characters. His principles of classification are vague and uncertain;
they only serve to announce the dawn of a new day which was soon to
rise on the science. The few lines which we have quoted from the
preface of the _Prodromus_ reveal, as through a fog, the mere idea of
a natural system. It is Bernard de Jussieu, demonstrator of botany
in the Jardin des Plantes at Paris, to whom belongs the glory of
working out the true natural system which was first established
in principle by Ray, although it does not appear that Jussieu was
acquainted with the works of the English philosopher.
“Others may perhaps have extended the limits, but he was the first
to show the way, to trace the method, to establish the principles.
Jussieu consigned his discoveries to no book, but in the Gardens
of Trianon the mind of the author is recognized. In examining the
characters, he remarked that some were more general than others,
and these furnished the first division. He recognized that the
germination of the seed and the respective disposition of the sexual
organs were the two principal and most persistent characteristics.
He adopted them, and made them the basis of the arrangement which he
established at the Trianon in 1759.”
Four years later, another French botanist, Michel Adanson, a
naturalist remarkable for the originality of his views and the
extent of his conceptions, published a book upon the families of
plants. He proposed a particular course for arriving at the true
natural method. But what was that course? He proposed classing all
the plants known according to a great number of artificial systems;
and after considering them from all possible points of view, he
proposed to arrange in the same group those plants which were classed
as allies in the greatest number of systems. In this manner Adanson
created sixty-five artificial systems, and by their comparison he
formed fifty-eight families. He was the first to trace the precise
characters and details of all these families; his work in this
respect is far superior to those of his predecessors.
The year 1789 was the date of the real establishment of natural
families among vegetables. It was in this year that Laurent de
Jussieu published his celebrated _Genera Plantarum_, which marked
a new era in the science of botany, and hastened the advent of a
natural system of zoological classification as well.
The catalogues of the Gardens of the Trianon, prepared by Bernard
de Jussieu, and his conversations with his nephew, were the source
whence the latter drew his inspirations.
That the French botanist had acquainted himself with the principles
of Ray’s classification is unquestionable; in fact, Jussieu
possessed the happy art of adapting the labors of others to
perfecting his own conceptions. He made use of the simple language
and accurate descriptions of Linnæus, divested of his pedantry. Ray
had demonstrated that rigorous definitions in natural history are
impossible, and, accepting the decision, Jussieu does not attempt to
found his family orders or genera on any single character belonging
to objects so various in their habits and organization as plants.
During the last forty or fifty years other botanists have attempted
various systems of classification. In those of De Candolle,
Endlicher, Lindley, and of Brongniart, the distribution of plants
into groups is founded, as in those of Ray and Jussieu, on the
consideration of the cotyledons; of the polypetalous, monopetalous,
and apetalous flowers; finally, upon the mode of insertion of the
stamens. Names have changed; things remain the same; and if in
their details the series of families or orders present certain
differences, it only arises from the fact that a linear series is
incompatible with the natural system, and that the connection of
the intermediate groups may be expressed in various ways without
affecting the general principles of the system. “The formation
of natural orders by Jussieu,” says Ad. Brongniart, “is even now
a model which directs botanists in their studies to the affinity
which connects the various forms of vegetation. Many of these orders
have doubtless been subjected to important modifications, both in
extending and limiting them; the numbers have been more than doubled;
but the number of species now known is increased more than sixfold.
Since the publication of the _Genera Plantarum_, many points in the
organization of plants which were either scarcely touched upon or
were altogether unsuspected, have now been considered, and it is
found that they do not destroy, but confirm, and perfect the work of
Jussieu. One is even astonished to find that the numerous discoveries
in the anatomy and organography of plants since the beginning of
the century have not introduced greater modifications into the
constitution of the natural groups admitted by the author of the
_Genera Plantarum_. It is here that we recognize the sagacity of the
savant who established them, and the soundness of the principle which
guided him.”
[Illustration: Flowers, Curious and Beautiful
1, Edelweiss; 2, Nigella Arvensis; 3, Parnassia; 4, Rhododendron;
5, Ophrys Arachnites; 6, Cypripedium Calceolus; 7, Nepenthes; 8,
Gnaphalium Dioicum; 9, Ophrys Muscifera]
The natural classification of plants, their distribution into
families, well defined, and founded upon affinities, have been
perfected and placed upon a basis more and more certain in our
own days. Botanists have set themselves the task of unraveling and
establishing the characters which dominate, and those which are
subordinate, in each family; numbers have spread themselves over
the globe, exploring the most distant regions, interrogating the
solitudes of forests and plains which no European had hitherto
visited, and have studied in their native wilds many exotic plants,
comparing them with already known species, thus giving us a means of
pointing out more precisely the tribes, genera, and species of each
natural family. Monographs of a great number of such families have
thus been written with great research. The study of the formation and
evolution of organs; the discovery of the true mode of reproduction
in cryptogams, still unknown in Jussieu’s time; the investigation
of the inflorescence, of the fruits, of the ovules, of the embryos,
have furnished elements for perfecting the limits of families and
advancing natural classification.
Auguste Pyramus de Candolle is one of the botanists of the last
century who has most contributed to the general adoption of natural
families. His _Essai sur les Propriétés des Plantes_ is celebrated
for the knowledge which it displays of the comparative physiological
and medicinal action of vegetables, and the physical organization
which naturally connects certain plants as a group. His _Prodromus
Systematis Naturalis Regni Vegetabilis_, continued by his pupils and
his son, is a wonderful work for the extent and precision of its
details.
In Great Britain, from the days of Ray, we have always had zealous
followers of the science of botany, more especially in the class
which may be called field botanists. Withering, Sir James Edward
Smith, and hundreds of followers more or less eminent, employed
their leisure in the fascinating and healthy pursuit of plants, and
perhaps the most valuable contributions to science are the detailed
descriptions of species, with their habits and habitats, with which
they have enriched our botanical literature. Nor was the study of
the physiology of plants--a science which may be said to owe its
existence to the researches of Grew and Malpighi--neglected. To the
former belongs the merit of having pointed out the difference between
seeds with one and seeds with two cotyledons, on which Ray founded
the first division of his system of classification.
The German botanists have always been distinguished for their patient
and laborious investigations; and it was reserved for the first of
Germans, the poet Goethe, to effect the last great revolution that
the ideas of botanists have undergone. In 1790, shortly after the
appearance of De Jussieu’s _Genera_, he published a pamphlet on
the _Metamorphoses of Plants_. At this time the functions of the
organs of plants were supposed to be pretty well understood. The
notion had, however, existed in a form more or less vague, from the
times of Theophrastus, that the various parts of the flower were
mere modifications of leaves, although their appearance was very
different--a doctrine which Linnæus seems to have entertained at
one time, as he speaks, in his _Prolepsis Plantarum_, of the parts
of a flower being mere modifications of leaves whose period of
development was anticipated. Goethe’s mind was, as he himself tells
us, one more adapted to see agreements in things than to mark their
distinctions. We are not surprised to find, therefore, that he takes
up this theory, and demonstrates that the organs to which so many
different names are applied--namely, the bracts, calyx, corolla,
stamens, and pistil--are all modifications of the leaf: the bract
being a contracted leaf; the calyx and corolla a collection or whorl
of several; the stamens contracted and colored leaves; and the
pistils leaves rolled up upon themselves and variously coherent.
These views of the poet met at first with little attention from
botanists, and we are chiefly indebted to Robert Brown for the
elucidation of Goethe’s theory. In his _Prodromus of the Plants of
New Holland_, and in many papers in the _Linnæan Transactions_, he
demonstrates its truth as well as its practical value; showing, by
the use of the microscope, that the law was applicable not only to
the external parts of plants, but that it was followed in their
development also. Robert Brown contributed largely to perfecting the
natural method of classification. His great work upon the flora of
Australia has greatly extended the circle of our studies for that
comparison of characters which is the basis of botanical genera and
tribes.
The number of families of flowering plants admitted in the present
day, as the result of the investigations of the eminent men whose
names have been mentioned, and many others which could not be quoted
here without swelling our pages to undue proportions, number
three hundred and three; and many of these are again subdivided by
botanists who have made certain families their special study.
The primary groups into which flowering plants are divided, and in
which therefore the families or orders are themselves comprised in
the classification at present accepted, being founded upon the degree
of cohesion and adhesion in the petals and stamens, are undoubtedly
somewhat artificial. The problem of how the orders are themselves
to be combined into natural groups is one which still engages the
attention of systematic botanists.
The vegetable kingdom is divided by Dr. Lindley into seven classes:
FLOWERLESS PLANTS (CRYPTOGAMS)
{ A Thallus is a fusion of root,
{ stem, and leaves into one general
{ mass, and Thallogens are
{ Stems and leaves { destitute of breathing pores,
I. THALLOGENS { imperceptible. { and multiply by the formation
{ of spores, in their interior or
{ upon their surface.
{ Beyond Thallogens are multitudes
{ of species, flowerless
{ like them, but approximating
{ to more complex structures,
{ sometimes acquiring the stature
{ of lofty trees with breathing
{ Stems and leaves { pores; their leaves and stems
II. ACROGENS { quite perceptible. { distinctly separated; they multiply
{ by reproductive spores
{ like the Thallogens. Their
{ stem, however, does not increase
{ in diameter, but at their
{ summit, as the name of the
{ class indicates.
FLOWERING PLANTS (PHANEROGAMS)
{ The Rhizogens are a collection
{ of anomalous plants,
{ mostly leafless and parasitical,
{ having the loose cellular organ-
{ ization of Fungi, although
{ traces of a spiral structure are
{ usually found among their
{ tissues. Some of them spring
{ directly from the shapeless cell-
III. RHIZOGENS { Fructification { ular mass which serves at once
{ springing from { for stem and root, and seems
{ a Thallus. { to be analogous to the Thallus
{ of the Fungi. Their flowers
{ resemble those of more perfect
{ plants; their sexual organs are
{ complete, but their embryo,
{ which is without any visible
{ radicle or cotyledon, simply
{ appears to be a spherical or
{ oblong homogeneous mass.
{ In Endogens the embryo
IV. ENDOGENS { Cotyledon single. { has but one cotyledon; the
{ Permanent woody { leaves have parallel veins; the
{ stem confused. { trunk contains bundles of spiral
{ Leaves parallel- { and dotted vessels, surrounded
{ veined. { by wood cells, arranged in a
{ confused manner.
V. DICTYOGENS { Cotyledon single.
{ Wood of the stem, { Dictyogens are distinguished
{ when perennial, { from Endogens by the stems,
{ arranged in rings { which have concentric circles,
{ concentric with { and the leaves which fall off
{ the veined pith. { the stem by a clean fracture.
{ Leaves netted.
VI. GYMNOGENS { Cotyledons, two or
{ more. Wood of the { Gymnogens are Exogens
{ stem in concentric { which have no style or stigma,
{ rings, and youngest { the reproductive organs being
{ at the circumfer- { so constructed that the pollen
{ ence. Seeds quite { falls immediately upon the
{ naked. { ovules.
{ Exogens have an embryo with
{ two or three more cotyledons;
{ leaves with netted veins;
{ Cotyledons, two. { the trunk consisting of woody
{ Wood with concen- { bundles, composed of dotted
VII EXOGENS { tric rings. Leaves { vessels and woody fibres;
{ netted-veined. { arranged round a central pith,
{ Seeds inclosed in { either in concentric rings or
{ seed-vessels. { in a homogeneous mass, but
{ always having medullary plates
{ forming rays from the centre
{ to the circumference.
FRUITS AND SEEDS
--LORD AVEBURY
Fruits and seeds, though not generally so conspicuous as flowers, are
not less interesting.
In considering them, it is fortunately not necessary to use many
technical terms, though it is impossible to avoid them altogether.
In order to understand the structure of the seed, we must commence
with the flower, to which the seed owes its origin. Now, if you take
such a flower as, say, a geranium, you will find that it consists of
the following parts: Firstly, there is a whorl of green leaves, known
as the sepals, and together forming the calyx; secondly, a whorl of
colored leaves, or petals, generally forming the most conspicuous
part of the flower, and called the corolla; thirdly, a whorl of
organs more or less like pins, which are called stamens, in the heads
or anthers of which the pollen is produced. These anthers are in
reality, as Goethe showed, modified leaves; in the so-called double
flowers, as, for instance, in our garden roses, they are developed
into colored leaves like those of the corolla, and monstrous flowers
are not infrequently met with, in which the stamens are green leaves,
more or less resembling the ordinary leaves of the plant. Lastly, in
the centre of the flower is the pistil, which also is theoretically
to be considered as constituted of one or more leaves, each of which
is folded on itself, and called a carpel. Sometimes there is only one
carpel. Generally the carpels have so completely lost the appearance
of leaves, that this explanation of their true nature requires a
considerable amount of faith, though in others, as for instance
in the Columbine (Aquilegia), the original leaf-form can still be
traced. The base of the pistil is the ovary, composed of one or more
carpels, in which the seeds are developed. I need hardly say that
many so-called seeds are really fruits; that is to say, they are
seeds with more or less complex envelopes.
We all know that seeds and fruits differ greatly in different
species. Some are large, some small; some are sweet, some bitter;
some are brightly colored; some are good to eat, some poisonous; some
spherical, some winged, some covered with bristles, some with hairs;
some are smooth, some very sticky.
We may be sure that there are good reasons for these differences.
In the case of flowers much light has been thrown on their various
interesting peculiarities by the researches of Sprengel, Darwin,
Müller, and other naturalists. As regards seeds also, besides
Gærtner’s great work, Hildebrand, Krause, Steinbrinck, Kerner,
Grant Allen, Wallace, Darwin, and others, have published valuable
researches, especially with reference to the hairs and hooks with
which so many seeds are provided, and the other means of dispersion
they possess. Nobbe also has contributed an important work on seeds,
principally from an agricultural point of view, but the subject as a
whole offers a most promising field for investigation.
It is said that one of our best botanists once observed to another
that he never could understand what was the use of the teeth on the
capsules of mosses. “Oh,” replied his friend, “I see no difficulty in
that, because if it were not for the teeth, how could we distinguish
the species?”
We may, however, no doubt, safely consider that the peculiarities of
seeds have reference to the plant itself, and not to the convenience
of botanists.
In the first place, then, during growth, seeds in many cases require
protection. This is especially the case with those of an albuminous
character. It is curious that so many of those which are luscious
when ripe, as the peach, strawberry, cherry, apple, etc., are
stringy, and almost inedible, till ripe. Moreover, in these cases,
the fleshy portion is not the seed itself, but only the envelope,
so that even if the sweet part is eaten the seed itself remains
uninjured.
On the other hand, such seeds as the hazel, beech, Spanish chestnut,
and innumerable others, are protected by a thick, impervious shell,
which is especially developed in many Proteaceæ, the Brazil-nut, the
so-called monkey-pot, the cocoanut, and other palms.
In other cases the envelopes protect the seeds, not only by their
thickness and toughness, but also by their bitter taste, as, for
instance, in the walnut. The genus Mucuna, one of the Leguminosæ, is
remarkable in having the pods covered with stinging hairs.
In many cases the calyx, which is closed when the flower is in
bud, opens when the flower expands, and then after the petals have
fallen closes again until the seeds are ripe, when it opens for the
second time. This is, for instance, the case with the common herb
Robert (Geranium robertianum). In Atractylis cancellata, a south
European plant, allied to the thistles, the outer envelopes form an
exquisite little cage. Another case, perhaps, is that of Nigella,
the “devil-in-a-bush,” or, as it is sometimes more prettily called,
“Love-in-a-mist,” of old English gardens.
Again, the protection of the seed is in many cases attained by
curious movements of the plant itself.
The sleep of flowers is also probably a case of the same kind, though
it has, I believe, special reference to the visits of insects; those
flowers which are fertilized by bees, butterflies, and other day
insects, sleep by night, if at all; while those which are dependent
on moths rouse themselves toward evening, and sleep by day. On the
other hand, in the dandelion (Leontodon), the flower-stalk is upright
while the flower is expanded, a period which lasts for three or four
days; it then lowers itself and lies close to the ground for about
twelve days, while the fruits are ripening, and then rises again when
they are mature. In the Cyclamen the stalk curls itself up into a
beautiful spiral after the flower has faded.
The flower of the little Linaria of our walls (L. cymbalaria) pushes
out into the light and sunshine, but as soon as it is fertilized it
turns round and endeavors to find some hole or cranny in which it may
remain safely ensconced until the seed is ripe.
In some water-plants the flower expands at the surface, but after
it is faded retreats again to the bottom. This is the case, for
instance, with the water lilies, some species of Potamogeton, Trapa
natans, etc. In Valisneria, again, the female flowers are borne
on long stalks, which reach to the surface of the water, on which
the flowers float. The male flowers, on the contrary, have short,
straight stalks, from which, when mature, the pollen detaches
itself, rises to the surface, and, floating freely on it, is wafted
about, so that it comes in contact with the female flowers. After
fertilization, however, the long stalk coils up spirally, and thus
carries the ovary down to the bottom, where the seeds can ripen in
greater safety.
Farmers have found by experience that it is not desirable to grow the
same crop in the same field year after year, because the soil becomes
more or less exhausted. In this respect, therefore, the powers of
dispersion possessed by many seeds are a great advantage to the
species. Moreover, they are also advantageous in giving the seed a
chance of germinating in new localities suitable to the requirements
of the species. Thus a common European species, Xanthium spinosum,
has rapidly spread over the whole of South Africa, the seeds being
carried in the wool of sheep.
There are a great many cases in which plants possess powers of
movement directed to the dissemination of the seed.
Some plants even sow their seeds in the ground. In other cases the
plant throws its own seeds to some little distance. This is the
case with the common Cardamine hirsuta, a little plant six or eight
inches high, which comes up of itself abundantly on any vacant spot
in kitchen-gardens or shrubberies. The seeds are contained in a pod
which consists of three parts, a central membrane, and two lateral
walls. When the pod is ripe the walls are in a state of tension. The
seeds are loosely attached to the central piece by short stalks.
Now, when the proper moment has arrived, the outer walls are kept in
place by a delicate membrane, only just strong enough to resist the
tension. The least touch, for instance, a puff of wind blowing the
plant against a neighbor, detaches the outer wall, which suddenly
rolls itself up, generally with such force as to fly from the plant,
thus jerking the seeds to a distance of several feet.
In the common violet, besides the colored flowers, there are others
in which the corolla is either absent or imperfectly developed. The
stamens also are small, but contain pollen, though less than in the
colored flowers. In the autumn large numbers of these curious flowers
are produced. When very young they look like an ordinary flower-bud,
the central part of the flower being entirely covered by the sepals,
and the whole having a triangular form. When older, they look at
first sight like an ordinary seed capsule, so that the bud seems to
pass into the capsule without the flower-stage.
Some species of Vetch, and the common Broom, throw their seeds,
owing to the elasticity of the pods, which, when ripe, open suddenly
with a jerk. Each valve of the pod contains a layer of woody cells,
which, however, do not pass straight up the pod, but are more or less
inclined to its axis. Consequently, when the pod bursts, it does not,
as in the case of Cardamine, roll up like a watch-spring, but twists
itself more or less like a corkscrew.
I have mentioned these species because they are some of the commonest
British wild flowers, so that during the summer and autumn we may in
almost any walk observe for ourselves this innocent artillery. There
are, however, many other more or less similar cases.
Thus the Squirting Cucumber (Momordica elaterium), a common plant
in the south of Europe, and one grown in some places for medicinal
purposes, effects the same object by a totally different mechanism.
The fruit is a small cucumber, and when ripe becomes so gorged with
fluid that it is in a state of great tension. In this condition a
very slight touch is sufficient to detach it from the stalk, when
the pressure of the walls ejects the contents, throwing the seed
some distance. I have seen them even in England sent nearly twenty
feet; but in a hotter climate the plant grows more vigorously, and
they would doubtless be thrown further. In this case, of course, the
contents are ejected at the end by which the cucumber is attached to
the stalk. If any one touches one of these ripe fruits, they are
often thrown with such force as to strike him in the face.