INTRODUCTION xxvii 



appear at all in the flora of eastern North America. Amelanchier, 

 which is very widely distributed through eastern North America, 

 with a number of species, of which two are small trees, has but one 

 shrubby Chinese species. In Crataegus the difference between the 

 floras of the two regions is even more remarkable. In all of eastern 

 continental Asia only twelve species have been found ; in eastern 

 North America are more forms of Crataegus than of any other genus 

 of plants, and probably a thousand species. In Rubus the difference 

 in the number of species in the two regions is probably not great ; 

 several of the American species, however, produce more valuable 

 fruit than any of the Asiatic species. Potentilla fruticosa L. ap- 

 pears in the two regions with two other related species in eastern 

 Asia and one in eastern North America. The composition of 

 Prunus is unlike in the two regions. Of the true Plums (Prunophora) 

 there is only a single species in eastern continental Asia {Prunus 

 salicina Lindl.), confined to southern and Western China, no plum 

 tree being found anywhere in the north ; in eastern North America 

 plum trees have a wide distribution from the valley of the St. 

 Lawrence River to Florida and Texas, a larger number of species 

 occurring in the Arkansas-Texas region than in any other part 

 of the world. Padus, on the contrary, is represented in eastern 

 North America by only four species, while in eastern continental 

 Asia about seventeen species are recognized. None of these, 

 however, equal the American P. serotina Ehrh. in size or in 

 value as a timber tree. Laurocerasus appears in eastern North 

 America in two species and in eastern China in three species. 

 Cerasus has but three eastern North American representatives and a 

 much larger number in eastern continental Asia ; and Amygdalus, 

 Persica, and Armeniaca occur in eastern Asia and not in eastern 

 North America. 



CoNNARACE^. — Rourea in southern China is the only representa- 

 tive of this family in the two regions. 



Leguminos^. — Of the genera of woody plants of this family 

 the following occur in eastern North America but not in eastern 

 continental Asia : Lysiloma, Prosopis, Parkinsonia, Cercidium, 

 Amorpha, Eysenhardtia, Robinia, Coursetia, and Ichthyomethia ; 

 and the following in eastern continental Asia and not in eastern 

 North America : Fordia, Ormosia, Millettia, Maackia, Caragana, 

 Clitoria, Pueraria, Rhynchosia, Dalbergia, Euchresta, Mezoneurum, 

 Caesalpinia, Pterolobium, Entada, and Albizzia. The following 

 genera have representatives in the two regions : Pithecolobium, 

 Acacia, Leucaena (probably naturalized in southern China), Mimosa, 



