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THE HIGH ALPINE SAXIFRAGES
The Scottish Highlands are rich in Saxifrages and ten
species are to be found there. Some of them inhabit the lower slopes and
valleys, while other are widespread on the mountains themselves; five
species are more or less confined to the highest summits. They are the
Purple Saxifrage (Saxifraga oppositifolia), which, although not
confined to the highest regions, as it may be found at comparatively low
altitudes, is very common on our higher mountains; the Tufted Saxifrage (S.
caespitosa) only found near the summits of the highest mountains; the
Drooping Mountain Saxifrage (S. cernua) a very rare species only
found on the summit of Ben Lawers and now nearly extinct; the Alpine Brook
Saxifrage (S. rivularis) found beside streams and springs near the
summit of Ben Nevis, Ben Lawers and Lochnagar; and the Alpine Saxifrage (S.
nivalis) found not uncommonly on the higher Scottish mountains.
Of these Saxifrages, the first two are cushion-type
alpines and the others are rosette types.
While not as showy as many of the Swiss Saxifrages, our
Alpine Saxifrages are very attractive and interesting plants.
THE CUSHION SAXIFRAGES
 Purple Saxifrage
(Saxifraga oppositifolia)
This
is one of our most beautiful alpine flowers, and only those who have seen
it in bloom in its natural surroundings can have any idea of how lovely it
really is. Its large, purple blooms are to be found on the lower slopes
among the melting snows in early April, at a time when colour is almost
non-existent on the mountain sides. By May it is blooming wherever the
snow has cleared on the highest peaks and corries. By mid-June its
flowers have faded, and its seed is set and distributed long before the
snows of early autumn have arrived.
The Purple Saxifrage prefers most rocks and is found
more especially on the northern and eastern corries and slopes, where the
sun’s heat is much less and water is more abundant. Its long roots
penetrate deeply into the cracks and crevices of the rocks, where they
escape the hard winter frosts and are able to tap the water supply in the
deeper soils.
Above the ground is a short, tough stem, which is
buried as far as possible in the soil. This stem give out slender
branches, which creep along the rocks giving out other branches which are
covered in tufts of leafy shoots. The whole system is very compact and
seldom rises more than on inch above the soil The result of this
compactness is the formation of dense cushion, which appears like a clump
of green leaves, the branches being absolutely hidden by the closeness of
the leaf tufts. The leaves themselves are evergreen, very small and shiny,
and arranged in pairs, each pair being closely pressed to the one above.
This helps us prevent undue transpiration.
The leaves are interesting in having evolved a very
ingenious device to check excessive transpiration. The leaves of plants
are usually covered on the under surface by pores, known as stomata, by
which the plant breathes, taking in oxygen and carbon dioxide which are
used in the respiratory and photosynthetic processes. Through these
stomata water escapes from the plant as vapour in the process of
transpiration. To get rid of surplus water, some plants, especially those
inhabiting wet places, possess special water pores of hydathodes at the
tips of the leaves, or at the point of teeth along the margin. The Purple
Saxifrage possesses such a hydathode at the apex of each leaf. To control
the escape of water, this plant, in common with some other species of
Saxifrage has a special mechanism. The tissue around the pore has the
power of secreting chalk. Water leaving the leaf by this pore dissolves
some chalk which is deposited on the surface of the pore. On dry days
when evaporation is rapid, a heap of chalk accumulates quickly and soon
closes the pore, preventing the exudation of any further water. At night,
when evaporation is less, the escaping water dissolves some of the
accumulates chalk and allows the water to exude again.
The amazing thing is, that although this plant grows on
rocks which contain little or no chalk, such as granite or gneiss, the
roots by reason of special selectivity are able to obtain enough chalk to
continually supply the chalk glands.
Each leaf tuft sends up a short stalk surmounted by a
beautiful, reddish purple flower, which is very large in comparison to the
size of the plant often being nearly an inch in diameter.
The individual flower is bell-shaped, the five petals
being united for more than half their length. The flowers, being large
and numerous almost hid the cushion thus making themselves very
conspicuous to insect visitors, which, as in the case of the Moss Campion,
are mainly butterflies whose long tongues alone can reach the nectarines
at the base of the flower, and for whom it holds out its reddish-purple
sign. Each flower contains ten stamens in two whorls. The ovary, at the
base of which are found the nectarines, is surmounted by two styles.
The stamens mature before the stigmas and a butterfly
must visit the newly-opened flower to be dusted with pollen. On visiting
an older flower the butterfly will leave some pollen on the now receptive
stigma. Thus cross-fertilization is assured and an abundant supply of
fertile seeds will be formed.
Tufted Alpine Saxifrage
(Saxifraga caespitosa)
This
species, like the preceding, also forms a cushion, but it is only to be
found at great heights and is much rarer. It cushions are not so compact
and leaves are short and green and divided into two or three lobes. These
leaves have no chalk glands as in Saxifraga oppositifolia.
In this species the flowers are small and white, and
one or two to each stalk. Each petal has a number of greenish veins
running down toward the nectaries. These veins guide the butterflies and
the flies which pollinate the flowers. The flower stalks are two to three
inches high and are covered with a glandular down as in some lowland
species. This acts as a barrier to crawling insects which would otherwise
mount the short stalk and steal the nectar, without giving any benefit to
the plant.
To find this plant we must climb to the highest summits
by way of the precipitous corries, where in the screes and rock clefts one
may have the good fortune to find its small flowers. It is practically
confined to the Cairngorm and Ben Nevis ranges.
THE ROSETTE SAXIFRAGES
We now pass from the Cushion Saxifrages to those which
belong to the Rosette group. In this series we again find the short main
stem or stock buried as far as possible in the soil. Immediately from the
top of this stock spread out compact rosettes of leaves pressed close to
the surface of the soil. This rosette arrangement is very common among
alpine plants. The leaves are arranged so that each one receives the
maximum of light and are pressed close to the soil. This makes it
impossible for another plant to grow within the radius of the leaves, an
important factor where competition for space is severe. The lowness of
the habit is very well adapted to the windy regions these plants inhabit.
The flowering shoot is long and upright and surmounted by the bloom. This
tall shoot protects the flowers from creeping insects and also makes the
flowers very conspicuous.
Droping Mountain Saxifrage
(Saxifraga cernua)
This
is one of our rarest alpine plants, being confined to the broken schist
formations near the summit of Ben Lawers, where it is becoming exceedingly
rare and very seldom flowers.
It is fond of damp, shaded rocks and does not exhibit
such marked modifications against drought as many alpines do. The very
short stock of this plant develops a number of small bulbs covered with
reddish-brown scales, in much the same way as the Meadow Saxifrage
(S. granulata) of the Lowlands. The likeness
between this plant and the Drooping Saxifrage has made some authorities
think that it is but a starved mountain edition of the same plant. The
bulbs are very easily detached and give rise to new plants. This method
of propagation is known as vegetation reproduction and is common among
alpine plants, being found in many widely differing families (Polygonum,
Poa, Deschampsia, etc.).
The stock is crowned by several radical leaves. These
are on rather long, weak stalks and are kidney-shaped (reniform) with
angular lobes and are almost glabrous on the upper surface. There are a
few short hairs on the under surface.
>From the midst of the leaves rises a fairly tall,
flowering stem which droops slightly at the summit. There are a few small
leaves on this stem and in their axils there are often small, brownish
bulbils, which detachment, give rise to plants as in the case of the root
bulbils. The flowering stem is crowned with one to three small flowers.
These are white, and each petal has several well marked veins which
converge on the nectary at the base and act as guides to insect visitors.
The chief visitors are bees and small flies.
Very often, however, the plant produces no flowers,
relying on vegetative reproduction to continue the species. This is
probably one reason for its increasing rarity and for the fact there is a
great danger of the plant becoming totally extinct. Vegetative
reproduction when not aided by cross-fertilized seeds must result in the
gradual undermining of the race and its eventual extinction.
Why this plant should be confined to Ben Lawers is
impossible to explain. Perhaps it was a happy accident that deposited its
seeds there in some distant past, who can tell? Some bird, perhaps, who
after a lost flight from the Arctic regions landed on this high peak and
left some seeds of the plant behind. Or, perhaps, its explanation can
only be found way back in the Great Ice Age. This is only one of the
many fascinating mysteries of the plant world, which will probably never
be explained.
Alpine Saxifrage
(Saxifraga nivalis)
To
find this uncommon alpine, we must climb into the wild corries and risk
our necks upon the cool, damp, north-eastern precipices of our highest
mountains. We may find it very rarely on Braeriach and Cairn Toul, and
more abundantly on the Ben Lawers and Ben Nevis Range. It may also be
found in Skye.
It possesses a very short stock which is of a hard,
tough structure. The toothed leaves are arranged in a close rosette on
the summit of the stock. They are of a leathery texture and obovate in
form, tapering downwards to form a stalk. The thick leaves are well
constituted to dry conditions, the fleshy tissues conserving water and the
thick cuticle reducing transpiration.
The flowering stems, which are from two to five inches
in height, are erect and unbranched and are hairy in the upper part. It
is usually naked, but sometimes bears one or two small leaves.
The four to twelve fairly large, white flowers are
collected together into a compact terminal head. The sepals are about the
same length as the petals. Within the corolla are situated two whorls of
five long and five short stamens and two styles.
The flowers, which secrete nectar, are visited by small
bees and flies. The long stamens move in towards the centre of the flower
and, when they have shed their pollen, they recede their place being taken
by the shorter ones. When all the pollen is shed and all danger of
self-pollination has gone the two styles spread apart and become
receptive. This is the mode of pollination inmost of the white and
yell-flowered Saxifrages.
Alpine Brook Saxifrage
(Saxifraga rivularis)
This
rare alpine is confined to the edges of brooks and springs near the
summits of Ben Lawers and Ben More in Perthshire, of Cairn Toul and
Lochnager, and perhaps one or two other summits of the Cairngorms, and of
Ben Nevis and Aonach Mor.
The short stock produces a few long-stalked, smooth
leaves, which are three to five lobed and resemble those of Saxifraga
cernua. The slender, flowering stems also possess several long-stalked
leaves of simpler form, the upper ones forming a pair of bracts below the
two or three flowers which are produced on short, slender pedicels. They
are small, the calyx being as long as the corolla, and as they are not
very conspicuous they are little visited by insects and are probably
self-fertilized.
Occasionally it produces bulbils in the axils of its
lower leaves and these resemble those of S. cernua. Thus in the
event of no flowers being formed in bad seasons, when the snows have lain
late, the plant can propagate itself vegetative by their means. |
