congregations of simple fibreless cells united in rows, or gathered
round one another, spreading on all sides. At the bottom of the scale
of plant life are the _Algæ_, comprising some 10,000 species, from
the minute fresh-water desmids, one-millionth of an inch in length,
with their whip-like cilia, the two-hundredth millionth of an inch
long, to the giant sea-weeds or tangles, hundreds of feet in length,
that cover thousands of square miles of ocean. The green scum of
stagnant ponds; the waving filaments in streams; the shell-coated
microscopic diatoms that people the ocean, tingeing its depths with
olive green, nourishing the whales that play therein, and whose
skeletons form deposits hundreds of miles in length; the rose and
purple weeds that flourish in shallow seas, and are cast upon their
shores, are all members of a group which is perhaps the venerablest
of living things. For although their generally fragile forms have
been fatal to their preservation as fossils, there is little doubt
that the algæ flourished in dense masses in primeval oceans, and were
the chief, if not the sole, representatives of plant-life on the
earth during millions of centuries. Like the foraminifera and other
low animal organisms, they illustrate the persistency of the earlier
forms, in virtue of their simplicity of structure, despite changing
conditions, whereas the more complex structures, by reason of the
greater delicacy of their parts, can less readily adapt themselves to
altered surroundings, and therefore have a much narrower distribution
both in time and space.
Next to the algæ in ascending order are those fantastic products of
decay, the quick-growing, short-lived _Fungi_, animal-like in their
mode of nutrition, plant-like in their fixity; then the _Lichens_,
which, it is now generally agreed, are composite plants, being a
special kind of parasite fungi growing on algæ. These are widely
spread, living after the adaptive manner of simple forms, where
nothing else can live, unwithered by the heat, unsmitten by the
frost; redeeming the earth’s desolate places, from treeless desert
flats far as the lines of enduring snow; spreading their flowerless
patches of richest colors in metallic-like stain over rock and ruin;
incrusting the trees with tint of freshness or touch of age, with
hoary fringe or mock hieroglyph; and in their decay yielding rich
soil wherein fern and flowering tree may strike root.
In the _Mosses_, whose glossy, many-colored masses weave softest
carpet over the earth, sharing in the service rendered by the humble
lichens, the cells have become more developed into rudimentary
root, stem, and leaf, manifesting still further transition toward
unlikeness in parts due to division of function. But the structure is
still cellular--_i. e._, there are no tissues and fibres. The mosses
represent the intermediate form between the lowest and the highest
cryptogams, between the green algæ--out of which the liverworts were
probably developed--and the ferns, which arose out of liverworts.
In the _Ferns_, the larger number of cells have joined together to
form fibrous vessels, lengthening of thickening in varying shape
and texture, according to the functions to be discharged by them,
resulting in the woody tissue which enters into the structure of
all the higher plants. The cells which are thus converted into
tissue cease to grow; the formative protoplasm becomes the formed,
having given up its life for the plant, and locked up in the
compacted material a store of energy for service both within the
plant and by the agency of the plant. The ferns and club-mosses and
horsetails of the present day are the dwarfed representatives of
the stately and luxuriant, although sombre, flowerless trees that
composed the dense jungles of green vegetation in the _Devonian_ and
succeeding _Primary_ periods. These are distinguished as the Era
of Fern Forests, during which our fossil fuel was chiefly formed;
and although the palm-like vegetation of the tropics more nearly
approaches its _Devonian_ prototype, it falls far behind it in size
and abundance.
II. The _Phanerogams_ have their flowers with stamens and pistils
conspicuous, and are divided, according to the formation of their
seeds, into:
1. _Gymnosperms_, or naked-seeded, the ovules not being inclosed
within a seed-vessel or ovary, but carried upon a cone, as in pines
and allied species.
2. _Angiosperms_, or cover-seeded, the ovules being inclosed within
an ovary.
This group is subdivided into (_a_) plants having one seed-leaf from
which they are developed, as palms, lilies, orchids, grasses; and
into (_b_) plants having two seed-leaves, as oaks, beeches, and all
trees and shrubs not included in the foregoing species.
In naked-seeded plants the pollen or male element falls on the
exposed ovules; in cover-seeded plants it falls on the stigma, passes
down the pistil into the seed-vessel, and enters the ovule through an
opening in it called the microphyle, or “little gate.”
While the gymnosperms are, on the one hand, most nearly allied in
the order of descent to ferns, the sombre flowers which they bear
giving them, only by strict botanical classification, a place among
phanerogams, they are, on the other hand, more complex in structure
than the single seed-leaf plants, because their bark, wood, and pith
are clearly defined, as in the double seed-leaf plants. Their lowest
representatives comprise the cycads or palm-ferns, so called from
their resemblance to palms, for which, with their crown of feathery
leaves, they are often mistaken. Next in order is the much more
varied and widely distributed conifer family, notably pines, firs,
and larches, and, lesser in importance, cedars and cypresses. A still
higher class, various in its modes of growth, marks the transition,
to angiosperms, the flowers of both having many features in common.
The single seed-leaf angiosperms have no visible separation of their
woody stuff into bark, stem, and pith, and have no rings of growth,
the wood exhibiting an even surface, dotted over with small dark
points. Their leaves have parallel veins or “nerves,” as in the
onion and tulip, and the blossom-leaves, or petals, are grouped in
threes or multiples of three. Among their several representatives we
may single out the lilies for their beauty and fragrance, and the
cereals for their value and importance, both classes being in near
connection, since the grasses from which man has developed wheat,
barley, oats, rice, and maize are, in a botanical sense, degenerate
descendants of the lily family.
The double seed-leaf plants include all the highest and most
specialized varieties. Bark, stem, pith, and concentric rings of
growth are clearly defined; the leaves are netted-veined, and the
petals grouped in fours or fives or multiples of these numbers. The
lowest class, represented by the catkin-bearers, as the birch and
alder, the poplar and the oak, and by plants allied to the nettle and
to the laurel, are nearly related to the highest gymnosperms. Next in
order are the crown-bearers, or flowers with corollas, as the rose
family, which includes most of our fruit yielders, from strawberries
to apples; while the highest and most perfect of all are plants in
which the petals are united together in bell-shape or funnel fashion.
Such are the convolvulus and honeysuckle, the olive and ash, and at
the top of the plant-scale, the family of which the daisy is the
most familiar representative. Its position among plants corresponds
to man’s position among animals. As he, in virtue of being the most
complex and highly specialized, is at their head, albeit many exceed
him in bulk and strength, so is the daisy with its allies, for like
reasons, above the giants of the forest.
The primary function for which the organs of plants known as flowers
exists is not that which man has long assumed. He once thought
that the earth was the centre of the universe until astronomy
dispelled the illusion, and there yet lingers in him an old _Adam_
of conceit that everything on the earth has for its sole end and
aim his advantage and service. Evolution will dispel that illusion.
But our delight in the colors and perfumes of flowers will not be
lessened, while wonder will have larger field for play in learning
that the colored leaves known as flowers, together with their scent
and honey, have been developed in furtherance of nature’s supreme
aim--the preservation and increase of the species. And truly the
contrivances to secure this which are manifest in plant-life are
astounding even to those who perceive most clearly the unity of
function which connects the highest and lowest life-forms together.
It is difficult, nay, wellnigh impossible, to deny the existence of a
rudimentary consciousness in the efforts of certain plants to secure
fertilization. Take, for example, the well-known aquatic plant,
_Vallisneria spiralis_. When the male flowers detach themselves and
float about the water, the female flowers develop long spiral stalks
by which to reach them, and become fertilized by the discharge of
pollen on their pistils. Most flowers have their male and female
organs within the same petals, and in some cases fertilize themselves
by scattering the pollen from the bursting stamens on the stigma or
head of the pistil. But nature is opposed to this; “tells us in the
most emphatic manner that she abhors perpetual self-fertilization,”
with its resultant puny and feeble offspring; and we find a number
of contrivances to prevent this, and to secure fertilization by the
pollen of another plant, to the abiding gain all round of the plant,
whose blood, as we may say, is thus mixed with that of a stranger.
Two agencies--insects and the wind--undesignedly effect this; while
in the dispersion of the matured seed, birds and other animals play
an important, although equally unconscious, part.
Plants which are wind-fertilized have no gayly colored petals or
sepals, and do not secrete water. Such are the naked-seeded groups
whose sombre flowers are borne on dull brown cones; and, among
cover-seeded groups, grasses and rushes, with their feathery flowers;
and willows and birches, with their long waving clusters of catkins.
All of these provide against the fitfulness of the wind, which is
as likely to blow the pollen one way as another, by producing it in
large quantities.
Plants which are insect-fertilized seek to attract their visitors
by secreting honey and developing colored floral organs. The way in
which this came about is probably as follows:
The common idea about flowers is that they are made up of petals
and sepals, whereas the _essential_ parts are the stamens and
pistils--_i. e._, the male, or pollen-producing organs, and the
female, or seed-containing organs. The earliest flowers consisted of
these alone, having no colored whorl of petals within another colored
whorl of sepals, but were only scantily protected by leaves, as are
many extant species. These the food-seeking insects then, as now,
visited for the sake of the pollen, to the detriment of the plant,
which lost the fertilizing stuff and gained nothing in return. To
arrest this, certain plants began, especially when in the act of
flowering, to secrete honey and store it in glands or nectaries,
or near their seed-vessels, where the insects could not get at it
without covering their bodies with some of the pollen, which they
rubbed on the pistils of the plant next visited, and thus fertilized
the ovule, provided that the plants were nearly related. Honey is
sweeter to the taste than pollen, and the plants that produced the
most honey stood the better chance of visits from insects, and
therefore of fertilization, to the advantage of this species over
others. As a rule, those which secrete honey have hairy coverings
at the base of the petals, or other contrivances to prevent it
being washed out by the rain or dew, or seized by useless insects,
and we find curious interrelations established between plants and
their desired visitors. Certain flowers adapt themselves to certain
insects, and _vice versâ_, as where the plant has secreted the
honey at the bottom of a long tube and the insect has developed a
correspondingly long proboscis to gather it. By these and kindred
devices the pollen is preserved for its sole function, the energy
of the plant being conserved in the smaller quantity which it has
to produce. As the honey was secreted as counter-attraction to the
pollen, so the colored floral envelopes were developed to attract
the insects, to the honey-secreting plant, and those floral whorls,
both of petals and sepals, are modified or transformed stamens
which have exchanged their function of pollen-producers for that of
insect-allurers. And as both stamens and pistils are leaves aborted
or modified for the special function of reproduction, Goethe’s
well-known generalization that the leaf is the type of the plant has
a large measure of truth in it.
But before speaking further about color-development in plants, it may
be useful to say a little about color itself. Since everything is
black in the dark, and moreover has no color in itself, it follows
that color is in some way a property of light. Now light, which is
itself invisible, is due to vibrations or oscillations set up in all
directions by any luminous body--whether the sun or a rushlight--in
the ethereal medium which pervades all space, and is composed of
rays of different refrangibilities--_i. e._, change of direction
in passing from one medium to another. White light is due to a
combination of all these rays, ranging through innumerable gradations
of color, from red to violet, and it is to the absence of one or
more of them that the infinite variety of colors is due. If a body
is quite opaque, or otherwise so constituted as to absorb none of
the rays, it appears white; if it absorbs them all it appears black;
if it absorbs green, blue, and violet, and not red, it appears red;
if it absorbs red, orange, and violet and returns or reflects green,
it appears green. The colors which bodies reflect are therefore
regulated by their structure; the way in which their molecules are
arranged determines the number and character of the light vibrations
or ether waves which are returned to the eye and which rule the color
we see--_e. g._, charcoal and the diamond are both pure carbon; the
dull opacity of the one and the trembling splendor of the other are
solely due to the arrangement of the several molecules of each.
It is thus obvious that any change in the nature or structure of a
thing is accompanied by change in its color, and to this cause the
various pigments in plants are to be referred.
All growth involves expenditure of the energy which the plant has
stored within itself, and which becomes active when the hydrocarbons
combine with oxygen, resulting in cellular change, and appearance of
other colors than the green, which is due to chlorophyl. Thus may be
explained the color of sprouting buds and young shoots and the more
or less intensified colors of leaves and flowers--one and all due to
oxidation, the minutest changes inducing subtle variations in color.
Whichever plants made the most show of color would the sooner catch
the eye of insects, however dim their perception of the difference
in colors might be, and would thus get fertilized before plants
which made less display. Thus have insects been the main cause in
the propagation of flowering plants; the plants in return developing
the color-sense in insects. The flower nourishes the insect, the
insect propagates the flower. Other contrivances to meet the need
for fertilization might be cited, as the markings upon the petals
to guide the insect to the nectary; the exhalation of scent by
inconspicuous flowers, or by such as would attract visitors at night,
and so forth; but enough has been adduced to show what is the chief,
if not the sole, function discharged by flowers--the attraction
of insects to aid in securing cross-fertilization. Nor does the
provision stop here. The fertilized seed is not left to chance,
but, like the fertilizing pollen, is intrusted to secondary agents,
to the care of the birds and the breezes. Where not scattered by
the bursting of the ovary it is winged with gossamer shafts, as
in the dandelion, and carried by the wind, floated on gentlest
zephyr or rushing storm to a genial soil. Such wind-wafted seeds,
like wind-fertilized flowers, are rarely colored; neither are the
seeds of the larger trees, since their abundance ensures notice by
food-seeking animals; nor the nuts, which are protected by shelly
coats. But other seeds inwrap themselves in sweet pulpy masses,
called fruits, whose skins brighten as they ripen, and attract the
eye of fruit-loving birds and beasts. The seeds pass through their
stomachs undigested, and are scattered by them in their flight over
wide areas. As with the brightest-hued and sweetest-scented flowers,
so it is with the brightest and juiciest fruits; they sooner attract
the visitor whose services they need, and thus gain advantage over
less-favored members of their species, developing by the selective
action of their devourers into the finest and pulpiest kinds.
PLANT GEOGRAPHY
--LOUIS FIGUIER
We can distinguish in Europe three great botanical regions. 1. The
region of the North; 2. The Middle region; and 3. The region of the
South, or Mediterranean.
The Northern region comprehends Lapland, Iceland, Sweden, Norway, and
the northern provinces of Russia. The vegetation is monotonous; the
ligneous species form only the one-hundredth part of the plants;
the cryptogams predominate. The trees are principally coniferous
and amentaceous. The oak, the hazel, and poplar are arrested at
60° N. lat.; the beech, the ash, and the lime at 63°; the conifers
at 67°; barley and oats can be cultivated up to 70°. Spitzbergen,
the most northerly island of Europe, situated between 76° 30′ and
81°, contains only ninety-three species of phanerogamous plants,
belonging principally to the families of _Graminaceæ_, _Cruciferæ_,
_Caryophyllaceæ_, _Saxifragaceæ_, _Ranunculaceæ_, and _Compositæ_.
Among these plants there is scarcely a single tree or shrub, but only
an under-shrub, _Empetrum nigrum_, and two small creeping willows.
Martius, to whom botanical geography is indebted for many valuable
observations, made a voyage along the western coast of Norway, from
Drontheim to North Cape, in recording which he has traced with a
vigorous hand the picturesque vegetation of that country. “While
disembarking I was much surprised to see cherry-trees bearing fruit
about the size of peas. Lilac, mountain ash, black currant, and _Iris
germanica_ were covered with expanding flowers. My astonishment
ceased, however, when I learned that the spring had been a very fine
one. The most common tree in the gardens and streets is the mountain
ash. I remarked also four oaks (_Quercus Robur_), which appeared to
suffer from the cold; in fact, upon the west coast of Norway the
northern limit of the oak lies half a degree south of Drontheim. The
ash is a more hardy tree, but it never attains the dimensions of the
oak in Sweden, and in latitude 61° 18′ I noted the last of them. The
lime lives at Drontheim, as do the poplar (_P. balsamifera_) and the
horse chestnut; the lilac blooms in every garden. All fruit trees can
only be cultivated as espaliers. Even in the most favored situations,
the apple, pear, and plum do not ripen every year. In the environs of
Drontheim, groups of elder, birch, fir, intermingled with ash, maple,
aspen, bird-cherry, hazel, juniper, and willow crown the heights. The
fields are dry and well exposed, while the meadows occupy the lower
ground.
“Toward the north I pushed on to Cape Ladehamer, which is crowned
with light-foliaged birches. In the fields and by the roadsides I
found a great many plants which occupy similar situations in France.
Nevertheless,” he continues further on, “the eye of the botanist
was rejoiced by the sight of a vegetation belonging at once to the
Flora of the Boreal regions of the Alps and of the seashore.” In the
thickets grow _Geranium sylvaticum_, _Aquilegia vulgaris_, _Aconitum
septentrionale_, _Pedicularis lapponica_, _Trientalis europæa_,
_Paris quadrifolia_; in the less sheltered places, _Cornus suecica_,
_Vaccinium Vitis-idæa_, _Polygonum viviparum_; in the marshes, the
Bleaberry and _Geum rivale_; upon the sandy seashore, _Plantago
maritima_, _Glaux maritima_, _Elymus arenarius_, _Triglochin
maritimum_, and many others equally interesting to the botanist.
[Illustration: Six Familiar Tree Forms
1. Willow; 2. Oak; 3. Sycamore; 4. Cedar; 5. Chestnut; 6. Olive]
“At Bodoë, in 67° 16′,” he continues, “I saw for the first
time houses covered with turf, upon which grew many tufts of
grass. According to my custom, I first examined the cultivated
vegetables, but I saw only a few potatoes, peas, radishes, a few
gooseberry-trees without fruit, and some fields of barley and rye. In
the meadows just above the sea-level I found some plants which would
have demonstrated to me, in the absence of other proofs, how much the
climate of this country approaches that of the most elevated Alpine
regions.
“At Hammerfest, which is under 70° 48′ north latitude, all attempts
at cultivation had disappeared. The energies of the place are turned
to commerce; it is from curiosity rather than for profit or utility
that a few vegetables are cultivated.
“Near the city I observed rich meadows, that were cut once a year,
and some herds of half-wild reindeer, which grazed and roamed
about freely. We shall deceive ourselves, however, if we consider
Hammerfest a dull or melancholy city. Its principal streets, on the
contrary, consist of very fair new wooden houses, well ordered,
and in all respects comfortable. These are the habitations of the
better class of inhabitants. The houses of the lower classes are
poorer and older; borrowing, however, a particular charm from the
flowery turf with which they are covered. The roofs are formed of
great squares of turf, on which a number of plants have germinated
and grow vigorously. In seeing these aerial gardens I have for the
first time been able to comprehend the phrase ‘_in tectis_’, which
often occurs in the writings of Linnæus, indicative of the locality.
In short, it was upon the roofs of houses that the learned botanist
of Upsala herborized at Hammerfest; indeed, I frequently borrowed
a ladder myself from the proprietor in order to gather the plants
which grew round the chimney of one of these picturesque old houses.
What I often found there were _Cochlearia anglica_, _Lychnis diurna_,
_Chrysanthemum inodorum_, Shepherd’s Purse, _Poa pratensis_, and _P.
trivialis_. In autumn, when the flowers of _Chrysanthemum inodorum_
are in full bloom, these hanging meadows rival in beauty those of
our own more genial climate, and give the city a smiling physiognomy
which contrasts most happily with the severe aspect of surrounding
Nature. _Ranunculus glacialis_, _Arabis alpina_, _Silene acaulis_,
_Saxifraga nivalis_, Bilberries, _Diapensia lapponica_, _Salix
reticulata_, _S. herbarcea_, etc., grow in the neighborhood.
“How great was my surprise on landing at the North Cape, in latitude
71°, to find myself in the middle of the richest subalpine meadows
that can be imagined! high and tufted grass, which reached my knees.
I found here, in short, at the northern extremity of Europe, the
flowers which had so often attracted my admiration at the foot of
the Swiss Alps; there they were, as vigorous, as brilliant, and much
larger than among the mountains.”
The mid-European region includes southern Russia, Germany, Holland,
Belgium, Switzerland, the Tyrol, and the British Isles, Upper Italy,
and the greater part of France. This region, whose exact limits it
would be difficult to trace, is very different from the preceding. It
is milder, more temperate; its woods and forests consist essentially
of oak (_Quercus Robur_), to which we may add chestnut, beech,
birch, elm, hornbeam, alder, etc.; but the oak predominates. These
trees, all of which lose their leaves during winter, give to the
landscape a very peculiar feature, varying with the season. This
region is especially favorable to the cultivation of the cereals. An
oblique line, drawn from east to west, with certain inflections of
its course, but ranging between the forty-seventh and forty-eighth
parallel, and inclining a little toward the north, would divide it
into two zones--one, the Northern, in which the vine and the mulberry
yield to the rigor of winter, whose forests are chiefly composed of
conifers, where the culture of the apple and pear takes their place,
and which includes more _Cyperacæ_, _Rosaceæ_, and _Cruciferæ_; the
other, the Southern, characterized by the culture of the vine, the
mulberry, and the maize, and in which _Labiatæ_ begin to predominate.