GEOGRAPHICAL DISTRIBUTION. 269 
whilst it is not improbable that species common with us may be 
very rare fifty years hence. In this manner it would really 
appear that fungi are much more liable than flowering plants 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. Tpiphytal 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 con- 
siderably influence the flora of any locality. Heat and humidity, 
therefore, are intimately concerned in the mycologic vegetation 
ofacountry. Fries has noted in his essay the features to which 
we have alluded. “The fact,” he says, ‘‘inust 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 destraction of a forest, or from the drainage, by ditches and 
