Regions outside the Polar Circles which enjoy, on the whole, cool moist climates, are specially favourable to lichen growth, and the recorded numbers are very large. The European countries are naturally those in which the lichen flora is best known. Whereas polar and high Alpine species are stunted in growth and often sterile, those in milder localities grow and fruit well, and the more highly developed species are more frequent. _Parmeliae_, _Nephromae_, _Usneae_ and _Ramalinae_ become prominent, especially in the more northern districts. Many Arctic plants are represented on the higher altitudes. A comparison has been made between the lichens of Greenland and those of Germany: of 286 species recorded for the former country, 213 have been found in Germany, the largest number of species common to both countries being crustaceous. Lindsay[1074] considered that Greenland lichens were even more akin to those of Scandinavia. There is an astonishing similarity of lichens in the Temperate Zone all round the world. Commenting on a list of Chicago lichens by Calkins[1075], Hue[1076] pointed out that with the exception of a few endemic species they resemble those of Normandy. The same result appears in Bruce Fink’s[1077] careful compilation of Minnesota lichens, which may be accepted as typical of the Eastern and Middle States of North Temperate America. The genera from that region number nearly 70, and only two of these, _Omphalaria_ and _Heppia_, are absent from our British Flora. The species naturally present much greater diversity. Very few Graphideae are reported. In other States of North America there occurs the singular aquatic lichen, _Hydrothyria venosa_, nearly akin to _Peltigera_. If we contrast American lichens with these collected in South Siberia near Lake Baikal[1078], we recognize there also the influence of temperate conditions. Several species of _Usnea_ are listed, _U. barbata_, _U. florida_, _U. hirta_ and _U. longissima_, all of them also American forms, _U. longissima_ having been found in Wisconsin. _Xanthoria parietina_, an almost cosmopolitan lichen, is absent from this district, and is not recorded from Minnesota. The opinion[1079] in America is that it is a maritime species: Tuckerman gives its habitat as “the neighbourhood of a great water,” and reports it from near Lake Superior. In our country it grows at a good distance from the sea, in Yorkshire dales, etc., but all our counties would rank as maritime in the American sense. _Lecanora tartarea_ which is rare in Minnesota is also absent from the Lake Baikal region. It occurs frequently both in Arctic and in Antarctic regions, and is probably also somewhat maritime in habitat. Many of the _Parmeliae_, _Nephromiae_ and _Peltigerae_, common to all northern temperate climes, are Siberian as are also _Cladoniae_ and many crustaceous species. There is only one _Sticta_, _St. Wrightii_, a Japanese lichen, recorded by Wainio from this Siberian locality.