INTRODUCTION xxi 



yields the most valuable nuts and the most valuable timber pro- 

 duced by any species of the genus. 



Leitneriace^, a family of a single species of Leitneria, is 

 North American. 



Myricace^. — Comptonia is confined to eastern North America, 

 but Myrica, with a small number of species, occurs in the two regions, 

 with one species, Myrica Gale L., common to them both. In 

 North America there is no species which at all resembles Myrica 

 rubra Lour, with its edible fruits. 



BETULACEiE. — In eastern North America Carpinus appears 

 as a small widely distributed tree, but in continental Asia seven 

 or eight species of the two sections, into which this genus has been 

 separated (Eucarpinus and Distigocarpus), are common. Ostrya is 

 represented in each region by a single species, the eastern American 

 Ostrya being much more generally distributed and more abundant 

 than the Chinese species, which appears to be confined to the moun- 

 tain forests of Hupeh and Szechuan. The monotypic Ostryopsis is 

 confined to Mongolia and China. Of Alnus there are five species 

 in eastern North America, four of these being shrubs and one a 

 small tree ; but in eastern continental Asia there are at least six 

 or seven species of this genus, and one of these, Alnus cremastogyne 

 Burk., is a large tree sometimes loo ft. high, shading the banks of 

 many streams in Western China with groves of splendid specimens. 

 Betula forms a considerable part of the forests of eastern Siberia, 

 and is common on many of the mountain ranges of China, especially 

 those in western Szechuan, where it reaches altitudes of 10,000 ft. 

 In eastern Asia, however, there is no species which, like Betula 

 nigra L. of eastern North America, can thrive on the banks of 

 streams in the nearly tropical heat of regions like Florida, Louisiana, 

 and Texas, where this tree grows to its largest size. The number 

 of species in the two regions is not very different, and as timber 

 trees the Birches of one region are probably as valuable as those 

 of the other. It is doubtful, however, if any eastern Asiatic Birch 

 tree ever grows to the size sometimes attained by Betula lutea 

 Michx., of the forests of north-eastern North America. 



Fagace^. — In eastern North America there is a single species 

 of Fagus ranging from eastern Canada to Florida and Texas, and 

 one of the largest and most common trees of all this region. In 

 eastern continental Asia Fagus does not extend into the north, 

 and appears to be confined to the mountain forests of the central 

 western provinces, in which three species are now known ; these 

 are smaller and less important trees than the American Beech. 



