found useful for working
out very delicate fossils.
APPENDIX II
TREATMENT OF SPECIMENS
1. The commonest form in which fossils are collected is that which has
been described as _impression material_ (see p. 12). In many cases these
will need no further attention after the block of stone on which they lie
has been chipped into shape.
In chipping a block down to the size required it is best to hold it
freely in the left hand, protecting the actual specimen with the palm
where possible, and taking the surplus edges away by means of short sharp
blows from the hammer, striking so that only small pieces come away with
each blow. For delicate specimens it is wise to leave a good margin of
the matrix round the specimen, and to do the final clearing with a
thin-bladed penknife, taking away small flakes of the stone with delicate
taps on the handle of the knife.
Specimens from fine sandstones, shales, and limestones are usually
thoroughly hard and resistant, and are then much better if left without
treatment; by varnishing and polishing them many amateur collectors spoil
their specimens, for a coat of shiny varnish often conceals the details
of the fossil itself. Impressions of plants on friable shales, on the
other hand, or those which have a tendency to peel off as they dry, will
require some treatment. In such cases the best substance to use is a
dilute solution of size, in which the specimen should soak for a short
period while the liquid is warm (not hot), after which it should be
slightly drained and the size allowed to dry in. The congealed substance
then holds the plant film on to the rock surface and prevents the rock
from crumbling away, while it is almost invisible and does not spoil the
plant with any excessive glaze.
2. For specimens of _casts_ the same treatment generally applies, though
they are more apt to separate completely from the matrix after one or two
sharp blows, and thus save one the work of picking out the details of
their structure.
3. Those blocks which contain _petrifactions_, and can therefore be made
to show microscopic details, will require much more treatment. In some
cases mere polishing reveals much of the structure—such, for instance,
were the “Staarsteine” of the German lapidaries, where the axis and
rootlets of a fossil like a treefern show their very characteristic
pattern distinctly.
As a rule, however, it is better, and for any detailed work it is
essential, to cut thin sections transversely across and longitudinally
through the axis of the specimen and to grind them down till they are so
transparent that they can be studied through the microscope. The cutting
can be done on a lapidary’s wheel, where a revolving metal disc set with
diamond powder acts as a knife. The comparatively thin slice thus
obtained is fastened on to glass by means of hard Canada balsam, and
rubbed down with carborundum powder till it is thin enough.
The process, however, is very slow, and an amateur cannot get good
results without spending a large amount of time and patience over the
work which would be better spent over the study of the plant structures
themselves. Therefore it is usually more economical to send specimens to
be cut by a professional, if they are good enough to be worth cutting at
all, though it is often advisable to cut through an unpromising block to
see whether its preservation is such as would justify the expense.
In the case of true “coal balls” much can be seen on the cut surface of a
block, particularly if it be washed for a minute in dilute hydrochloric
acid and then in water, and then dried thoroughly. The acid acts on the
carbonates of which the stone is largely composed, and the treatment
accentuates the black-and-white contrast in the petrified tissues (see
fig. 10). After lying about for a few months the sharpness of the surface
gets rubbed off, as the acid eats it into very delicate irregularities
which break and form a smearing powder; but in such a case all that is
needed to bring back the original perfection of definition is a quick
wash of dilute acid and water. If the specimens are not rubbed at all the
surface is practically permanent. Blocks so treated reveal a remarkable
amount of detail when examined with a strong hand lens, and form very
valuable museum specimens.
The microscope slides should be covered with glass slips (as they would
naturally be if purchased), and studied under the microscope as sections
of living plants would be.
Microscopic slides of fossils make excellent museum specimens when
mounted as transparencies against a window or strong light, when a
magnifying glass will reveal all but the last minutiæ of their structure.
4. _Labelling_ and numbering of specimens is very important, even if the
collection be but a small one. As well as the paper label giving full
details, there should be a reference number on every specimen itself. On
the microscope slides this can be cut with a diamond pencil, and on the
stones sealing wax dissolved in alcohol painted on with a brush is
perhaps the best medium. On light-coloured close-textured stones ink is
good, and when quite dry can even be washed without blurring.
The importance of marking the stone itself will be brought home to one on
going through an old collection where the paper labels have peeled or
rubbed off, or their wording been obliterated by age or mould.
A notebook should be kept in which the numbers are entered, with a note
of all the items on the paper label, and any additional details of
interest.
APPENDIX III
LITERATURE
A short list of a few of the more important papers and books to which a
student should refer. The innumerable papers of the specialists will be
found cited in these, so that, as they would be read only by advanced
students, there is no attempt to catalogue them here.
Carruthers, W., “On Fossil Cycadean Stems from the Secondary Rocks of
Britain,” published in the _Transactions of the Linnean Society_, vol.
xxvi, 1870.
*Geikie, A., _A Text-Book of Geology_, vols. i and ii, London, 1903.
Grand’Eury, C., “Flore Carbonifère du département de la Loire et du
centre de la France”, published in the _Mémoirs de l’Académie des
Sciences_, Paris, vol. xxiv, 1877.
*Kidston, R., _Catalogue of the Palæozoic Plants in the Department of
Geology and Palæontology of the British Museum_, London, 1886.
*Lapworth, C., _An Intermediate Text-Book of Geology_, twelfth edition,
London, 1888.
Laurent, L., “Les Progrès de la paléobotanique angiospermique dans la
dernière decade”, _Progressus Rei Botanicæ_, vol. i, Heft 2, pp. 319-68,
Jena, 1907.
Lindley, J., and Hutton, W., _The Fossil Flora of Great Britain_, 3
vols., published in London, 1831-7.
Lyell, C., _Principles of Geology_ and _The Student’s Lyell_, edited by
J. W. Judd, London, 1896.
Oliver, F. W., and Scott, D. H., “On the Structure of the Palæozoic Seed,
_Lagenostoma Lomaxi_”, published in the _Transactions of the Royal
Society_, series B, vol. cxcvii, London, 1904.
Renault, B., _Cours de Botanique fossile_, Paris, 1882, 4 vols.
Renault, B., _Bassin Houiller et Permien d’Autun et d’Epinac_, Atlas and
Text, 1893-6, Paris.
*Scott, D. H., _Studies in Fossil Botany_, London, second edition, 1909.
Scott, D. H., “On the Structure and Affinities of Fossil Plants from the
Palæozoic Rocks. On _Cheirostrobus_, a New Type of Fossil Cone from the
Lower Carboniferous Strata.” Published in the _Philosophical Transactions
of the Royal Society_, vol. clxxxix, B, 1897.
*Seward, A. C., _Fossil Plants_, vol. i, Cambridge, 1898.
Seward, A. C., _Catalogue of the Mesozoic Plants in the Department of
Geology of the British Museum_, Parts I and II, London, 1894-5.
*Solms-Laubach, Graf zu, _Fossil Botany_ (translation from the German),
Oxford, 1891.
Stopes, M. C., and Watson, D. M. S., “On the Structure and Affinities of
the Calcareous Concretions known as ‘Coal Balls’”, published in the
_Philosophical Transactions of the Royal Society_, vol. cc.
*Stopes, M. C., _The Study of Plant Life for Young People_, London, 1906.
*Watts, W. W., _Geology for Beginners_, London, 1905 (second edition).
Wieland, G. R., _American Fossil Cycads_, Carnegie Institute, 1906.
Williamson, W. C., A whole series of publications in the _Philosophical
Transactions of the Royal Society_ from 1871 to 1891, and three later
ones jointly with Dr. Scott; the series entitled “On the Organization of
the Fossil Plants of the Coal Measures”, Memoir I, II, &c.
Zeiller, R., _Éléments de Paléobotanique_, Paris, 1900.
*Zittel, K., _Handbuch der Palæontologie_, vol. ii; _Palæophytologie_, by
Schimper & Schenk, München and Leipzig, 1900.
Those marked * would be found the most useful for one beginning the
subject.
GLOSSARY
Some of the more technical terms about which there might be some doubt,
as they are not always accompanied by explanations in the text, are here
briefly defined.
Anatomy.—The study of the details and relative arrangements of the
internal features of plants; in particular, the relations of the
different tissue systems.
Bracts.—Organs of the nature of leaves, though not usual foliage leaves.
They often surround fructifications, and are generally brown and scaly,
though they may be brightly coloured or merely green.
Calcareous.—Containing earthy carbonates, particularly calcium carbonate
(chalk).
Cambium.—Narrow living cells, which are constantly dividing and giving
rise to new tissues (see fig. 33, p. 57).
Carbonates, as used in this book, refer to the combinations of some
earthy mineral, such as calcium or magnesium, combined with carbonic acid
gas and oxygen, formula CaCO_3, MgCO_3, &c.
Carpel.—The closed structure covering the seeds which grow attached to
it. The “husk” of a peapod is a carpel.
Cell.—The unit of a plant body. Fundamentally a mass of living protoplasm
with its nucleus, surrounded in most cases by a wall. Mature cells show
many varieties of shape and organization. See Chapter VI, p. 54.
Centrifugal.—Wood or other tissues developed away from the centre of the
stem. See fig. 65, p. 97.
Centripetal.—Wood or other tissues developed towards the centre of the
stem. See fig. 65, p. 97.
Chloroplast.—The microscopic coloured masses, usually round, green
bodies, in the cells of plants which are actively assimilating.
Coal Balls.—Masses of carbonate of calcium, magnesium, &c., generally of
roundish form, which are found embedded in the coal, and contain
petrified plant tissues. See p. 28.
Concretions.—Roundish mineral masses, formed in concentric layers, like
the coats of an onion. See p. 27.
Cotyledons.—The first leaves of an embryo. In many cases packed with food
and filling the seed. See fig. 58.
Cross Fertilization.—The fusion of male and female cells from different
plants.
Cuticle.—A skin of a special chemical nature which forms on the outer
wall of the epidermis cells. See p. 54, fig. 21.
Earth Movements.—The gradual shifting of the level of the land, and the
bending and contortions of rocks which result from the slow shrinking of
the earth’s surface, and give rise to earthquakes and volcanic action.
Embryo.—The very young plant, sometimes consisting of only a few delicate
cells, which results from the divisions of the fertilized egg cell. The
embryo is an essential part of modern seeds, and often fills the whole
seed, as in a bean, where the two fleshy masses filling it are the two
first leaves of the embryo. See fig. 58, p. 77.
Endodermis.—The specialized layer of cells forming a sheath round the
vascular tissue. See p. 55.
Endosperm.—The many-celled tissue which fills the large “spore” in the
Gymnosperm seed, into which the embryo finally grows. See fig. 57.
Epidermis.—Outer layer of cells, which forms a skin, in the multicellular
plants. See fig. 21, p. 54.
Fruit.—Essentially consisting of a seed or seeds, enclosed in some
surrounding tissues, which may be only those of the carpel, or may also
be other parts of the flower fused to it. Thus a peapod is a _fruit_,
containing the peas, which are seeds.
Gannister.—A very hard, gritty rock found below some coal seams. See p.
25.
Genus.—A small group within a family which includes all the plants very
like each other, to which are all given the same “surname”; e.g. _Pinus
montana_, _Pinus sylvestris_, _Pinus Pinaster_, &c. &c., are all members
of the genus _Pinus_, and would be called “pine trees” in general (see
“Species”).
Hyphæ.—The delicate elongated cells of Fungi.
Molecule.—The group of chemical elements, in a definite proportion, which
is the basis of any compound substance; _e.g._ two atoms of hydrogen and
one atom of oxygen form a molecule of water, H_2O. A lime carbonate
molecule (see definition of “Carbonate”) is represented as CaCO_3.
Monostelic.—A type of stem that contains only one stele.
Morphology.—The study of the features of plants, their shapes and
relations, and the theories regarding the origin of the organs.
Nucellus.—The tissue in a Gymnosperm seed in which the large “spore”
develops. See figs. 55 and 56, p. 76.
Nucleus.—The more compact mass of protoplasm in the centre of each living
cell, which controls its growth and division. See fig. 17, _n._
Palæobotany.—The study of fossil plants.
Palæontology.—The study of fossil organisms, both plants and animals.
Petiole.—The stalk of a leaf, which attaches it to the stem.
Phloem.—Commonly called “bast”. The elongated vessel-like cells which
conduct the manufactured food. See p. 57.
Pollen Chamber.—The cavity inside a Gymnosperm seed in which the pollen
grains rest for some time before giving out the male cells which
fertilize the egg-cell in the seed. See p. 76.
Polystelic.—A type of stem that appears, in any transverse section, to
contain several steles. See note on the use of the word on p. 63.
Protoplasm.—The colourless, constantly moving mass of finely granulated,
jelly-like substance, which is the essentially living part of both plants
and animals.
Rock.—Used by a geologist for all kinds of earth layers. Clay, and even
gravel, are “rocks” in a geological sense.
Roof, of a coal seam. The layers of rock—usually shale, limestone, or
sandstone—which lie just above the coal. See p. 24.
Sclerenchyma.—Cells with very thick walls, specially modified for
strengthening the tissues. See fig. 28, p. 56.
Seed.—Essentially consisting of a young embryo and the tissues round it,
which are enclosed in a double coat. See definition of “Fruit”.
Shale.—A fine-grained soft rock, formed of dried and pressed mud or silt,
which tends to split into thin sheets, on the surface of which fossils
are often found.
Species.—Individuals which in all essentials are identical are said to be
of the same species. As there are many variations which are not
essential, it is sometimes far from easy to draw the boundary between
actual species. The specific name comes after that of the genus, e.g.
_Pinus montana_ is a species of the genus _Pinus_, as is also _Pinus
sylvestris_. See “Genus”.
Sporangium.—The saclike case which contains the spores. See figs. 52 and
53, p. 75.
Spore.—A single cell (generally protected by a cell wall) which has the
power of germinating and reproducing the plant of which it is the
reproductive body. See p. 75.
Sporophyll.—A leaf or part of a leaf which bears spores or seeds, and
which may be much or little modified.
Stele.—A strand of vascular tissue completely enclosed in an endodermis.
See p. 62.
Stigma.—A special protuberance of the carpel in flowering plants which
catches the pollen grains.
Stomates.—Breathing pores in the epidermis, which form as a space between
two curved liplike cells. See fig. 23, p. 54.
Tetrads.—Groups of four cells which develop by the division of a single
cell called the “mother cell”. Spores and pollen grains are nearly always
formed in this way. See p. 75.
Tracheid.—A cell specially modified for conducting or storing of water,
often much elongated. The long wood cells of Ferns and Gymnosperms are
tracheids.
Underclay.—The fine clay found immediately below some coal seams. See p.
24.
Vascular Tissue.—The elongated cells which are specialized for conduction
of water and semifluid foodstuffs.
FOOTNOTES
[1]My book was entirely written before the second edition of Scott’s
_Studies_ appeared, which, had it been available, would have tempted
me to escape some of the labour several of the chapters of this
little book involved.
[2]The student would do well to read up the general geology of this very
interesting subject. Such books as Lyell’s _Principles of Geology_,
Geikie’s textbooks, and many others, provide information about the
process of “mountain building” on which the form of our coalfields
depends. A good elementary account is to be found in Watt’s _Geology
for Beginners_, p. 96 _et seq._
[3]See note on p. 28.
[4]This refers only to the “coal-ball”-bearing seams; there are many
other coals which have certainly collected in other ways. See Stopes
& Watson, Appendix, p. 187.
[5]For a detailed list of the strata refer to Watts, p. 219 (see
Appendix).
[6]Though the Angiosperm was not then evolved, the Gymnosperm stem has
distinct vascular bundles arranged as are those of the Angiosperm,
the difference here lies in the type of wood cells.
[7]The gametophyte generation (represented in the ferns by the
prothallium on which the sexual organs develop) alternates with the
large, leafy sporophyte. Refer to Scott’s volume on _Flowerless
Plants_ (see Appendix) for an account of this alternation of
generations.
[8]Material recently obtained by the author and Dr. Fujii in Japan does
contain some true petrifactions of Angiosperms and other plant
debris. The account of these discoveries has not yet been published.
[9]A fuller account of the Angiospermic flora can be had in French, in M.
Laurent’s paper in _Progressus Rei Botanicæ_. See Appendix for
reference.
[10]From the Cretaceous deposits of North America several fossil forms
(_Brachyphyllum_, _Protodammara_) are described which show clear
affinities with the family as it is now constituted. (See Hollick and
Jeffrey; reference in the Appendix.)
[11]The addition of _-oxylon_ to the generic name of any living type
indicates that we are dealing with a fossil which closely resembles
the living type so far as we have information from the petrified
material.
[12]See reference in the Appendix to this richly illustrated volume.
[13]For fuller description of this interesting cone, see Scott’s
_Studies_, p. 114 _et seq._
[14]A brackish swampy land is physiologically dry, as the plants cannot
use the water. See Warming’s _Oecology of Plants_, English edition,
for a detailed account of such conditions. For a simple account see
Stopes’ _The Study of Plant Life_, p. 170.
[15]The student interested in this special flora should refer to Arber’s
British Museum _Catalogue of the Fossil Plants of the Glossopteris
Flora_.
INDEX
(_Italicized numbers refer to illustrations_)
Abietineæ, 88, 89, 90.
— family characters of, 91.
Algæ, 44, 47, 165.
— brown, 166.
— green, 165.
— red, 165.
_Alnus_, 85.
Amber, 17.
Amentiferæ, 84.
Anatomy of fossil plants, likeness in detail to that of living plants,
53 et seq.
— — — — differences in detail from that of living plants, 69 et seq.
_Andromeda_, 84.
Angiosperms, comparison with Bennettitales, 103.
— early history of, 79 et seq.
— general distribution of in time, 177.
— later evolution of, 178.
— male cell of, 52.
Araliaceæ, 85.
Araucareæ, 88, 90, 111.
— description of, 90.
— primitive characters of, 89.
_Araucarioxylon_, 93, 95.
Arber, 173.
_Archæocalamites_, 152.
Artocarpaceæ, 85.
_Asterochlaena_, 126, 127, _86_, _89_.
_Bacillus_, 167.
Bacteria, 167.
_Baiera_, 101.
Bast, 57, _32_.
Bennettitales, 44, 102, 131.
— general distribution of in time, 177.
_Bennettites_, 103 et seq.
— external appearance of, 103.
— flower-like nature of fructification, 108.
— fructification of, 104, _71_, 105, _72_.
— seed of, 106, _73_.
Bertrand, 2.
_Betula_, 85.
_Bignonia_, 84.
Botryopterideæ, 125, 132.
— description of group, 125.
— fructifications of, 128.
— petioles of, 127, _89_.
— stem anatomy of, 126, _86_, _87_.
— wood of, 128, _90_.
_Botryopteris_, 126, 127.
— axis with petiole, 127, _88_, _89_.
_Bowmanites Römeri_, 158, 160.
_Brachyphyllum_, 89.
Brongniart, 2.
Bryophytes, 163.
_Calamites_, 147, 154, 157, 159, 160, 171.
— branch of, 147, _104_.
— _casheana_, 152.
— cone of, 150, _109_, 151, _110_.
— leaf of, 149, _107_.
— node of, 149, _106_.
— spores of, 152, _111_.
— young roots of, 150, _108_.
— young stem of, 148, _105_.
Cambium, 57, _33_, 65, _43_, 66, _44_.
Carbon, film of representing decayed plant, 12.
Carbonate of magnesium, 20.
Carbonates of lime, 19.
Carpels, modified leaves, 78.
Carruthers, 186.
Casts of fossil plants, 8, 9, _2_, 10, _3_, _4_, 11, 12.
— of seeds, 11, 12.
— treatment of specimens of, 184.
_Casuarina_, 83.
Cells, similarity of living and fossil types of, 53.
— principal types of, 53 et seq., _22_-_33_.
Cell wall, 47, _17_.
Centrifugal wood, 97, _65_.
Centripetal wood, 97, _65_, 116.
_Chara_, 16.
Characeæ, 163.
_Cheirostrobus_, 159, _118_, 160.
Chloroplast, 47, _17_.
Coal, origin of, 29 et seq.
— of different ages, 33.
— seams in the rocks, 24, _13_, _14_.
— vegetable nature of, 25 et seq.
— importance of, 17, Chap. III, p. 22 et seq.
“Coal balls”, 18, 19, _10_, 20, 21, 22, 27, _15_, 163, 185.
— — mass of, in coal, 28, _16_.
Coal Measures, climate of, 172.
Companion cells, 57, _32_.
Concretions, 21, 22, 27, _15_, 28.
— concentric banding in, 27, _15_.
Conducting tissue in higher plants, 49, _19_, 50, _20_.
Coniferales, conflicting observations among, 46.
— general distribution in time, 177.
— male cell of, 52.
_Corallina_, 166.
Cordaiteæ, 39-88, 112.
— comparison of fructifications with those of Taxeæ, 95.
— description of family, 92.
— general distribution in time, 177.
_Cordaites_, 40, 107, 176.
— fructification of, 95, 96, _64_.
— internal cast of stem, 10, _4_, 93, 94, 95.
— leaves of, once considered to be Monocotyledons, 82, 93.
— leaves of, 93, _61_, 94, _62A_.
— possible common origin with Ginkgo, 102.
— wood of, 94, _62B_.
Cork, 56, _29_.
— cambium, 56, _29_.
Cross fertilization, 179.
Cupresseæ, 88, 90.
— description of, 91.
_Cycadeoidea_, 103.
Cycads in the Mesozoic period, 40, 41, 42, 113.
— description of group, 109.
— general distribution of in time, 177.
— in Tertiary period, 85.
— large size of male cones of, 110.
— seeds of, 112.
— type of seed of, 76, _57_.
— wood of, 110.
_Cycas_, 109, 110, _74_.
— seed-bearing sporophyll of, 111.
— seeds of, 112, _76_.
— comparison with Ginkgo seeds, 112.
Darwin, 181.
Diatoms, 167, _121_.
Dicotyledons, 41, 44, 79.
— relative antiquity of, 81, 82.
— seed type of, 77, _58_.
Differentiation, commencement of in simple plants, 48.
— of tissues in higher plants, 49, _19_, 50 et seq., _20_.
Embryo of _Ginkgo_, 100.
— in seeds, 76, _57_, 77, _58_.
— of _Bennettites_, 106, _73_.
Endodermis, 55, _26_, 61.
Environment, 181, 182.
Epidermal tissues, 54, _21_, _22_, _23_, 125.
Epidermis cells, fossil impressions of, 13, 14, _8_, 59, _34_, 125.
Equisetales, 44.
— general distribution of in time, 177.
_Equisetites_, 146, _103_.
_Equisetum_, 9, 38, 40, 44, 145, 149, 152.
— underground rhizomes of, 43.
_Eucalyptus_, 83.
Europe, 87, 102.
— ancient climates of, 170.
Evolution, 43.
— in plants, various degrees of in the organs of the same plant, 45 et
seq.
Evolution in plants, cause of, 181.
— — — suggestions as to possible future lines of, 178.
Expedition, requirements for collecting, 183.
Extinct families, 44.
Ferns, sporangia of, 67, _45_.
— connection with Pteridosperms, 123.
— description of group, 124.
— fructifications of among fossils, 131, 132, _92_.
— general distribution of in time, 177.
— germinating spores of, 68, _47_.
_Ficus_, 83.
Flotsam, 6.
Flowering plant, anatomy of stem, 49, _19_.
Formation of rocks, key to processes, 6.
Fossil plants, indications of ancient climates and conditions, 168.
— — diagram illustration the distribution of, 177, _122_.
Fungi, fossils of, 164.
— parasitic, _119_, 164, 165, _120_.
Gamopetalæ, 84.
Gannister, 25, _14_.
Geikie, 186.
_Ginkgo_, leaf impression, 14, 7, 100, _69_.
— comparison with _Cycas_ seeds, 112.
— distribution in the past, 168.
— embryo of, 100.
— epidermis of fossil, 14, _8_, 100.
— foliage of, 99, _66_.
— only living species of genus, 98, _70_.
— possible common origin with _Cordaites_, 102.
— ripe seed of, 99, _67_.
— section of seed of, 100, _68_.
— seed structure of, 76, _57_.
— similarity to _Cordaites_, 96.
Ginkgoaceæ, 88.
Ginkgoales, 88, 98.
— description of group, 98.
— general distribution in time, 177.
Glacial epoch, 170.
_Glossopteris_, 173.
_Glyptostrobus_, 86.
Gondwanaland, 173.
Grand’Eury, 186.
Gum, 17.
Gymnosperms, 38, 41, 44, 86, 176, 179.
— connection with Pteridosperms, 124.
— general distribution in time, 177.
— relations between the groups of, 88, 89, 90.
Hairs, 54, _22_, 70.
— special forms among fossils, 70.
_Heterangium_, 119, 122, 123, 127.
— foliage of, 120.
— stem of, 120, _81_.
Hollick and Jeffrey, 89.
Horsetails, description of group, 145.
Hutton, 2.
Impression, form of fossil, _5_, 12, 13, _6_, 14, _7_, 15, 80, 81,
_59_, 60.
— treatment of specimens of, 184.
Investigators of fossil plants, 2.
Iron sulphide, 20.
Jet, 17.
Juglandaceæ, 83.
Kauri pine, 93.
Kew Gardens, 98.
Kidston, 186.
Labelling of specimens, 185.
_Lagenostoma_, 76, _56_, 118, 119, _80_.
_Laminaria_, 166.
Lapworth, 186.
Latex cells, 55, _27_.
Lauraceæ, 85.
Laurent, 186.
Leaves, starch manufacture in cells of, 58.
— fossil leaf anatomy, 59, _34_.
— general similarity of living and fossil, 58.
_Lepidocarpon_, 141, _100_.
_Lepidodendron_, 9, 10, _3_, 21, _12_, 67, _46_, 72, 75, 134, 144, 145,
157, 160, 171.
— anatomy of stem of, 136, 137, _95_, 138, _96_, 139, _97_.
— comparison of reproductive organs with those of living lycopods, 67,
_46_.
_Lepidodendron_, description of, 134.
— distribution in the past, 177.
— fructification of, 139, 140, _98_, 141, _99_.
— huge stumps of, 134, frontispiece.
— leaf bases, 10, _3_, 135, _93_.
— leaf traces of, 139, _97_.
— peculiar fructification of, 75, _54_.
— petrifaction of leaves, 21, _12_.
— rootlike organs of, 69.
— secondary thickening in, 70, _48_, 71, _49_.
— _selaginoides_, stem of, 137, _95_.
— wood of, 70, _48_, 71, _49_.
Liliaceæ, 82.
Limestone, 7, _1_, 24, 25, 36.
Lindley, 2, 186.
Literature on fossil plants, 186.
_Lithothamnion_, 166.
Liverworts, 163.
Lycopods, 38, 40, 42, 44, 67, 133, 175.
— description of group, 133.
— general distribution in time, 177.
— reproductive organs of, 67, _46_.
— secondary wood in fossil, 70, _48_, 71, _49_.
Lyell, 186.
_Lyginodendron_, 115, 116, 122.
— anatomy of stem of, 116, _78A_.
— petioles of, 117, 118, _79_.
— roots of, 117, _78B_.
— seeds of, 118, 119, _80_.
_Magnolia_, 83.
_Marattia_, 130.
Marattiaceæ, 125, 129.
— appearance of, 130.
— description of group, 129.
_Marchantites_, 163.
_Medullosa_, 72, 73, 119, 120, 121, _82_, _83_, 122, 123.
— foliage of, 121, _83_.
— probable seeds of, 121.
— steles of, 72, _50_, 73, _51_, 120.
Mesozoic, character of flora, 40.
Metaxylem, 57, _31_.
_Mycorhiza_, 165.
_Micrococcus_, 167.
Monocotyledons, 41, 44, 79.
— relative antiquity of, 81, 82.
Monostelic anatomy, 63, 126.
Mosses, scarcity of fossils of, 162.
Mosses, fossils of, 163.
Mountain building, from deposits under water, 6.
— — slow and continuous changes, 35.
_Muscites_, 163.
Mutation, 181.
_Nematophycus_, 166.
_Neuropteris_, leaf impression, _6_, 13.
— foliage of _Medullosa_, 122.
— with seed attached, 122, _85_.
_Nipa_, 85.
Nodules, 15, 16, _9_.
Nucleus, 47, _17_.
Oliver, 187.
_Osmunda_, 125.
Ovule, word unsuitable for palaeozoic “seeds”, 77.
Palisade cells, 55, _25_.
— tissue in leaves, 58.
— — — fossil leaf, 59, _34_.
Palms, 85.
Parenchyma, 55, _24_.
Petrifaction of cells, 4.
Petrifactions, 17.
— of forest débris, 18.
— treatment of specimens of, 184.
_Phyllotheca_, 173.
Plant, parts of, the same in living and fossil, 59.
— world, main families in, 44.
_Platanus_, 83.
Polypodiaceæ, 124.
Polystelic anatomy, 63, 72.
_Populus_, 83, 85.
Poroxyleæ, 88.
— description of group of, 96.
_Poroxylon_, anatomy of, 97, 116.
Primitive plants, 46.
Primofilices, 132.
Protococcoideæ, 47, _17_.
_Protodammara_, 89.
Protoplasm, 47.
Protostele, 62, 70.
Protoxylem, 57, _31_.
_Psaronius_, 129, 130.
— stem anatomy of, 131, _91_.
Pteridophytes, development of secondary wood in fossil forms of, 72.
Pteridosperms, 44, 104, 114, 131.
— description of group, 114 et seq.
— general distribution of in time, 177.
— summary of characters of, 123.
_Pteris aurita_, 62.
Quarries, 7, _1_.
_Quercus_, 83, 85.
Race senility, 180.
Ranales, 103.
Renault, 2, 156, 187.
Reproductive organs, likeness between those of living and fossil
plants, 67, _45_, _46_.
— — peculiar characters of some from the Palæozoic, 74.
— — simplicity of essential cells of, 52.
Rocks, persistence of mineral constituents, 36.
— fossils varying in according to the geological age, 37 et seq.
Roof of coal seam, 24, _13_, 25, _14_.
Roots, likeness of structure in living and fossil, 60, _35_.
_Salix_, 83.
_Sambucus_, 84.
_Schizoneura_, 173.
Sclerenchyma, 56, _26_, 59, _34_.
Scott, 2, 160, 187.
Secondary wood, development of in fossil members of families now
lacking it, 72.
Seeds, series of types from spores to seeds, 75, 76, _52_-_58_.
— position on the plant, 77, 78.
— Tertiary impressions of, 80, 81, _60_.
_Selaginella_, 75, 133, 134.
— with four spores in a sporangium, 75, _53_.
_Sequoia_, 86.
Seward, 187.
“Shade leaves”, 171.
Shale, 7, _1_, 11, 24, 25, 36.
Sieve tubes, 57, _32_.
_Sigillaria_, 142, 145.
_Sigillaria_, cast of leaf bases, 9, _2_, 144, _102_.
— description of, 144.
Silica, 17.
Silicified wood, 17, 80, 87.
Solms Laubach, 2, 187.
Specimens, treatment of, 184.
Sphenophyllales, 44, 153.
— description of, 153.
— general distribution in time, 177.
_Sphenophyllum_, 44, 153, 154, 160.
— cone of, 157, 116.
— _fertile_, 158.
— impression of foliage, 154, _112_.
— _plurifoliatum_, 153.
— sporangia of, 158, _117_.
— stem anatomy, 155, _113_, 156, _114_.
— stem in coal ball, 20.
— wood of, 156, _114_, _115_.
_Sphenopteris_, leaf impression, 11, _5_.
— foliage of Pteridosperms, 115, _77_.
Sporangium of ferns, 67, _45_.
— of lycopods, 67, _46_.
— of pteridophytes, 75, _52_, _53_, _54_.
Spores, germinating, in fossil sporangia, 68, _47_.
— peculiar structures among palæozoic examples of, 74.
— series of types from “spores” to “seeds”, 75, 76, _52_-_58_.
— tetrads of, 75, _52_, _53_, _54_.
Sporophyll, 75, _52_, _53_, _54_.
_Stangeria_, 110.
Stele, modifications of, 62, _36_-_42_.
Stems, external similarity in living and fossil, 60.
_Sternbergia_, cast of, 10, _4_.
— pith cast of _Cordaites_, 93.
_Stigmaria_, 69, 142, 143, 144, 145.
— rootlet of, 143, _101_.
Stomates, 54, _23_.
— in fossil epidermis, 14, _8_.
Stoneworts, 163.
Synclines, 23.
Taxeæ, 88, 90.
— comparison of fructification with that of Cordaiteæ, 95.
— description of, 92.
Taxeæ, fleshy seeds of, 89.
_Taxodium_, 86.
_Taxus_, 82.
Time, divisions of geological time, 34.
Tracheides for water storage, 56, 30.
Tree-ferns, 130.
_Trigonocarpus_, 11, 76, 82, 122, _84_.
— once supposed to be a Monocotyledon, 82.
— probably the seed of Medullosa, 121.
_Tubicaulis_, 127, _89_.
Unexplored world, 3.
Unicellular plants, 47, _17_.
— — division of cells in, 47, 48, _18_.
“Vascular bundles”, relation of to steles, 65, _42_.
— tissue, 57, _31_, _32_, _33_, 59.
— — continued growth of, 65, _43_.
— — importance in plant anatomy, 61 et seq.
_Viburnum_, 84, 85.
Watts, 187.
Westphalia, 19.
Wieland, 2, 102, 187.
Williamson, 2, 187.
_Williamsonia_, 104.
Wood, cells composing, 57, _31_.
— centrifugal development of, 97, _65_.
— centripetal development of, 97, _65_.
— parenchyma, 57, _31_.
— silicified, 17, 80, 87.
— solid rings of formed by cambium, 66, _44_.
— vessels of Angiosperms, 58.
Yellowstone Park, 17, 167.
Yew, 82.
_Yucca_, 82.
Zeiller, 2, 187.
Zittel, 187.
_Zygopteris_, 127.
_By the Same Author_
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Transcriber’s Notes
--Silently corrected a handful of palpable typos.
--Moved footnotes to a section immediately preceding the Index, and added
an entry for it to the Contents.
--Slightly reformatted tables to better fit dynamic flow on narrow
screens.
--Conjecturally restored one missing subtopic (“Coal, importance of”) in
the Index.
--In the text versions, delimited text in italics by _underscores_.
--In the text versions, included filenames of illustrations, for more
convenient reference (by another program).