GEOGRAPHICAL DISTRIBUTION. 269 



whilst it is not improbable that species common with ns 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 jBoleti 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 copse wood, 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 con- 

 siderably 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 tho 

 physical constitution of a locality, such as that resulting from 

 the destruction of a forest, or from the drainage, by ditches and 



