162 CLASSIFICATION OF PLANTS. 



of species in the principal orders is given for tropical, temper- 

 ate, and arctic regions), there is considerable discrepancy found 

 by comparing our orders in the same way. Cyperaceae, which 

 in our Flora contains y* 7 of all the species, would place us above 

 lat. 50° north ; Gramineae, TT , would do the same ; Compositae, 

 J, Leguminosae, y^-, would give us a latitude between 45° and 

 52° ; Ericaceae, Ty , and Euphorbiaceae, Jy, would place us be- 

 low 45°, or about in our true position ; Labiatae, y- 5 -, Umbel- 

 li ferae, j^ give about the same. 



In comparing our Flora with that of New York (see Nat. Hist. 

 N. Y. Bot. vol. ii. p. 523), we find a general correspondence 

 with the principles of Jussieu. The relative number of Cype- 

 raceae, T 2 y with us, J- in New York, shows the general decrease 

 of this order from the north toward the south. Labiatae, Eri- 

 caceae, Umbelliferae, Leguminosae, and Euphorbiaceae, confirm 

 the principles laid down — that the species of some orders, which 

 are extensively distributed, increase in number from the equator 

 toward the poles ; that others increase from toward the poles 

 to the equator ; and that others decrease from the temperate 

 regions both ways. 



315* From the limits of a text-book, including so many spe- 

 cies, we have been compelled to make the descriptions short. We 

 have aimed to make them correct, and as far as possible character- 

 istic. The greater number of the species we have examined 

 in their places of growth, during the last twenty years, from 

 the mountains to Florida, along the coast and through the inte- 

 rior, and at different seasons of the year. In those genera with 

 numerous species, it is impossible, in a limited description, to 

 enable the student to determine unerringly every species. We 

 would recommend to students who intend to pursue practical 

 botany to any extent beyond class duties in connection with our 

 book, the invaluable work of Torrey and Gray, The Flora of 

 JVorth America. 



316. We have adhered as much as possible to the old gen- 

 era. The disposition in botanists to increase the number of 

 genera by subdividing old ones, we conceive to be a great evil. 

 There may be good grounds, theoretically, in most cases, for the 

 subdivision, but practically it is increasing the difficulties, which 

 are already numerous enough, to the pursuit of this subject. 

 Andromeda, for example, a very natural genus, is divided into 

 Zenobia, Li/oni, Oxydendrum, Leucothce, and Cassandra, and a 

 pupil, even by knowing one species, would hardly fail to recog- 

 nize any other species of the genus. Other genera are treated 

 with as little respect. 



317. Wo have given the Linnaean Analysis, and the Dichot* 



