ation of characters
that makes mountain plants such favourites with florists: for they
possess of themselves that close-grown habit and that rich profusion of
clustered flowers which it is the grand object of the gardener by
artificial selection to produce and encourage.

When one talks of the 'the limit of trees' on a mountain side, however,
it must be remembered that the phrase is used in a strictly human or
Pickwickian sense, and that it is only the size, not the type, of the
vegetation that is really in question. For trees exist even on the
highest hill-tops: only they have accommodated themselves to the
exigencies of the situation. Smaller and ever smaller species have been
developed by natural selection to suit the peculiarities of these
inclement spots. Take, for example, the willow and poplar group. Nobody
would deny that a weeping willow by an English river, or a Lombardy
poplar in an Italian avenue, was as much of a true tree as an oak or a
chestnut. But as one mounts towards the bare and wind-swept mountain
heights one finds that the willows begin to grow downward gradually.
The 'netted willow' of the Alps and Pyrenees, which shelters itself
under the lee of little jutting rocks, attains the height of only a few
inches; while the 'herbaceous willow,' common on all very high
mountains in Western Europe, is a tiny creeping weed, which nobody
would ever take for a forest tree by origin at all, unless he happened
to see it in the catkin-bearing stage, when its true nature and history
would become at once apparent to him.

Yet this little herb-like willow, one of the most northerly and hardy
of European plants, is a true tree at heart none the less for all that.
Soft and succulent as it looks in branch and leaf, you may yet count on
it sometimes as many rings of annual growth as on a lordly Scotch
fir-tree. But where? Why, underground. For see how cunning it is, this
little stunted descendant of proud forest lords: hard-pressed by
nature, it has learnt to make the best of its difficult and precarious
position. It has a woody trunk at core, like all other trees; but this
trunk never appears above the level of the soil: it creeps and roots
underground in tortuous zigzags between the crags and boulders that lie
strewn through its thin sheet of upland leaf-mould. By this simple plan
the willow manages to get protection in winter, on the same principle
as when we human gardeners lay down the stems of vines: only the w