PBEFACE. Til 



System, have been very various. It has generally been endeavoured 

 to combine this special purpose with the main object of a classifi- 

 cation of plants, the facilitating the study of their nature, proper- 

 ties, and practical application ; tending thus to confoimd the find- 

 ing out the name of a plant with the study of botany. But, after 

 the example of Lamarck and De Candolle, it appears to be ne- 

 cessary to keep these two operations distinct from first to last, 

 otherwise the effect will continually be either to interfere with 

 the certainty of the one, or to lay unnecessary restraints on the 

 development of the other. Throughout the present Plora, there- 

 fore, the descriptions, whether of Orders, Genera, or Species, are 

 aiways preceded by such an artificial arrangement, key or index, 

 as has appeared to be the best adapted to the sole purpose of 

 referring the student to the individual description of the plant he 

 is examining. 



The particular method adopted is that originally proposed by 

 Lamarck, and applied in the above-mentioned work to the whole of 

 the French Flora. It has since then been less generally made use 

 of in local Floras than might have been expected ; but this is owing 

 less to any want of appreciating its practical usefulness than to the 

 great labour and difiiculty attending upon framing it satisfactorily. 

 As evidence, however, of the recognition of its utility, it wLU be ob- 

 served that the most eminent botanists have generally recourse to 

 it for the elucidation of genera or species whose distinctive charac- 

 ters offer any peculiar difficulties. 



The general principle of this system consists in the searching for 

 some striking character which will at once separate all the plants 

 belonging to the Flora into two groups, then, taking each group in 

 succession, dividing it again into two smaller ones in the same way, 

 and so on tUl the species become isolated. In this process cer- 

 tainty and rapidity are the two great objects ; and the most impor- 

 tant rules to follow are, first, the selection, at each operation, of cha- 

 racters so absolute as to afford the least room for hesitation as to which 

 of the two divisions the plant in question belongs to ; and, secondly, 

 the formation of subdivisions as nearly equal in point of number of 

 species as possible. But of the two objects, certainty has been 

 always considered as the most important, and brevity must often be 

 sacrificed to it. Take, for example, a genus of a dozen species, 

 differing in a most striking way from each other in the leaves, 

 which in some are very much divided, in others quite entire, and 



