found in the peculiar circumstances of the circumpolar regions. In
the tropics, trees and plants can thrive and blossom all the year
round; and even in temperate countries most small herbs and weeds
gain by keeping their foliage throughout the winter; but big trees in
cold climates would suffer much by the tearing and strewing of their
leaves in winter gales, while they would obtain little advantage by
retaining them on the tree during the long chilly season. Hence, if
any tree happened to possess any arrangement by which dead or dying
leaves could be removed without injury to the permanent tissues,
while, at the same time, the useful materials were withdrawn into
the young bark to await the spring awakening, such a tree would
obviously enjoy an advantage in the struggle for existence, and would
be likely to outstrip its evergreen neighbors in rigorous climates.
Now, as a matter of fact, the germ of such an arrangement is found
even in many herbs or small shrubs, such as, for example, the common
pelargoniums or “scarlet geraniums” of our flower-gardens. Everybody
who has ever kept these familiar plants in his own rooms must have
noticed how easily the dead leaves separate from the stem at their
base, by means of the swollen cellular mass where the leaf-stalk
joins the axis. All that the forest trees of northern climates had
to do, then, was just to take advantage of this nascent provision,
wherever it existed (mark this prior necessity), and render it more
fixed under the influence of natural selection. But if we may judge
by the actual sequel, it was not every kind of tree that could adapt
itself to the altered circumstances; as a matter of fact, the number
of species among northern forest trees is very small indeed, and even
out of this small number a good many are conifers, like the pines and
yews, whose narrow tough leaves are well fitted for withstanding and
battling against all the winter breezes. Still, among the conifers
themselves there are a few species, such as the larches, with tender,
delicate foliage, which have also become deciduous under stress
of altered conditions. At the present day the large-leaved and
flat-leaved evergreens are mostly confined to tropical, sub-tropical,
or at least warm temperate climates, and all the forest trees or
the circumpolar tracts are either deciduous, or else are tough
leathery-leafed conifers. The laurels and rhododendrons, with which
we strive artificially to brighten up our comparatively leafless
English winter, are either hardy representatives of the warm
temperate flora, or else mountain species from southern climates,
with constitutions just strong enough to endure our chilly season
in favored and carefully selected situations. Such evergreens have
generally very rigid and shiny leaves to protect them--a point well
marked in ivy and laurel as compared with Virginia creeper and
English hawthorn.
OUR MICROSCOPIC FOES
--A. WINKELRIED WILLIAMS
Of all the foes that are waging war against mankind, the most
dangerous and deadly are minute organisms belonging to the lowest
order of plant-life, and invisible to our naked eye. An immense
number of these always surround us, and are ready to make an attack
should they find a weak point in our defences.
Their presence in the air may be readily demonstrated by exposing
some material upon which they can feed, and watching the result. The
simplest method is to boil a potato, cut it in half, and immediately
place one-half under a bell glass purified by being washed in an
antiseptic solution such as corrosive sublimate. Expose the second
half to the open air for a short time, and place it also under a
glass. Let them remain for a few days, and then examine. If the first
half has been placed rapidly enough under the glass, we shall find
it unaltered. On the second half, however, we shall see a number of
small but growing spots, which will probably vary much in color.
These consist of colonies made up by immense numbers of most minute
plants, _i. e._, bacteria, and also of higher fungi. Certain species
of the bacteria constitute our dreaded foes.
Bacteria are non-nucleated unicellular plants, which may be roughly
classed into two divisions according to their shape, the circular
forms being called micrococci, the elongated forms bacilli. In size,
they are most minute, being only visible under the highest powers
of the microscope. Many are provided with cilia, by the lashing of
which they are capable of independent movement. They are composed of
a peculiarly resistant protoplasm, which is condensed at the surface,
so that by the action of certain caustics they can be separated from
many tissues on which they may be lying, the caustics destroying
these tissues.
Bacteria have enormous power of reproduction, which is accomplished
by division of the cells and fission. Many also form globular spores
by a condensation of their protoplasm. The spores have a much higher
power of resistance than the bacteria themselves, and may under
unfavorable circumstances be quiescent while awaiting better times to
take on full development.
Their _habitat_ is almost everywhere. In water, bacteria exist in
great numbers; they are even found in springs at their sources.
This indicates their presence in the soil, where they are found in
great numbers. We have already seen that they exist in the air, but
being, for their size, heavy bodies, they are invariably attached
to less dense particles of dust. Out at sea, we find the air free
from bacteria, although in the water they abound. The higher we
ascend, the fewer we find. In towns, the air teems with them; in
the country but few exist. In the healthy living body, there are
no bacteria, except in the alimentary canal and upper respiratory
passages. It must not be supposed that all bacteria are the
forerunners of disease; such is the case with only certain forms
to which the significant term pathogenic bacteria is applied. Many
authorities assert that the non-pathogenic forms may, under certain
circumstances, develop into pathogenic forms. This, however, has
not been definitely settled, since we are only able to separate the
different classes of bacteria by their action on cultivating media
and on the living body. We have not yet been able to develop by
cultivation a virulent form from a non-virulent, although we have by
repeated cultivation diminished the virulence of the most malignant
bacteria.
Of all the pathogenic bacteria we have the most direful tale to tell.
Of one, discovered by Dr. R. Koch--namely, that of tubercle--the
terrible ravages on human life by ferocious animals in India (over
24,800 fatalities per annum) are but trifling compared to the
ravages stealthily done in our midst by this the smallest of the
class of most minute living units. According to Dr. Koch’s estimate
one-seventh of the human race die of pulmonary consumption, and
this is only one, certainly the most prolific, of the many diseases
directly caused by the tubercle bacillus.
Happily for warm-blooded animals, these terrible death-dealers differ
from most other bacteria, for although they can remain alive for some
time outside the body, they are unable to develop in the outside
world, and this considerably limits their number. A temperature above
96° Fahr. is necessary for their growth, and there are only a very
few soils on which they can be cultivated, such as blood-serum and
meat jelly. Moreover, they develop more slowly than other known
bacteria, which may consequently outgrow them, and prevent their
development. How, then, are we to account for the fact that tubercle
is such a widely spread disease, not only among all the races of men,
but also among many of the lower animals? The consideration of the
following facts answers this question.
The tubercle bacillus can form resting spores; consequently, when
once the tissues of a part have their vitality so lowered that the
entrance of the bacilli is allowed, they can retain their hold with
great tenacity. Although the bacilli can not develop outside the
body, their vitality is preserved for a long time. Certain animal
products used for food, such as the milk of tubercular cows, contain
the bacilli. Experiments such as causing animals to inhale the
tubercle bacilli, or the introduction of them into the blood, or
sometimes the feeding on tubercular matter, result in tuberculosis.
Pulmonary consumption presents an example of the most typical way in
which the tubercle bacillus performs its deadly work. In the majority
of cases, the bacilli are inhaled with the air, but may also infect
the lungs from the blood carrying them from tuberculosis in other
parts of the body. The bacilli are incapable of independent movement.
This difficulty is too readily overcome in the body, as the streams
of blood and lymph easily carry them along.
Their movements in the body may be aided by certain scavengers that
are crawling about in our tissues and circulating in our blood;
namely, the wandering cells of connective tissue and the white blood
corpuscles. These take up the bacilli by wrapping their substance
around them; then, for a time, they crawl about carrying with them
the bacilli. In this attempt to devour the tubercle bacillus,
they often find they have caught a Tartar, who in turn feeds and
multiplies in them, and thus their wandering days soon end.
Many other diseases are known to be caused by bacteria, such as
anthrax, cholera, pneumonia, typhoid fever, erysipelas, leprosy,
suppuration, and ordinary blood-poisoning. Before Sir Joseph Lister
introduced the system of antiseptic surgery, bacteria were a most
fertile source of danger in surgical operations by the decomposition
and suppuration they set up in the wounds.
In this short paper it is impossible to describe the characteristics
of any other pathogenic bacteria, but perhaps enough has been written
to show the great danger to which we are exposed from attacks by an
immense army of minute foes.
FOREST FORMATIONS
--M. J. SCHLEIDEN
It is difficult to give the character of the various wood-formations
in woods with even a small proportion of that vividness and reality
which the landscape painter so readily attains by drawing, foliage,
color, and effect of light. Nevertheless, the differences are
striking enough to all who approach nature with open senses. Even the
fir and pine woods exhibit essential differences in their features;
the former with straight stems arranged parallel to each other
like columns, with the conical crowns of verticillate branches; the
latter bearing on the gnarled, curved trunks, the lines of which
cross in all directions in perspective, a flat umbel of foliage, a
bearing which is most purely and nobly exhibited by the stone pine.
These pine-woods, which extend over miles of country in the Mark
of Brandenburg, are repeated in more luxuriant development in the
“pine-barrens” of North America. Here, as there, loving a sandy soil,
they extend in a broad band several hundred miles long, down to the
coast of North Carolina, forming by their mass a very prominent
feature in the physiognomy of the whole country.
Still more striking is the distinction between the particular
formations of the leafy woods; the crowded arrangement of the social
beeches, limes, or elms produces woods with dusky shades and a soil
void of vegetation, while the proud oak, repressing the growth of all
other trees in its immediate neighborhood, stands alone upon a soil
pleasantly clothed with grass and herbs, or unites in small groups to
form those wonderful woodland landscapes to which the immortal pencil
of Ruysdäel so often introduces us.
Differently acts the massive lustre of the magnolia woods of the
southern part of North America, from the elegant beauty of the
African acacia groves, or the ghost-like transparency of the northern
birch, and the whole tropical world unfolds a multiformity, the
description of which would be an inexhaustible theme.
When the dense foliage hinders the action of the sun and the
refreshing breeze, and thus retards the decomposition of the
vegetable masses, where the ground, flat and without any declivity,
allows the accumulation of water, and the more since the heaped-up
bodies of dead plants continually increase the barriers to the
efflux, and the humus formed greedily sucks up the moisture--there
are formed the most extensive swamps. By the progressive action of
the remains of vegetation the ground becomes elevated, and such
spongy, semi-fluid masses often lie, at length, far above the
level of the surrounding plain, the sun’s heat never sufficing,
even when storms remove the protecting roof, to dry up the marsh,
or to restrain its increase. Such a swamp rises twelve feet above
the surrounding plains in Virginia, between the towns of Suffolk
and Walden, and is called by the inhabitants “the Great Dismal,”
giving origin to considerable rivers and supplying them with water.
The North American cypress (Cupressus disticha) it is which with
its delicate but dense foliage gives rise to the formation of
these structures. It is the same tree which forms the terrible
evil-renowned cypress swamps of Louisiana, on the banks of the
Red River and the Mississippi. Gigantic trunks of unprecedented
mightiness crowd together, interweaving their branches and spreading
an obscure twilight in the brightest day. The soil consists
merely of half-decayed blocks piled one upon another, alternating
with a fathomless mud, in which the voracious alligators and
snapping-turtles wallow, the sole lords of this hell, steaming up
almost beneath the tropical sun--thus in the height of summer; in
the spring the thick, miry floods of the issuing streams impetuously
overflow this malignant vegetation for many miles. Thus these
cypress-swamps, of which Seatsfield has given us such a vivid
picture, correspond in inland countries to the mangrove-woods which
border the mouths of almost all the tropical rivers. Composed of a
very few species of plants, among which the mangrove-tree is the most
common, they are especially striking from the great number of strong
roots springing out high up the stem, and bearing this aloft above
the surface. The peculiar habitation of this plant is the _brackish
water_, which consists, at the ebb, of the fresh water of the river,
which is dislodged by the sea-water at the flood. The numerous roots
often form a so thickly entangled mass that the interspaces may be
stopped up by the falling leaves, collecting thus a soil for a new
vegetation, beneath which, at different hours of the day, roll the
waves of the river and the sea. But more frequently the roots merely
operate to retard the flow of the water and to retain in their
interlacements the vegetable and animal bodies driven down the river,
which then decay here in contact with sea-water and its salts. In
these regions the terrible sulphureted hydrogen gas is developed so
abundantly, poisoning the atmosphere, that the natives who have lived
in these abodes from their youth upward totter about as it were like
spectres, while death almost inevitably snatches off the Europeans
who enter there.
As the hill between mountain and level land, so between the
wood-formation and the plain a link is formed by the bush and the
plains, displaying merely small, isolated groups of trees.
A portion of the so-called woods on the northern coast of Australia
must be reckoned here, those which clothe the enormous tract
extending southward into the interior from Raffles Bay and Essington.
They exhibit a wholly peculiar physiognomy, which is repeated almost
everywhere throughout this strange country. The trees and bushes
have leathery leaves, the majority of them being covered with a
white, resinous powder, which gives them the most monotonous, dismal,
pallid look possible. The principal trees are species of Eucalyptus,
Acacia, Leptospermum and Melaleuca. Many other plants, scarcely to
be reckoned by the side of those named, live beneath the shelter
of those lofty grayish stems, which stand far apart, and by their
meagre, incessantly trembling foliage, remind us of the weeping
willow. Handsome tufts of grass, with long, slender halm, grow
throughout the whole extent of these bushes, and in them nestle the
kangaroo, with the ring-dove and other birds. The sun’s rays readily
penetrate the narrow leaves, always waving on their long petioles,
and produce an uncertain light mingled with fleeting shadows. The eye
sees far up through the vault of twigs and leaves, and is arrested,
not so much by the density of vegetation as by the continually
changing glance of an uncertain mystic light.
Still lighter, still less representative of the closed conditions of
woods, is the proper palm-form where the social kinds are grouped
together. The real palm-groves on the northern border of Sahara and
on the shores of the Brazilian rivers more resemble open columned
halls with perforated roofs; and on the dry soil of the elevated
plains of Mexico the stems of the yucca, fourcroya, and other
high-stemmed liliaceous plants are collected in a very peculiar way,
affording neither shade from the sun nor shelter from the wind. To
these approach the deformed masses of the Maguey-plants, with their
broad, thick, rigid, dull-green leaves, sharply toothed on their
borders, and their flowering stalks twenty feet high, rounded off
into strange, fantastic, and impenetrable bush by cacti of manifold
forms.
The impenetrable chaparrals in the extensive plains between the
Nueces and the Rio Grande, formed of mosquito-shrubs, six to seven
feet high, entwined with lianes; the palmetto-fields on the shores
of the Sabine, Natchez, and other rivers of Texas, formed of rush
and dwarf palms; the low acacia bush of Australia Felix, and
lastly the wide jungles traversed by the elephants and tigers in
the East Indies, and formed of bamboo and other lofty grasses, are
all peculiarly characterized formations of bush, which often not
attaining the height of a man, or but little exceeding it, do not
all betray at the first glance the frequently insuperable obstacle
they oppose to the intruder, and even after man has settled in the
neighborhood can only be traversed by paths which the wild animals
have made.
With a kind of feeling of disappointed expectation rides the traveler
in the prairies of the West, anything but refreshing appears the
monotonous surface uniformly overgrown with high grass, the line of
the horizon unbroken even by the smallest elevation. He rides and
rides, but ever boundless space expands before his eyes, in the same
uniformity, in the same calm simplicity.
[Illustration: Bacteria and Vegetable Germs
3, Pneumonia; 5, Anthrax; 7, Diphtheria; 8, Tuberculosis; 9, Leprosy;
10, Tetanus; 11, Influenza; 12, Typhus; 14, Cholera]
Situated under similar latitudes and climatal conditions, the pampas
of Buenos Ayres have a character similar to that of the North
American prairies, only man by his influence on nature has here and
there impressed a peculiar stamp. The thistle and artichoke, coming
with the Europeans, have quickly made themselves masters of the free
soil, and with incredible rapidity overspread districts of many
square miles with their spiny vegetation, which has here developed in
a luxuriance unknown in Europe. These thistle-wastes have become a
terrible nuisance, themselves robbers, depriving better plants of the
soil, inaccessible hiding-places for the great thievish, sanguinary
cats, and the still more dangerous human bandits, the thorny weed of
semi-civilization.
From the western border of northern France, through Belgium, North
Germany, and Russia, almost to the eastern confines of Siberia,
extends a broad plain rarely interrupted by low chains of hills,
and just as rarely affording fitting soil for extensive growth of
wood, which, on the whole, confines itself to the more favorable
soil moistened by the vicinity of rivers. Along the southern border
of this plain extends a chain of hills and mountains, now projecting
forward like capes into the broad surface, now retreating into
broad or narrow creeks, the coast of a sea formerly covering the
whole plain. Over all this endless expanse has one single species
of plant established an almost exclusive predominance, the heath,
which has lent its name to those tracts of land. Conditions similar
to those which produce the distinction between the pine barrens
and cypress swamps in North America are also active here to cause
an essential difference. The great flatness of the ground, even
geological conditions in many places, as where slight elevations of
the land forming flat inclosed basins, prevent, in many situations,
the free discharge of water, and the heath, backed by the special
vegetation produced by the moisture, forms by the annual accumulation
of vegetable matter, which in water only becomes to a certain degree
carbonized or decomposed, those black masses of the remains of
plants which as peat bear such an important part in the economy of
the inhabitants. Thus, in various modes of distribution, alternate
arid, dry sandy heaths with moist, spongy peat heaths or moors.
On the margin of the latter, more rarely actually upon them, and
on the heaths of Luneburg are often found splendid oaks, which,
overshadowing one of those pleasant straw-thatched houses and thrown
out by the background of the peculiar red tint of the glancing
heather, produce a picturesque charm which would not have been
expected here. With these great moors may be associated the peat
moors of some of the higher mountain chains of the Brocken, the Röhn,
and the Fichtel-Gebirge, and so on, and the so-called mosses of South
Germany and Switzerland.
In another climate, in another zone of vegetation, exist similar
conditions, stretching across the extreme north of Europe. As there
the arid sandy heaths alternate with the wet moors, so here in a
more varied manner do the dry, waterless tracts, with the marshy
grounds. But we are here in Wahlenberg’s region of lichens and
mosses. The arid situations are clothed, in expanses over which the
eye can not reach, with dry, lead-gray lichens, among which the
reindeer seeks his meagre sustenance, and in the half-fluid grounds,
which will not bear the lightest footsteps, a luxuriant vegetation
of mosses deceives us, in the distance, with the aspect of a smiling
meadow. Here the incautious wanderer sinks into the water, which is
rather concealed than displaced by the mosses, while on those lichen
heaths, tundras, the Laplanders call them, in summer the glowing soil
makes every step a torture.
The wood-formations of the South American catingas may be opposed
to the northern leafy woods and, in like manner, the plains of the
llanos of Venezuela to the Russian steppes. In the former, of which
A. von Humboldt has given such a vivid sketch, the sleep of nature
commences with summer, in the hot, dry season; the vegetation becomes
dried up and falls to dust, leaving the ground bare; animal life, in
the quadrupeds, flies from the dead land, while the crocodiles and
boas burrow into the mud of the gradually exhausted rivers of the
steppes, and with this become fixed, till the first torrent of rain,
which conjures up a fresh, youthful vegetation on the barren soil and
awakens them to life.