viii PREFACE. 



The twelve plants we have analyzed and identified above, 

 are either exogenous or endogenous. Thus it appears that 

 the student may identify plants of both classes without 

 understanding what the terms Exogens and Endogens sig- 

 nify. 1^0 one, however, is expected to consider the dis- 

 tinction between them of small importance. 



In counting the parts of the floral circles, it is absolutely 

 necessary to ascertain their habitual number. Thus, in 

 Acer (Maple) the calyx-lobes (and the petals, if present) 

 are usually 5, though sometimes anywhere between 4 and 

 12. We must always examine several flowers before we 

 can be safely guided by the key. Looking in it for Acer, 

 we shall miss it if we have not previously known that 

 the calyx-lobes are usually five in number. 



In the first part of the book, treating of Structural 

 Botany, the plan has been to exclude all detail which is 

 not absolutely necessary to the beginner. 



When in the second part a figure in parenthesis is 

 found at the right of a paragraphic figure, it indicates the 

 paragraph giving the next previous step in the identifica- 

 tion ; see, for instance, 1 89 (175). When the name of a 

 plant found in a j)aragraph has in parenthesis a figure at 

 the left, this figure denotes a previous paragraph, in which 

 it was met with already; and, again, a figure standing at 

 the right gives reference to one of the subsequent para- 

 graphs, in which, for some reason, the plant's name will 

 again be found. 



Terms and symbols, the meaning of which some readers 

 are likely not to know, are explained in the Glossary. 



In the sections of the key which treat of sedges 

 and grasses, the student will find references to plates, 

 crowded with engravings, appended to Gray's and Wood's 

 manuals. Thus, in § 565, the notations, Gr. YIII., 62, 



