276 M. E. P. Fries on the Geographical 
Garden of Upsala. The poverty of Sweden in representatives 
of the Tuberaceze is a remarkable peculiarity of the country— 
one genus only, and in fact only one single, recently discovered 
species of that genus, viz. the Tuber niveum (Terfezia Leonis, Tu- 
lasne), being found in two places in Ostrogothia; and even 
there it appears to be rare. On the contrary, in Central and 
Southern Europe these Fungi are common; and even in the 
south of England their species are tolerably numerous. The 
reason for the presence of a greater variety of species of this 
group of Fungi in England is to be found in the circumstance 
that the Tuberacez are developed chiefly during the winter, and 
because England, by reason of its insular position, enjoys milder 
winters and has a greater rainfall, and thereby furnishes more 
favourable conditions for the vegetation of these Fungi. In 
Sweden, on the contrary, the severe cold of winter and the frozen 
soil preclude the growth of Tuberacez. These Fungi, in con- 
clusion, have their centre in the warmer regions of the temperate 
zone ; for in hot climates their evolution is often interrupted or 
destroyed by the excessive heat. 
II. 
Heat and humidity are the two conditions generally recog- 
nized as most concerned in the vegetation of a country. No 
order of plants is more dependent on these conditions than the 
Fungi,—a fact peculiarly true in reference to the higher forms, 
or true Fungi, Hymenomycetes and Gasteromycetes, many of 
which do not make their appearance unless the weather is pecu- 
liarly favourable, or, in other words, after very abundant rains. 
Plants of this sort, which only show themselves under extraordi- 
nary atmospheric conditions, are called “ meteoric.” 
The fact must not be lost sight of in this place, 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 con- 
stitution 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 fungaceous flora of America with that of Eu- 
ropean countries, we observe that the former equals in its rich- 
ness and the variety of its forms that of the Phanerogamous 
flora; it is probable, however, that, in the lapse of more or 
fewer years, this richness will decrease in consequence of the 
extension of cultivation—as is illustrated, indeed, in what has 
