^36 LETTER L. 



always to contrast characters in pairs, and to refer 

 from one contrast to another, till at last there is no- 

 thinof left out of which a further contrast can be 

 drawn up ; at that point, where comparison ceases, you 

 ought to find the object of your search. This, which is 

 called the dichotomous analysis, is that, in fact, which 

 the human mind habitually, though unconsciously, 

 employs in all its operations ; and it possesses the great 

 merit of being unerring, provided the comparisons 

 are made with due caution. The best mode of in- 

 structing you how to use it, is to select a few examples ; 

 first, of plants conformable to the characters assigned 

 to their orders ; and, secondly, of others which offer 

 exceptions to their characters. 



The Pellitory (Parietaria officinalis), is a plant quite 

 conformable to the characters assigned to its order. 

 Take it as a test. You look to the first pair of cha- 

 racters, or contrast No. 1. in the table, and you have 

 no difficulty in deciding that it belongs to " Plants 

 having distinct and visible flowers ;" the No. 2. at 

 the end of that line carries you to contrast No. 2. where 

 it agrees with ** Leaves not veined," &c. Then, you 

 proceed to No. 3. where you find that the Pellitory 

 agrees with " Flowers incomplete, that is, having no 

 corolla." You are now referred to No. 97* where you 

 see that your plant corresponds with the character 

 " Calyx present in some kind of state ;" this takes 

 you to No. 105. where you have no difficulty in 

 selecting. " Ovary superior," referring to No. 119. as 

 that which suits your plant. At 119, "Leaves with 

 stipules" corresponds with the Pellitory, and thus you 



