vm PBEFACE. 



suppose that about lialf tlie species belong to eaeli of the groups so 

 separated, but one species is found in which the leaves are slightly 

 divided, or some entire and some divided. Here, in order safely to 

 guide the student, you must either first separate this ambiguous 

 species by some character which the others have not, or repeat 

 it under each of the subdivisions formed, thus lengthening by one 

 step the process by which the several species are isolated. 



Freed from the trammels of the artificial index, the plants can be 

 arranged in the body of the work as they should be in the her- 

 barium, according to the method the best calculated to facilitate 

 their study. The only question remaining is, which of all the 

 proposed methods should be adopted. But a few years since it was 

 in this country still a matter of controversy, or even bitter dispute, 

 whether the so-called Linnaean or Jussisean systems should be pre- 

 ferred ; but happily the point is now so far settled that the Linnsean 

 Classes and Orders are only retained when they correspond with 

 Jussisean families, or generally as an artificial key to genera. For 

 the classification of plants for study, the Natural Method (as it is 

 appropriately, although perhaps somewhat arrogantly, termed) is 

 now almost universally adopted. Indicated by Linnseus, attempted 

 by Adanson, first carried out by Jussieu, subsequently improved 

 by Brown, De Candolle, and other great botanists of our own days, 

 and nibbled at by almost every petty botanical aspirant, it cannot well 

 bear the name of any one of its promoters, even of Jussieu himself, 

 without arresting it at that stage of progress which it had attained 

 in his day. Its greatest inconvenience, and at the same time one of 

 its greatest charms to the speculative mind, is a want of absolutism 

 in its details, which shall in every instance carry conviction into 

 every mind. Natural affinities depend on a great variety of points, 

 the relative importance of which will be diSerently appreciated by 

 men of different capacities or of a different turn of mind ; and the 

 very principle of the system is, that it is not to be transmitted by 

 the dicta of any one master, whatever his recognized genius, but 

 that every one should be admitted to contribute to its improvement 

 by new discoveries, or by a more accurate estimate of affinities. 

 This opens the door to arbitrary, fantastical, and paradoxical inno- 

 vations which have extensively prevailed over the whole botanical 

 world, and have been carried to an extraordinary pitch by would-be 

 philosophers of the German school. Scarcely two general systematic 

 works agree entirely in the arrangement and limits of the families 



