and the causes affecting its recent diminution. 71
amounted to some forty-six species and varieties, while
during the interval between then and my recent visits other
forty seem to have shared the same fate.4 In fact, with a
few exceptions, it is now only the more common and generally
distributed species that survive. Nor have the lichens of the
Forest thus diminished merely in number of species, but also
in the quantity in which the survivors occur. This has been
very marked since my observations first commenced, and
nothing in the character of its lichen-flora is more striking
than that species which some eighteen years ago were both
general and plentiful are now to be seen only here and there
in very small quantity. And not only so, but what is still
more singular, many of these are seen only in a sterile or
fragmentary condition, presenting often a sickly appearance,
as if they were slowly dying out.
What, then, are the causes to which such a great diminu-
tion of, and change upon, the lichen-flora of the Forest are
to be attributed ? Certainly not to any process of decay or
death inherent in the lichens themselves; for of all plants
they are the longest-lived, and the veritable "patriarchs" of
the vegetable kingdom. Indeed so great is the longevity of
many species, that, were any of the original trees of the
Forest still in existence, we might expect to find flourishing
upon them the selfsame individuals which centuries ago
appeared upon their trunks and branches. The phenomena
under notice are therefore entirely owing to certain external
causes which tend directly to the decrease and decay of
species. Of these the first and most obvious is the destruction
of the older trees,6 whether by the storms of heaven or the
hand of man, in most parts of the Forest. Now it is a well-
known fact that lichens, more especially those belonging to
the higher genera, are of extremely slow growth, and conse-
4 But even though thus greatly diminished, the lichen-flora of the
Forest compares not unfavourably with some similarly situated woodland
tracts, such as Windsor Forest, where poverty is equally marked.
5 The trees indigenous to the Forest are chiefly oak, hornbeam, beech,
and hawthorn, with here and there birch, holly, and maple. In addition
to these have been introduced, especially near the towns and villages,
ash and elm, which, however, are now but sparingly seen.