ants to
shift their localities, or increase and diminish in number.

The fleshy fungi, _Agaricini_ and _Boleti_ especially, are largely
dependent upon the character of woods and forests. When the
undergrowth of a wood is cleared away, as it often is every few years,
it is easy to observe a considerable difference in the fungi. Species
seem to change places, common ones amongst a dense undergrowth are
rare or disappear with the copsewood, and others not observed before
take their place. Some species, too, are peculiar to certain woods,
such as beech woods and fir woods, and their distribution will
consequently depend very much on the presence or absence of such
woods. Epiphytal species, such as _Agaricus ulmarius_, _Agaricus
mucidus_, and a host of others, depend on circumstances which do not
influence the distribution of flowering plants. It may be assumed that
such species as flourish in pastures and open places are subject to
fewer adverse conditions than those which affect woods and forests.

Any one who has observed any locality with reference to its Mycologic
Flora over a period of years will have been struck with the difference
in number and variety caused by what may be termed a "favourable
season," that is, plenty of moisture in August with warm weather
afterwards. Although we know but little of the conditions of
germination in Agarics, it is but reasonable to suppose that a
succession of dry seasons will considerably influence the flora of any
locality. Heat and humidity, therefore, are intimately concerned in
the mycologic vegetation of a country. Fries has noted in his essay
the features to which we have alluded. "The fact," he says, "must not
be lost sight of that some species of fungi which have formerly been
common in certain localities may become, within our lifetime, more and
more scarce, and even altogether cease to grow there. The cause of
this, doubtless, is the occurrence of some change in the physical
constitution of a locality, such as that resulting from the
destruction of a forest, or from the drainage, by ditches and
cuttings, of more or less extensive swamps, or from the cultivation of
the soil--all of them circumstances which cause the destruction of the
primitive fungaceous vegetation and the production of a new one. If we
compare the fungal flora of America with that of European countries,
we observe that the former equals, in its richness and the variety of
its forms, that of the phanerog