Ordnance gazetteer of Scotland > Volume 6

64 BOTANY.
Principal Dawson and others have conclusively established that the coal trees grew near broad
estuaries and on immense flat plains near the sea-level, but not in swamps and shallow water
as was at one time supposed. Such trees as the Sigillarim and Lepidodendra, of which our Coal
Measures are largely composed, would grow for many generations of trees upon such sites ; and
then came a period when the plain was submerged under the sea, the whole of the forest being
covered with thick deposits of sand and gravel and other sediment carried down by streams
from the adjoining land.
THE POST-GLACIAL PERIOD AND THE REINTRODUCTION OF PLANT LIFE TO SCOTLAND.
In considering the botany of an insular country, the first thoughts that naturally occur to
the inquiring mind are — Where did its plant life come from ? Is it peculiar to the country
itself, or is it the same as is found on the nearest continent ? and, if the same, How came it
to be distributed ? or does it represent only some of the continental plants ? These are questions
that deserve consideration. As far as Britain is concerned, we may conclude that we owe
nearly the whole of our present flora to the European continent, as there is good evidence that
at more than one period Britain was not insular, but formed part of the continent itself.
Besides, the flora of both corresponds in so many respects, that, allowing for variations in
climate, soil, and elevation, we can account for all, or most all, the differences that occur.
Within the limits of Britain it might be thought that we should find the same plants
growing from Lands End to John o' Groat's House ; but this is not so, and the botanist from
the south of England will find in Scotland from the Tweed to the Pentland Firth many plants
that he does not find in his southern home, and also numbers awanting which are to him
familiar friends. He will find some peculiar anomalies in the botany of Scotland which require
careful consideration, and which shed considerable light on the changes of climate under-
gone by the country, and also on the way in which the vegetation was killed out during the
' glacial period,' and again redistributed when a time of higher temperature returned.
If the botanist proceeds along our coasts, he will find such plants as Armeria maritima,
Cochlearia officinalis, Sedum Rhodiola, Plantago maritima, and some others in great abundance.
But if he goes inland he will find very few stations for those plants until he ascends to near the
summits of our highest mountains. The questions must naturally occur to him — Why are those
plants not found in the intermediate zone as plentifully as at the sea coast or near the
mountain summits ? and how came they to be distributed either from the sea coast to the
highest elevations, or from the highest elevations to the sea coast, without being equally
distributed over the intermediate zone ?
AVe may premise that during the ' glacial periods ' the plant life of Britain was almost, if
not altogether, destroyed ; and that, in any case, the only forms of vegetation were such as
are found at the present time near the level of the sea along the shores of Greenland or in
the Arctic zone in Scotland, where similar forms occur, and which is at an elevation of over
3000 feet above sea-level — in other words, the summits of our highest mountains. At the
time of the ' glacial periods ' this zone in Scotland, instead of being at the mountain summits,
was at the sea-level, and it is from this point that these plants must have been redistributed,
and not only these plants but many others. The peculiarity of such plants as Anneria marititna,
Cochlearia officinalis, Sedum Rhodiola, and Plantago maritima is, that they are not confined to
one zone, but exist wherever congenial climatic conditions are met with, at various elevations
from the sea-level to the mountain tops. The first necessity for their growth is abundance of
moisture, and the second a situation free from other forms of vegetation; and it is this latter
cause that accounts for their not appearing frequently in the intermediate zone, as there are so
few suitable stations within its limits where there are wet rocks, or where the soil is so poor
that other forms of vegetation do not grow so strongly as to choke these plants. There are,
however, one or two stations in the intermediate zone where we know Cochlearia officinalis ('the
Scurvy Grass ') grows, such as the upper part of Borthwick Water in Roxburghshire, where it is
found abundantly from 700 up to 1200 feet above sea-level, with straggling plants at lower
elevations. It is found also at Roberts Linn at the head of the Slitrig, another tributary of the
Teviot. There is also a station near Innerleithen in Peeblesshire, at an elevation of about 450
feet; and it grows on the ruins and also the ground at Melrose Abbey, but here it was probably
cultivated by the monks. Armeria maritima (' the Sea Pink ') is found as a border-edging in
many gardens in the intermediate zone ; but if other forms of vegetation are not carefully kept
under by weeding, it quickly dies out, and it has no greater enemy than grass. Sedum Rhodiola
(' Roseroot Sedum ') is found growing abundantly in gardens, and frequently spreads on borders
and flower-plots so much that it becomes a weed. It is occasionally found growing on the
ledges of wet cliffs in the intermediate zone. It appears to be more abundant on the west
than on the east of Scotland. Plantago maritima (' the Sea Plantain ') is found abundantly