The genus _Agaricus_ occupies the first place, and surpasses, in the number of species, all the other generic groups known. It appears, from our present knowledge, that the _Agarici_ have their geographic centre in the temperate zone, and especially in the colder portion of that zone. It is a curious circumstance that all the extra-European species of this genus _Agaricus_ may be referred to various European subgenera. In tropical countries it appears that the _Agarici_ occupy only a secondary position in relation to other genera of fungi, such as _Polyporus_, _Lenzites_, etc. North America, on the other hand, is richer in species of _Agaricus_ than Europe; for whilst the majority of typical forms are common to both continents, America further possesses many species peculiar to itself. In the temperate zone, so close is the analogy prevailing between the various countries in respect to the _Agaricini_, that from Sweden to Italy, and as well in England as North America, the same species are to be found. Of 500 _Agaricini_ met with in St. Petersburg, there are only two or three which have not been discovered in Sweden; and again, of fifty species known in Greenland, there is not one that is not common in Sweden. The same remarks hold good in reference to the _Agaricini_ of Siberia, Kamtschatka, the Ukraine, etc. The countries bordering upon the Mediterranean possess, however, several peculiar types; and Eastern and Western Europe present certain dissimilarities in their Agaric inhabitants. Several species, for example, of _Armillaria_ and _Tricholoma_, which have been found in Russia, have been met with in Sweden only in Upland, that is, in the most eastern province; all the species which belong to the so-called _abiegno-rupestres_ and _pineto-montanæ_ regions of Sweden are wanting in England; and it is only in Scotland that the species of northern mountainous and pine-bearing regions are met with--a circumstance explicable from the similarity in physical features between Sweden and the northern portions of Great Britain. The species of _Coprinus_ appear to find suitable habitats in every quarter of the globe. The _Cortinariæ_ predominate in the north; they abound in Northern latitudes, especially on wooded hills; but the plains offer also some peculiar species which flourish during the rainy days of August and September. In less cold countries they are more scarce or entirely absent. The species of the genus _Hygrophorus_ would at first seem to have a similar geographical distribution to those of the last group; but this is really not the case, for the same _Hygrophori_ are to be found in nearly every country of Europe, and even the hottest countries (and those under the equator) are not destitute of representatives of this wide-spread genus. The _Lactarii_, which are so abundant in the forests of Europe and North America, appear to grow more and more scarce towards both the south and north. The same may be stated in regard to _Russula_.