250 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



tain that they can bear many degrees of frost without injury. 

 Some species, at least, are to be found in a growing state when- 

 ever the soil is actually free from frost, and many seem to 

 flourish most vigorously at a low temperature. Fungi, how- 

 ever, decrease in frequency as we approach to colder regions, 

 and though common in the tropics, where the air is sufficiently 

 moist, a circumstance on which they depend far more than on 

 the quantity of rain, their maximum is obtained in temperate 

 regions. Sweden, with its various soil, large mixed forests, and 

 warm sumnaer temperature, seems to produce more species 

 than any part of the known world ; and next in order, perhaps, 

 are the United States, as far as South Carolina, where they 

 absolutely swarm. A moist autumn after a genial summer, is 

 most conducive to their growth, but cold wet summers seldom 

 are productive. The portion of the Himalayas which lies im- 

 mediately north of Calcutta, is perhaps almost as prolific in 

 point of individuals as the countries named above, but the 

 number of species on examination proves far less than might 

 at first have been suspected. It is probably not above a fifth 

 of what occurs in Sweden. 



246. As regards geographical distribution, we do not observe 

 the same marked distinctions which occur amongst Algae. A 

 large portion of the species are common to similar latitudes 

 and climatic conditions, and there are few marked distinctions 

 of genera. Agaricus and Polyporus occur in all parts of the 

 world, and the same may be said of the different groups into 

 which they have been broken up with few exceptions. A few 

 genera, such as Secotiuin, Montagnites, Gyrophragmium,, 

 occur only in the warmer regions, having their northern limit 

 in the north of Africa, or the coast of the Mediterranean ; but 

 it can scarcely be said of any that it is absolutely confined to 

 any one of the main divisions of the world. Mitremyces, 

 which was once supposed to belong only to the United States, 

 has now appeared in Australia, Java, and the Himalayas; 

 Podaxon occurs in Carolina, Africa, the Cape de Verds, and 

 India ; Trichoscytaie paradoxa, first found in Java, has now 

 been found in Ceylon, New Zealand, the Sikkim Himalayas, 

 and Carolina; Aseroe belongs to New Zealand and Ceylon, as 



