+Habit of Growth in Plants+ 313
Tropical forest—Perching orchids not parasites—Mistletoe—
Yellow rattle—Saprophytes—Murderer fig-tree—Mutualism—Corn
blue-bottle—Clover and bacteria—Symbiosis in white poplar
and fungus—Sea anemone and algæ—Bryony tendril—Mycetozoa.
+Glossary+ 335
LIST OF ILLUSTRATIONS
+NEPENTHES RAFFLESIANA+ _Frontispiece_
PAGE
+WATER BUTTERCUP+ 36
+VALLISNERIA+ 37
+CATTLEYA WALKERIANA+ (_A Brazilian Orchid_) 41
+YOUNG SCOTCH FIR GROWING IN HOUSE-LEEK+ 44
+CREEPING GRASS+ 56
+POA BULBOSA+ 57
+LILY BULBILS+ 60
+CLOVER DODDER+ 64
+SECTION OF ROOT CAP+ 68
+TURKEY OAK BARK+ 76
+SCOTCH FIR BARK+ 77
+SNAKE-BARK MAPLE+ 78
+TURKEY OAK STEM+ (_struck by lightning_) 79
+PLANE TREE BARK+ 80
+HORSE-CHESTNUT BARK+ 81
+WHITE POPLAR BARK+ 82
+SYCAMORE BARK+ 83
+TREE-FERN BARK+ 84
+STEM OF YELLOW WATER-LILY+ 87
+STEM OF WHITE WATER-LILY+ 87
+GROUP OF BEECH-TREES WITH INTERLACING STEMS
AND ROOTS+ 93
+CONVOLVULUS+ 94
+NETTED VEINS+ 100
+MONOCOTYLEDON+ 101
+DICOTYLEDON+ 102
+TAMARIND SEEDLING+ 103
+STOMATA+ 107
+LEAF SECTION+ 109
+YOUNG SHOOT OF EUCALYPTUS+ 116
+MATURE FORM OF EUCALYPTUS LEAVES+ 117
+OAK IN WINTER+ 127
+OAK IN SUMMER+ 129
+HORSE-CHESTNUT+ 135
+YOUNG BEECH+ 138
+UNFOLDING ARUM LEAF+ 140
+UNFOLDING LEAVES OF HART’S-TONGUE FERN+ 140
+PEAR LEAF+ 140
+BUDS OF WAYFARING TREE+ 145
+PRIMROSE+ 153
+POINSETTIA+ 157
+WINTER CHERRY+ 160
+WALLFLOWER+ 162
+SWEET-PEA+ 165
+BIRCH FRUIT+ 168
+WILD ARUM+ 170
+PRIMROSE+ 179
+MAIDEN PINK+ 181
+ARISTOLOCHIA+ 186
+STAPELIA+ 188
+HYPERICUM+ 189
+TOAD-LILY+ 191
+POLLEN-GRAINS+ 196
+WHITE-LILY PISTIL. SECTION OF PISTIL+ 197
+POLLEN TUBE+ 198
+SECTION OF COCOA-NUT+ 203
+SPINDLE-TREE+ 204
+NUTMEG AND MACE+ 205
+CLEMATIS OR TRAVELLERS’ JOY+ 206
+SECTION OF PEACH+ 216
+POPPY CAPSULE+ 217
+WOODY PEAR+ 218
+PINE-CONES+ 223
+SEED-POD OF MARTYNIA+ 230
+BIRCH SEED+ 232
+PARACHUTE+ 234
+DANDELION SEED+ 235
+GOAT’S-BEARD+ 236
+COCOS-DE-MER+ 238
+BROOM AND SWEET-PEA PODS+ 242
+STIPA PINNATA (FEATHER GRASS)+ 244
+BIGNONIA SEED+ 252
+DOUBLE EMBRYO OF ORANGE+ 255
+BROAD BEANS+ 258
+GROWING MUSTARD SEEDS+ 261
+BEECH COTYLEDONS+ 264
+ACORN+ 266
+HORSE-CHESTNUT+ 267
+YOUNG DATE-PALM+ 269
+TRANSFUSION DIAGRAM+ 278
+SKELETON LEAF+ 284
+SUNDEW+ 300
+VENUS FLY-TRAP+ 304
+SARRACENIA FLAVA+ 306
+BLADDERWORT+ 308
+PITCHER OF NEPENTHES RAFFLESIANA+ 309
+BUTTERWORT+ 311
+PERCHING ORCHID+ 317
+RAFFLESIA ARNOLDII+ 320
+GIANT COW-PARSNIP+ (_Heracleum Giganteum_) 325
+CORN BLUE-BOTTLE+ 326
+BRYONY TENDRIL+ 331
+TRICHIA THROWING OUT SPORES+ 332
“To me be Nature’s volume broad display’d,
And to peruse its all-instructing page;
Or, haply catching inspiration thence
Some easy passage raptur’d to translate,
My sole delight.”
+Thomson.+
CHAPTER I
_ADAPTATION_
“My heart is awed within me, when I think
Of the great miracle that still goes on
In silence round me—the perpetual work
Of Thy creation, finished, yet renewed
For ever. Written on Thy works, I read
The lesson of Thine own eternity.”
+Bryant.+
CHAPTER I
ADAPTATION
The study of plants appears to me to be one of the most delightful and
instructive that can be taken up by young people. It has this advantage
over many other pursuits that it can be carried on almost everywhere,
for, even if the student’s lot is to live in a town, there are
generally botanic gardens within reach, and visits paid in the country
are made the more enjoyable when some special study can be carried on
in the daily walks.
Then collections of dried leaves and flowers can be formed during the
summer, and the arrangement and classification of these will provide
pleasant winter occupation.
I fear that many young people are apt to consider botany a very dry
study. They are naturally repelled by the long words and many technical
terms used in describing plants.
It has long been my belief that the study of botany should be
approached through the garden rather than the schoolroom, beginning
with a country ramble which should be an object-lesson opening out
endless paths for future study.
Our Heavenly Father has given us a beautiful world to live in, and,
when our eyes have once been opened to observe what lies around us,
nature becomes like an exquisite book of pictures, always revealing to
us something new and wonderful as we turn over each fresh page.
It is suited to all ages; the baby child begins by gathering daisies
and buttercups, while older children make wild-flower collections and
perhaps work in their own little gardens watching the growth of seeds
and slips.
The beauty of ferns and mosses is sure to lead to some painstaking
study of those fascinating growths.
Later on the fact that all trees have flowers comes as a surprise to
the unobservant, and thus, when rightly guided, young people can hardly
fail to love a pursuit that promises such endless sources of interest.
In the chapters that will follow on the subject of plant life, I do
not purpose to write for quite young children, as my hope is that
older readers will explain what is written, and make it interesting to
the little ones as they walk in gardens and fields, giving as it were
object-lessons on buds, leaves, and flowers, and training young minds
to search for themselves into the wonders that lie around them.
How much there is to learn about, even in the simplest things, some of
the succeeding chapters will endeavour to show, for example:
How young plants grow out of seeds;
How those seeds are dispersed;
How much is folded up in a bud;
How flowers are formed;
How the bark splits off different trees.
Any one of these subjects would need very careful, patient observation
truly to understand it.
I stand as it were only on the threshold of scientific research, and
look with wonder at the work of such a student as Darwin, who gave
twenty long years to observation of the common earth-worm before he
wrote his deeply interesting book upon it. Again, we see Sir John
Lubbock giving years of his life to the growing of seeds and their
seed leaves, in order to learn exactly how plants begin their life,
and two very thick volumes are required to contain the vast amount of
information he has thus obtained.
These two examples will suffice to show that the minutest objects in
nature are worthy of reverent attention, and if these chapters tend to
awaken young people to a perception of this fact and act as a humble
guide to new lines of thought, I shall feel that they have not been
written in vain.
I fear it is impossible to explain the processes nature is carrying on
in the plant-world without occasionally using scientific words, but,
when I am obliged to do so I shall try to explain their meaning,[1],
and when once we rightly understand an exact expression we soon begin
to use it, because it is more convenient and often saves repeating a
long sentence.
[1] See glossary at the end of the book.
I would ask my readers to try and obtain from their gardens and fields
the various objects mentioned at the close of each chapter, and
compare them with the plates, learning all about them as they read the
letterpress.
This will, I feel sure, add much interest to the study, for having
something to collect and examine tends to lighten mental work and
enables us better to understand descriptive writing.
In this introductory chapter I will simply take a general view of
vegetable growth and its adaptation to the situation in which it is
found.
In many respects plants require the same conditions as animals, birds,
and insects; they must have air, food, moisture and light in order to
attain healthy growth, and although they differ from animals in being
usually stationary, their life is carried on in a very similar way. Let
us take a forest tree as a type.
It is anchored in the soil by its roots which are its feeding organs;
through them it draws up various kinds of nourishment from the earth
in which it stands.
The roots by several chemical processes render the elements they have
taken up from the soil fit for the nourishment of the tree; they send
it up through the stem and branches into the leaves, and these being
the breathing organs have essential work to do in receiving from the
air, and giving out again, certain gases which contribute largely to
maintain the life and vigour of the tree. Thus it grows year by year,
producing annually its flowers and seed, which is the end and aim of
all plant life.
We can trace another analogy with animal life, in the necessity for
pure sweet air, plants growing in a vitiated or smoke-laden atmosphere
soon showing unmistakable signs of weakness. The stunted hedges and
trees on the fringe of London always remind me of the poor, ill-grown
children of the slums.
Besides the plant life which we see around us in the shape of trees,
shrubs, and flowers, there are lower and perhaps still more wonderful
forms of vegetable life affording endless fields of study.
Mosses, lichens, and fungi we are familiar with everywhere in the
country, but below these again are such growths as the green stain[2]
which makes the tree trunks in moist places as brilliant in colour
as the leaves themselves. Looked at through a lens we see the colour
arises from a growing plant of extremely simple form, little more in
fact than a succession of cells, each living and increasing “after its
kind.”
[2] _Protococcus._
Again, if we consider the process of fermentation, we find that when it
is set up in a cask of wine its action is due to the growth of a minute
vegetable that feeds upon the alcohol and sugar, and by robbing the
wine of those two elements turns it into vinegar or acetic acid.
A somewhat similar growth causes the thick jelly-like substance we
sometimes find in our inkglass when it has been allowed to remain too
long without renewal; the minute germs floating in the air have found
the ink suitable to them, and thus their mycelium[3] begins to form at
the bottom of the glass, to the great discomfort of the writer.
[3] First form of fungoid growth.
The yeast with which our bread is fermented is another of these minute
plants, and consists of oval cells which multiply with great rapidity
when placed in a pan of flour, and kept in a warm atmosphere.
By the careful study of these lower forms of vegetable life, Pasteur,
Koch, Frankland, and others have discovered and classified the germs or
microbes,[4] as they are called, which give rise to various diseases.
In books upon the subject, their different shapes are figured as they
appear when immensely magnified, so that we can see that which will
give rise to consumption, erysipelas, or cholera, and one reads with
deep wonderment of all that science has ascertained of late years as
to the presence in the air of these seeds of disease which are ever
floating more or less around us. But for the restraining hand of God,
it appears as if universal sickness and death would be our fate.
[4] Small living atoms.
Leaving these lower forms of growth, we may consider the three
divisions into which plants are naturally classed as to their duration
of life.
Annuals are those which grow and flower, and form their seeds in one
year, within which their life-history is closed.
Biennials produce leaves only in the first year; by their aid they lay
up stores of nutriment in the form of tuberous roots, on this food they
can exist through the winter, produce flowers the following summer,
perfect their seeds, and then die.
To this class we owe such useful plants as the carrot, parsnip,
beetroot, and many others which afford us such nourishing vegetable
diet.
Perennial plants live on for an indefinite number of years, flowering
annually, in some cases dying down to the root in autumn, and producing
fresh foliage the following year.
Water plants seldom have a fixed root, but remain floating, borne up
and kept in position by the water, their roots being the means by
which, in conjunction with the leaves, they derive nourishment from air
and water. It is well worth while to observe the two forms of leaves
in the water buttercup. Those on the surface are three-lobed, flat,
and round, they absorb from the air such gases as the plant requires;
while the leaves beneath the surface are divided into threads so as
to offer no obstruction to the flow of water and enable the plant to
collect needful food from the water. It can vary the form of its leaves
according to its requirements, since in running streams it may often be
found with the hair-like leaves only.
[Illustration: WATER BUTTERCUP.]
On the other hand, if its seeds are sown in moist earth, the seedlings
will grow and develop those flat leaves only which are characteristic
of land plants. This water buttercup, therefore, gives us a wonderful
example of adaptation to surrounding influences.
[Illustration: VALLISNERIA.]
Adaptation is remarkably shown in the Vallisneria, a grass-like
water-plant, found in Southern Europe;[5] it grows in freshwater lakes,
rooted in the mud, and yet its flowers need to be fertilised in the
air. In order to effect this, the small male flowers detach themselves
from their stems, and, rising through the water, float about upon its
surface. The female flowers are borne on a stalk, spirally twisted, so
that it can uncoil and allow the flower to reach the top of the water
whether it be deep or shallow. There the two kinds of flowers meet, the
seeds are formed and the stem coils up again and brings the capsule
below the surface, where it gradually matures.
[5] It can generally be met with at naturalists’ shops where aquaria
are sold.
The water-lily can grow a long or short stem as the depth of the water
may require to enable its leaves to lie flat upon the surface. I have
gathered lily flowers in my lake with stems from four to five feet
long, where the plant happened to be growing in deep water.
In such plants as the mare’s-tail (_Hippuris vulgaris_), we find the
stem specially adapted to a submerged life. Growing out of mud at
the bottom of a stream the plant upholds its slender stalks by two
different methods. Inside the epidermis (or outer skin) a strand of
rather tough tissue running through the centre gives flexible support,
whilst the rest of the space is filled up with very large air cells,
which give such buoyancy to the stems that even if they are three feet
in length they are kept upright in the water, rising ten or twelve
inches above the surface. It is a valuable as well as a curious plant,
as it has the property of absorbing the gases emitted by stagnant
water, and tends thus to purify the air.
The same power of adaptation is to be found in sea-weeds. Those growing
on rocky shores having short fronds covered with fructification, while
out at sea, ribbons of oar-weed may be found many yards in length,
formed, like the gulf-weed, of tough texture to bear the friction of
waves and storms.
If we were travelling in a Mexican desert, we should find those
remarkable plants which can be so well studied in the cactus-house at
Kew Gardens. Bearing in mind that for many months the plant must do
without a drop of rain, or in fact without moisture of any kind, it has
been necessary that the leaf-surface should be reduced to prevent loss
of moisture by evaporation, and so spines take the place of leaves, and
the stems are encased in a thick leathery skin, which protects the
plant from the burning heat of the sun. Very little moisture escapes
through this thick green epidermis; therefore when rain falls the
plants receive and store up their liquid food, and live sparingly upon
it during the long periods of drought, which last for three-quarters
of the year. Some of these cacti, as we see them at Kew, are tall,
straight-stemmed plants, others low-growing rounded masses, little
spiny cushions, almost like vegetable hedgehogs.
In the arid prairies of Texas, advantage is taken of the watery stores
of the cactus, for when other supplies fail, its fleshy stems are cut
open, and horses and cows greedily devour the succulent food, which
answers the purpose of drink, as well as affording nutritious fodder.
Our British spurge-plants have green leaves, a thin epidermis, and all
the ordinary characters of the plants of a temperate region, but by
comparing them with the spurges found in Madeira, we see how climate
causes adaptation to differing conditions. One of these spurges growing
in my greenhouse has a tall column-like stem, no leaves, and a thick
leathery skin, which would enable it to bear a hot, dry climate. It
thus mimics the giant cacti of Mexico.
[Illustration: +CATTLEYA WALKERIANA+ (_a Brazilian Orchid_).]
We may trace another contrast in our common groundsel and the large
succulent groundsels of the Cape and the Canary Isles, with their thick
fleshy leaves, the difference in form and texture being simply an
expression of the wonderful modification due to climate.
The lovely tribe of orchids make the same provision for long periods of
drought. Many of the species live in countries where the rainy season
lasts about six months, and is succeeded by as many months of dryness
and heat.
The air-plants we obtain from these countries have large pseudo-bulbs,
that is, the stems are enlarged so as to be storehouses of nutriment
upon which the plant exists, and by means of which it brings out the
gorgeous flowers which make Brazilian forests such fairylands of
beauty; every tree-branch being laden with parasitic orchids, their
lovely blossoms lasting month after month without the aid of rain or
dew, because Nature has provided each plant with its special store of
food, and has thus adapted it to the position it is created to adorn.
Another of these perching-plants is _Tillandsia Usneoides_, known in
Florida as Spanish moss, and often called “old man’s beard.” It hangs
from the tree-branches in tufts, like grey hair, and grows in such
profusion that it is collected and used for stuffing cushions. This
curious plant has no roots, but simply hangs from the branches, and
lives like the orchids by absorbing water from the moist air in the
humid forests where it is found.
The absorption by the long, hanging, grey roots of the orchids in one
case, and by the finely-divided leaves and stems in the other, are both
instances of the wonderful way in which Nature “adapts” the parts of a
plant to its requirements.
It often happens that seeds, blown hither and thither by the wind,
chance to fall upon places which are quite unsuitable to their mode
of growth; then we have an opportunity of seeing how their power of
adaptation enables them to triumph over almost insuperable difficulties.
I have observed a tiny plant of groundsel growing out of a chink in
a wall where there was scarcely any soil from which it could derive
nourishment, contriving to live on, however, and make the best of its
hard lot. Its stem, which should have been a foot high, could only
attain about two inches, and instead of dozens of leaves it had but
four, and yet it survived and even produced two small flowers, thus
touchingly displaying its power of adaptation.
[Illustration: YOUNG SCOTCH FIR GROWING IN HOUSE-LEEK.]
Another more remarkable instance which occurs to me was that of a
seedling Scotch fir, which had rooted itself in a lump of house-leek
on the top of a garden wall. For eight years the young tree managed to
live and grow, until it became a symmetrical well-branched fir-tree,
almost twelve inches high. By a supreme effort it produced a crop of
miniature cones, and soon after it died from drought and starvation,
the wonder being that it could have lived so long upon the modicum
of food the barren wall supplied, besides having to endure at times
periods of scorching heat as well as drought. The chief interest in
this example is centred in the fact that as soon as fruit-bearing has
been attained, then, and not till then, the little tree died, showing
how persistently under all hindrances and difficulties a plant will
endeavour to carry out the purpose of its creation.
We have seen in these instances some striking examples of the way in
which plant-life is adapted to its surroundings. Our examples have
been such as are easy of attainment, and such as we can verify with
our own eyes; but even more wonderful are the adaptations hidden away
in the recesses of the plant, and as we progress in our study these
arrangements of cells and tissues will be revealed to us. In order
however to see them, and to understand their true significance, we must
proceed step by step to study the parts of an ordinary plant; because
it is only by first mastering all we can of one part of a plant, and
then comparing that part with other plants, that we can hope to gain
real knowledge. Accordingly in our next chapter we shall take the root
as our starting-point, and ascertain its functions and uses, and the
part it has to play in the economy of the plant.
Specimens to be obtained:—Green stain on treebark (_Protococcus_);
yeast; annual, biennial, and perennial plants; water buttercup leaves;
vallisneria; water-lily stems; mare’s-tail plant; cacti; spurge;
orchids; tillandsia; plants growing in wall crevices.
CHAPTER II
_ROOTS_
“While thus through all the stages thou hast push’d
Of treeship—first a seedling, hid in grass;
Then twig; then sapling; and, as century roll’d
Slow after century, a giant bulk
Of girth enormous, with moss-cushion’d root
Upheaved above the soil.”
+Cowper.+
CHAPTER II
ROOTS
Let us begin our study of roots by considering the way in which plants
obtain their nourishment from the earth, and are kept in an upright
position by means of their root-fibres. These being out of sight, we
may easily not be familiar with this part of the economy of plant life,
but we shall soon see what important duties the roots have to fulfil,
and how much they vary in character and appearance according to the
soil, the climate, and the work they are required to do. The greater
number of annual plants (those which live only one year) have fibrous
roots, and of these we can find examples almost everywhere. A piece of
groundsel or tuft of grass will answer our purpose. On pulling it out
of the ground we see a bunch of whitish threads or fibres springing
from the crown of the plant (which is the junction between the stem and
the root), and on these slender fibres are hairs which are really the
active part of the root, for it is only through these hairs that the
rootlets are able to absorb the liquid from the soil, the fibres simply
acting as channels to convey the watery nourishment to the stem and
leaves.
Common earth consists of small particles of mineral substances such as
flint, chalk, or iron, and also of such vegetable matter as decayed
leaves and rotten wood.
The spaces between the particles are more or less filled with air, each
mineral particle being enveloped with a film of water. However dry
the soil may appear, this will always be found to be the case. It may
be tested by weighing in an agate balance some dry soil on a summer’s
day. There is a very delicate instrument called a hygroscope, which can
tell us when there is the slightest amount of moisture in the air, and
a clever German writer, Von Sachs,[6] has termed this film of water,
which gathers round earth-particles, hygroscopic water. It has been
ascertained by careful experiment that it is only on this delicate
watery film that the root-hairs of plants are able to feed. As these
hairs drain away the hygroscopic film it is always being renewed by the
free water which comes from rain and dew. The free water of the soil is
constantly passing from the surface to the subsoil, and by this action
plant-food, in the form of soluble earth salts, is presented to the
roots. The passage of the water is of the highest service to the roots,
since the warm air follows the water through the soil, and helps to
oxidise the mineral particles; these are thus rendered soluble, and are
taken up by the fine films of water, and so indirectly the roots are
fed. If, however, there is no outlet for the water and the soil becomes
water-logged this beneficial action is retarded, and to land-roots the
water is hurtful.
[6] Author of “Vegetable Physiology.”
We can now understand why stagnant water in the ground is so injurious
to plant-life, as it prevents the needful air from coming into contact
with the roots, and this is the reason why farmers are careful to
remove the surplus water from their fields by thorough drainage and
ploughing. Roots adapt themselves very wonderfully to their situation.
This piece of grass, which we are examining, if it grew in sandy soil,
would have its root-fibres covered with a downy growth to enable them
the more readily to absorb every particle of moisture in the sand.
Dr. Bonar speaks of the date-palm as having this same characteristic.
“These palm roots are peculiarly fitted to obtain every drop of water
that the sand contains; they consist of long fleshy strings or ropes,
shooting straight down into the sand, in numbers quite beyond our
reckoning, and extending over a large circle.”
The tendency of fibrous roots to bind sand together is taken advantage
of on many of our sea-coasts, where the sand blows inland and renders
acres of ground sterile and useless. There, if the _Carex arenaria_
(a kind of sedge) is planted, its roots will spread far and wide,
interlacing and creeping through the sandy soil, until in time the
latter becomes solid and no longer drifts inland.
An allied species of grass, _Psamma arenaria_ (or marrem grass) grows
abundantly at Bournemouth, and wishing to ascertain how far one of its
underground stems extended, with some amount of patience I disinterred
about six or seven feet of it in a bank on the sea-shore where it was
accessible. As it seemed to have no end, I could not ascertain its
entire length.
Another instance of root growth adapting itself to situations occurs to
me. In visiting the Cheddar Cliffs in Somersetshire I was struck by the
beauty of a plant which grew here and there out of the crevices of the
rocks. Its tufts of vivid green leaves looked so healthy and vigorous I
could not help wondering how it could obtain moisture enough to produce
such foliage, placed as it was high up on the dry face of a rock.
Failing to reach its roots in any other way, I climbed up to a spot
where I could remove some of the horizontal layers of stone. At last I
lifted a flat piece of rock just above one of those plants, and there I
saw at a glance the secret of its vigorous growth:
The roots had spread out over the surface of the stone for a distance
of eight or nine inches in a perfectly flat layer of fine fibrous
rootlets no thicker than a sheet of paper; these would doubtless suck
up abundant moisture whenever the rain beat upon the rocks, and there,
pressed closely between the two layers of stone the plant has its
water-supply stored up, and is enabled to look fresh and green when
other vegetation is suffering from drought.
In plant-life there is a marvellous variety in root-structure. Roots
differ much, not only in form, but in texture and duration of life, so
that to gain a true knowledge of them we must carefully examine those
of herbs, shrubs, and trees, and observation will soon teach us the
fact that there exists a close correlation between the form and texture
of the root and the size and character of the plant. The external
shape will depend principally upon whether a tap-root is developed
or no. Such, for instance, as the carrot and the dock are those of
the true tap-root character. Of branching roots we may find endless
modifications amongst ordinary field or garden flowers from the fibrous
roots of the little groundsel to the large fleshy tubers of the dahlia.
Between these two types there are others of an intermediate kind, but
it is possible to recognise amongst common plants the roots belonging
to one or other of the types I have described. For the purposes of
study we may broadly group roots into classes according to their method
of collecting and absorbing food. Thus we find one group growing in
soil and feeding upon the soluble earth salts and moisture of the soil.
Another group will be found growing in water, like the water-lily and
pond weeds. A third group simply hangs down in space from some perching
plant like the tropical orchid, whilst a fourth and very small group
consists of parasitic roots, of which a very common example is the
mistletoe. We will now study each of these groups separately.
I have already spoken of some kinds of fibrous roots, and may add that
if the root of a land plant is immersed in water, it will after a time
develop a different kind of fibre, capable of receiving nourishment
from water instead of earth. I remember seeing an instance of this in
the case of a laurel bush which grew near a well in our garden. We had
occasion to examine the water, and found that the laurel had thrown
down its roots below the surface, where they grew luxuriantly, finely
subdivided, of a delicate ivory white, owing to the absence of light,
and more than a yard in length. They had adapted themselves to the duty
of absorbing water only, but had we replanted them in earth they would
have withered, from their unfitness to take up the hygroscopic water of
which I have already spoken. On the other hand, if the seeds of a plant
formed to live in the water, such, for instance, as the water-lily, are
sown in ordinary soil, they adapt themselves to the new conditions,
and are able to live on the hygroscopic water they find around the
particles of earth.
[Illustration: CREEPING GRASS.]
Some plants send out a horizontal stem (culm) along the ground, with
a bud and some roots growing out of it at regular intervals. Each of
these joints (or nodes) takes root and forms a separate plant. What
are called strawberry runners are stems of this kind, and so are the
creeping stems of _Potentilla reptans_.
[Illustration: POA BULBOSA.]
I once found a plant of the latter growing on a low wall, and, as I
imagine, because it desired to reach the ground and root itself there,
it had thrown down a stem a yard and a half long with eight young
plants growing upon it at intervals ready to form so many colonies
when they should reach the ground.
One may frequently find stems of various grasses running along the
ground, and taking root at each joint. I have one such spray in my
herbarium, with twelve young plants upon it at regular intervals.
Some plants store up nourishment in their roots, as may be seen in one
of our common seaside grasses (_Poa bulbosa_); this soon withers after
flowering, and becoming uprooted, its bulbs, which are like small round
cheeses strung together, may be seen blowing about in the wind.
With such a provision as this, the parent plant is able to bear
extremes of cold and drought.
It is well for us that plants have this power of storing up their food
underground, for to it we owe such useful tubers as the potato and
Jerusalem artichoke.
One of our native plants, the earth-nut (_Bunium flexuosum_), has a
single round tuber which is eatable when roasted, and is often dug up
by children. Long ago, when England was liable to famines, even this
small tuber was valued as a means of eking out the labourer’s daily
meal. It is worth while to examine the curious divided tubers of some
of our common orchises, such as the spotted orchis (_O. maculata_), or
the meadow orchis (_O. morio_). The tuber which produces the leaves and
flowers withers away at the end of the summer, but it leaves behind it
a second tuber in which is stored up the nourishment required to enable
it to bring forth leaves and flowers in the following spring.
Tubers are in reality underground stems which have thickened into
rounded balls to contain plant food.
[Illustration: LILY BULBILS.]
If we examine a potato we shall see that it contains true buds in the
little hollows on its surface; these are called “eyes,” and each of
them if sown in the ground will produce a new potato plant. If a potato
is left in a damp cellar, each of these eyes will send out a stem, thus
proving that the “eye” has the nature of a bud. If we cut the potato in
half we shall see it is of an even substance mainly composed of starch,
but if we halve an onion it will be found to consist of rings or
layers of a thick fleshy nature, which proves it to be a bulb and not
a tuber. The onion is like a large bud growing underground, instead
of on a tree branch. We can prove how similar the onion and the bud
are, by searching on a lily stem for buds or bulbils, which are often
produced in the axils of the leaves; if we plant such a bud it will
throw out fibres and become a bulbous-rooted plant. Some of our native
grasses seem to have a singular power of adapting themselves to their
position. For instance, the common Timothy grass (_Phleum pratense_),
which usually lives by means of a fibrous root, can, if needful,
produce a bulb which enables it to keep living in a very dry place, but
if removed to a wet soil it returns to a fibrous root. Other grasses
have been observed to alter their root-growth in the same way, adapting
themselves to their surroundings.
+Air Roots.+
These absorb the watery vapour of the air; they cannot adapt themselves
to live in earth, but under certain conditions they can put forth other
kinds of roots that are partially adapted for growing in soil.
I may here give some personal observations about a certain _Hoya_ plant
that came into my possession so long ago as 1855. This muchenduring
plant lived in a hanging basket for many years, in the dry air of a
sitting-room. Its leaves were sometimes shrivelled from lack of water,
and it never had vigour enough to produce flowers. At last, after
enduring this life for twenty years, it was placed in a stove-house
where the moist heat suited its requirements. Then it flowered
charmingly, and even now is showing a further degree of enterprise
by growing a bunch of fibrous roots at the end of one of its stems. I
imagine it intends to plant itself into another pot standing near. I
am watching it with much curiosity, because if it does this, the old
plant will prove that it has a high degree of intelligence, and that
although it remained quiescent for so many years, it was only from lack
of opportunity to do more than quietly endure its privations.
In tropical countries, some plants and trees such as _Monstera_ and
_Philodendron_ send down slender aerial roots called lianes, many
hundred feet in length.
In the Aëroid House at Kew, I remember seeing these lianes coming down
from the roof of the house in search of water and earthy nourishment.
It seemed like actual intelligence that directed these roots to a tank
of water twenty-five feet distant from their starting-point above.
Whilst we are considering this subject, I may mention the curious root
action of a kind of fig-tree growing in the tropics which is sometimes
known by the name of the “Murderer.” Its seed often falls, or is
dropped by birds, amongst the leaves in the head of a palm-tree, there
it begins to grow and forms root after root, gradually descending the
stem of the tree and clasping it so tightly that at last the palm is
strangled and falls to the ground carrying its destroyer with it, where
it roots and grows into a tree.
+Parasitic Roots.+
As in human society there are thievish characters who live by preying
upon their neighbours, so in vegetable society we find quite a number
of different plants growing at the expense of others, inserting their
roots into the stems and roots of trees instead of drawing their
nourishment from the ground. Careful distinction must be drawn between
such plants as ivy, virginian creeper, clematis, lichens, &c., which
simply grow and climb on the bark of trees, and the true parasites
which are nourished by the juices of the trees and plants into which
their routs penetrate.
[Illustration: CLOVER DODDER.]
Some plants are only partially parasitic, such as the cow-wheat
(_Melampyrum_) and the yellow rattle (_Rhinanthus_). These represent
a very deceitful kind of growth. To all appearance the plants are
getting an honest living, the leaves are perfectly green and capable of
performing all the duties of leaves, and yet, if we remove a little of
the soil the plant will be found to be attached to, and growing from
the roots of some strong kind of grass, and is deriving its nourishment
from the food collected by those grass roots.
Yellow rattle grows abundantly in undrained marshy fields, where it
is easy to obtain the plant, so as to examine its mode of growth. We
may then go on to a clover-field and seek for that true parasite and
most troublesome enemy to the farmer, the clover-dodder (_Cuscuta
trifolii_). Its seeds are frequently mixed with the clover, and when
sown they germinate on the surface, but the little thread-like stem,
instead of entering the ground, feels about in the air until it reaches
a young clover-plant. It soon clasps its victim with its fast-growing
stem; as the clover grows the dodder coils around it and is carried
away from the ground.
As the wiry stem gains strength, it developes a series of suckers that
eat into the clover stem and rob it of the food it has collected; it
lives, flowers, and grows at the other’s expense. The rate of growth
of the dodder exceeds that of the clover, so that the latter is both
exhausted and choked by its snake-like enemy.
I once sowed a patch of flax in a garden, and not knowing that it too
had a parasitic enemy, I was greatly puzzled to find quantities of
pinkish threads growing out of the flax stems. These threads bore round
bunches of tiny flowers. All this was very pretty and interesting, but
it resulted in my patch of flax becoming a mass of interlacing threads
and dying a miserable death, fairly strangled by the flax dodder.
Another species of _Cuscuta epilinum_, grows on furze and also on
heather, it having the twine-like stems by which dodder may readily be
known.
We are all familiar with the mistletoe, its leathery leaves and its
white berries.
This plant grows out of the branches of poplar, hawthorn, and apple,
and very occasionally upon the oak.
In France and Belgium the custom of bordering the fields with single
rows of Lombardy poplars seems to favour the growth of mistletoe, for
its large green bunches form quite a feature in the landscape, and
cannot fail to be observed by the traveller as he journeys in the
railway train. I have been told that mistletoe is sufficiently abundant
to be used in Normandy as cattle-food.
If a mistletoe-berry is gently pressed upon a young branch of an
apple-tree, its own viscid juice will cause it to adhere, and before
long it germinates and sends its roots into the tissues of the tree; as
it grows, it fuses with them, and derives all its root nourishment from
the substances in the branch. Of course the tree is weakened by this
parasite, the sucking roots of which disturb the flow of the sap; woody
knots are apt to form, and not unfrequently the branch is killed by the
intruder which has fastened upon it.
Having touched upon the four principal kinds of roots, we will now take
a single root-fibre and examine it more closely. It seems scarcely
possible that such a brittle, feeble thread should be able to penetrate
into the ground and make its way amongst stones and sharp-edged
fragments of earth without being bruised or torn. The chief friction
is borne by the growing-point, and this always has for its protection
a root-cap; the section of the growing-point of root-fibre given in
the plate shows the outer skin, called the epidermis, and over that
is the root-cap shaped like a thimble formed of small cells. As they
are worn away outside and become dead tissue, owing to friction with
the soil, the cells are constantly being renewed from within. The root
is thus enabled to grow and perform its part in maintaining the life
of the plant. The presence of this root-cap and the absence of leaves
are the marks by which a true root is known and distinguished from an
underground stem. With a small lens one can see this extinguisher-like
cap protecting the extreme point of the root, and it is well to examine
a variety of specimens, and see how they differ slightly in size and
shape.
[Illustration: SECTION OF ROOT CAP.]
The one especial office of the root is to absorb liquid nourishment
from the soil for the benefit of the plant, and, as I have already
explained, this is done mainly through the hairs which grow upon the
fibres of the roots. For instance, there is no absorption in old
tree-roots, such as we sometimes see above the ground, nor in carrots,
turnips, and parsnips, but thrown out from such bulbous plants are
the fibres and their hairs which enable them to grow to maturity. We
may naturally inquire how the solid materials in the soil, which are
needful to the growth of the stem and leaves, can possibly be taken up
by these extremely minute hairs.
We may look upon the earth as being a sort of storehouse of
indigestible, unprepared plant-food which must be altered in its
character before it will be fit for absorption by the roots. Some
substances, such as sugar, will readily dissolve in water; others,
such as starch and sand, are insoluble, but the effect of rain-water
and atmospheric air passing through the soil, converts this insoluble
dormant food into soluble active food.
The root-hairs convey this food to the small fibres, and through them
as channels it passes on to larger ones, until it reaches the stem and
goes to feed the growing leaves and flowers.
In order to remain in a healthy state, roots must absorb oxygen gas,
and for this reason gardeners, when they find the soil growing caked
and hard on the surface, dig and rake the flower-borders in order that
air may freely permeate the soil and find access to the roots of the
plants.
Roots appear to be endowed with certain remarkable attributes, about
which learned books have been written of late, giving the result of
patient investigation as to their power of movement, the way in which
they are affected by gravitation, the influence of light, and other
forces.
The experiments of Darwin and other scientists have revealed very
singular facts about the movements of plants. The term used to describe
their motion is one we must learn, as it frequently appears in
botanical works. Circumnutation we may translate as wavering around,
and it well describes the curious way in which rootlets, for instance,
are always moving slowly from one side to the other, describing a kind
of oval zig-zag track through the earth. The fibres appear to have
a discriminating power, enabling them to choose convenient crevices
through which to penetrate hard soil, to avoid stone, and to seek out
any attractive food which lies in their way.
As soon as roots emerge from the seed they at once turn from the
light and seek to bury themselves in the earth; the plumule from
which the leaves will spring has exactly the reverse tendency, and
invariably seeks the light and grows upwards. This can be proved by
growing some mustard seeds on a piece of flannel about the size of a
shilling, floating it on water in a saucer exposed to light from a
single window; as soon as the leaves appear, they will lean towards the
light, whilst the roots will point towards the dark part of the room.
If a germinating seed is even placed with the root uppermost, and the
plumule pointing downwards, it will very speedily right itself, the
stem will turn and grow up, and the root will seek the ground.
The amazing strength of growing tree roots can be imagined when we
watch a tree in full leaf during a high wind. As the terrific force of
the gale sways the trunk backwards and forwards the roots are subjected
to an enormous strain. Like great india-rubber cables they give and
retract, and when the wind subsides we find the trunk as rigid as ever.
If my readers will seek for the specimens enumerated below, and compare
them with the remarks made in this chapter, they will have such a
general idea of the functions of roots as will, I trust, enable them
to enjoy the study of more advanced works upon the subject.
Specimens to be obtained and compared with the descriptions in this
chapter:—Sedge or marrem grass growing on a sandy sea coast; plants
growing between layers of stone; tree roots at the edge of a pond;
strawberry runners; a plant of _Potentilla reptans_; creeping grasses;
_Poa bulbosa_ roots from the seaside; potato. Earth nuts; lily bulbils;
Timothy grass; cow-wheat (_Melampyrum_); yellow rattle (_Rhinanthus_);
clover dodder (_Cuscuta trifolii_); flax dodder (_Cuscuta epilinum_);
mistletoe. Root fibres of various plants. Mustard seed sown on flannel.
CHAPTER III
_TREE STEMS_
“If thou art worn and hard beset
With sorrows, that thou wouldst forget,
If thou wouldst read a lesson, that will keep
Thy heart from fainting and thy soul from sleep,
Go to the woods and hills! No tears
Dim the sweet look that Nature wears.”
+Longfellow.+
CHAPTER III
TREE STEMS
A walk through a wood on a bright day in February will afford us many
interesting intuitions about the growth of trees.
We are apt to think of winter as a dead season, and long for summer
days once more, that we may pursue our botanical studies; but as soon
as February begins there is already a secret work going on within the
tree-stems, the sap is rising from the roots, and this ascent is easily
to be traced if we look carefully at the trunks of those trees, such as
the oak, elm, and others, which have rugged bark. The wood within is
swelling; fresh layers of material will, a little later on, be added to
the inner side of the bark as a result of this ascent of the sap.
As the bark is hard and inelastic, it cannot expand in proportion, and
therefore has to crack and split in yielding to the internal pressure.
If we look for these fresh cracks, we shall see the clean new bark
within, which, before long, will harden and become of the same shade of
grey as the rest of the stem.
[Illustration: TURKEY OAK BARK.]
It is at this season, too, that the plane-tree sheds off its fragments
of bark in greatest quantity, as one may plainly see in the London
squares, where this tree grows so remarkably well. Its stem is always
peeling more or less throughout the year, and possibly that fact may be
one of the reasons of its flourishing so well in the midst of smoke and
fog.
[Illustration: SCOTCH FIR BARK.]
Trees shed their bark in many different ways.
A reference to the illustrations will show the concentric rings of the
horse-chestnut, the square pieces of the sycamore, which are due to
the cleavage being both vertical and horizontal, the hexagonal shape of
the divisions of the Scotch fir, the rugged bark of the Turkey oak, the
sycamore and other species.
[Illustration: SNAKE-BARK MAPLE.]
Where a woodpecker or a nuthatch has bored a hole into the living wood
of a tree-stem, it is interesting to watch how the injury is repaired.
New bark begins to form at the edges of the wound, and to this a layer
is added each year, until at last the hole is filled up, and only a
scar is left to show where it once existed.
[Illustration: +TURKEY OAK STEM+ (_struck by lightning_).]
I have been able to watch this repairing process going on for twelve
years in the case of a Turkey oak, which was injured by lightning. I
was watching the progress of the storm from one of our upper windows,
and happened to be looking at this particular tree in the park, when
out of a lurid cloud above it, a streak of forked lightning descended
upon the tree, and rent off the bark of one side from the top to the
bottom, carrying away portions of it to a distance of fifty feet or
more, leaving a white gash which looked pitiful enough for many months.
Year by year a wave of new bark rolls on, covering the bare place by
slow degrees, but it is never destined to be quite healed in this case,
for the inner wood was killed to some extent by the lightning, so it
has become a home for the boring beetles, who are riddling it with
holes wherein to lay their eggs.
[Illustration: PLANE-TREE BARK.]
[Illustration: HORSE-CHESTNUT BARK.]
Such a tree becomes a happy hunting ground for the woodpecker, who is
attracted by the insect diet he finds there. The large holes he makes
in getting at his prey will let in the rain, so that after a time the
moist rotten wood forms a suitable place for various fungoid growths,
and all these agencies work together for the destruction of the wood
until the tree becomes a hollow stem, and the leafage above is solely
produced by the sap carried upward by the bark.
[Illustration: WHITE POPLAR BARK.]
[Illustration: SYCAMORE BARK.]
Let us inquire a little more carefully into the formation of a
tree-stem, and the different parts of which it consists. Some rather
hard names are given to the four principal parts of a tree trunk but,
by reference to the plate, and by knowing the meaning of the names,
I hope they will soon be mastered, and then our future walks in the
woods will be fuller of interest than ever, when once we understand
something about the hidden work that is being carried on in those grand
old trunks around us. A tree may be compared to a large manufactory. As
we stand outside the building we see the brick walls and the roof, and
smoke is coming out of the chimneys. We know that a great deal of work
is being done inside, and carts are leaving its doors laden with the
products of the machinery within, but how the work is done we cannot
tell from the outside. We perhaps desire to obtain this knowledge, and
under the guidance of the manager, we are taken from room to room and
see the marvellous processes by which raw material is converted into
exquisite fabrics, or it may be clay is turned into priceless china
or porcelain. We leave the building full of wonder at the things we
have seen, and those particular manufactures will ever afterwards be
invested with a special interest for us, because we have seen with our
own eyes how they are produced.
[Illustration: TREE-FERN BARK.]
Just in the same way we shall look upon trees in a new light, if we are
able in some measure to follow the processes nature is carrying on in
them year by year so as to ensure the foliage, flower, and fruit, which
minister so much to our pleasure and profit.
The four names we must learn about in order to understand the
formation of wood are these. First the outer bark, called epidermis,
from two Greek words _epi_ upon, and _derma_ the skin. _Cortex_, a
Latin word meaning bark. Fibro-vascular bundles; this long phrase
refers to certain threads or fibres which exist in stems and give
them toughness and elasticity. From such fibres in the flax plant we
obtain linen, and from the hemp fibres ropes are made. _Fibro_ comes
from the Latin _fibra_, a thread or fibre; and _vasculum_ is Latin
for a little vessel; we know the word better, perhaps, in another
sense as _vasculum_, the tin box in which botanists place their plant
collections.
These thread-like vessels are well called bundles, because they exist
in little masses in the substance of the stem.
Most young people know what is called King Charles’s Oak in the stem of
the brake fern, so plainly seen when it is cut across with a penknife.
The dark markings are the ends of the fibro-vascular bundles which
happen to resemble an oak tree in form, though some think them more
like an eagle with outstretched wings, so the fern is named _Pteris
aquilina_, from _aquila_, an eagle.
The fourth word is pith, the white substance in the centre of the stem,
which can readily be seen by dividing a piece of elder branch, when the
middle will be found full of white pith.
When we have these four parts of the stem clearly in our minds it will
be possible to go on with our study and learn about the spaces between,
which are filled with different kinds of cells.
The honey-comb formed by bees consists of small cells, little hollow
spaces in which they store the honey or bee-food. Woody structure
consists largely of cells of various shapes to contain sap and other
substances. A beautiful specimen of cell net-work may be obtained
by placing a thin slice of either white or yellow water-lily stem
on a piece of glass and, holding it up to the light, a fine sort of
lace-work will be seen. These are the cells which convey air and water
through the stem up to the leaves and flowers. Or if we examine a
flower petal with a magnifying glass we shall find it to be entirely
composed of minute cells.
[Illustration: STEM OF YELLOW WATER-LILY.]
[Illustration: STEM OF WHITE WATER-LILY.]
In these little spaces are stored very many and very different
materials, all necessary to the growth of a tree; we shall try and
learn about them by degrees; at present we must endeavour to obtain a
clear idea of their structure.
A tree-stem increases in size yearly by the growth of fresh cells
within the outer bark, and this active increase of tissue is due mainly
to what is called the cambium layer, which is developed only in the
spring and summer and does not exist in winter; it forms bast, or
phloëm, on the outer side next the bark, and on the inner side next the
pith it creates woody tissue.
Our English lime tree has a layer of fibre beneath the bark which is
worth examination; it is the same in character, but not so wide or
strong, as the bast which we import from Russia in mats to protect
vegetation from frosts. Squirrels are very fond of this soft material;
they strip it cleverly off the branches of our lime trees to form a
warm lining for their nests.
It is easily found by cutting the outer bark off any small branch of
lime within reach, when we can peel off the inner layer of bast, or
phloëm, as botanists call it.
The phloëm from the lace-bark tree of the West Indies is like the
finest possible net-work, and is used for many ornamental purposes.
_Liber_ (Latin for the inner rind of a tree) is another term applied to
this cell formation.
The study of different forms of woody fibre will be found most
interesting.
I obtained one of my best specimens of it by placing a very old Swedish
turnip in water for some months until the soft parts had melted away
and only the round ball of fibre remained. If any one wishes to follow
my example I would suggest placing the turnip and its pan of water in
some outhouse where its perfume will not incommode any one. A maid
came to me one day with a sad account of a fearful smell which had
been noticed for some time in a lumber-room at the top of the house,
and very naturally she thought that the plumber should be called in
to remedy the evil. I had almost forgotten my interesting skeleton,
but in due time I traced the odour to its right cause, and the turnip
was banished to a distant spot, where many washings and some soaking
in chloride of lime changed it into a really beautiful specimen of
woody fibre. I possess now only a quarter of it, for botanists have so
earnestly begged for pieces of it that I have been persuaded to share
it with them.
I have sometimes picked up on the seashore old cabbage-stems bleached
to a delicate ivory white, forming really beautiful instances of woody
fibre. These we can prepare for ourselves, if desired, by soaking the
stems in water until they can be brushed perfectly clean, and then
bleached by mixing a little chloride of lime in water and letting them
soak in it till they are white and free from odour.
In a manufactory there must of necessity be a series of windows on
the different floors, not only to let in light but for purposes of
ventilation. Now, the processes of tree-growth are carried on without
light in the stem, but air is necessary, and it is supplied by means
of small apertures called lenticels. These are not open holes, but
are more like gratings which admit a small amount of air through
loosely-packed cells.
These lenticels are the small brown specks which may be traced in
great numbers on the young branches of almost any tree. They remain
open through the spring and summer, admitting the needful air to the
interior of the bark, but when the tree-growth is over for the season,
and air is no longer needed, a layer of cork forms within the lenticel
which entirely shuts it up and keeps out the wintry cold. Thus it
remains sealed up till, by the growth of the cambium layer in the
following spring, the corky barrier is split open and air is again
admitted.
These lenticels are nature’s ventilators, opening and shutting in this
curious way in order that the manufacture which is going on beneath the
bark may receive from the outer air the various gases essential to the
work which is being carried on within.
I have said that many and various things are stored in the stem-cells
of trees. It would occupy too much space to attempt to make anything
like a complete list of the liquids and solids which are obtained from
trees, but I will enumerate a few of those with which we are familiar
from their usefulness in every-day life.
Turpentine is obtained from various kinds of firs—the Scotch fir,
larch, and others. Burgundy pitch from the spruce fir. A kind of tar is
also prepared from Scotch fir and larch. From various kinds of cinchona
we obtain quinine, so valuable as a remedy for fever. Camphor is a
product of a Chinese tree. Tannin, by which skins are converted into
leather, is obtained from the bark of the oak-tree. A kind of sugar is
made from the sap of the maple, which is largely used in America. Gum
arabic and a great number of gums used in medicine are produced by
foreign trees of various kinds. The interior pith of a West Indian palm
tree produces the sago of commerce.
Stems, like every other part of a plant, are to be seen in endless
variety when we come to examine them for ourselves. In common garden
plants such as the calceolaria and petunia, the consistence is soft,
and such stems are known as herbaceous; these generally die down in
autumn. Roses and rhododendrons have stems of a harder and more rigid
character, and seem to be intermediate between the soft herbaceous
stems and tall tree trunks.
If in some country ramble we resolve to make the trunks and bark of
trees our study, we shall find much that is interesting and well worthy
of observation.[7]
[7] For instance, I have noticed some curious examples of trees growing
together. A Turkey oak and Silver fir in my own grounds are closely
united at the base. The fir-seed and the acorn must have germinated
in such close proximity that the stems have almost grown into each
other. The group of beeches shown in the plate gives another example of
interlacing stems and roots.
[Illustration: GROUP OF BEECH-TREES WITH INTERLACING STEMS AND ROOTS.]
The Lombardy poplar, with its tall bending stem, the graceful willow
and the silver birch, contrast strongly with the thick and sturdy
trunks of the elm and oak. Even these two differ, the wood of the elm
being short and brittle, whilst that of the oak is hard and flexible.
Again, we may note the slender drawn-up stems of trees growing thickly
together in a wood, where light and air are in a measure shut out,
and compare them with other specimens standing in a park in free air
and light. There we see trees, growing as nature intended, with grand
sturdy trunks and welldeveloped branches spreading out on all sides.
Lastly, in this chapter, we may note the climbing stems; these are
especially numerous and diversified in their manner of growth. Almost
every part is modified and adapted to assist the stem to climb. The
common ivy develops upon the surface of its stem numerous rootlets, and
by their clasping nature the ivy is enabled to ascend the smoothest
tree-trunk. The hop and the convolvulus climb by means of their habit
of twining around some rigid stem or twig. Then the peas and vetches
send out little clasping tendrils in the place of leaflets, whilst that
lovely ornament of the hedges—traveller’s joy—climbs by occasionally
using the leaf stalk for a clasping holdfast. Not less interesting are
the plants that climb by means of their hooks; the common bramble is
of this kind; it scrambles over the hedge in a very enterprising and
aggressive manner, while its spines and hooks effectually prevent it
from slipping back.
[Illustration: CONVOLVULUS.]
A very highly developed organ of climbing is that to be found upon
the stems of the small Virginian creeper (_Ampelopsis Veitchii_). On
the points of its small tendrils we shall discover little globular,
crimson-coloured pads, which, when pressed against a tree or wall,
secrete a kind of vegetable glue. This fixes the tendril and enables
the weak slender stem to climb upwards. In these instances, as well as
others mentioned earlier in the chapter, we have again evidences of how
wonderfully plants are adapted to their wants and environment.
Things to observe and collect:—The various ways in which trees shed
their bark; how trees repair holes in the stem; fibres in flax stem and
in hemp; specimens easily obtained by sowing linseed and hemp-seed;
section of brake-fern stem; section of elder stem; thin section
of white or yellow water-lily stem; flower petal; piece of bast
matting; West Indian lace-bark; turnip and cabbage stalk prepared as
specimens of woody fibre; lenticels on various trees; suitable leaves
for skeletonising—holly, magnolia, tulip-tree, pear, poplar, aspen,
mahonia, plum and maple; suitable capsules—poppy, stramonium, henbane,
winter-cherry, campanula, and the calyces of the yellow-rattle.
CHAPTER IV
_LEAVES_
“These naked shoots
Barren as lances, among which the wind
Makes wintry music, sighing as it goes,
Shall put their graceful foliage on again,
And more aspiring, and with ampler spread,
Shall boast new charms, and more than they have lost.
Then each, in its peculiar honours clad,
Shall publish even to the distant eye,
Its family and tribe.”
+Cowper.+
CHAPTER IV
LEAVES
We have learned in the previous chapters that the roots are the means
by which a plant gathers out of the earth the various constituents
which are needful to maintain its life.
The leaves have also to do their part in collecting from the air such
gases as are required to effect the processes carried on within the
substance of the leaf.
The leaf is really the digestive organ of the plant; it feeds,
breathes, and gives off in the form of vapour any excess of water
not required for its work. For these purposes sunlight and air are
necessary.
A leaf consists of a stalk, called a petiole, and the flat green part,
which we may call the blade.
If we hold a leaf up to the light we see a network of veins, and it is
by their help the leaf becomes a broad expansion of tissue, so exposed
that it gets the fullest possible benefit from the sunlight and air.
This fibrous network gives strength to the leaf, and answers to the
bones in animal structure.
[Illustration: NETTED VEINS.]
The fibro-vascular bundles, which we see in the stem, go up through
the petiole, and branch out in a beautiful and regular manner. We may
observe this arrangement very clearly in a skeleton leaf, the midrib
forming a backbone to the whole structure, while the smaller veins tend
off to the edge of the leaf, and then overlap so as to form a system of
girders supporting the edge, and preventing the wind from tearing the
delicate tissues into shreds.
The arrangement of leaf network is called venation, and by a glance at
it we can at once see to which of the great divisions in botany a plant
belongs. If the fibres are straight and run parallel to each other
without being netted, then we know the leaf is that of a plant which
begins its life with only one seed-leaf; such are all the species of
corn and grass, bulbs, palm-trees, bananas, and others.
The long name applied to this division of plants must be explained, as
it is a term we cannot do without, and I must own it looks formidable
until we understand its meaning.
[Illustration: MONOCOTYLEDON.]
The first leaf that comes out of a seed is called a cotyledon, from
_kotúle_, a cavity, or cup. The Greek for one is _mónos_, so plants
with one seed-leaf are called monocotyledons.
If we sow a date-stone or a few seeds of Indian corn in moist soil they
will grow readily, and afford us nice little specimens of a one-seed
leaf-plant.
If we see that a leaf has netted veins, then we know its seed produced
two leaves at first,[8] so plants belonging to this great division are
called dicotyledons.
[8] The Maranta and a few other plants are exceptions to this rule.
[Illustration: DICOTYLEDON.]
In order to watch the growth of two-leaved seedlings, we may select a
broad bean, or some of the seeds out of tamarind jam; either will grow
readily in a pot of earth, if it is placed in a sunny window, or near a
stove, and kept moist.
Orange and lemon pips may sometimes be found sprouting within the
fruit, and either of these seeds will germinate, and form charming
little evergreen plants to brighten a town window-ledge.
[Illustration: TAMARIND SEEDLING.]
Now we need not be afraid of those two long words which are used to
describe one-leaved and two-leaved seedlings, since we know their
meaning, and it will be interesting when we come across some new plant
to see to which division it belongs, because knowing that will mean
knowing a great deal besides.
All our English trees (with the exception of the firs, which have
many seed-leaves) are dicotyledons; they increase their stems from
the outside, and are therefore called exogens, and most of our plants
belong to this division.
The monocotyledons increase from the centre, that is to say, the
second leaf grows out of the first, and the third leaf and its stem
grow out of the sheath of the second leaf, and so on; and this is
the law of their growth, whether they be corn plants or palm-trees.
These sheathing leaves and the straight veins will always enable us to
recognise a one-seed leaf-plant at sight.
The development of the stem has a marked influence upon the arrangement
of the leaves; these, in such plants as the cyclamen, sundew, or
primrose, are said to be radical; that is, growing from the root.
Close observation will reveal the cause to be the non-development of
the internodes, the leaves being crowded upon a very short, suppressed
stem, and thus we get the beautiful little rosettes we find in the
daisy and plantain. When the stem is of greater length the leaves
are ranged at definite intervals, the spaces between the leaves (the
internodes) varying in length in proportion to the size of the leaf.
Small leaves are thus much thicker upon the tree than larger ones.
This will readily be seen if we compare a branch of sycamore with one
of elm, the former having its large leaves much further apart than the
latter.
Then, also, the arrangement of leaves upon the stem (_phyllotaxis_)
varies much. If we take a spray of beech we shall find that its buds
are placed alternately on either side of the stem, so that the third
bud is exactly below the first, and the second bud is in a line with
the fourth, and so on. This is also the plan of the elm, hazel, lime,
hornbeam, and many other trees. In the alder and whitebeam the buds
occur in three rows, and in some of the willows in series of eight.
The leaves of the horse-chestnut are borne in pairs on alternate sides
of the stem, and this plan is common to a number of plants, especially
those of the type of the dead nettle and speedwell.
Quite a distinct arrangement is that to be found in the woodruff and
bedstraws, where the leaves are placed in a ring (a whorl) at regular
intervals on the stem.
The botanical student should carefully observe the differing methods
of leaf arrangement, since, as branches are developed from buds, the
varying order in their position must naturally modify the general
aspect of a tree, and has also much physiological importance. We shall
find that buds are so placed that each leaf shall receive its full
share of sunlight and air, for it needs this position in order to
enable it to carry out the wonderful work of assimilation which it has
to perform.
The upper surface of a leaf is covered by a thin layer of cells, known
as the epidermis (or skin); this does not prevent the light from
falling through, and its outer surface is protected by a thickening,
known as the cuticle. This is of great use in controlling the escape of
moisture, otherwise the leaf would soon shrivel up in a hot sun. In a
young seedling leaf the cuticle is not developed, and it can therefore
breathe out moisture very rapidly; later on, when the cuticle is
formed, it controls the escape of moisture, which can then only exude
through the under surface of the leaf.
We can easily peel off a portion of the skin from the under surface
of the leaf, and if we place it in a little water between two pieces
of glass and look at it in a microscope we shall see that it consists
of an extremely thin layer of cells, with numbers of little openings
called stomata (from the Greek _stoma_, a mouth), answering somewhat
to the lenticels to be found in young tree-stems, only those are solely
for the admission of air, while these little mouths are to let in and
out not only air, but water, vapour, and oxygen.
These stomata look like little crescent-shaped slits with a curved cell
on either side, and as they curve more or less, the mouths are opened
or shut as the plant may require. These little mouths play a very
important part in the economy of the leaf, and they exist in immense
quantities on its under surface.
[Illustration: STOMATA.]
It has been calculated that a million stomata exist on a single leaf
of the lime tree. When the root has taken up more moisture than is
required, then it is the office of these pores, or stomata, in the
leaf to give out this extra water in the form of vapour, and we can
thus see how the action of leaves must influence climate. If forests
are recklessly cut down, the bare country, with no foliage to throw
moisture into the air, may become an almost barren desert, and again
in marshy places, where the air is too damp, a wise reduction in the
number of trees may alter the climate to a healthy condition.
Remarkable results have been obtained by planting the Australian
gum-tree, _Eucalyptus globulus_; it thrives well in malarious places,
and at once produces a marked hygienic change in the air. A Monsieur
Gimbert relates that “A farm some twenty miles from Algiers was noted
for its pestilential air, and in the spring of 1867, 13,000 eucalyptus
trees were planted there, since which time not a single case of fever
has occurred.
“The gum-tree grows rapidly and absorbs as much as ten times its weight
of water from the soil, and emits camphoraceous antiseptic vapour from
its leaves. It is therefore often called the fever-destroying tree.”
Experiments have been made to try and find out how much moisture is
really given out by leaves. It was found that a sunflower three and
a half feet high, with a leaf expanse of over five thousand inches,
exhaled one pint of liquid in the course of the day.
No wonder, therefore, that trees tend to make the air damp.
Each stomate leads into air spaces between the cells, and is thus
connected with the interior of the leaf.
[Illustration: LEAF SECTION.]
The tissue and cells of a leaf (bifacial)[9] can be understood by
reference to the accompanying diagram. Between the upper and under
surfaces of a leaf there is a layer, more or less thick, of soft green
tissue known as _mesophyll_, and if we hold a leaf to the sunlight we
shall see the veins traversing this tissue.
[9] That is, a leaf like the beech or sycamore, having an upper and
under surface; vertical leaves, like the iris, have palisade tissue on
both sides.
The upper part of the mesophyll consists of elongated cells arranged
at right angles to the surface, and placed so evenly parallel to each
other that they have been compared to the pales of a fence, and are
called palisade tissue. These cells contain a quantity of the green
substance called _chlorophyllon_ (from _chloros_, green, and _phyllon_,
a leaf), so named because to this bright green substance we owe all the
lovely verdure of our woods and gardens.
Below this palisade tissue is another of quite a different form,
consisting of large spongy cells, and therefore known as spongy tissue.
In its intercellular spaces are stored those secretions which make
certain herbs, such as thyme, marjoram, and others so fragrant when
bruised.
The chemical changes which are ever going on in these various layers,
require a constant supply of the outer air, and this is secured by the
little openings, called stomata, on the under surface of the leaf,
which have been already described; these constitute the breathing
apparatus of the leaf, for they open and shut, and regulate the
supply of air into little air chambers, from which it passes into the
structure of the plant.
Before going any further I must try and explain a little about the
wonderful substance called protoplasm.[10]
[10] Greek: _proto_, “first”; _plasma_, “anything moulded.”
If we have ever watched a potter at work, we know he takes a lump of
clay and moulds it according to his purpose, into a rough pot, or a
lovely vase; now protoplasm seems to be just such a foundation material
from which the Divine Creator causes animal and vegetable forms to
proceed. _First material_ seems to me to be a term that actually
expresses the meaning of the word protoplasm.
It lines the cell walls of leaves, it is capable of forming fresh
cells, it can absorb moisture and other matters, it contracts and
expands, it has power of movement, as one may readily see when a
portion of a leaf is placed in a microscope, so as to show the grains
of bright green chlorophyll circulating in the lining of each little
cell.
Learned volumes would be needed to explain the nature of protoplasm, so
I must be content with these simple facts about its nature, and proceed
to the chemical action going on in leaves.
In ordinary atmosphere there is a very small quantity of a gas called
carbon-dioxide.[11] The leaves absorb this gas from the air, and
because there is so little of it, each tree needs to spread out an
immense amount of foliage, that it may drink in, by its means, all the
carbon-dioxide that can possibly be obtained.
[11] Carbon meaning charcoal, and dioxide meaning two parts oxygen.
Sometimes called carbonic-acid gas.
When this gas comes in contact with the chlorophyll in a leaf, one part
of the oxygen is set free, and returns to the air in a pure condition,
thus making it more healthy for us to breathe; then the carbon and the
remaining oxygen combine with water in the leaf cells, and form starch,
the leaves retain the carbon, to build up their own structure; it
enters indeed so largely into the composition of vegetable substance,
that in some cases if we could burn one hundred parts of it, fifty
parts of the ashes would prove to be carbon or charcoal.
In a rough sort of way we may see for ourselves how much carbon there
is in woody fibre, by lighting an ordinary wooden match and letting it
burn itself out; the black portion that remains will be a piece of
charcoal not very much smaller than the original match.
Of course, in the process of burning, the match has lost the resin, and
other organic substances which were stored up in the cells of the wood;
all these have passed into the air, and only the carbon remains. If,
however, instead of this slow manner of combustion, we had set light to
a whole box of matches so that it burnt fiercely, the flame would have
been strong enough to consume the charcoal, and nothing would then be
left but mineral ashes.
When charcoal burners are at work in a forest, we may see them making a
stack of wood, which they cover with a thick layer of clay so that the
wood may burn away very slowly; in this case the charcoal will be left
in the same way as when we burnt the single match.
As long as the upper side of leaves are soaking in the sunlight, starch
is being formed, as I have described; but during the night the starch
thus formed is dissolved, and passing through the leaf fibres finds its
way into every part of the plant, either to be used in forming new
tissue, or else to be stored up for future use.
The net-work of veins act as a service of tiny pipes, to convey the
liquids up and down the petiole (leaf-stalk).
Generally the water given off from the stomata is in the form of
vapour; but in some plants drops of water exude from the apex or point
of the leaf through the water pores. In _Saxifraga crustata_, there
are pores round the edges of the leaves, through which water, highly
charged with lime and other salts, passes out, and as it evaporates a
white deposit of lime remains which is quite visible in the form of a
frosted edging to the leaves.
There is an American plant called the jewel-weed, which shows to
perfection this power of distilling drops of water. I will quote a
short description of its appearance at night-fall.
“Upon the approach of twilight, each leaf droops as if wilted, and from
the notches along the edge, the crystal beads begin to grow until its
border is hung full with its gems. It is Aladdin’s lantern that you see
among a bed of these succulent pale green plants, for the spectacle is
like dreamland.”[12]
[12] “Sharp Eyes,” by Wm. Hamilton Gibson.
A very similar effect may be observed if we visit a plant of
Lady’s-mantle (_Alchemilla vulgaris_) at early morning after a warm
dewless night; each leaf will be found beautifully decked with dewdrops
at equal distances round the edge of the leaves where the pores have
exuded the moisture with which they are charged.
Nasturtium and fuchsia may also be examined for this purpose and will
show exudation from their leaf pores.
If a small quantity of wheat is grown in some cocoa fibre, it will
illustrate this power of giving off water, for when the little blades
are a few inches high, they will be found each morning tipped with a
large dewdrop, the result of exudation during the night.
In countries where the sun is intensely hot, if the leaves of trees
were to be exposed to its full power, they would probably wither, and
vegetation would perish.
[Illustration: YOUNG SHOOT OF EUCALYPTUS.]
Against this danger some trees are enabled to make special provision,
by changing the form of their leaves, and their mode of hanging on the
branch. In Australia, for instance, where the sun is almost vertical,
the acacias and eucalyptus trees, instead of holding their leaves flat
or horizontally as trees do in England, so that they may catch every
ray of sunlight, avoid the heat as much as possible, by holding them
edgeways to the light.
[Illustration: MATURE FORM OF EUCALYPTUS LEAVES.]
While eucalyptus trees are young, and partially shaded by surrounding
vegetation, their leaves are flat and oval, and English seedlings
of this tree usually retain such leaves from five to ten years, our
climate not being hot enough to require the mature form of leaf which
hangs vertically, and is of an entirely different form.
Reference to the plates will show a young shoot of _Eucalyptus
globulus_ and a branch of the older leaves, with their edges only
exposed to sunlight.
The curved sickle-shaped leaves of the eucalyptus afford very little
shade to the traveller in Australia for this reason, that only fine
intercrossing lines of shadow are seen on the ground. To make this
clear, let my readers take a sheet of notepaper out of doors on a sunny
day and hold it perfectly flat, so as to expose it to all the sunlight
it can receive upon its surface, as if it were a growing beech-leaf,
and it will throw a large shadow on the ground. Then hold it edgeways
to the sun, and it will form the kind of thin line of shadow that would
be cast by a mature eucalyptus leaf.
Preparation for the fall of the leaf begins in spring, when a fine
line or ridge may be traced just below the junction of the leaf with
the stem. This dark line is in reality a thin layer of cork, which,
during the summer months, continues to grow inwards to form in due time
a covering for the bare place on the stem that will be left when the
leaf falls off; this is called the leaf-scar.
It is interesting to watch this line, growing more and more visible as
the year goes on.
Another curious fact is, that some of the starch which the leaves have
been making during the summer, becomes stored up in autumn at the base
of the leaf-stalk, so as to afford nourishment to the bud which will
arise out of the axil of the leaf. When a weak solution of iodine is
applied to it, this starch turns blue, and in this way its presence can
be ascertained.
The fall of the leaf appears to take place mainly because the starch
has the effect of softening the cells of the leaf-stalk; as it dries up
it loses its hold of the twig, and either the wind or a slight frost
will suffice to bring the leaves down to the ground in showers.
Another reason for their fall is, that their year’s work is done. Like
good servants, they have been hard at work all through the summer and
autumn months, taking in stores of nourishment for the benefit of the
tree, and giving out volumes of oxygen, so helpful for the maintenance
of human life. They have secured and laid up sufficient nutriment
for the development of the next year’s buds, and having done this,
their special office being at an end, they fall beneath the tree to
become leaf-mould, which, in its turn when fully decayed, will yield
nourishing elements to be carried by the winter and spring rains to the
tree roots.
I might add many more useful objects which we owe to trees, and I
commend it to my young readers as an instructive study to try and make
out a complete list of the useful products of our English trees. I
imagine we do not yet know all that might be obtained from them, new
discoveries continue to reveal their value in the way of medicines;
for instance, the crystals of the willow (called salicine) are now
frequently prescribed as a remedy for rheumatism. Euonomine and many
others might be included amongst the valuable gifts which nature has
stored in the cells of tree-stems.
Specimens to be obtained:—Leaves with straight veins, such as grass
or corn, hyacinth, narcissus, or any bulbous plants; leaves with
netted veins, such as oak, ivy, vine, &c.; monocotyledon seedlings;
dicotyledon seedlings. Leaf-skin to be examined through a microscope,
in order to see stomata, chlorophyll, network, and cells. Examine
waterpores in leaves when exuding moisture. Observe shadows thrown
by leaves held flat and edgeways to the sun. Compare young and old
eucalyptus leaves. Observe line of cork below leaf-scars.
Leaves can be made into beautiful skeletons by soaking a good many
together in a pan of soft water until the upper and under surfaces of
the leaves are sufficiently decayed to be easily removed by a soft
brush; the fibre which is left can then be bleached with chloride
of lime. When mounted with fine wire these skeleton leaves form an
interesting group to place under a glass shade.
CHAPTER V
_BUDS_
“Oh! who can speak the joys of spring’s young morn,
When wood and pasture open on his view,
When tender green buds blush upon the thorn
And the first primrose dips its leaves in dew.”
+Clare.+
CHAPTER V
BUDS
How we watch for the buds as tokens of the coming spring! We delight to
see them daily growing larger, and opening out their leafy treasures to
the sun.
The re-clothing of the trees has always an element of wonder about it;
the change is truly a resurrection; a few days of warm sunshine and
gentle rain, and then the dry, dead-looking branches begin to bud and
blossom as if by a miracle.
We may, however, trace the secret of this sudden change, if we look
back to the processes Nature was carrying on during the previous
summer, and we may learn from her many a useful lesson of foresight and
preparation.
If during the summer we lift up the branch of any deciduous tree
and search amongst the leaves, we shall find that the buds for the
following year are already there, waiting to be developed in due time.
When the leaves turn dry and sere, they fall off and leave the buds to
be hardened and matured by the rain, snow, and frost of winter.
Certain species of Turkey oak, young beeches, hornbeams in hedges, and
other trees, appear to retain their leaves, to some extent, as if to
protect the buds until the rising sap in spring loosens their hold upon
the branches, and makes them fall off.
The plane-tree appears to be an exception to most trees in the curious
protection it affords its young buds. If we search for these in the
summer or autumn, they are not to be found, for the leaf-stalk is so
swollen and hollow at the base as to enclose the bud within it; even
when the leaf falls off, the bud is covered by a tough outer case
coated with resin, and within are many fur-lined scales. When these are
removed we see the tiny leaves wrapped in silky coverings, and when the
warmth of spring enables them to expand, their under surfaces have
such a thick coat of down that the plane is known in some countries as
the cotton-tree. From its fruit being in the form of hanging circular
balls, its name in America is the button-wood. The need of this
special protection against cold is shown by the fact that if severe
frost returns after the leaves have expanded, they frequently shrivel
and perish. Some Japanese maples have the same arrangement of hollow
leaf-stalks to contain the buds.
[Illustration: OAK IN WINTER.]
When buds are situated at the end of a branch they are called terminal,
and their office is to increase the length of the branch.
When they grow in the axil of a leaf (that is, where the leaf-stalk
joins the stem) then they are called axillary, and as they grow out and
form fresh stems and leaves, the branch broadens on either side.
[Illustration: OAK IN SUMMER.]
Seeing that the branches of a tree thus spring from the buds, it
follows that the position and development of the buds upon the stem,
as we tried to show in the last chapter, have much to do with the
ultimate shape of the tree. The development of the axil buds, as well
as of the terminal bud, gives rise to a branched tree like the oak;
these buds, however, are often erratic, and in some trees the terminal
bud of the shoot is often suppressed and the axil buds grow with extra
vigour, whilst in other instances the terminal bud grows strongly and
the axil buds either grow feebly or are altogether suppressed. In the
bamboos, palms, and sugar-cane we get good examples of this terminal
bud-growth, the axillary buds being suppressed; the suckers that grow
from the axils of the lower leaves of the palm are often evidence of
the presence of axillary buds, although they are, as a rule, dormant.
We are all more or less familiar with the character of ordinary forest
trees, the rounded outline of the oak, the slender sprays of the birch,
the spreading branches of the beech, but perhaps we may not have
remarked how much these variations of form are due to the position
of the buds upon the branches. We will suppose that on a winter’s
day we are looking at the tracery of some elm-branches against the
sky; the form of each branch shows that the terminal bud in this tree
usually ceases to grow, and allows the lateral shoots to increase in
length, and take its place; this produces short, twiggy branches, and
a stem which makes a tall tree rather than a wide-spreading one. The
horse-chestnut, again, produces its flowers in the terminal buds; this
arrests their growth, and side shoots have to grow on instead, thus
usually giving height rather than breadth to the tree. We may note
the differing outline of the willow, birch, and many others where the
terminal buds do not cease to grow, but each year continue to add to
the breadth as well as the height of the tree.
In pine-trees the buds are produced at the ends of the branches, and
several shoots proceed from one bud.
The spiral arrangement of leaves is well seen in a young coniferous
shoot, also in the flower-bud, and especially in the fir-cone itself,
in which an ever-varying double spiral can be traced.
Loudon remarks, “The perfection of a fir consists in height rather
than in lateral expansion; buds are produced very sparingly and nearly
always at the extremities of the shoots. Provision is thus made for the
upward growth of the tree more than for side expansion.”
When we speak of a coniferous shrub having lost its leader, we mean
that the terminal bud on the topmost shoot having been broken off, one
or more of the lower branches must rise up and take its place, and
thus lateral buds in time become terminal and grow upright instead of
sideways.
A silver fir, that I have been observing for years past, bears such a
crop of heavy cones on its slender upper branches that the leader is
almost invariably broken off by the weight, and the lateral shoots have
to take its place, to the great detriment of the central stem, which is
twisted and curved out of shape by the efforts the tree makes to repair
its terminal shoot.
In other trees, again, the unfolding of all the buds is nearly
simultaneous, but in the fir tribe the bud which terminates the summit
of the tree and is destined to form its leading shoot and increase its
height is developed last; this delay seems a provision of nature for
the safety of the most important shoot which the tree can produce,
ensuring its height rather than its breadth, and the production of
timber by the preservation of its permanent trunk rather than by its
temporary branches.
If a willow is deprived of the upper part of its stem and so made a
pollard tree, it develops a bushy head of small stems which spring from
the other buds thrown out to repair the loss of the central stem. This
pollarding is often resorted to in order to obtain wood of the right
kind for basket-making, and young ash trees are thus treated, so that
slender rods suitable for hop-poles and tool-handles may spring from
the lopped stem.
When buds are found growing on any other part of a plant except those
just mentioned, they are called adventitious buds. These may be found
growing on the edges of the leaves of the marsh tway-blade; they also
spring out of the flat surface of the fronds of the viviparous fern.
Under favourable conditions every part of a plant will produce buds,
and, taking advantage of this fact, florists increase their stock of
succulent plants by putting the leaves on a wet surface, which induces
them quickly to send out buds and roots. Such plants as begonias,
gloxinias, hoyas, and sedums are readily increased by this mode of
propagation. Underground stems will often send out buds, and they
produce the underwood from the stumps of fallen trees.
We are all familiar with the suckers of trees which spring up in our
lawns and gravel paths often many yards away from the parent tree;
these all arise from active buds on underground stems. Gardeners
are always careful to prune away such growths at the base of their
wall-fruit-trees, since they rob their valuable peaches, nectarines,
and apricots of strength and nourishment. These well-named “suckers”
spring from the common stock upon which the choice fruit-trees were
grafted, as one may see by gathering a leaf from a sucker and comparing
it with a peach or nectarine leaf.
On the oak, chestnut, lime, beech, and other trees there are sometimes
to be found dormant buds in the form of rounded knobs covered with bark
and increasing in size with the growth of the tree; these, in the event
of other buds perishing, will start into active growth and do their
part in preserving the life of the tree.
Such woody balls when found on the oak are worth examination, as when
divested of their bark they show exquisite structure of woody fibre.
The small bulbils we find in the axils of lily stems, on the
cuckoo-flower, on _Dentaria bulbifera_, and on some species of Allium,
are all adventitious buds, which drop off in due time and become young
plants.