ii PBEPAGE. 



To this end, an analytical key, pointing out the orders 

 of the plants apt to claim the student's attention, is pre- 

 fixed to the American standard manuals of Chapman, 

 Gray, and Wood. These contrivances may be success- 

 fully employed, though with a loss of much time, by 

 more advanced students ; but, notwithstanding their indis- 

 putable value, they will usually prove far from answering 

 the wants of beginners. For them I have elaborated the 

 analytical key, which makes the second part of this book. 

 By a limited number of antitheses, it points out the very 

 genus to which any phaenogamous species whose name we 

 want to know, belongs. 



This contrivance is based on what is called the dicho- 

 tomal method, and thus far agrees with the keys indicated 

 above ; but by pointing out directly the genera, instead of 

 the orders, it is, of course, fitted for a comparatively rapid 

 identification. 



The dichotomal method was introduced by De la 

 Marck, a contemporary and friend of De Candolle. He 

 suggested and proved that he who wants to elaborate a 

 most useful botanical key, must not take hold of some one 

 part or organ of the vegetable exclusively, regarding its 

 peculiar state as a sufficient differential character of the 

 plant, when brought contrasted to another ; that he must 

 not care whether he always associates plants, which natu- 

 rally seem to be allied, or whether he contrasts them, pro- 

 vided this contrast helps to characterize them beyond all 

 doubt ; and, lastly, that opposite things become more evi- 

 dent by tlieir juxtaposition {contraria juxta se joosita 

 niugis ducescunt). This method has been adopted by 

 many for the pui-pose ftf making intelligent young people 

 fond of botany. 



Suppose we have a dozen flo\vering plants before us. 



