Transcriber's note:
Italic text has been marked with _underscores_. Please see the
end of this book for further notes.
[Illustration: A LIVING BRIDGE
Such a bridge is described by Sir J. D. Hooker in his _Himalayan
Journals_.]
THE ROMANCE OF
PLANT LIFE
INTERESTING DESCRIPTIONS OF
THE STRANGE AND CURIOUS IN
THE PLANT WORLD
BY
G. F. SCOTT ELLIOT
M.A. CANTAB., B.SC. EDIN., F.R.G.S., F.L.S., ETC.
AUTHOR OF
"A NATURALIST IN MID AFRICA," "NATURE STUDIES--PLANT LIFE"
ETC.
WITH THIRTY-FOUR ILLUSTRATIONS
PHILADELPHIA
J. B. LIPPINCOTT COMPANY
LONDON: SEELEY & CO. LIMITED
1907
CONTENTS
CHAPTER I
THE ACTIVITY OF VEGETABLES
PAGE
Plants which move--Sensitive Plant--A tourist from Neptune--The
World's and the British harvest--Working of green leaves--Power
of sunshine--Work done by an acre of plants--Coltsfoot,
dandelion, pansies, in sunshine and in cold--Woodsorrel and
crocus--Foxglove--Leaves and light--Adventures of a carbon
atom--The sap--Cabbages and oaks requiring water--Traveller's
tree--The water in trees--An oasis in Greece--The associate life
of its trees and flowers 13
CHAPTER II
ON SAVAGES, DOCTORS, AND PLANTS
Savages knew Botany--First lady doctors and botanical
excursions--True drugs and horrible ornaments--Hydrophobia
cure--Cloves--Mustard--Ivy--Roses and Teeth--How to
keep hair on--How to know if a patient will recover--Curious
properties of a mushroom--The Scythian lamb--Quinine: history
and use--Safflower--Romance of ipecacuanha--Wars of the spice
trade--Cinnamon, logwood, and indigo--Romance of pepper--Babylonian
and Egyptian botanists--Chinese discoveries--Theophrastus--Medieval
times--The first illustrated book--Numbers of plants
known--Discoveries of painters and poets 27
CHAPTER III
A TREE'S PERILOUS LIFE
Hemlock spruce and pine forests--Story of a pine seedling--Its
struggles and dangers--The gardener's boot--Turpentine of
pines--The giant sawfly--Bark beetles--Their effect on music--Storm
and strength of trees--Tall trees and long seaweeds--Eucalyptus,
big trees--Age of trees--Venerable sequoias, oaks,
chestnuts, and olives--Baobab and Dragontree--Rabbits as
woodcutters--Fire as protection--Sacred fires--Dug-out and
birch-bark canoes--Lake dwellings--Grazing animals and forest
destruction--First kind of cultivation--Old forests in England
and Scotland--Game-preserving 40
CHAPTER IV
ON FORESTS
The forests of the Coal Age--Monkey-puzzle and ginkgo--Wood,
its uses, colour, and smell--Lasting properties of wood--Jarrah
and deodar--Teak--Uses of birch--Norwegian barques--Destruction
of wood in America--Paper from wood pulp--Forest
fires--Arid lands once fertile--Britain to be again covered by
forests--Vanished country homes--Ashes at farmhouses--Yews
in churchyards--History of Man _versus_ Woods in Britain 55
CHAPTER V
FLOWERS
Man's ideas of the use of flowers--Sprengel's great
discovery--Insects, not man, consulted--Pollen carried to set
seed--Flowers and insects of the Whinstone Age--Coal Age
flowers--Monkey-puzzle times--Chalk flowers--Wind-blown
pollen--Extravagant expenditure of pollen in them--Flower of the
pine--Exploding flowers--Brilliant alpines--Intense life in
flowers--Colour contrasts--Lost bees--Evening flowers--Humming
birds and sunbirds--Kangaroo--Floral clocks--Ages of flowers--How
to get flowers all the year round--Ingenious contrivances--Yucca
and fig--Horrible-smelling flowers--Artistic tastes of birds,
insects, and man 68
CHAPTER VI
ON UNDERGROUND LIFE
Mother-earth--Quarries and Chalk-pits--Wandering atoms--The
soil or dirt--Populations of Worms, Birds, Germs--Fairy
Rings--Roots miles long--How roots find their way--How they do the
right thing and seek only what is good for them--Root _versus_
stones--Roots which haul bulbs about--Bishopsweed--Wild
Garlic--Dandelion, Plantain--Solomon's Seal--Roots throwing
down walls--Strength of a seedling root 82
CHAPTER VII
HIGH MOUNTAINS, ARCTIC SNOWS
The life of a cherry tree--Cherries in March--Flowering of
gorse--Chickweed's descendants--Forest fires in Africa--Spring
passing from Italy to the frozen North--Life in the
Arctic--Dwarfs--Snow-melting soldanellas--Highland Arctic-Alpine
plants--Their history--Arctic Britain--Edelweiss--An
Alpine garden 97
CHAPTER VIII
SCRUB
Famous countries which were covered by it--Trees which are colonizing
the desert--Acacia scrub in East Africa, game and lions--Battle
between acacia and camels, etc.--Australian half-deserts--Explorers'
fate--Queen Hatasu and the first geographical
expedition recorded--Frankincense, myrrh, gums, and odorous
resins--Manna--Ladanum--Burning bush--Olives, oranges, and
perfume farms--Story of roses--Bulgarian attar of roses--How
pomade is made--Cutting down of forests and Mohammed 107
CHAPTER IX
ON TEA, COFFEE, CHOCOLATE, AND TOBACCO
English tea-drinking--Story of our tea--Assam coolies--Manufacture
in India and China--Celestial moisture--Danger of tea--The
hermit and his intelligent goat--Government coffee and
cafés--Chicory--Chocolate--Aztecs--Kola and its curious
effects--Tobacco--Sir Walter Raleigh--Great emperors and
tobacco--Could we grow tobacco?--Story of a Sumatra cigar--Danger
of young people smoking tobacco 120
CHAPTER X
ON DESERTS
What are deserts like?--Camel-riding--Afterglow--Darwin in
South America--Big Bad Lands--Plants which train themselves
to endure thirst--Cactus and euphorbia--Curious shapes--Grey
hairs--Iceplant--Esparto grass--Retama--Colocynth--Sudden
flowering of the Karoo--Short-lived flowers--Colorado Desert--Date
palms on the Nile--Irrigation in Egypt--The creaking
Sakkieh--Alexandria hills--The Nile and Euphrates 131
CHAPTER XI
THE STORY OF THE FIELDS
What was Ancient Britain?--Marshes and bittern--Oak forest--Pines--Savage
country--Cornfield--Fire--Ice--Forest--Worms--Paleolithic family--The
first farmers--Alfred the Great's first Government agricultural
leaflet--Dr. Johnson--Prince Charlie's time--Misery of our
forefathers--Oatmeal, milk, and cabbages--Patrick Miller--Tennyson's
_Northern Farmer_--Flourishing days of 1830 to 1870--Derelict
farmhouses and abandoned crofts--Where have the people gone?--Will
they come back? 143
CHAPTER XII
ON PLANTS WHICH ADD TO CONTINENTS
Lake Aral and Lake Tschad--Mangrove swamps of West Africa--New
mudbanks colonized--Fish, oysters, birds, and mosquitoes--Grasping
roots and seedlings--Extent of mangroves--Touradons
of the Rhone--Sea-meadows of Britain--Floating pollen--Reeds
and sedges of estuarine meadows--Storms--Plants on
ships' hulls--Kelps and tangles in storms--Are seaweeds
useless?--Fish 156
CHAPTER XIII
ROCKS, STONES, AND SCENERY
An old wall--Beautiful colours--Insects--Nature's chief aim--Hard
times of lichens--Age of lichens--Crusts--Mosses--Lava flows
of great eruptions--Colonizing plants--Krakatoa--Vesuvius--Greenland
volcanoes--Sumatra--Shale-heaps--Foreigners on railway
lines--Plants keep to their own grounds--Precipices and
rocks--Plants which change the scenery--Cañons in America 166
CHAPTER XIV
ON VEGETABLE DEMONS
Animals and grass--Travellers in the elephant grass--Enemies in
Britain--Cactus _versus_ rats and wild asses--Angora kids _v._
acacia--The Wait-a-bit thorn--Palm roots and snails--Wild yam
_v._ pig--Larch _v._ goat--Portuguese and English gorse--Hawthorn
_v._ rabbits--Briers, brambles, and barberry--The bramble
loop and sick children or ailing cows--Briers of the
wilderness--Theophrastus and Phrygian goats--Carline near the
Pyramids--Calthrops--Tragacanth--Hollies and their ingenious
contrivances--How thorns and spines are formed--Tastes
of animals 177
CHAPTER XV
ON NETTLES, SENSITIVE PLANTS, ETC.
Stinging nettles at home and abroad--The use of the nettle--Sham
nettles--Sensitive plants--Mechanism--Plants alive, under chloroform
and ether--Telegraph plant--Woodsorrel--Have plants
nerves?--Electricity in the Polar regions--Plants under electric
shocks--Currents of electricity in plants--The singing of trees
to the electro-magnetic ear--Experiments--Electrocution of
vegetables 191
CHAPTER XVI
ON FLOWERS OF THE WATER
The first plant--Seaweeds in hot baths--Breaking of the meres--Gory
Dew--Plants driven back to the water--Marsh plants--Fleur-de-Lis--Reeds
and rushes--Floating islands--Water-lilies--_Victoria
regia_--Plants 180 feet deep--Life in a pond, as seen
by an inhabitant--Fish-farming--The useful Diatom--Willows
and Alders--Polluted streams--The Hornwort--The Florida
Hyacinth--Reeds and grass-reeds--The richest lands in the
world--Papyrus of Egypt--Birds and hippopotami--Fever and
ague 200
CHAPTER XVII
ON GRASSLANDS
Where is peace?--Troubles of the grass--Roadsides--Glaciers in
Switzerland--Strength and gracefulness of grasses--Rainstorms--Dangers
of Drought and of swamping--Artificial fields--Farmer's
abstruse calculations--Grass mixtures--Tennis lawns--The
invasion of forest--Natural grass--Prairie of the United
States, Red Indian, Cowboy--Pampas and Gaucho--Thistles
and tall stories--South Africa and Boers--Hunting of the
Tartars--An unfortunate Chinese princess--Australian shepherds
herds 213
CHAPTER XVIII
POISONS
Poisoned arrows--Fish poisons--Manchineel--Curare--A wonderful
story--Antiaris--Ordeals--The Obi poison--Oracles produced
by poisons--Plants which make horses crazy and others that
remove their hair--Australian sheep and the Caustic Creeper--Swelled
head--Madness by the Darling Pea--Wild and tame
animals, how they know poisons--How do they tell one another?--The
Yew tree, when is it, and when is it not poisonous? 226
CHAPTER XIX
ON FRUITS
Bright colours of fruits--Unripe fruits and their effects--An
intemperate Fungus--Oranges--Prickly pear and the monkey--Strong
seeds--Bill-of-fare of certain birds--A wood-pigeon and beans--Ants
and seeds--Bats, rats, bears, and baboons--The rise in
weight of a Big Gooseberry--Mr. Gideon and the Wealthy
Apple--Crossing fruits--Breadfruit and banana--Dates--Figs--
Olives--Pineapples by the acre--Apples and pears--Home and Canadian
orchards 240
CHAPTER XX
WANDERING FRUITS AND SEEDS
Ships and stowaway seeds--Tidal drift--Sheep, broom, migrating
birds--Crows and acorns--Ice--Squirrels--Long flight of birds--Seeds
in mud--Martynia and lions--The wanderings of
Xanthium--Cocoanut and South Sea Islands--Sedges and floods--Lichens
of Arctic and Antarctic--Manna of Bible--The Tumble
weeds of America--Catapult and sling fruits--Cow parsnips--Parachutes,
shuttlecocks, and kites--Cotton--The use of hairs
and wings--Monkey's Dinner-bell--Sheep-killing grasses 254
CHAPTER XXI
STORY OF THE CROPS
Bloated and unhealthy plants--Oats of the Borderers, Norsemen,
and Danes--Wheat as a wild plant--Barley--Rye--Where was
the very first harvest?--Vine in the Caucasus--Indians sowing
corn--Early weeds--Where did weeds live before cultivation?--Armies
of weeds--Their cunning and ingenuity--Gardeners' feats--The
Ideal Bean--Diseased pineapples--Raising beetroot and
carrot--Story of the travels of Sugar-cane--Indian Cupid--Beetroot
and Napoleon 269
CHAPTER XXII
PLANTS AND ANTS
Meaning of Plant Life--Captive and domesticated germs--Solomon's
observations denied by Buffon but confirmed by recent writers--Ants
as keepers and germinators of corn--Ant fields--Ants
growing mushrooms--Leaf-cutting ants--Plants which are
guarded by insects--The African bush--Ants boarded by Acacias
and by Imbauba trees--Ants kept in China and Italy--Cockchafer
_v._ ant--Scale insects--A fungus which catches worms 281
CHAPTER XXIII
THE PERIL OF INSECTS
The Phylloxera--French sport--Life history of the
Phylloxera--Cockchafer grubs--Wireworm--The misunderstood
crows--Dangerous sucklings of greenflies--"Sweat of heaven" and
"Saliva of the stars"--A parasite of a parasite of a
parasite--Buds--The apple-blossom weevil--Apple-sucker--The
codlin moth and the ripening apple--The pear midge--A careless
naturalist and his present of rare eggs--Leaf-miners--Birds
without a stain upon their characters--Birds and man--Moats--Dust
and mites--The homes of the mites--Buds, insect eggs, and parent
birds flourishing together 290
CHAPTER XXIV
RUBBER, HEMP AND OPIUM
Effects of opium--The poppy-plant and its latex--Work of the
opium-gatherer--Where the opium poppy is grown--Haschisch of the
Count of Monte Cristo--Heckling, scotching, and retting--Hempseed
and bhang--Users of haschisch--Use of india-rubber--Why
plants produce rubber--With the Indians in Nicaragua--The
Congo Free State--Scarcity of rubber--Columbus and
Torquemada--Macintosh--Gutta-percha 301
CHAPTER XXV
ON CLIMBING PLANTS
Robin-run-the-Hedge--Bramble bushes--Climbing roses--Spiny,
wiry stems of smilax--The weak young stem of a liane--The
way in which stems revolve--The hop and its little harpoons--A
climbing palm--Rapidity of turners--The effect of American life
on them--Living bridges--Rope bridges in India--The common
stitchwort--Tendrils--Their behaviour when stroked or tickled--Their
sensibility--Their grasping power--The quickness with
which they curve and their sense of weight--Charles
Darwin--Reasonableness of plants--Corkscrew spirals--The pads
of the Virginian Creeper--The ivy--Does it do harm?--Embracing
roots--Tree ivy 313
CHAPTER XXVI
PLANTS WHICH PREY ON PLANTS
The kinds of cannibals--Bacteria--Spring flowers--Pale, ghostly
Wood-flowers--Their alliance with fungi--Gooseberries growing on
trees--Orchid-hunting--The life of an orchid--The mistletoe--Balder
the Beautiful--Druids-Mistletoe as a remedy--Its parasitic
roots--The trees it prefers--The _Cactus Loranthus_--Yellow Rattle
and Eyebright, or Milk-thief, and their root-suckers--Broomrape
and toothwort--Their colour and tastes--The scales of the
toothwort which catch animalcula--Sir Stamford Raffles--A flower a
yard across--The Dodder--Its twining stem and sucker-roots--Parasites
rare, degenerate and dangerously situated 327
CHAPTER XXVII
PLANTS ATTACKING ANIMALS
Brittle Star _v._ algæ--Fungus _v._ meal-worm--Stag-headed
caterpillars--Liverwort _v._ small insects--Natural
flower-pots--Watercups of Bromeliads--Sarracenia and inquiring
insects--An unfortunate centipede--Pitcher plants: their crafty
contrivances--Blowflies defy them and spiders rob
them--Bladderwort's traps which catch small fry--Hairs and their
uses--Plants used as fly-papers--Butterwort _v._ midges--Its use
as rennet--Sundew and its sensitive tentacles--Pinning down an
insect--Suffocating and chloroforming the sundew--Venus' fly-trap
which acts like a rat-trap--Have plants a nervous system? 340
CHAPTER XXVIII
MOSSES AND MOORS
Peat-mosses and their birds--Moorlands--Cotton-grass--Scotch
whisky--Growth of peat-moss--A vegetable pump--Low-lying
and moorland mosses--Eruptions and floods of peat--Colonizing
by heather and Scotch fir--Peat-mosses as museums--Remains
of children and troopers--Irish elk--Story of the plants in
Denmark--Rhododendrons and peat--Uses of peat--Reclaiming the
mosses near Glasgow 353
CHAPTER XXIX
NAMES AND SUPERSTITIONS
Giving names the first amusement--Curious and odd names--A spiteful
naturalist--The melancholy Bartzia--Common names--British
orchids--Dancing girls and columbines--Susans--Biblical names--Almond,
apple, locust--Spikenard--Tares--Effects of darnel--Daffodil--Acanthus
leaf--Ghost-disturbing branches--Elder or bour tree--Its powers and
medicinal advantage--Danewort--Mandrake--How to pull it up--The
insane root--Its properties--Plants which make bones pink--The
betel nut--Henna--Egyptian and Persian uses--Castor oil--Leeks,
onions, and garlic--Ancient use of them 363
INDEX 375
LIST OF ILLUSTRATIONS
FACE PAGE
I. A SENTINEL PALM IN THE ANDREAS CAÑON, CALIFORNIA 24
II. THE GARDEN OF EDEN 32
III. A GIANT DOUGLAS FIR 40
IV. A DRAGON TREE IN THE CANARY ISLANDS 48
V. SHOOTING THE HOZU RAPIDS IN JAPAN 52
VI. A FOREST FIRE 66
VII. THRASHING CORN IN CHILE 83
VIII. WISTARIA IN KAMAIDO PARK, JAPAN 98
IX. GATHERING OLIVES IN THE SOUTH OF FRANCE 108
X. THE EGYPTIAN QUEEN HATARU'S EXPEDITION 113
XI. WEIGHING THE DAY'S WORK 120
XII. A TOBACCO PLANTATION IN CUBA 127
XIII. GIANT CACTUS NEAR ACONCAGUA VALLEY, CHILE 134
XIV. THEN 146
XV. AND NOW 147
XVI. A RICEFIELD IN CHINA 160
XVII. CULTIVATED BAMBOO IN A CHINESE PLANTATION 178
XVIII. CALTHROPS 185
XIX. A LEAF RAFT 205
XX. FELLING OF GIANT TREES IN CALIFORNIA 215
XXI. A BUSHMAN DIGGING UP ELEPHANT'S FOOT 220
XXII. PINEAPPLES AS A FIELD CROP 240
XXIII. BANANA CARRIERS IN JAMAICA 248
XXIV. A COCOANUT GROVE IN CEYLON 259
XXV. COTTON-FIELDS IN GEORGIA, U.S.A. 265
XXVI. RICEFIELDS IN THE CEYLON HILLS 272
XXVII. SUGAR CANE IN QUEENSLAND 279
XXVIII. GATHERING RUBBER IN TEHUANTEPEC 304
XXIX. A LIVING BRIDGE 313
XXX. IN A KENTISH HOP GARDEN 316
XXXI. CINNAMON PEELING IN CEYLON 331
XXXII. FUNGUS IN CATERPILLAR 340
XXXIII. AN ARCTIC ALPINE PLANT 354
XXXIV. LAKE DWELLINGS IN EARLY BRITAIN 359
THE ROMANCE OF PLANT LIFE
CHAPTER I
THE ACTIVITY OF VEGETABLES
Plants which move--Sensitive Plant--A tourist from Neptune--The
World's and the British harvest--Working of green leaves--Power
of sunshine--Work done by an acre of plants--Coltsfoot,
dandelion, pansies, in sunshine and in cold--Woodsorrel and
crocus--Foxglove--Leaves and light--Adventures of a carbon
atom--The sap--Cabbages and oaks requiring water--Traveller's
tree--The water in trees--An oasis in Greece--The associate life
of its trees and flowers.
When we remember either the general appearance or the way in which
a cabbage or a turnip appears to exist, it does not seem possible
to call them active. It is difficult to imagine anything less
lively than an ordinary vegetable. They seem to us the very model
of dullness, stupidity, and slowness; they cannot move even from
one field to the next; they are "fast rooted in the soil"; "they
languidly adjust their vapid vegetable loves" like Tennyson's Oak.
In fact one usually speaks of vegetating when anybody is living a
particularly dull, unexciting kind of life in one particular place.
And it even seems as if the books, which are supposed to give us the
best information about the study of plants, and which are not very
attractive little books, quite agree with the ordinary views of the
subject.
For one finds in them that plants differ from animals in being
"incapable of motion." This, of course, just means that an animal, or
rather most animals, can walk, swim, or fly about, whilst plants have
roots and do not move from one spot to another. But it is not true to
say that plants cannot move, for most plants grow, which means that
they move, and in some few cases, we find that plants behave very
much in the same way as animals do when they are touched or excited
in any way.
We shall have to speak about tendrils, roots, and insect-catching
plants later on. But it is perhaps the Sensitive Plant which shows
most distinctly that it can shrink back or shrink together when it is
bruised or roughly handled.
It will be described in its place, but just to show that this plant
can move of its own accord, it is only necessary to hold a lighted
or burning match about an inch or so below the end of a long leaf.
If one does this then all the little leaflets begin to fold up, and
finally the main stalk droops; soon afterwards other leaves higher
up the stalk begin to be affected in the same way, and fall limply
down one after the other. It is supposed that this movement frightens
a grazing animal, who will imagine there is something uncanny about
the plant and leave it alone. There are many respects in which this
reaction of the Sensitive Plant resembles that found in animals. It
does not take place if the plant is chloroformed or treated with
ether; the leaves also get "fatigued" if too often handled, and
refuse to rise up again.
There are, however, only a very few plants in which an immediate,
visible answer to a stimulus can be detected. But all plants are
at work; they have periods of rest which correspond to our sleep,
but during their ordinary working hours they never slacken off, but
continue vigorously active.
The life of man is so short that it is difficult to realize all
that is being done by the world of plants. It is necessary to get
beyond our human ideas of time. That is most conveniently done by
considering how our plant world would strike an inhabitant of the
planet Neptune. Our theoretical Neptunian would be accustomed to a
year of 60,127 days (164 of our years); we will suppose that three of
our years are a Neptunian week, and that ten of our days are about
three-quarters of a Neptunian hour, whilst two earth-hours would be a
minute to him.
If such a being were to observe our earth, he would be astonished
at the rapidity of our vegetable world. The buds would seem to him
to swell visibly; in the course of an hour or two, the bare boughs
of the trees would clothe themselves with the luxuriant greenery of
midsummer. Hops would fly round and round their poles, climbing at
the rate of a foot a minute. Bare places, such as the gravel heaps
near a sandpit, or the bare railroad tracks at a siding, would be
perhaps in one week entirely covered by rich grass and wild flowers.
In six Neptunian months a forest of graceful larches would spring up
to a height of seventy or eighty feet.
So that, if one thinks Neptunially, the activity of plants can be
easily realized.
The truth is that we are so familiar with common annual events, such
as the regular harvest every year, that we never seem to realize what
it means. There are some 1,400,000,000 human beings on the earth
to-day, and they entirely depend on the work done every year by
cultivated and wild plants.
Even in one of the least agricultural of all civilized countries,
such as Great Britain, the cultivation of plants is still the largest
national industry. In 1897 we grew enough corn to give a ration of
1lb. per diem to every inhabitant for 68 days, and we manage to get
a large amount from every acre (28 to 33 bushels per acre). In most
other countries the relative importance of land and of agriculture
generally is very much greater than it is in Britain.
Moreover, it seems at first sight as if all this harvest had been
made out of nothing at all. Plants do take in a small amount of
mineral matter from the earth, but these minerals form but a very
little part of the bulk of a tree or any vegetable substance.
A piece of wood can be burnt up in a fire and very little indeed of
it is left. A few ashes will indeed remain, which are the minerals
taken in from the earth, but all the rest has vanished into the
atmosphere. The water which was contained in the wood has become
steam and is evaporated; the woody matter consisted chiefly of
compounds of a chemical substance, carbon, which also becomes an
invisible gas (carbonic acid gas) in a fire and goes back into the
atmosphere.
When the piece of wood was formed in a growing tree, it is easy to
see where the water came from: it was taken in by the roots. Just
as flowers drink up the water in a vase, and wither if they do not
receive enough, so all plants suck up water by their roots. The
carbonic acid gas is taken into plants through their leaves and is
worked up into sugar, starch, wood, and other matters inside the
plant.
But there is another very interesting point about the way in which
wood is burnt in a fire; heat and light are obtained from a wood
fire. Where did that heat and light come from?
If you walk in summer, under a tree in full leaf, it is much cooler
than it is in the sunshine outside. This shows what happens: the
sunshine has been taken up or absorbed by the leaves of the tree. It
does not pass through the foliage, but the heat and light are stopped
by the leaves.
The light and heat which were used up by the leaves in making wood,
sugar, and starch come back again when that wood or starch is burnt.
So that the burning up of a bit of wood is just the opposite to the
formation of that wood in sunshine in a living tree. The important
point is that it is the sunshine which is used by plants to make
all these refractory bodies, such as water, carbonic acid gas, and
others, unite together to form sugar, starch, and wood.
As the earth revolves upon its axis, sunlight falls successively on
every acre of land. Almost everywhere it is intercepted by green
foliage. Each leaf of every plant receives and absorbs as much as it
can, and, for so long as the light lasts, its living particles are
hard at work: water or sap is hurrying up the stem and streaming out
of the leaves as water vapour. Carbonic acid gas also is hurrying
into the leaves; inside these latter first sugar and then starch is
being manufactured, so that the green cells become filled with starch
or sugar.
So soon as the light fails, the work begins to slacken. When darkness
sets in, the starch changes to sugar and passes down the leaf-stalk
into the stem, where it is used up in growth, in the formation of new
wood or in supplying the developing flowers or young buds.
Next morning when the sunlight touches the plant all its little
living cells set to work again, and another day's task is begun. It
is very difficult to understand what is going on inside the leaf. If
you were to imagine a square yard of leaves all taking in sunshine
and making starch as they do in fine weather; then if you weighed
all these leaves, and then weighed them again one hour after they
had been in the sunshine, of course that square yard of leaf surface
should be heavier, because a certain amount of starch has been formed
in it. The amount actually made in one hour has been estimated by
Dr. Horace Brown as 1/500 lb. So that 100 square yards of leaves
working in sunshine for five hours might make one pound of starch.
But one can estimate the activity of plants in another way. Look at
the amount of work done by the Grass, etc., on an acre of pasture
land in one year. This might entirely support a cow and calf during
the summer; all the work done by these animals, as well as all the
work which can be done on the beef which they put on, is due to the
activity of the grasses on that acre. Moreover it is not only these
large animals that are supported, but every mouse, every bird, every
insect, and every worm which lives on that piece of ground, derives
all its energy from the activity of the plants thereon.
All work which we do with our brains or muscles involves the
consumption of food which has been formed by plants under the warm
rays of the sun.
So that man's thoughts and labour, as well as that of every living
creature, is in the first instance rendered possible by sunshine.
But the sunlight, besides this all-important function, affects plants
in other ways.
One of the most interesting of the early spring flowers is the
Coltsfoot. On bare blackish and unsightly heaps of shale one may see
quantities of its golden blossoms. Now if one looks at them on a
fine sunny day, every single blossom will be widely opened and each
will turn towards the sun.
In wet cold weather every blossom will hang its head and be tightly
closed up. Exactly the same may be observed with the Dandelion, which
is, indeed, still more sensitive than the Coltsfoot. In cold wet
weather it is so tightly closed that it is barely possible to make
out the yellow colour of the flower, but on warm sunny days it opens
wide: every one of its florets drinks in as much as possible of the
genial sunshine. Both opening and closing are produced by the warmth
and light of the sun's rays.
It is also the same with Pansies. On a fine day they spread out
widely, but in cold wet weather the heads hang over and the whole
flower shrinks together.
Perhaps the most interesting of them all are the little Woodsorrel
and the Crocus.
Both are exceedingly sensitive to sunlight, or rather to the cold. A
mere cloud passing over the sun on a fine spring morning will close
up the flowers of the Crocus. In cold weather, if you bring one of
its flowers indoors and put it near a bright light it will open
widely, sometimes in a few minutes.
What produces these changes? It is very difficult to say, but every
change helps towards the general good of the plant. In warm sunny
weather insects are flying about, and they can enter the flower if it
is open. These insects help in setting the seed (as we shall see in
another chapter). In cold wet weather the flowers are best closed,
as the rain might injure the florets and because also no insects are
abroad.
Both the Foxglove and the Blue Vetch (_Vicia Cracca_) are specially
ingenious in their way of obtaining light. For the stalk of every
separate blossom bends so that its head turns to the best lighted or
sunniest side. Thus, if you have Foxgloves planted against a wall,
every flower will turn away from it; if you plant them in a circular
bed, every one turns to the outside, so that every flower can get the
sunlight.
Every one who has kept plants in a window knows that the stems turn
towards the light. This has the effect of placing the leaves where
they can get as much sunshine as possible. The leaves themselves are
also affected by sunlight. They seem to stretch out in such a way
that they absorb as much of it as they can.
That, of course, is what they ought to do, for they want to obtain
as much as possible of the sunlight to carry on the work of forming
sugar and starch inside the leaf.
Not only each leaf by itself endeavours to place itself in the
best light-position, but all the leaves on the same spray of, for
instance, Elm, Lime, or Horsechestnut, arrange themselves so that
they interfere with one another as little as possible.[1] Very little
light is lost by escaping between the leaves, and very few of the
leaves are overshaded by their neighbours on the same branch.
[1] Kerner, _Natural History of Plants_; also Scott Elliot,
_Nature Studies--Plant Life_.
Thus all co-operate in sunlight-catching. But, when a number of
different plants are competing together to catch the light on one
square yard of ground, their leaves try to overreach and get beyond
their neighbours.
On such a square yard of ground, it is just the competition amongst
the plants, that makes it certain that every gleam of light is used
by one or other of them.
Every one of all those plants of itself alters the slope of its
leaves and turns its stems so as to get as much light as possible.
This light, as we have seen, is taken in by the plant. It is used to
make the gas, carbonic acid,[2] unite with water: when these are made
to join together, they form sugar; if the sugar is burnt the heat and
light appear again.
[2] The gas Carbonic acid consists of one part of Carbon and
two of Oxygen. It is invisible, just as are the gaseous states
of many liquids and solids. Water-vapour is not visible, though
water (liquid) and ice can of course be seen. Starch, sugar, cell
wall substance, etc., all contain Carbon, Oxygen, and Hydrogen.
Vegetable fat is not well understood, but starch helps to form it.
By changing the amount and arrangement of the molecules in sugar,
starch or vegetable fats, and many other substances can be formed.
But it is the sunlight that makes all this possible.
Thus the sun not merely supplies the motive power for all animal
and vegetable activity but, by its influence, flowers, leaves, and
stems move and turn in such ways that they are in the most convenient
position to intercept its light.
The sunlight, though all-important in the life of most plants, kills
many kinds of bacteria and bacilli which love the darkness. The
well-known radium rays are also destructive to bacteria, and hinder
the growth of certain fungi (Becquerel's rays have a similar effect).
The X-rays are not so well understood, but one can close the leaflets
of the Sensitive Plant by means of them.
Carbonic acid gas forms but a small proportion of the atmosphere
which surrounds a growing plant. Yet there is no lack of it, for when
the leaf is at work forming sugar the particles of gas are rushing
into the leaf, and other particles come from elsewhere to take their
place. Every fire and every breath given off by an animal yields up
carbonic acid, so that it is constantly in circulation.
This is more easily seen by tracing the probable history of an atom
of carbon. We will suppose that it enters a grass leaf as carbonic
acid gas and becomes starch: next evening it will become sugar and
may pass from cell to cell up the stem to where the fruit or grain
is ripening. It will be stored up as starch in the grain. This grass
will become hay and in due course be eaten by a bullock. The starch
is changed and may be stored up in the fat of the animal's body. When
this is eaten at somebody's dinner, the fat will most probably be
consumed or broken up; this breaking up may be compared to a fire,
for heat is given off, and the heat in this case will keep up the
body-temperature of the person. The carbon atom will again become
carbonic acid gas, for it will take part of the oxygen breathed in,
and be returned to the atmosphere as carbonic acid gas when the
person is breathing.
Another atom of carbon might enter the leaves of a tree: it will be
sent down as sugar into the trunk and perhaps stored up as vegetable
fat for the winter. Next spring the vegetable fat becomes starch and
then sugar: as sugar it will go to assist in forming woody material.
It may remain as wood for a very long time, possibly 150 to 200
years: then the tree falls and its wood begins to decay.
The bark begins to break and split because beetles and woodlice and
centipedes are burrowing between the bark and the wood. Soon a very
minute spore of a fungus will somehow be carried inside the bark,
very likely sticking to the legs of a beetle. This will germinate
and begin to give out dissolving ferments which, with the aid of
bacteria, attack the wood. Our carbon atom is probably absorbed
into the fungus. Very soon the mushroom-like heads of this fungus
begin to swell and elongate; they burst through the bark and form a
clump of reddish-yellow Paddock-stools. A fly comes to the fungus
and lays an egg in it. This egg becomes a fat, unpleasant little
maggot which eats the fungus, and amongst others devours our carbon
atom, which again becomes fat in its body. Then a tomtit or other
small bird comes along and eats the maggot. That bird stays out too
late one evening and is eaten by an owl. The owl, satisfied with a
good meal, allows itself to be surprised and shot by a keeper. When
its body is nailed to a door and decays away, the carbon atom again
takes up oxygen and becomes carbonic acid gas, which escapes into the
atmosphere, and is ready for a fresh series of adventures.
We must now consider the water which with carbonic acid gas makes up
sugar, etc. All plants contain a large percentage of water. This may
be as much as 95 to 98 per cent in water plants, and 50 to 70 per
cent. in ordinary tissues; it is contained in every sort of vegetable
substance.
But there is also a stream of water or sap which is almost always
entering the roots, rising up the stem, and passing into the leaves.
On these leaves there are hundreds of minute openings called stomata,
by which the water escapes as water-vapour into the atmosphere. A
single oak leaf may have 2,000,000 of these stomata.
It is this current of sap which keeps the leaf fresh and vigorous; it
is also by this current that every living cell is supplied with water
and kept in a strong, healthy condition.
The amount of water used in this way is very great; in four months
an acre of cabbages will transpire or give out through its leaves
3,500,000 pints of water and an acre of hops from 5-1/2 to 7
millions. A single oak tree, supposed to have 700,000 leaves, must
apparently have given off into the atmosphere during five months
230,000 lb. of water.
Sometimes the water is so abundant in the plant that it collects
as drops on the tips of the leaves and falls off as fluid water. A
very young greenhouse plant (_Caladium nymphaefolium_) was found by
Molisch to give off 190 water-drops a minute, and in one night it
exuded one-seventeenth of a pint.
The water is found stored up in the stems or leaves of plants,
especially those of hot or dry climates. The Madagascar Traveller's
Tree, _Ravenala_, has a considerable amount of water in a hollow at
the base of its leaf, and it is possible to drink this water. The
usual story is to the effect that a panting traveller finds this
palm in the middle of the desert, and saves his life by quenching
his thirst with its crystal-clear water. Unfortunately the tree
never grows far from marshy ground or springs, and the water, which
I tasted for curiosity, had an unpleasant vegetable taste, with
reminiscences of bygone insect life.
These are, of course, exceptional cases; as a rule the tiny
root-hairs search and explore the soil; the sap or ascending current
passes up the stem and pours out into the atmosphere. There the
vapour is hurried off by winds, and eventually condenses and, falling
as snow or rain on the earth, again sinks down into the soil.
It is very difficult to understand how the sap or water rises in the
trunks of tall trees; we know that along the path of the sap inside,
the root-hairs and other cells in the root, the various cells in
the stem, and finally those of the leaf, are all kept supplied and
distended or swollen out with water. All these living cells seem to
have the power of absorbing or sucking in water,[3] and eventually
they are so full and distended within, that the internal pressure
becomes almost incredible. Wieler found in the young wood of a Scotch
fir that the pressure was sixteen atmospheres, or 240 lb. to the
square inch. Dixon, when experimenting with leaf-cells, found ten,
twenty, or even thirty atmospheres (150 to 450 lb. to the square
inch). No locomotive engine has cylinders strong enough to resist
such internal pressures as these. It is an extraordinary fact, and
one almost incredible, that the cells can stand such pressures.
[3] The ascent is assisted by the osmotic absorption of water at
the root and by evaporation at the leaves.
[Illustration:
_Stereo Copyright, Underwood & Underwood_
_London and New York_
A SENTINEL PALM IN THE ANDREAS CAÑON, CALIFORNIA
This and such palms are often placed at the mouths of cañons to
indicate water, and may, indeed, thus save the lives of passing
travellers.]
Yet these minute living cells not only exist but work at this high
tension, and, in some cases, they live to about fifty years.
In this favoured country of Great Britain, it is unusual to find any
serious lack of water. But in Italy or Greece, every drop of it is
valuable and carefully husbanded.
Sometimes in such arid dry countries, a small spring of water
will form around itself a refreshing oasis of greenery surrounded
everywhere by dreary thorn-scrub or monotonous sand. All the plants
in such a spot have their own special work to do: the graceful trees
which shade the spring, the green mosses on the stones, the fresh
grass and bright flowers or waving reeds, are all associated in a
common work. They protect and shelter each other; their dead leaves
are used to form soil; their roots explore and break up the ground.
It is true that they are competing with one another for water and for
light, but they are all forming a mutual protection, and producing an
annual harvest.
In a climate like our own we cannot, like the Greek, suppose a Nymph
in the shape of a lovely young woman watching over the spring, for
she would infallibly suffer from rheumatism and ague.
But every living cell in every plant in such an oasis depends upon
the water of the spring. All the plants there form an association
which can be quite well compared to a city or some other association
of human beings. They do compete, for they struggle to do the most
work for the good of the community, and they incidentally obtain
their livelihood in the process.
Most plant societies or associations such as those which cover Great
Britain are not so obviously dependent on one particular spring, but
the plants composing them are associated in a very similar way.