and the causes affecting its recent diminution. 75
Such causes as those now mentioned, tending to the
diminution of the lichen-flora of the Forest, were probably
more or less at work in the days of Forster; but there can
be no question that of recent years they have been much
more actively and extensively in operation. It will therefore
be very interesting to the lichenist of the future—some fifty
or a hundred years hence—to compare the above list of
lichens with those that the Forest may then present. Some
species belonging to the higher genera extant in Forster's
time, and some also belonging to the lower genera, noted in
the catalogue as extinct, can never again be expected to
occur, since they are not elsewhere to be found within such
a measurable distance as that their spores could be readily
disseminated in the Forest. But now that the Forest is
strictly preserved and left to the operations of natural laws,
there is every reason to believe that many species and
varieties now germinating and slowly growing upon their
different substrata may eventually be found developed into
perfect thalli or fertile plants. This, however, must be the
work of time : for though readily germinating, the subsequent
evolution of lichens is in most cases a very protracted process,
resulting from their peculiar twofold manner of life—lethargic
in dry, and active only in wet, weather.