P R K I"' A c i : . 



The design of this work is to illustrate the Botany of the United 

 States by figures, with full analyses, of one or more species of each 

 genus, accompanied by descriptive generic characters and critical 

 observations. The figures in all cases are drawn directly from 

 nature, by Mr. Sprague, and from the living plant whenever that is 

 practicable. In almost every instance, the whole plant, or a branch 

 or smaller portion, in flower and often also in fruit, is delineated of 

 the natural size ; and the microscopical analyses, as numerous as 

 the compass of an octavo page will allow, are so chosen as to display 

 the principal floral characters of the genus, from the aestivation of 

 the flower-bud to the fruit, the seed, and the embryo. When need- 

 ful, on account of size or of subgeneric diversity, two plates are de- 

 voted to the illustration of a single genus. On the other hand, char- 

 acters which are uniform or nearly so throughout a whole order are 

 not repeated upon every plate. 



The illustrations are not drawn from various orders and classes at 

 random or convenience ; but the natural families are taken up in 

 regular sequence, according to the arrangement now most prevalent 

 among botanists (following very nearly, though not implicitly, thp 

 order adopted in the Flora of North America by Dr. Torrey and 

 myself), and all our genera of each family are published together, 

 in their proper places ; thus rendering the volumes systematically 

 complete, as they appear. This plan, which has never been carried 

 out, so far as I am aware, in any extensive publication of the kind, 

 while it should increase the immediate usefulness and value of the 

 work, at the same time renders still more onerous what is at best a 



