At About 5,000 Feet European Forms
Of Plants Become Abundant.
Several species of Honeysuckle, St.
John's-wort, and Guelder-rose abound, and at about 9,000 feet we
first meet with the rare and beautiful Royal Cowslip (Primula
imperialis), which is said to be found nowhere else in the world
but on this solitary mountain summit.
It has a tall, stout stem,
sometimes more than three feet high, the root leaves are eighteen
inches long, and it bears several whorls of cowslip-like flowers,
instead of a terminal cluster only. The forest trees, gnarled and
dwarfed to the dimensions of bushes, reach up to the very rim of
the old crater, but do not extend over the hollow on its summit.
Here we find a good deal of open ground, with thickets of shrubby
Artemisias and Gnaphaliums, like our southernwood and cudweed,
but six or eight feet high; while Buttercups, Violets,
Whortleberries, Sow-thistles, Chickweed, white and yellow
Cruciferae Plantain, and annual grasses everywhere abound. Where
there are bushes and shrubs, the St. John's-wort and Honeysuckle
grow abundantly, while the Imperial Cowslip only exhibits its
elegant blossoms under the damp shade of the thickets.
Mr. Motley, who visited the mountain in the dry season, and paid
much attention to botany, gives the following list of genera of
European plants found on or near the summit: Two species of
Violet, three of Ranunculus, three of Impatiens, eight or ten of
Rubus, and species of Primula, Hypericum, Swertia, Convallaria
(Lily of the Valley), Vaccinium (Cranberry), Rhododendron,
Gnaphalium, Polygonum, Digitalis (Foxglove), Lonicera (Honey-
suckle), Plantago (Rib-grass), Artemisia (Wormwood), Lobelia,
Oxalis (Wood-sorrel), Quercus (Oak), and Taxus (Yew). A few of
the smaller plants (Plantago major and lanceolata, Sonchus
oleraceus, and Artemisia vulgaris) are identical with European
species.
The fact of a vegetation so closely allied to that of Europe
occurring on isolated mountain peaks, in an island south of the
Equator, while all the lowlands for thousands of miles around are
occupied by a flora of a totally different character, is very
extraordinary; and has only recently received an intelligible
explanation. The Peak of Teneriffe, which rises to a greater
height and is much nearer to Europe, contains no such Alpine
flora; neither do the mountains of Bourbon and Mauritius. The
case of the volcanic peaks of Java is therefore somewhat
exceptional, but there are several analogous, if not exactly
parallel cases, that will enable us better to understand in what
way the phenomena may possibly have been brought about.
The higher peaks of the Alps, and even of the Pyrenees, contain a
number of plants absolutely identical with those of Lapland, but
nowhere found in the intervening plains. On the summit of the
White Mountains, in the United States, every plant is identical
with species growing in Labrador. In these cases all ordinary
means of transport fail. Most of the plants have heavy seeds,
which could not possibly be carried such immense distances by the
wind; and the agency of birds in so effectually stocking these
Alpine heights is equally out of the question. The difficulty was
so great, that some naturalists were driven to believe that these
species were all separately created twice over on these distant
peaks. The determination of a recent glacial epoch, however, soon
offered a much more satisfactory solution, and one that is now
universally accepted by men of science. At this period, when the
mountains of Wales were full of glaciers, and the mountainous
parts of Central Europe, and much of America north of the great
lakes, were covered with snow and ice, and had a climate
resembling that of Labrador and Greenland at the present day, an
Arctic flora covered all these regions. As this epoch of cold
passed away, and the snowy mantle of the country, with the
glaciers that descended from every mountain summit, receded up
their slopes and towards the north pole, the plants receded also,
always clinging as now to the margins of the perpetual snow line.
Thus it is that the same species are now found on the summits of
the mountains of temperate Europe and America, and in the barren
north-polar regions.
But there is another set of facts, which help us on another step
towards the case of the Javanese mountain flora. On the higher
slopes of the Himalayas, on the tops of the mountains of Central
India and of Abyssinia, a number of plants occur which, though
not identical with those of European mountains, belong to the
same genera, and are said by botanists to represent them; and
most of these could not exist in the warm intervening plains. Mr.
Darwin believes that this class of facts can be explained in the
same way; for, during the greatest severity of the glacial epoch,
temperate forms of plants will have extended to the confines of
the tropics, and on its departure, will have retreated up these
southern mountains, as well as northward to the plains and hills
of Europe. But in this case, the time elapsed, and the great
change of conditions, have allowed many of these plants to become
so modified that we now consider them to be distinct species. A
variety of other facts of a similar nature have led him to
believe that the depression of temperature was at one time
sufficient to allow a few north-temperate plants to cross the
Equator (by the most elevated routes) and to reach the Antarctic
regions, where they are now found. The evidence on which this
belief rests will be found in the latter part of Chapter II. of
the "Origin of Species"; and, accepting it for the present as an
hypothesis, it enables us to account for the presence of a flora
of European type on the volcanoes of Java.
It will, however, naturally be objected that there is a wide
expanse of sea between Java and the continent, which would have
effectually prevented the immigration of temperate fortes of
plants during the glacial epoch.
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