Cultivation of foreign species of trees

The tree flora of Europe is, compared with the flora of other continents on the northern hemisphere, very poor in genera and species. Data given by Professor H. MA YE, ) concerning the number of genera and species of trees in the cool and temperate zones in Europe, North America and Asia are, in this respect, illuminating, even if they are not absolutely correct. In these zones there are in Europe only 7 genera and 18 species of coniferous trees, whereas the corresponding figures for the eastern part of North America are 13 and 30, for the western part of North America 22 and 50, and for eastern Asia 26 and 100. Of deciduous trees, there are in Europe 30 genera and 60 species, in the eastern part of North America 100 and 220, in the western part of North America 34 and 70, and in eastern Asia 150 genera and 400 species. Very marked is the scarcity of genera and species in the northern parts of Europe. E. g., Suomi has only 4 genera and the same number of species of coniferous trees and 12 genera and 18 species of deciduous trees, out of which number 2 species of coniferous trees and 3—4 of deciduous trees are of economic value. The tree flora of Scandinavia is almost as poor: only the deciduous trees are represented by a few additional species. Investigation of the history of vegetation gives evidence that the tree flora of Europe has not always been so poor in genera and species as at present. During the tertiary period, stately forests abounded which in richness of genera and species were quite comparable with the present forests of North America. Sequoia, Taxodium, Chamaecyparis, Thuya, Magnolia, Liquidambar, Liriodendron and other coniferous and broadleaf trees which are not in the present time natives of the European flora, but are so in North America, were distributed over large areas, till the catastrophe of the glacial period almost totally destroyed this rich tree flora north of the Pyrenees,