not yet in use) are simple cells. He pointed out that they possess
nuclei, like those of tissue-cells, and compared their increase by
fission with the cleavage of the egg. Single cells were thus shown to
be not only capable of locomotion, which was already known, but able
to provide for their own support. The Protozoa and Protophyta (_i.e._,
the simplest animals and plants, which are not always to be clearly
separated) are now known to be autonomous cells, increasing by fission,
and often forming colonies. Conjugation (fusion of similar individuals)
often precedes fission, and when it was proved (1861-5) that ova and
spermatozoa are true cells, it was seen that fertilisation, as we know
it in the higher animals, is only a special form of the conjugation
observed among the Protozoa. To the Protozoa it is now possible to
trace, without any startling break of continuity, all the multicellular
organisms, their tissues, the growth of those tissues by repeated
fission, their eggs, and the process of fertilisation which precedes
cleavage. The old Greek riddle, "Which came first, the fowl or the
egg?" may now receive the answer: "Neither; their common starting-point
is to be found in the Protozoa, which, even when adult, represent the
primitive unicellular condition, to which all the higher animals revert
once in every generation."
It is not without reason that biologists dwell on the unifying
influence of the cell-theory, which has become a chief support of that
still wider unifying influence, the _Origin of Species by Natural
Selection_. When it was discovered that all living things, whether
plants or animals, consist of nucleated cells which increase by
fission, and that in all of them cell-fission is started anew from time
to time by a cell-fusion, it was strongly suggested that resemblances
so striking and so universal can only proceed from a common descent.
During the last half-century the study of cells has led to a great
increase of knowledge respecting all bodily functions, whether in
health or disease. We now look to it as perhaps the most hopeful source
of new light upon the important question of hereditary transmission.
The Scientific Investigation of the Higher Cryptogams.
We now resume the history of a study which down to the end of the
eighteenth century had yielded only meagre and uncertain results (see
above, pp. 85-88). At the date in question it had been ascertained
that the spores (then called "seeds") of ferns, and probably of other
cryptogams, are capable of propagating the species, but no one knew
precisely what part the spore played in the life-history, or could
explain the true difference between a cryptogam and a flowering plant.
The great improvements in the construction of the compound microscope
which were effected between 1812 and 1830 rendered it possible to
elucidate much more thoroughly the structure and development of the
chief groups of cryptogams. The sexual reproduction of algæ was
explored; moving filaments (spermatozoids) were seen to enter the
chambers in which embryos afterwards formed; the conjugation of similar
cells was observed in algæ and fungi, and recognised as a simple mode
of sexual reproduction. The resemblance of the spermatozoids of mosses
and ferns to animal spermatozoa was noted, and their participation in
the process of fertilisation was more and more closely followed until
at length Hofmeister in 1851 saw them fuse with the egg-cell of a fern.
Suminski, whose full name, Lesczyc-Suminski, is unpronounceable by
Englishmen, had discovered (in 1848) that the prothallus of a fern,
which is the product of the germinated spore and had been hitherto
taken for the cotyledon, bears two kinds of reproductive organs, one
of which liberates spermatozoids, while an egg-cell is developed
within the other. He did not correctly describe all the details, but
he showed where the essential reproductive organs form, and where
fertilisation is effected. The masterly researches of Hofmeister
(1849-57) fused what had been a number of partial discoveries into a
connected and luminous doctrine. He proved that the prothallus is one
of two generations in the life-history; that it begins with a spore and
ends with a fertilised egg-cell; that in the higher cryptogams there
is a regular alternation of generations; that the prothallus of the
fern answers to the leafy moss, while the leafy fern is the equivalent
of the moss-capsule; that the egg-cell is the same structure in both
cryptogams and flowering plants; that the pollen-tube and the seed are
found to-day only in flowering plants; that the gymnosperms make a
transition from the higher cryptogams to the angiosperms; that unity
of plan pervades the whole series of mosses, ferns, fern-like plants,
gymnosperms, and angiosperms. Before Darwin's _Origin of Species_ had
appeared Hofmeister presented to evolutionists a clear example of a
descent in which every principal term is well authenticated, while the
extremes are far apart.
The Enrichment of English Gardens.
If some unreasonably patriotic Englishman should be seized with the
whim of keeping none but truly British plants in his garden, he
might enjoy the shade of the fir, yew, oak, ash, wych-elm, beech,
aspen-poplar, hazel, rowan-tree, and the small willows, but he would
have to forego the common elm, the larger poplars and willows, the
larches, spruces, and cypresses, the rhododendrons, and all the shrubs
popularly called laurels. Of fruits he might have the crab-apple, sloe,
wild cherry, gooseberry, currants (black and red), the raspberry,
strawberry, and blackberry, but none of the improved apples, pears,
or plums, and no quinces, peaches, or apricots. His vegetable garden
might yield cabbages, turnips, carrots, and celery (all deficient in
size, flavour, and variety), but no cauliflowers, Brussels sprouts,
parsley, lettuces, peas, beans, leeks, onions, or spinach. The
handsomest of his flowers would be dog-roses, mallows, and primroses.
Before Europe was sufficiently enlightened to care about exact records
valuable foreign plants had already been introduced. Vines, apples,
pears, cherries, and plums, besides improved vegetables, such as the
cauliflower, bean, garden-pea, and cucumber, had been brought from
temperate Asia or Egypt. Wheat and barley, neither of them native
to Europe, had to some extent replaced rye and oats, which may have
existed naturally in those European countries which border on Asia.
Britain, while yet a Roman province, shared in these benefits, and
it is believed that the common elm, besides certain fruit-trees and
pot-herbs, have been continuously grown in our island through all
the troubled ages which separate us from the Romano-British times.
Leek, garlic, and onion are ancient acquisitions. To our Old-English
forefathers garlic was the _spear-leek_, distinguished by its long,
narrow leaf from the broad-leaved common leek, just as a garfish was
distinguished from other fishes by its long body and pointed head;
onion was the _enne-_ or _ynne-leek_ (onion-leek); the most
important of the three was probably that which retained the root-word
without prefix—the leek proper.
During many centuries, when the rights of small proprietors were
little respected and knowledge was scanty, the religious houses were
distinguished by the diligence with which they tended their gardens.
Flowers, fruits, and simples were cultivated, and plants were now
and then imported from foreign monasteries. The English names of the
plants, which are often adaptations of Latin words, still testify to
the care of gardeners who were in the habit of using Latin.
Much improvement was not to be expected so long as England suffered
from frequent and desolating wars within her own borders. When these
at last subsided, great English gardens, such as those of Nonsuch,
Hatfield, Theobalds, and Hampton Court, began to parade their beauty;
strange trees, shrubs, and flowers were brought from the continent,
and as early as Queen Elizabeth's time our shrubberies and walks were
admired by spectators familiar with the best that Italy and France
could show. The new horticulture was, however, long an exotic among
us, and John Evelyn, whose _Sylva_ appeared in 1664, was "the
first to teach gardening to speak proper English."
In the latter part of the sixteenth century the following new plants
among others were brought from central or southern Europe: The poppy
and star anemones, the hepatica, the common garden larkspur, the winter
aconite, the sweet-William, the laburnum, Rosa centifolia (of eastern
origin, the parent of countless varieties and hybrids), the myrtle, the
lavender, the cyclamen, the auricula, Iris germanica, and many other
Irids, the oriental hyacinth, several species of Narcissus, the white
and Martagon lilies, and the absurdly named dog's-tooth-violet (really
a lily). The botanist Clusius introduced the jonquil and the Tazetta
narcissus from Spain to the Low Countries. The Judas-tree (_i.e._,
tree of Judæa) was brought from the Mediterranean, where the hollows of
the hills are filled in April with its pale-purple blooms. The white
jasmine was imported from Asia, and the castor-oil plant from Africa.
The great accessions of geographical knowledge made during the
fifteenth and sixteenth centuries were slow to affect horticulture.
Ships were then few and small, and the passage from Hispaniola or
Calicut to Cadiz or Lisbon occupied weeks or even months. Moreover,
the conquests of Spain and Portugal (Goa, the Moluccas, Brazil,
the West Indies, Peru, and Mexico) lay mostly within the tropics,
and could furnish hardly any plants capable of enduring a European
winter. Special pains were, however, taken to bring over some valuable
food-plants which were thought likely to thrive in Europe. Before
any European landed in America the potato had been cultivated by the
Indians of Peru, a country which, though lying almost under the line,
rises into cool mountain-districts. Potato-tubers were soon introduced
to Spain and Italy, and a little later to other parts of Europe;
Raleigh's planting of potatoes on his estate near Cork came a few
years later. The edible tomato, which is distinguished from the wild
form by its enlarged fruits, was apparently cultivated in Peru before
the first landing of the Spaniards. The unusually high proportion of
edible plants among the first importations from America and other
distant countries is worthy of remark. Early explorers eagerly sought
for valuable food-plants, but the number of such as could be cultivated
alive in Europe was very limited, and since the sixteenth century the
attention of collectors has been fixed upon ornamental species simply
because of the dearth of others.
European flower-gardens were enriched during the sixteenth century
by the following American species: the so-called French and African
marigolds (both from Mexico), sunflowers, the arbor-vitæ (Thuja
occidentalis), Yucca gloriosa, and the Agave, misnamed the American
Aloe.
About the same time the horse-chestnut, lilac, and syringa, or
mock-orange, were first brought to central and western Europe, and
with them the tulip, richest and most varied of flowering bulbs. All
these reached Vienna from Constantinople, but how and when they were
brought to Constantinople, or what were their native countries, are
still doubtful questions. The horse-chestnut is believed to be a native
of Greece, where it is said to grow wild among the mountains; probably
it extends into temperate Asia as well. It is said to have reached
Constantinople in 1557. Longstanding tradition derives the lilac
from Persia, but botanists say that it is also indigenous to parts
of south-eastern Europe. The garden-tulip is believed to be native
to temperate Asia and also to Thrace; it is, of course specifically
distinct from the wild tulip of northern Europe.
Chief among the travellers to whom we owe the acquisition of these
favourite plants was Augier Ghislen de Busbecq, a Fleming, who was
twice sent by the emperor as ambassador to the sultan. Busbecq was
a keen observer and collector, and during his long and toilsome
journeys was ever eager to pick up curiosities or to note new facts.
Quackelbeen, a physician in Busbecq's suite, is named as another
helper. The botanists Mattioli and Clusius, who presided in succession
over the imperial gardens of Vienna, and Gesner of Zurich, described
the plants; it is from them that we draw such imperfect knowledge as
we possess of the way in which they were brought to central Europe.
Clusius relates that Busbecq in 1575 received a parcel of tulip-seed
from Constantinople, and being obliged to journey into France, left
it with Clusius to be germinated. The tulips which came up were of
various colours, an indication of long cultivation. The Turks, like the
Persians, took great delight in gardens.
As North America became permanently occupied by the English, facilities
for the transport of live plants to Europe steadily increased. Ships
began to sail frequently to and fro, for the crossing of the Atlantic
was but a small affair in comparison with the voyage round the Cape
of Good Hope. Educated men here and there practised the learned
professions in the American plantations, and among them a sprinkling of
naturalists was found. Hothouses, the amusement of wealthy amateurs in
Germany, France, and Holland, made it possible to protect the plants
of mild climates from the winter cold of northern Europe. By the end
of the seventeenth century our gardens had acquired many beautiful and
curious American plants, besides a few from the East Indies, and not
long afterwards the gains became so frequent that the botanists of
Europe found it hard to name the new species as fast as they came in.
Lovers of horticulture will tolerate a little further information
concerning the early use of hothouses. As soon as glass began to
be employed in domestic architecture, the construction of warmed
and glazed chambers, in which plants could be grown, was attempted.
Writers of the first century A.D. mention them, and Seneca
explains how the temperature might be kept up by hot water. This and
other refinements of the Roman Empire passed into oblivion during the
long decline of civilisation, but revived with the revival of the
arts. In the sixteenth century William IV., Landgraf of Hesse, who is
remembered, among other things, as a patron of the botanist Clusius,
built himself a green-house, which could be taken down and put
together again. A still more famous orangerie was that of Heidelberg,
which served as an example to the kings and nobles of Europe.[39] Henri
IV. built one at the Tuileries, and long afterwards Louis XIV. had one
at Versailles. Madame de Sévigné describes the orangerie of Clagny
as a palace of Armida, and the most enchanting novelty in the world.
The pine-apple was brought over from Barbadoes in the seventeenth
century, and Evelyn speaks of having tasted the first pine-apple grown
in England at the table of Charles the Second. For two hundred years
the hothouse yielded no greater dainty, but rapid transit has now
made pine-apples so cheap that it is no longer worth while to raise
them in England. Fagon, who was during many years first physician to
Louis XIV., was a considerable botanist. He was born and died at the
Jardin des Plantes, and here, on his retirement from practice, he built
hothouses; it would be interesting to know what he grew in them.
In the first half of the seventeenth century the younger Tradescant,
who, like his father before him, was gardener to our Charles I.,
brought over from America the spider-wort, named Tradescantia after
him,[40] the false acacia and the tulip-tree. The magnolias, or some of
them, the Virginian creeper, and the scarlet Lobelia cardinalis were
among the gifts received from North America about the same time. The
dwarf Lobelia (L. Erinus) was not brought over from the Cape of Good
Hope till 1752, and Lobelia splendens and fulgens (both from Mexico)
not till the nineteenth century. One of the passion-flowers, which are
all American, came over about this time; but Passiflora cærulea, the
favourite ornament of the greenhouse, was only imported from Brazil in
1699. The evening primrose, the "convolvulus major and minor" (Ipomæa
purpurea and Convolvulus tricolor), were other acquisitions from North
America.
From the second half of the seventeenth century dates the introduction
of the garden nasturtium (Tropæolum majus) from Peru; T. minus from
Mexico had been brought over nearly a hundred years earlier. The
sensitive plants and the pine-apple now became frequent objects in
English greenhouses. John Evelyn and Bishop Compton were eminent
patrons of English horticulture during this age.
The first half of the eighteenth century brought us the Aubretia and
the sweet pea from southern Europe, the first Pelargoniums (scarlet
geraniums) from the Cape, the camellia and Kerria japonica from the
far east. The West Indian heliotrope was introduced in 1713; the
better-known Peruvian species not till 1757. Phloxes began to be
imported from North America. Two or three foreign orchids were already
known, and the number now began to increase; but it was not till the
nineteenth century that they came over in crowds. Our list gives no
notion whatever of the number of new species added now and subsequently.
Of the accessions made during the latter half of the eighteenth century
we must at least mention the mignonette from North Africa, white arabis
from the Caucasus, the common rhododendron from Asia Minor, Rosa
indica and Hydrangea hortensis from China, South African gladioli,
which now begin to be numerous, and chrysanthemums from China and
Japan. The first calceolarias were brought from great heights on the
Andes, the first begonias from Jamaica, and the first fuchsia from
Chili.
We can make only one remark about the multitudinous accessions of
the nineteenth century. It is surprising to note how recently many
established favourites have been brought to the knowledge of English
gardeners. Anemone japonica (Japan) and Jasminum nudiflorum (China)
date from 1844, while the Freesias (Cape Colony) are as recent as
1875. The dahlia, after two unsuccessful attempts, was established
here as recently as 1815; Nemophila insignis came over from North
America in 1822; the common musk and the monkey-plant a few years
later; the chionodoxas (Crete and Asia Minor) in 1877. The first of the
foliage-begonias (Begonia rex from Assam) dates only from 1858, and the
first of the tuberous species from 1865.
Importation of foreign species has not been the only method by which
English gardens have been enriched. New varieties and hybrids have
been produced in bewildering numbers by the gardeners of Europe, and
many of these far surpass in beauty the wild originals. Botanists
and nurserymen could relate in great detail the steps by which our
favourite roses, calceolarias, begonias, and cinerarias have been
developed from a few natural stocks, sometimes of uninviting appearance.
Horticulture has repaid the debt which it owed to the explorations
of botanists by furnishing countless observations and experiments
bearing upon inheritance. When these have been properly co-ordinated,
they will yield precious knowledge, not only to botanists but to all
students of biology.
Humboldt as a Traveller and a Biologist.
The career of Alexander von Humboldt (b. 1769, d. 1859), nearly
coinciding with the period on which we are now engaged, was devoted
to a gigantic task—nothing less than the scientific exploration of
the globe. His great natural powers were first cultivated by wide and
thorough training, not only in astronomy, botany, geology, mineralogy,
and mining, which had an obvious bearing on his future enterprise,
but also in anatomy, physiology, commerce, finance, diplomacy,
and languages. Thus equipped, he sailed in 1799 with the botanist
Bonpland to South America, and spent the next five years in exploring
the Orinoco and Amazon, the Andes, Cuba, and Mexico. The expedition
marks an epoch in scientific geography. It is enough to mention the
collection of data for the more accurate mapping of little-known
countries, the exploration of the river-systems of equatorial America
and the discovery of a water-connection between the Orinoco and the
Amazon, the ascent of lofty mountains, the study of volcanoes, the
description of remarkable animals such as the howler-monkey and
the gymnotus (electric eel), and of remarkable plants, such as the
bull's-horn acacia, whose enlarged and hollow spines are occupied
by ants.[41] After his return to Europe Humboldt published many
important treatises on terrestrial magnetism, geology, meteorology,
and plant-distribution. His new graphical method of isothermal lines
did much for the study of climate in all its bearings. His _Personal
Narrative_ not only disseminated much interesting information, but
inspired a new generation of explorers. Darwin agreed with Hooker that
Humboldt was the greatest of scientific travellers.
In 1829 Humboldt traversed the Russian Empire from west to east,
but the time allowed (half a year) was altogether insufficient for
the examination of so vast a territory; a few notable results were,
nevertheless, secured.
After some fifteen or twenty years spent in European society, the
inspiration drawn from long and arduous journeys in South America began
to fail. The conversation of the _salons_, the troublesome flattery
of the King of Prussia, and the propensity to write copiously,
stimulated, of course, by the eagerness of the public to buy whatever so
eminent an investigator chose to put forth, sterilised the last half of
a career which had opened with such magnificent promise.
The best of Humboldt's work became absorbed long ago into the confused
mass of general knowledge. This is the common fate (not by any means an
unhappy one) of those who refuse to concentrate upon a single study.
Among biologists he is chiefly remembered by his numerous discussions
of plant-distribution, which are now considered less remarkable for
what they contain than for what they leave out. While his travels were
fresh in his mind, Humboldt was impressed by facts of distribution
which could not be explained by present physical conditions,[42] but
the influence of climate as the more intelligible factor gradually
assumed larger and larger proportions in his mind. The writers of
text-books, founding their teaching upon Humboldt, often overlooked
altogether qualifications which he had shown to be necessary. When
Darwin and Wallace pointed out how immensely important is the bearing
upon present distribution, not only of the physical history of the
great continents, but also of their biological history, and in
particular of the interminable conflicts of races of which they have
been the scene, naturalists began to perceive how inadequate are
horizontal and vertical isothermal zones to explain all the striking
facts of distribution, whether of plants or animals (see _infra_ p 129).
Premonitions of Biological Evolution.
The eighteenth century had done much to impress the minds of men with
an orderly development in sun and planets (Kant and Laplace), in
the institutions of human societies (Montesquieu), and in the moral
aspirations of mankind (Lessing). Many bold attempts had been made
to trace a like orderly development in the physical life of plants
and animals (Buffon, Erasmus Darwin, etc.), but neither was the proof
cogent nor the process intelligible. Cautious people therefore, and
those whose prepossessions inclined them to adopt a very different
origin for terrestrial life, held during all this time a position of
some strength against speculative philosophers who tried to explain
the variety and perfection of living nature by unconscious and
unintelligent factors.