CLASSIFICATION OF PLANTS. 149 



SYSTEMATIC BOTANY, OR THE CLASSIFICATION OF PLANTS. 



HAVING, in the preceding pages, described all the parts and organs which enter into 

 the composition of individual plants, we are prepared to take a wider view, and deter- 

 mine the mode by which masses of plants may be grouped together. This is termed 

 Classification. 



This department of botanical science is vastly more extensive than that which 

 treats of the structure of plants ; so that it is not possible, in a treatise like the present, 

 to consider the subject in any lengthened detail. We therefore purpose, after offering 

 some introductory remarks, to consider the Linnsean and the natural systems of classifi- 

 cation, and to name the most common or important plants which have been arranged 

 under each head. 



The necessity for a- classification of plants must have been felt at all periods, even 

 in the Grecian and Roman eras, when the total number of known species did not exceed 

 1,000 ; but since, at the present day, upwards of 100,000 species have been named and 

 described, the necessity has become absolute. The only question on which botanists 

 have been at issue refers to the principles on which that classification should be 

 founded. In the first place it is imperative that each plant should have a distinctive 

 appellation, or any description of it would be in vain. Then, again, since 100,000 

 distinct names, assuming for a moment that so many could have been invented, could 

 not have been borne in mind by any person, the next step in the process would be to 

 ascertain if any of this number could be grouped together under one name, but yet 

 having a special term to indicate its individuality. 



The success of this inquiry would, of course, depend upon the existence or other- 

 wise of any anatomical characters which would at a glance be found common to both. 

 Such resemblances were soon discovered ; and the term Rose, for instance, was found to 

 suffice for very many species, with the addition of white, red, &c., to mark their indi- 

 viduality. Thus the term Rose denoted a genus, and white the species ; and in this mode 

 the number was reduced within reasonable proportions. 



But this first was not the last step, for it was ascertained that on some one point, or 

 on many points, the genera resembled each other; and thus the term Icosandria, for 

 example, was devised, which should comprehend the Rose, and the Apple, and the 

 Strawberry, and others having these characters in common. This then gave rise to a 

 system of classes and orders, the term Icosandria representing one of the classes. The 

 orders were subdivisions of the classes, and referred to certain minutiae in which all the 

 members of the orders did not agree. Thus the nameless plant became at length the 

 Rosa Alba, of the class Icosandria, and order Polygamia. 



This is precisely the plan adopted in the classification of animals. Thus the Cow is 

 the Bos taurus of the class Mammalia and order Ruminantia. It is not, however, a 

 perfect plan; and as tne number of objects to be included have continually increased, 

 it has been found necessary to invent a more general term as that of family which 

 shall comprehend a number of classes. Reversing, then, the order of classification which 

 has already been given, we may first refer a plant to a f amity ; next to a class and 

 order; and then find its generic and specific names. 



The term variety has also been introduced to indicate the existence of ?ome trifling 

 change in a species ; and although the boundary between a species and a variety is not 

 capable of nice def nition, yet it may be stated that a variety does not so reproduce 



