would the Highlands be without their glorious lochs, which glisten like
silver in ever hollow and valley? What pen can depict their beauties?
Lomond, where the rocky islets float like swans upon the scintillating
water; Loch Maree, nestling neath the strange peaks of Slioch and Ben
Eighe; Loch-an-Eilean, lying like a diamond upon the black mantle of
encircling pines; savage Loch Einich and Loch Avon, imprisoned by grim
precipices, the relics of a far away prehistoric world; the hundreds of
small tarns breaking the brown monotony of desolate moorlands and mountain
side, or appearing like oases amid sterile wastes of stone and debris, as
the beautiful Pools of Dee in the Larig Ghru.
as are these lochs scenically, they are also extremely beautiful and
interesting in themselves. Many of them, especially the smaller tarns,
are gardens of beauty wher the pure white chalices of the Water Lily and
its golden-hued cousin attract and hold the eye of the passer-by with
their sheer loveliness, while the Water Crowfoot, the Water Lobelia and
the Bog Trefoil enrich Nature’s delightful garden. Even below the surface
are mossy green pastures of Water Milfoil, Hornwort and Pondweeds where
the fishes glide amid the snake-like stems.
chapter, I intend to describe the various floral inhabitants of these
delightful stretches of water, and show how marvelously they have been
modified to enable them to live in the strange element they have chosen as
find that the loch flora can be divided into three clearly defined groups.
consists of those plants which live entirely in the water with only their
flowers or specialized floating leaves above the surface. They include
such plants as Water Lilies, Pondweeds, Water Milfoils, Water Crowfoot,
etc., which live in fairly deep water.
second consists of those plants that live along the shallow loch shores,
usually with their roots below water and the leaves and flowers above.
They include such plants as Water Lobelia, Water Plantain and Bog-Ban,
which form a fringe of verdure and beauty around the lochs.
consists of those plants which prefer a moist habitat, but are unable to
live with their roots in the water and are found the bank and interstices
of loc side rocks beyond the reach of serious inundation. They include
such plants as the Mars Willow-herb, Marsh Valerian, etc., which are
actually marsh-land plants, and have been described in Chapter XVII.
COMPLETELY SUBMERGED AQUATIC PLANTS
plants have become so adapted to watery conditions that they can live
submerged below the surface, only sending up flowering shoots in the air.
have already seen, oxygen s a vital necessity for plants as it is for
animals. The oxygen taken in during respiration is used for the oxidation
of food substances and the subsequent release of energy provides the
necessary stimulus to growth and other vital processes.
It may at
first appear impossible for plants to respire in water, but we must
remember that water contains much dissolved oxygen, which is absorbed by
the leaves and stems. No stomata occur on the leaves as these would allow
entry of water and would result in the death of the plant, hence the
dissolved gas is just absorbed by the epidermal cells.
see that it is possible for plants to respire although submerged and we
see that one condition of life is satisfied. But what about the
absorption of carbon-dioxide so necessary in the production of sugars and
starch by the process of photosynthesis?
again, owing to the solubility of carbon-dioxide in water, the plant is
able to absorb enough for its requirements, and it can also use the
carbon-dioxide given out in respiration.
leaves and stems of water plants contain chlorophyll, even in the
epidermal cells, and they are thus able to synthesize sugars during
daylight, in the same way as land plants do.
examine the stems, roots or leaves of aquatics under the microscope, we
shall find that their tissues consist of large, empty spaces traversed by
chains of cells; in fact their tissues are like a sponge, the empty spaces
of which are filled with air, or rather oxygen, given off during
photosynthesis. The reason for this is, that the roots and the stems are
often imbedded in waterlogged mud where no oxygen exists, and, as they are
therefore unable to respire, would eventually die. By means of the
internal air passages, air is able to reach these buried organs and keep
problems faced by aquatic plants are many. The amount of light is less
below the surface, and this further decreased by the presence of
impurities and of other water plants such as Algae, Duckweed, etc. For
this reason chlorophyll occurs in the epidermal layers of the leaves, so
that the plant may profit from all the available light.
again, one must take into account the action of currents, which would tear
ordinary leaves to shreds. For this reason most aquatics have tough,
leathery leave which are often cut into fine segment which branch out in
the direction of the currents and offer little resistance to the their
all aquatics, except Duckweeds and Frog-bit, have their roots in the mud
at the bottom of the lochs and obtain nutriment from the soil like
ordinary plants. The depth of the water determines the size of the plant,
as the aquatic send up long, slender, leafy branches to just below the
surface where the light is strongest. Thus many aquatics have stems of
great length, often attaining as much as four or five feet.
most aquatics flower above the surface of the water, the branches sending
up long peduncles into the air where the flowers open and are
cross-pollinated. After fertilization the peduncles often curve
downwards, so that the seeds are formed below the water.
origin of the aquatic flora has been much discussed, but opinion inclines
towards the theory that aquatic plants have descended from ancestors who
were ordinary terrestrial plants. We may look upon them as pioneer
colonists, whose ancestors decided to make their homes in the watery
medium. They may have done so because of pressure from more virile
competitors, who forced them to take to the water in order to survive, in
the same way that early colonists forced the native tribes into the
inhospitable mountain regions. Or, we may liken them to adventurers
pushing out into unknown territory and leaving the safer, more hospitable
regions for more timid, less enterprising types.
families of plants have certain aquatic or water-loving species, but it
will be noticed that the more recent families have few or none. Thus the
composites, the most numerous and the most modern family, possess very few
real aquatics. This shows that the aquatic habit has evolved
comparatively late in the life of the family and points to the fact that
it is an acquired habit.
Britain we have two principal species, viz., Myriophyllum spicatum
and M. verticillatum. They may be found in almost all of our
Scottish Highland lochs.
former is a typical under-water aquatic and forms mossy, dark green beds
which reach to the surface of the loch. If we examine a bed carefully, we
shall find that the individual plants which make it are rooted firmly in
the mud at the bottom of the loch.
perennial stems creep through the mud, giving out fine rootlets at the
nodes, these obtaining all the nitrogen and salts required by the plant.
creeping stem sends up fine branches which ascend almost to the surface
and are usually much branched themselves, and are covered in whorls of
four or five pinnate leaves composed of six or seven hair-like segments
which give a mossy effect to the plants when crowded together in the
water. These fine segments present a large aggregate surface to the
water, although presenting little opposition to its passage.
leaves absorb the dissolved carbon dioxide from the water and this, with
the action of the chlorophyll and sunlight, forms sugars. They also give
out oxygen as terrestrial plants do in sunshine, this action also give out
oxygen as terrestrial plants do in sunshine, this action being of great
biological importance, for as we know, animal life is continually
breathing out carbon dioxide, organic acids and bacteria. In the
comparatively still waters of ponds and lakes, the gradual solution of
carbon dioxide and the continual concentration of bacteria, etc., would
make the water unfit for life.
Fortunately the plants, by absorbing the carbon dioxide and giving out
oxygen, fulfil a dual purpose by clearing the water of excess carbon
dioxide and by supplying oxygen which kills harmful bacteria and keeps the
water pure and sweet. This beneficial effect is strikingly exhibited in
an indoor aquarium which can only be made a success by the introduction of
branch of Myriophyllum spicatun is terminated by a slender spike of
small green flowers, which gradually lengthens until the little heads of
flowers project beyond the surface of the water into the fresh air and the
sunshine, where they open and are fertilized.
examine the flowers we shall find that the lower ones are female and the
upper male, but none of them are perfect. The male flowers consist of a
small greenish calyx and four minute greenish petals, the stamens having
very short filaments with long anthers which project beyond the sepals and
petals. When ripe their pollen is distributed by the wind, their position
at the top of the flowering stem thus being very advantageous.
female flowers have no petals and are very small with four tiny stigmas.
After fertilization each flower forms a very small round capsule which
ultimately breaks into four sections, each with a seed inside. These
sections are drifted by the currents and gradually becoming waterlogged
fall to the bottom to form new plants, perhaps far from their parent.
sometimes discover in our Scottish lakes the other species of Water
Milfoil (Myriophyllum verticillatum). In this species the flowers
are found in the axils of the upper leaves and are always immersed in
water. Otherwise the plant is difficult to distinguish from M.
species of Pondweed may be found by the enthusiastic botanist in the
Highland Lochs, pools, and in the slower streams. Of these a number of
species are completely submerged and will be dealt with here, but the
species with floating leaves will be described later on.
the species have broad, pellucid leaves and form dense masses in the
water, whilst the other two have very fine, narrow leave.
former we have a fine species in the Shining Pondweed (potamogeton
lucens) which inhabits fairly deep, still water, and is more likely to
be found in lochs or in deep pools in rivers. It is found in
Inverness-shire and most the Highlands to the southward, as well as in
Skye and Sutherland.
stems may be as much as six feet in length, whilst the oblong, wavy,
brown, pellucid leaves with several green veins may be as much as ten
inches in length. In clear water, the leaves may be found almost to the
base of the plant, but in turbid water only the upper leaves are fully
lengthen until the surface of the water is almost reached. In the axils
of the upper leaves, and carefully wrapped up in the transparent stipules,
we shall find the flower buds. In summer the stout flower stalks elongate
and burst through their membranous cover to rise above the water where the
thick cylindrical spike of flowers betrays the presence of the plant. The
greenish flowers contain no nectar and are wind pollinated, and thus we
see that in spite of its high specialization to aquatic conditions, the
plant is still dependent on the open air for the perpetuation of the race.
fine species, which I found in great luxuriance in a small pond near the
boat-of-Garten, in Speyside, is the Long-stalked Pondweed (P.
praelongus), which has a similar distribution to P. lucens. It
has stout, whitish stems clothed with oblong, sheathing leavs, which are
three or four inches in length and rather concave in form. They have a
similar texture to those of P. lucens, and their shiny brown
surface makes one think of some marine seaweeds. The flowers are produced
in large, dense spikes on long thick stalks.
and well distributed species to be found throughout the Highlands is the
Perfoliate Pondweed (P. perfoliatus). It resembles the foregoing,
but is rather smaller in all its parts. The oval leaves, which completely
embrace the stem, are very thin and transparent and are beautiful objects
when seen under the water. The dense spike of flowers is produced on a
stout, short stalk.
fine-leaved species are to be found in most parts of the Highlands and
inhabit streams as well as still waters. The Small Pondweed (P.
pusillus) forms a tangled mass of fine, thread-like stems and narrow,
linear leaves of a dull, olive-green colour. It does not form a rhizome
and the plants float freely in the water, or are attached by adventitious
roots given off from stems. The small spikes only just appear above the
the summer the stems produce green, bud-like objects, which drop to the
bottom in the autumn when the stems and leaves die down. The following
spring, they sprout and give rise to new stems, leaves and roots. The
production of such winter buds is common among aquatics, the advantage to
the plant being that the buds pass the winter at the bottom of the water
where freezing is rare.
species, P. filiformis, is a rather similar plant, but the leaves
are almost hair-like, and it perennates by means of structures called
turions. The two lower internodes of each leafy shoot swell up and become
stocked with starch, and in the autumn, when the stems die down, these
tubers fall to the bottom of the pond to recommence the species the
Pipewort (Eriocaulon heptangular)
remarkable plant is the only European representative of the American
family Eriocaulceae, and its only stations in Europe are in
Connemara, in western Ireland, and at two places in Scotland, viz., Iona
and Dunvegan, Skye. The plant is almost certainly native in these areas
and was discovered as long ago as 1764.
Pipewort Family is mainly tropical, but several species are found in North
America. How our present plant crossed the Atlantic to Scotland and
Ireland is a mystery. It will be noticed, however, that it only occurs in
areas in close proximity to the Atlantic. Now very often seeds of plants
inhabiting the islands of the Caribbean Sea and the surrounding shores are
washed up on the western coasts of Britain by the North Atlantic Drift.
Sometimes they germinate, but they rarely establish themselves in our
climate; this does not, however, preclude the chance of the survival of
adaptable species. Once the seeds arrive on our shores, it would be
fairly easy for sea-birds to transport the seeds upon their feet from the
seashore to neighboring lakes. The element of chance involved would
explain to neighboring lakes. The element of chance involved would
explain the scattered distribution of the plant.
Pipewort is not the only American plant to be found wild in Britain, about
six species being listed. The best known are the Blue-eyed Grass (Sisyrinchium
angustifolium), a member of the Iris Family, and the Orchid, the Irish
Lady’s Tresses (Spiranthes Romanzoffiana). In view of the preceding
facts it will be seen that the Pipewort is a very interesting plant.
aquatic plants, it has a slender rhizome creeping in the mud at the bottom
of the lake, the branches having a pipe-like appearance as they consist of
long, white, cylindrical sections. One the plant is established, it soon
forms large colonies by means of this quick growing, spreading rhizome.
nodes arise several very narrow leaves, which have the pellucid, soft
texture, that we have noticed as characteristic of the underwater leaves
of the Pondweeds, although, of course, the Pipewort is not related to
middle of the tuft of radical leaves arises the leafless, erect, flowering
stem which may attain as much as two feet in height, and has a six-to
eight-angled structure. At its summit is produced a dense head of
flowers, which when young is protected by a long sheath, but on growing
the stem pushes the flower head out of this sheath.
flower heads are composed of many tiny flowers, the central ones bearing
stamens only, whilst the outer ones have pistils only. The flowers are
intermixed with tiny chaffy bracts, the outer of which are large and form
an involucre which protects the immature flowers before the head opens
flower consists of four perianth segments, the outer two of which are
black in colour and fringed at the summit, whilst the inner two are lead-colored
with a black spot at the base. In the males the two inner segments are
united to form a cup-like perianth containing the four stamens. The
females contain a rounded two-chambered ovary, surmounted by two stigmas.
flowers are obviously adapted to insect pollination and are in fact
visited by flies who come in search of nectar, and on being disappointed
content themselves with the pollen of the central flowers. They usually
alight on the outer female flowers and then cross into the males flowers,
so that any transported pollen will be left on the female flowers and
Shoreweed (Littorella uniflora)
one of the commonest and most widely distributed of the plants which
prefer the lochs and tarns for their habitat. It is to be found
throughout the whole area of the Highlands and climbs the mountains to
plant, which inhabits the shallow shore waters, is usually totally
submerged, the possesses a short, perennial stock from the summit of which
arise several fleshy, narrow leaves, which are usually two or three inches
in length. They possess no stomata and respire like other submerged
plants, but if the level of the lake recedes and the plant is partially
exposed, the aerial leaves then produce stomata so that respiration and
assimilation can continue.
gives rise to runners so that in time the plants form mats of leaves and
stems beneath the surface. These colonies are so dense that other plants
are unable to penetrate them, hence competition is mainly between plants
of the same species.
flowers are of two sorts. The males are produced on erect, leafless
peduncles, which are each terminated by one or rarely by two flowers,
consisting of four narrow, green sepals and a four-lobed, greenish-white,
tubular corolla. The four stamens are the most conspicuous part of the
flower and possess very long filaments terminated by large, oval, yellow
females are stalkless and must be carefully searched for among the bases
of the leaves. They consist of four narrow, green sepals surrounding a
greenish, pear-shaped corolla which is closely applied to the ovary. The
flower is remarkable for its long, stiff, erect style, and as it often
happens that the lower part of the plant is in water, the need of such a
long style becomes apparent. The flowers produce no nectar and are
adapted to wind-pollination.
not think, however, that one has only to visit the lake shore during the
flowering season to find the flowers of the Shorewood. Usually it remains
submerged and then it does not flower at all, the leaves becoming long and
grass-like and the plant depending on vegetative reproduction by means of
Awl-wort (Subularia aquatica)
an interesting little plant which may be found in some of the higher
Scottish lakes and tarns. I have found it in bleak, wind-swept Loch
Etchachan, near the summit of Ben MacDhui, in that wildest of all lakes
Loch Avon and in many of the small tarns in the Lochaber Mountains.
first approaches the shores of Loch Avon, one is astonished by its
completely barren, desert-like aspect. Only here and there a patch of
green shows that vegetation does exist, but in the main the scene is one
of sublime grandeur, of precipitous cliffs and boulder-strewn shores. If
we look closer, however, and the season in summer, we may notice a soft
green carpet on the gravelly lake bottom. This is the lowly Water Awl-wort,
often the only plant to be seen, but in certain places the Water Lobelia
bears it company.
remarkable among the mountain plants in being an annual, the seeds
commencing to germinate as soon as the temperature of the water begins to
rise in the spring, and this may not be before June in the higher lochs
which often have a covering of ice in early May.
plant is rarely over three inches in height and in the higher lochs, where
the growing period is short, only one or two inches, the very short stem
giving rise to a tuft of fine roots which anchor the plant in the gravelly
leaves are all radical and almost cylindrical in form, very slender and
pointed, and are completely glabrous, rarely rising above the surface of
midst of the leaves arises a short, naked stalk or scape which may
protrude through the surface into the air, but if the water is deep it
remains below the surface. The stalk gives rise to a raceme of small
white flowers, the petals of which are very minute. When the flowers are
produced above the surface they may be visited by small insects, but as
they are very inconspicuous they are usually self-fertilized. When the
flowers are unable to reach the surface they perfect themselves under
water and do not open.
flowering period is very short, probably not more than ten to twelve
weeks, and during that time the seed must germinate, the leaves are
produced, the flowers are pollinated and the seeds set and distributed, so
that it is not astonishing that the plant is so small
AQUATICS WITH FLOATING LEAVES
section of aquatics contains some of our most beautiful native flowers and
also some very interesting species.
Highland lochs we can find the beautiful and chaste White Water Lily,
surely the queen of British flowers; its lovely golden cousin the Yellow
Water Lily; the Water Crowfoots, of which many varieties abound; the less
interesting Bur-reeds and the very common Floating Pondweed.
White Water Lily (Nymphaea alba)
in the depths of the western Highlands, where from the hilltops one can
see the inspiring outlines of the Black Coolins against the setting sun,
where Rum and Eigg float like galleons on the shimmering Atlantic, there
lies, in a peaceful glen, a beautiful tarn, whose mirror-like face
reflects back the purple-mantled mountains and the black pines that fringe
its further banks.
where all is peace and not intruding footsteps break the silence, Nature
has had the happy thought to adorn the placid waters with the queenly
flowers of the White Water Lily.
will find hundreds of great, pure white blossoms floating on the silver
loch like fairy ships. Here one can study these beautiful treasures amid
scenes untrammeled by man, as the soft south-west wind with its elusive
tang of the sea gently ruffles the large, round leaves, breaking up the
mirror-like surface of the water into a million scintillating wavelets.
often admired the White Water Lily since then, but never under conditions
where Nature dwelt in such exquisite surroundings.
It is one
of the loveliest members of a very beautiful family of which many,
including those with flowers of brilliant blues, reds and yellows are
cultivated in our ornamental gardens and greenhouses. The gigantic
Victoria regia of South America and the sacred Lotus belong to this
same delightful family.
Lily is a perennial plant with a very thick, fleshy rootstock which is
usually buried in the soil at the bottom of the lake. If we examine this
rootstock in the springtime, we shall find that near one end there is a
large green bud, which is the commencement of the Water Lily plant. The
rootstock will be found to be marked at regular intervals with a scar,
marking the position of the leaves and flower stalks of other years. Each
year the rootstock lengthens, the new portion of the present year giving
rise to the new plant next year.
days length and become warmer, the bud swells and gives rise to several,
thick, rubber-like stems surmounted by the leaves which at this stage are
curled up tight. The stems continue to grow until they attain the surface
of the water, where the leaves open and lie flat. At the same time the
flower stem, which was contained among the leaf stalks, reaches the
surface, the flower at this time being enclosed in a spherical bud and
protected by the smooth, thick, outer sepals.
If we cut
across one of the stems, we should find that four tubes run along the
whole length of them. These tubes are hollow and filled with air which
helps to keep the stems buoyant, so that they can support the large leaves
and flowers, as well as resist currents.
is very large, often six to eight inches in diameter, and is almost round
except for one side which is deeply heart-shaped. The stem is situated in
the middle of the under surface instead of at the base as in most plants.
Each leaf lies flat upon the surface of the water, and as the lower
surface is in constant contact with the water, no stomata are situated
upon it. It is usually reddish in colour below, but of a bright green
above and very smooth and highly polished. This is an important feature
as any water which may splash upon the supper surface (and this may happen
frequently on a windy day) immediately runs off the smooth surface, and
does not lie upon t and choke the stomata.
flowers commence to open in June and float upon the surface. They are
very large, often as much as four inches in diameter and the petals are
dazzlingly white, sometimes fading into rose-pink at the base, and are
scentless. This is a reverse of what one would expect, as in the plant
world most white flowers are highly perfumed and open in the evening when
their scent attracts night-flying insects. The Water Lily, however, open
during the day, closing in the early evening, and as its blooms are very
conspicuous, it has no need of perfume to attract day-flying insects.
examine a flower carefully, we shall find that it has four large green
sepals, which protect the flower whilst in bud and also at night and in
wet weather, when the flower is closed.
the sepals, we shall find several rows of pure white petals which are
glossy and of a fleshy texture. The petals pass gradually into the many
rows of stamens, in which the outer stamens have petal-like filaments
surmounted by sort anthers, and the inner ones have fine filaments
surmounted by long anthers.
centre of the flower are situated the many carpels which are imbedded in
the fleshy receptacle and radiate from the common centre. Each cell is
surmounted by short anthers, and the inner ones have fine filaments
surmounted by long anthers.
centre of the flower are situated the many carpels which are imbedded in
the fleshy receptacle and radiate from the common centre. Each cell is
surmounted by the stigmas which form a ring around the receptacle.
flowers are visited by a host of insects, bees, flies and beetles being
the chief benefactors, but many other insects also visit this beautiful
flower for pollen and the nectar which is secreted at the base of the
flowers have been pollinated they close and the stems gradually fill with
water, the weight of which drags the flower down to the bottom of the
pond, where the flower decays and the seeds are released to float along
the bottom until they come to rest on the mud to give rise to new plants.
no sight in these islands is lovelier than that of a loch or tarn covered
with the great green leaves and glorious flowers of this exquisite plant.
Happily, the White Water Lily is by no means rare, and one can find many
loch and tarns in the Highlands covered by its delightful blooms.
Water Lily (Nuphar lutea)
plant is very common in lochs and tarns all over the Highland area, and in
many lochs in the Hebrides. It is very handsome and, although lacking the
chaste beauty of its white cousin, it can hold its own with most of our
large, cordate leaves spread out flat upon the surface of the water and,
as they are highly polished, any water splashing upon them rolls off.
flowers, which are produced several inches above the surface and are
bright yellow in colour, are cup-shaped in form and have five or six
large, fleshy, concave sepals which are greenish on the outer surface, and
are the advertising agents of the flower.
of the twelve to fifteen petals, which are arranged in whorls around the
ovary, are rounded, resembling the petals of normal flowers, but the inner
ones are small and oblong in form passing gradually into the stamens.
stamens and ovary are very similar to those of the White Water Lily.
flowers, which smell rather strongly, attract hosts of flies, bees and
butterflies, and are pollinated as in the case of the preceding.
certain Highland lochs we have yet another water lily, the Least Yellow
Water Lily (N. pumila). This plant is much smaller in all its
parts, and the stigma has only eight to ten rays compared to fourteen to
twenty in the case of the larger plant.
Bur-reed (Sparganium minimum)
species is a close relative of the Branched Bur-reed (S. erectum),
a common plant around the marshy edges of the lochs and streams (see
are very weak and are rooted in the mud at the bottom of the loch, and as
they ascend to the surface of the water, the deeper the loch the longer
are stems. From their upper part long, floating, grass-like leaves are
given off. The wind-pollinated flowers are produced on aerial stalks, and
are arranged in spherical heads, the upper ones consisting entirely of
male flowers, the lower two or three being female.
floating Bur-reed (S. natans), which may be found rarely in deeper
waters, is very similar to the preceding, but is large n all its parts and
appears to be a variety of the Branched Bur-reed.
dealt in an earlier chapter with the Insectivorous plants inhabiting the
bogs. The present subject is another member of this interesting group of
plants, but it prefers lochs, ponds, ditches and marshy pools for its
Bladderwort is divided into four species, three of which may be found in
the Highlands, usually at fairly low altitudes. They are the Common
Bladderwort (U. bulgaris); the Lesser Bladderwort (U. minor)
and the Intermediate Bladderwort (U. intermedia).
of these fascinating plants will fill us with astonishment. Their amazing
way of life and the intricacy of the mechanism which enable them to lead
it, are not equaled anywhere else in the plant world.
take a plant of the Common Bladderwort out of water, we shall find that no
roots attach it to the bottom of the pond and that it is free-floating in
composed of an intricate mass of slender green branches, which give rise
to many bright green leaves, consisting of many finely-cut segments. If a
leaf segment is examined under the microscope, it will be seen to be
covered with short, tiny, pointed hairs.
carefully examine the leaves. We shall see that they are clothed by
several bladder-like structures which are rounded in form and are hollow
within. To the early botanist these represented air-sacs by which the
plant was supported in the water. Their actual function is much amazing
than that as they are actually very efficient traps with a very delicate
produced upon short stalks which arise from the main leaf branches. The
entrance to the vesicle is a tiny rounded portal, surrounded by fine,
branching hairs which stand upright around its edge.
the function of this strange structure? A very instructive experiment can
be arranged as follows. A leaf with two or three vesicles attached is
placed in a watch-glass containing a few drops of pond water. This water
will probably contain many minute organism call Water Fleas (Daphnieae).
Now focus the microscope upon a bladder and watch the entrance carefully.
If we are lucky we shall see one of these tiny water fleas approach the
entrance to the vesicle. Attracted, perhaps, by it bright green interior,
it tries to enter and in so doing will touch the fine hairs, and these
immediately drive the water flea into the bladder. At the same time a
valve in the entrance shuts like a spring trap effectually imprisoning the
flea can be seen swimming around in the bladder, but gradually its
movements become slower until it stops and in an hour or two it will be
seen to be dead.
the object of this seemingly wanton destruction? Obviously the plant is
not activated by the pleasure of the hunt or by any wish to destroy. We
can find the answer to this question by carefully opening a vesicle along
its long axis and placing it, with the inner surface uppermost, under the
microscope. The walls of the inner surface will then be seen to be
covered by four or five branched, star-like hairs, the absorbing organs
whose function is to absorb the products of decay given off by the
decomposing water flea.
see that the Bladderwort catches these water organisms in order to
supplement its food supply. As we have seen, the plant produces no roots
and hence cannot obtain salts, such as nitrates, from the soil, but the
decaying water fleas supply nitrogen salts to the plant and hence makes up
for this deficiency.
state of Nature little organisms are always being chased by larger ones,
and often enter the bladders, thinking to find refuge within their bright
the submerged plant gives rise to stout scape about six to twelve inches
high. It is naked except for a few small scales at the base and gives
rise to a raceme of four to eight conspicuous, pale yellow flowers.
consists of two ovate, green, similar sepals, one being produced upwards
and other one downwards.
corolla s bright yellow or even orange in colour and two-lipped, having a
close resemblance to that of the Antirrhinum. The lower lip is very
swollen and concave with a prominent palate, the lips being inclined at an
angle of forty-five degrees to make a landing stage for bees, and it is
produced backwards as a short, conical spur in which the nectarines are
lip is much smaller, half erect and three-lobed and meets the lower lip,
the corolla being almost closed.
is a globular structure situated at the base of the corolla and is
surmounted by a single style with a bi-lobed stigma situated in the roof
of the mouth-like flower. The two stamens are adnate with the corolla,
the two anthers being situated in the roof behind the stigma.
bee alights upon the lower petal, it pushed it proboscis between the lips
of the corolla and, on its way down to the spur, it will tough the stigma
which immediately folds up. Beyond this the proboscis is dusted with
pollen by the anthers. On withdrawing the pollen will not tough the
stigma, as it has moved out the way, thus avoiding self-fertilization.
fertilization the ovary forms a rounded capsule containing many small
does not depend on seeds alone for the continuation of the species, for in
autumn the stems form large buds, which drop off and remain dormant at the
bottom of the pond during the long winter, opening in spring to form new
plants. At this time the bladders are full of water and anchor the plant,
but as the flowering season approaches the bladders fill with air and the
plant becomes buoyant, thus being able to produce its flowers above the
Bladderwort differs in being smaller in all its parts and with only one or
two bladders to each leaf.
Intermediate Bladderwort is rather different as the bladders are not borne
on the leaves, but instead are produced on colorless shoots buried in the
mud. The nature of these shoots is rather obscure as they are geotropic,
i.e. they grown down into the ground n the same way is roots, but they do
not have a root structure. The flowers are bright yellow and nearly as
large as those of the Common Bladderwort. This species is rather rare and
local in its distribution.
Crowfoot (Ranunculus aquatilis)
the commonest and most widely distributed of all aquatic plants is the
lovely little Water Crowfoot which we can be fairly sure of finding in
running streams, in quiet lochs, in stagnant pools and on damp mud.
assumes many different forms in relation to the varied conditions under
which it lives, and hence has been divided into many sub-species and
commence my description of this interesting group of plants with the
species found in running water. There are two or three supposed varieties
of this type, included under the name Ranunculus fluitans.
plant all the leaves are submerged beneath the water. It is firmly rooted
at the bottom of the stream and sends up fairly stout stems, which take up
a position parallel to the current, where they offer the least resistance
to its passage. The leaves are large and cut up into very fine, hair-like
segments which also lie parallel to the current, and are an adaptation to
havitat as the current would cut a large entire leaf into ribbons.
axis of the leaves fairly stout peduncles rise above the surface of the
water. The flowers are the only aerial portion of the plant, and the
stout peduncles are well able to resist the force of the current and keep
the flowers upright in the air.
flowers are pure white in colour and larger than in most varieties of
Water Crowfoot. This is probably in order to make them more conspicuous,
as smaller flowers would hardly be seen against a background of running,
flower, which possesses a green calyx of five spreading sepals and a
corolla of five white obovate petals with a yellow patch at the base of
each where the nectar is situated, are visited by the smaller bees and
flies, and are pollinated in a similar way to those of the Buttercup (see
fertilization the peduncles bend downwards and the seeds are released in
the water, which distributes them far from the parent plant. It thus
colonizes large areas and may form a mass of vegetation in the centre of
the stream, thus slowing the current and causing the deposition of silt.
quiet waters around the edges of lochs and ponds, we may meet with several
other varieties of Water Crowfoot, which all agree in having much divided
submerged leaves. These dissected leaves spread out like a fan in the
still waters and carry on photosynthesis in the same way the leaves of the
completely submerged aquatics, e.g. Myriophyllum.
stems, however, are supported by the floating leaves, which also carry on
photosynthesis. The leaves are rounded in form and divided into three to
five wedge-shaped segments, or may have five quite rounded segments.
types, including R. circinatus, the submerged leaves spread out
around the stem and on being taken out of the water they do not collapse
as in R. fluitans, but remain rigid. In other types there are also
floating leaves and here are included R. peltatus and R.
heterophyllus. They form dense colonies, as their floating leaves
obstruct the light from entering the water, they make if difficult for
other plants to thrive in their territory. In winter they sink to the
bottom of the loch and are safe from frost and ice.
muddy fringes of lochs, ponds, or streams, we may find more types of this
ubiquitous plant. They are the Mud Crowfoot (R. Lenormandi) and
the Ivy-leaved Crowfoot (R. hederaceus).
both creeping plants whose weak stems give off adventitious roots at the
nodes, and branch in all directions with the result that one plant may
cover quite a large area.
leaves, which are on short, erect stalks and are kidney-shaped, with five
rounded segments, are smooth, shiny and bright green in colour, and in
shallow water they float upon the surface.
flowers are only half-an-inch across in the case of the Mud Crowfoot,
whilst in the Ivy-leaved Crowfoot the petals are hardly larger than the
sepals. In these plant the flowers are seldom visited by insects, and
hence they depend on self-fertilization to obtain seed.
variety, R. trichophyllous, often to be found upon mud, is an amphibious
type and can live either submerged or exposed, its leaves being cut into
fine segments, whilst the stems are short and tufted. The flowers are
very small and pinkish in colour, and are usually self-fertilized.
of these plants will give us a good idea of the role played by environment
in forming the structure of plants.
no doubt that all the above plants arose from the same ancestors, but
owing to very different conditions of life the various types are evolving
away from the parent type to become more and more specialized to a certain
type of habitat. Thus R. fluitans could not compete with a still
water type and vice-versa.
aquatic Ranunculus that may be found in wet places, on the edges of lakes
and streams, is the Lesser Spearwort (R. Flammula). It possesses
long, lanceolate or ovate leaves which are produced above the surface of
the water. The flowers are yellow and born upon fairly stout peduncles,
and are very similar to those of the Buttercup, but are smaller. This
plant has also evolved several varieties, one of which, R. scoticus,
grows under water n a few lakes in north-west Scotland, its leaves being
reduced to awl-like petioles. Another variety, R. reptans, a
slender, creeping plant with linear leaves, may sometimes be found in
already dealt with the submerged Pondweeds in the preceding section of
this chapter, and we are now concerned with the type which has floating as
well as submerged leaves. The typical example, and the most widespread
and common, is the Floating Pondweed (Potamogeton natans).
plant is a fine example of adaptation to aquatic conditions. It has a
long, white rhizome, which creeps along the mud at the bottom of the pond,
giving off many fibrous roots which anchor it firmly. The rhizomes of
many different plants cross over each other and form a dense mass of stems
and roots which hold together the mud, leaves and other debris covering
the pond bottom.
rhizome arise the long, slender, pliant, leafy stems which grow up to the
surface of the water, supported by the air which collect in the spongy
tissue of the stem. At the nodes the under-water stem often gives rise to
thin, brown, pellucid, narrow leaves which remain submerged and absorb
carbon-dioxide and oxygen from the water, and until the floating leaves
are produced, the plant is dependent on this source.
stem reaches the surface, the upper leaves, which have been carefully
rolled up inside cylindrical, transparent sheaths, break out of their
prison and, supported on long stalks, they open out and float on the
surface of the water. They are leathery and elliptical in form with dark
green, polished upper surface on which the stomata are developed. The
under surface is brownish with a thick impermeable cuticle. These leaves
provide the plant with by far the greater portion of its oxygen and
often reach three or four feet in length, depending on the depth of the
water. Once the floating leaves are fully developed, a stout cylindrical
flowerstalk appears from a tubular sheath in the axil of one of the
floating leaves. It is terminated by a long spike of green flowers.
flowers consist of four tiny green perianth segments surrounding four
sessile green carpels. Opposite the join between each carpel is a
absence of colour and perfume shows that the flowers do not depend on
insects for pollination, but they are in fact wind-pollinated. If we
visit a colony in summer, we shall see that the surface of the water has a
yellow tinge from the abundant pollen which has been blown from the
stamens. This gives point to the fact that wind-pollination is a wasteful
way of obtaining fertilization, as enormous quantities of pollen never
reach the pistils of other spikes.
species, P. heterophyllus, is also a common and well distributed
plant, but it prefers the more acid types of lochs and pools. The
floating leaves are much smaller, being only one or two inches in length,
whilst the submerged leaves are very long and narrow with a few parallel
veins. Sometimes no floating leaves are formed and it is then
distinguished with difficulty from submerged leaved species.
P. alpines is closely related to P. lucens
(see page 221), but it has shortly-stalked, reddish, floating leaves
which in shallow water may even become erect. In deep water narrow,
stalkless, submerged leaves are also formed. This species is found in
most of the Highland area south of the Caledonian Canal and in the South