PREFACE. 19 



the fruit, and following out a series of easy steps in the analysis. 

 This key is founded upon the most obvious distinctions which will 

 well answer the purpose, and is so contrived as to provide for all the 

 exceptional instances and variant cases I could think of. I shall be 

 disappointed if the attentive student is not able by it to refer to its 

 proper order any to him unknown plant of the Northern States of 

 which he has flowering specimens in hand. Referring to the Order 

 which the Key leads him to, the student will find its most distinctive 

 points, — which he has chiefly to consider, — brought together and 

 printed in italics in the first sentence of the ordinal description, and 

 thus can verify his results. 



The Synopsis which follows will then lead him to the genus, to be 

 verified in turn by the full generic description in its place ; and the 

 progress thence to the species, when there are several to choose 

 from, is facilitated by the arrangement under divisions and sub- 

 divisions, as already explained. 



It will be seen that the Key directs the inquirer to ascertain, 

 first, the Class of the plant under consideration, — which, even with- 

 out the seeds, is revealed at once by the plan of the stem, as seen in 

 a cross-section, and usually by the veining of the leaves, and is 

 commonly confirmed by the numerical plan of the flower ; — then, 

 if of the first class, the sub-class is at once determined by the pistil, 

 whether of the ordinary kind, or an open scale bearing naked ovules. 

 If the former, then the choice between the three divisions is de- 

 termined by the presence or absence of the petals, and whether 

 separate or united. Each division is subdivided by equally obvious 

 characters, as, p. 21, first the number of stamens, then, whether the 

 calyx is free from or connected with the surface of the ovary. 

 And, finally, a series of successively subordinated propositions, — 

 each set more indented upon the page than the preceding, leads 

 to the name of the order sought for, followed by the number of 

 the page upon which that order is described in the body of the 

 work. 



