INTRODUCTION. 47 



The orders of the twenty-fourth class are natural, and therefore not to be 

 defined by an artificial character. They are : 



Filices ; or Ferns. 



Musci ; or Mosses. 



Algce ; or Lichens, Sea Weeds, &c. 



Fungi; or Mushrooms, &c. 



The method by which the name of a plant can be discovered is very 

 simple. The student first examines it to ascertain to what class it belongs ; 

 this being accomplished, he next ascertains to what order it appertains ; 

 when this is satisfactorily done, by a reference to a botanical work or 

 works, he will find that the order in question is probably subdivided into sec- 

 tions, and by comparing his plant with the characters of these subdivisions, 

 he will find that it corresponds to one of them ; by then examining it, in 

 reference to the characters of the genera composing this subdivision, he will 

 discover to what genus it belongs ; and by a comparison of it with the 

 description of the species of that genus he will finally identify it. This 

 system, however, beautiful and simple as it is, has gradually been abandoned 

 from its only being fitted for this identification of a species, and not at the 

 same time conveying any information as regards the structure, natural alli- 

 ances or properties of plants. 



Natural System. 



The great object proposed to be attained by a natural system of arranging 

 plants, is to group together such species as most closely resemble each other, 

 not in one point only, but in all important characters, and hence all points of 

 resemblance or dissimilarity are allowed due weight. By pursuing this plan, 

 it must be evident that the essential characters of the various groups, when 

 fully detailed, actually show in what particulars the plants composing it 

 agree among themselves, and differ from those of other groups. This plan 

 being pursued from the highest classes down to the species, will enable the 

 student not only to ascertain the name of an individual plant, but also will 

 give him a tolerably correct idea of the structure, habits, and even, in many 

 cases, sensible properties of the group to which it belongs. Although this is 

 called a natural system, no one that has been proposed is truly so, for whilst 

 they all express the natural affinities of plants in a greater or less degree, 

 they are all artificial to a certain extent, as every classification of the objects 

 of nature must be, which is devised by the finite mind of man. 



Numerous systems have been proposed, founded on the peculiar views of 

 the devisers of them. Some writers, as Jussieu, &c, commence their expo- 

 sition with the lowest order, and gradually ascend to the highest ; whilst 

 others, as Decandolle, &c, begin with the most perfect, and conclude with 

 the least organized. In the succeeding pages the system of Decandolle, with 

 some slight modifications, has been adopted as that most generally known 

 and followed. 



The vegetable kingdom may be divided into two great series, the Flower- 

 ing and the Flowerless plants, answering to the old divisions of Ph&no- 

 gamia and Cryptogamia. The flowerless series may naturally be separated 

 into two classes. The first, or Acrogens, including those having a stem, 

 or decided axis of growth, and usually furnished with leaves ; their stems in- 

 crease from the apex only, and scarcely at all in diameter. The second, or 

 Thallogens, have no such division of parts, being stemless, leafless, and 

 flowerless. 



