societies, “Are the planets inhabited?” It may still be left in the
hands of young collegians, notwithstanding the fact that our largest
telescopes give only negative testimony.
In a solar eclipse in February, 1736, that was annular in shape, just
before the sun was completely hidden, the narrow horn of light seemed
to break into a series of dots, or luminous points, which, when noted
again a century later and described by Francis Baily, received the
name of “Baily Beads.” It was attempted to explain this as caused by
the moon’s mountains cutting off the last rays of sunlight, or else as
produced by irradiation. But with the advent of stronger telescopic
power the phenomenon has come to an end.
David Rittenhouse, of Norristown, whom Thomas Jefferson considered
“second to no astronomer living,” built an orrery worth a thousand
dollars, to illustrate mechanically the motions of all the planets,
and though the instrument is still treasured in the University of
Pennsylvania, and its duplicate at Princeton, among the relics of a
past age, it is assigned to the category of toys. Mural circles, much
depended upon to measure the declination of heavenly bodies, have
fallen into disuse, supplanted by improved transit instruments.
[Illustration: THREE-INCH TRANSIT, BY WARNER & SWASEY.]
XVI. PROBLEMS FOR FUTURE STUDY.
Many problems are in store for the future. The field for research still
opens wide. How the solar activity is to be maintained was answered by
Newton in the suggestion that comets falling into it kept up its supply
of matter and energy. Waterston, in 1853, propounded the thought that
meteoric matter may be the aliment of the sun. Now the prevalent theory
is that a contraction of the sun’s volume, constantly in progress,
but so slight as to be invisible to the most powerful telescope, is
competent to furnish a heat supply equal to all that can have been
emitted during historic periods.
Professor Newcomb answers the question, “How long will the sun endure?”
by saying, “The physical conclusion to which we are led by a study of
the laws of nature is that the sun, like a living being, must have a
birth and will have an end. From the known amount of heat which it
radiates we can, even in a rude way, calculate the probable length of
its life. From fifteen to twenty millions of years seems to be the
limit of its age in the past, and it may exist a few millions of years,
perhaps five or ten, in the future.”
[Illustration: CAROLUS LINNÆUS OF SWEDEN, FATHER OF MODERN BOTANY.
This illustration was prepared by a Swedish society, and represents
the famous botanist after his return from the exploration of
Lapland, and with a bunch of his favorite flower (_Linnæa
borealis_) in his hand.
]
STORY OF PLANT AND FLOWER
BY THOMAS MEEHAN,
_Vice President Academy of Natural Sciences, Philadelphia_.
Botany, in its general sense, signifies the knowledge of plants. In the
earlier periods of human history plants appealed to mankind as material
for food or medicine; and down to comparatively recent times botanical
studies were pursued mainly in these directions. Dioscorides, a Greek,
who lived in the first century of the Christian era, is the earliest
writer of whom we have knowledge that can lay a claim to botanical
distinction, but the medical property of plants was evidently the chief
incentive to his task. It was not until the beginning of the sixteenth
century that botany, in its broad sense, became a study, and Le Cluse,
a French physician, who died in 1609, may be regarded as one of its
patriarchs. Still the medical uses of plants were steadily kept in
view. The English botanist, John Gerarde, who was a contemporary of Le
Cluse, or Clusius, as botanists usually call him, wrote a remarkable
work on botany,—remarkable for his time,—but this was styled a
“Herbal,” as were other famous botanical works down to the beginning of
the present century.
Following the year 1700, the knowledge of plants individually became so
extended that systematic arrangement became desirable. The first real
advance in this direction was made by Carl Von Linné, commonly known by
its Latin form, Linnæus, a Swede, born in 1707, and whose talents for
botanical acquirements seemed almost innate. In his twenty-third year
he saw the need of a better system, and commenced at once the great
work of botanical reform. He saw that plants with a certain number of
stamens and pistils were correlated, and he founded classes and orders
on them. Flowers with five stamens or six stamens would belong to
his class pentandria or hexandria, respectively, and those with five
pistils or six pistils pentagynia, or hexagynia, accordingly; and so on
up to polyandria, or polygynia—many stamens or pistils—of which our
common buttercup is an illustration. He further showed that two names
only were all that is necessary to denote any plant, the generic name
and its adjective, as, for instance, _Cornus alba_, the white Dogwood;
and that the descriptions should be brief, covering only the essential
points wherein one species of plant differed from another. This
became known as the sexual system. It fairly electrified intelligent
circles. People generally took to counting stamens and pistils, and
large numbers took pride in being botanists because they could trace
so easily the classes and orders of the plants they met. The grand old
man died in 1778, and though his artificial system had to give way to
a more natural method, he is justly regarded as the father of modern
botany.
[Illustration: THE GREEN ROSE.
Flower with leaves for petals.]
With the incoming of the nineteenth century, botany took a rapid start.
It ceased to be a mere handmaid to the study of medicine. Chemistry,
geography, teleology, and indeed the chief foundations of biology had
become closely interwoven with botanical studies; and thus the progress
of botany through the century has to be viewed from many standpoints.
In classification, what is known as the natural system has replaced
the sexual. Plants are grouped according to their apparent
relationships. Those resembling in general character the Rose form
the order _Rosaceæ_; the Lily, _Liliaceæ_. Sometimes, however,
a striking characteristic is adopted for the family name, as
_Compositæ_, or compound flower, for the daisy and aster-flowered
plants; _Umbelliferæ_, or umbel-flowering, as in carrot or parsley;
_Leguminosæ_, having the seed vessels as legumes, like peas and beans.
[Illustration: HEAD OF WHITE CLOVER, WITH A BRANCH FROM THE CENTRE.]
Classification has, however, derived much assistance from a wholly
new branch of the science known as Morphology. This teaches that all
parts of plants are modifications of other parts. What Nature may have
intended to be a leaf may become a stem; the outer series of floral
envelopes, or calyx, may become petals; petals may become stamens;
and even pistils may become leaves, or even branches. The green rose
of the florists is a case in which the leaves that should have been
changed into petals to form a perfect rose flower have persisted in
continuing green leaves, though masquerading as petals; and it is not
unusual to find in the rose cases where the pistils have reverted
to their original destination as the analogue of branches, and have
started a growth from the centre of the flower. So in an orange, the
carpels, or divisions, are metamorphosed primary leaves. Two series of
five each make the ten divisions. Sometimes the axis starts to make
another growth, as noted in the rose, but does not get far before it
is arrested, and then we have a small orange inside a larger one, as
in the navel orange. Just the reverse occurs sometimes. The lower
series is suppressed, and only the upper one develops to a fruiting
stage, when the small red oranges known as the Tangerines are the
results. Illustrations of these transformations of one organ to another
are frequent if we look for them. The annexed illustration shows a
condition of the white clover, which, instead of the usual round head,
has started on as a raceme or spike.
These wanderings from general forms were formerly regarded as monsters,
of no particular use to the botanical student, but are now welcomed as
guiding stars to the central features of Morphology. The importance of
this branch of botany, in connection with classification, can readily
be seen.
The studies in the behavior of plants have made remarkable progress
during the century, and this also derives much aid from morphology. The
strawberry sends out runners from which new plants are formed; but,
tiring of this, eventually sends the runner upward to act as a flower
stalk. What might have been but a bunch of leaves and roots at the end
of the runner is now converted into a mass of flowers and pedicels
at the end of a common peduncle. In some cases Nature reverses this
plan. After starting the structure as an erect fruit-bearing stem, it
sends it back to pierce the ground as a root should do. This is well
illustrated by the peanut.
In the common _Yucca_, the more tropical species have erect stems;
but in the form known in gardens as Adam’s needle and thread—_Yucca
filamentosa_—the erect stem is sent down under the surface of the
ground, and is then a rhizome, instead of a caudex, or stem.
[Illustration: PEANUT.
A pod magnified.]
Modification in connection with behavior is further illustrated by
the grapevine and Virginia creeper. The whole leading shoot is here
pushed aside by the development of a bud at the base of the leaf, that
takes the place of a leading shoot. The original leader then becomes a
tendril, and serves in the economy of the plant by clinging to trees
or rocks, or in coiling around other plants in support. Great progress
has been made in this department of botany within recent years. Darwin
has shown that the tendrils of some plants continue in motion for some
time in order to find something to cling to. The grapevine especially
spends a long time in this labor if there is difficulty in reaching a
host. The plant preserves vital power all this time, but no sooner is
support found, than nutrition is cut off, and the tendril dies, though,
hard and wiry, it serves its parent plant as a support better dead
than alive. The amount of nutrition spent in sustaining motion is found
to be enormous. A vine that can find ready means of support grows with
a much more healthy vigor than one that has difficulty in finding it.
Many plants present illustrations.
Much advance has been made in the knowledge of the motions of plants
as regards their various forms. Growth in plants is not continuous;
but is a series of rests and advances. In other words it is rhythmic.
The nodes, or knots, in the stems of grasses are resting-places.
When a rest occurs, energy may be exerted in a different direction,
and a change of form result. This is well illustrated by the common
Dogwood of northern woods, _Cornus florida_ on the eastern, and
_Cornus Nuttallii_ on the western slope of the American continent. On
the approach of winter the leaf is reduced to a bud scale, and then
rests. When spring returns these scales resume growth and appear as
white bracts. In the annexed illustration the scales that served for
winter protection to the buds are seen at the apex of the bracts. In
other species of Dogwood the bud scales do not resume growth. Energy
is spent in another direction. In this manner we have an insight as to
the cause of variation, which was not perceived even so recently as
Darwin’s time. We now say that variation results from varying degrees
of rhythmic growth—force; and that this again is governed by varying
powers of assimilation.
[Illustration: OUTLINE OF A WHITE DOGWOOD FLOWER (_Cornus florida_),
SHOWING BUD-SCALES DEVELOPED TO BRACTS.]
The Darwinian view, that form results from external conditions of which
the plant avails itself in a struggle for existence, is still widely
accepted as a leading factor in the origin of species. Those which can
assume the strongest weapons of defense continue to exist under the
changed conditions. The weaker ones do not survive, and we only know of
them as fossils. This is termed the doctrine of natural selection.
The origin and development of plant-life, or, as it is termed,
evolution, has made rapid advancement as a study during the century.
That there has been an adaptation to conditions in some respects, as
contended by Mr. Darwin and his followers, must be correct. The oak
and other species of trees must have been formed before mistletoe and
other parasites could grow on them. In the common Dodder—species of
_Cuscuta_—the seeds germinate in the ground like ordinary plants. As
soon as they find something to attach themselves to, they cut loose
from mother earth and live wholly on the host. As a speculation it
seems plausible that all parasites have arisen in this way. Some,
like the mistletoe, having the power, at length, to have their seeds
germinate on the host-plant, have left their terrestrial origin in
the past uncertain. A number of parasites, however, do not seem to
live wholly on the plants they attach themselves to. These are
usually destitute of green color. The Indian pipe, snow plant of the
Pacific Coast, and Squaw root of the Eastern States are examples;
the former called ghost-flower from its paleness. These plants have
little carbonaceous matter in their structure, and hence are regarded
as having formed a kind of partnership with fungi. This is known
now as symbiosis, or living together of dissimilar organisms, each
dependent mutually. The fungus and the flowering plant in these cases
are necessary to the existence of each other. They demand nitrogen
instead of carbonhydroids. The Squaw root, _Conopholis Americana_,
though attached to the subterranean portions of the trunks of trees,
is probably sustained by the fungus material in the old bark, or even
in the wood, rather than by the ordinary food of flowering plants.
Lichens, as it is now well known, are a compound of fungi and water
weeds (algæ), and this doctrine of symbiosis is regarded as one of the
great advances of the century.
It is but fair to say that the doctrine of evolution by the influence
of external conditions in the change of form, though widely accepted
at this time, is not without strong opponents, who point to the
occasional development or suppression of parts on the same plant,
though the external conditions must be the same. For instance, there
are flowers that have all their parts regular, as in the petals of a
buttercup; and irregular, as in the snap-dragon or fox-glove. But it
has been noted that irregular flowers have pendulous stalks, while the
regular ones are usually erect. But once in a while, on the same plant,
flowers normally drooping will become erect. In these cases the flowers
are regular. In the wild snap-dragon or yellow toad-flax, _Linaria
vulgaris_, one of the petals is developed into a long spur; the other
four petals have, in early life, become connate and transformed into
parts of the flower wholly unlike ordinary petals. But now and then
the original petals will all develop spurs, resulting in the condition
technically known as peloria.
Linnæus gave this name to this condition because it was supposed to be
“monstrous,” or something opposed to law and order. Through the advance
in morphological botany we have learned to regard it as the result of
some normal law of development, innate to the plant, and which could
as well be the regular as the occasional condition. In other words,
there is no reason why Nature might not make the five-spurred flower as
continuous in a wild snap-dragon as in a columbine. Many similar facts
are used by those who question the Darwinian law of development.
[Illustration: YELLOW TOAD-FLAX.
Flower in the peloria state.]
That nutrition has more to do in the evolution of form than external
forces has received much aid, as a theory, from the advance during
recent times of a study of the separate sexes of flowers. On coniferous
trees, notably the firs, pines, and spruces, the male and female
flowers are produced separately. The female, which finally yield the
cones, are always borne on the most vigorous branches. When these
branches have their supply of nutrition shortened and become weak, only
male flowers are produced. On the other hand, branches normally weak
will at times gain increased strength, and then the male flowers give
female ones. This is often seen in corn fields. The generally weak
tassel will have grains of corn through it. It is not infrequent to
find what should normally be perfect ears on stalks weaker than usual.
In these cases the upper portion of the ear will have male flowers only.
[Illustration: GRAINED CORN-TASSEL.]
In connection with the doctrine of development, much attention has been
given during the century to fertilization of flowers and the agency of
insects in connection therewith. On the one hand it is contended that
in all probability the flowers in the earlier periods of the world’s
history had neither color nor fragrance. In this condition they were
self-fertilizers, that is, were fecundated by their own pollen. In
modern phraseology they were in and in breeders. When the struggle for
existence became necessary, those which could get a cross with outside
races became more vigorous in their progeny, and thus had an advantage
in the struggle. In brief, without an occasional introduction of new
blood, as it might be termed, there was danger of a race dying out.
To support this view, Mr. Darwin published the result of a number of
experiments. Many of them favored either side, but the average was
in favor of the view that crossing was advantageous. Against this it
has been urged that an average in such cases is not conclusive. If a
number, though the minor number of cases, showed superiority by close
breeding in his limited experiments, a new set of observations might
have changed the averages, so as to make the minor figures in one
instance the major in others. Again, it is contended that to increase
a plant by other means than by seeds must be the closest kind of
reproduction; yet some plants, coeval with the history of man, have
been continued by offsets and are as strong and vigorous as ever. The
Banana is an illustration. Under cultivation it produces only seedless
fruits. It is raised wholly from young suckers or offsets from the
roots. Mythology gives it a prominent place in the Garden of Eden, and
its botanical name, _Musa paradisiaca_, originated in this legend.
Though much has been recorded in this line to weaken the force of the
speculations that flowers late in the history of the earth developed
color and sweet secretions in order to attract insects to aid in
cross-fertilization, they are strongly supported by the fact that a
large number of species, notably of orchids, are seldom fertilized
without insect aid in pollination.
But there are anomalies even here. Some plants capture and literally
eat the insects that should be regarded as their benefactors. These
are classified as insectivorous plants. Some seem to catch the insects
in mere sport, while in the act of conveying pollen to them. These are
known as cruel plants. There are numerous illustrations of this among
the families of _Asclepias_ and _Apocynum_, the milk-weed family. In
our gardens a Brazilian climber, _Arauga_, or _Physianthus albens_,
is frequently grown for its waxy flowers and delicious odor, but the
treacherous blossoms are frequently strung with the insects it has
caught.
In the northern part of America a common wild flower of one of these
families, _Apocynum androsmæfolium_, has this insect-catching habit.
Numerous small insects meet death, and hang to the flowers like scalps
to the wild Indian.
Considerable advance has been made in vegetable physiology, though
no one has as yet been able to reach the origin of the life-power in
plants. The power that enables an oak to maintain its huge branches in
a horizontal direction, or that can lift or overturn huge rocks, or
split them apart as the lightning rifts a tree trunk, is yet unknown.
On the opposite page is an illustration of a circumstance frequently
observed, wherein even a delicate root fibre can pierce a potato or
other structures.
[Illustration: BANANA FLOWERS.]
Possibly the greatest botanical advance of the century is in relation
to cryptogamic plants, those low organisms which as mildews and moulds
are most familiar to people generally. As microscopes increase in
power, new forms are discovered. Over forty thousand species have
already been described, and we may fairly say that there are nearly
half as many forms of vegetable life invisible to the naked eye as can
be seen by our unaided visual organs. Their wants and behaviors are
very much the same as in the flowering plants or higher orders, as
they are usually termed. But there is one great difference in this,
that they feed mainly on nitrogen, and have no use for carbon. They
care little for light, but yet have an upward tendency under certain
forms, as do those which seek the light. The agarics that revel in
the darkness of a coal mine, yet curve upward as heartily as a corn
sprout in the open air. Just as in flowering plants, also, they are
mostly innocuous, and indeed many absolutely beneficial to man, a very
small portion only being poisonous, or connected with the diseases of
the human race. Even in these cases their power is closely guarded
by nature. The spores of fungi are found to require such a nice
combination of conditions before they germinate, that, unless these
occur, they will retain their vegetative power many years in a state
of absolute rest. The mycelium of the mushroom, as the real plant—the
cobwebby portion under ground—only starts to grow when just so many
degrees of heat, neither more nor less, with just so much moisture, and
the proper food, are all at hand together; and large numbers are known
to be very select in the kind of food they will make use of at all.
One genus, known as _Cordyceps_, will only start when the spore comes
in contact with the head of a caterpillar. And various species of the
genus will avoid a kind of caterpillar that another would enjoy. In our
own country we have one that feeds on the larvae of the May Beetle,
and is known as _Cordyceps Melolonthæ_. In Australia is a very pretty
species, which takes on the appearance of the antlers of a deer. This
is known as _Cordyceps Andrewsii_.
[Illustration: THE CRUEL-PLANT.
Butterfly caught in the flower.]
[Illustration: OLD POTATO PENETRATED BY ROOTLET WITH A NEW POTATO.]
The most minute of these are known as microbes. They are chiefly
composed of a single cell, in the midst of which is the protoplasm, or
material in which life resides, but the exact nature of which is still
a mystery.
[Illustration: A FUNGUS (_Cordyceps Andrewsii_) GROWING FROM THE HEAD
OF A CATERPILLAR.]
One of the most useful and fascinating studies in modern times is
Geographical Botany. It is found to have a close relation to the
history of man, and to the changes which have occurred on the surface
of the earth. Plants follow man wherever he wanders; and though every
other trace of man should be abolished on the American continent,
the plants that came with him from the Old World would enable the
future historian to follow his tracks here pretty well. No one has any
historical evidence that what is now the Pacific Ocean was once land,
and that the area between the Pacific Ocean and the Mississippi was
once a huge sea, but botany tells the plain story. Only for botany we
should not know that the land now serving as the poles was once within
the tropics; and mainly by fossil gum trees on the American continent,
and the existence still of a few plants common to Australia, have we
the knowledge of some land connection between these distant shores.
Island floras, some of the species of which are now found only in
very limited areas, tell of large tracts submerged of which only the
mountain peaks are left as small islands, lonely in a wide expanse of
water, while other islands, with only a limited number of well known
species, tell of new upheavals within modern times.