2 MANUA.L OF BOTANY 



plants known to exist on the earth. It is absolutely necessary 

 ■ therefore, for the purpose of study, or in order to obtain any 

 satisfactory knowledge of such a vast number of plants, 

 that we should arrange them according to some definite and 

 fixed rules ; but before we proceed to describe tine systeilas that 

 have been devised at various times for their arrangement, it 

 wiU be necessary to define the principal terms which are in 

 common use in such systems. 



1. Species. — By tbe term species we understand a collection 

 of individuals which resemble each other more nearly than they 

 resemble any other plants, so that we may infer that they have 

 all been derived originally from one common stock. Thus, if we 

 walk into a field of Beans, Peas, or Clover, we observe thousands 

 of individuals, which, although differing to a certain extent in 

 size, and in some other unimportant characters, we at once 

 associate together imder a common name. In like manner we 

 commonly observe around us, in the gardens and fields, similar 

 collections of individuals. Such collections of plants, thus seen 

 to resemble one another in all their important parts, constitute 

 our first idea of a species ; and that idea is at once confirmed if, 

 on propagating them, we obtain other plants exactly resembling 

 the parents. Species are, however, under special conditions, 

 liable to variations, and we have then formed what are termed 

 varieties and races. 



a. Varieties or Suh-species. — It has just been observed that 

 if a species be propagated it will reproduce its parent, or, 

 in other words, produce a plant resembling its parent in all its 

 important parts. But this will only happen when the new in- 

 dividual has been exposed to the same influences of soil, heal, 

 light, moisture, and other conditions, as its parent ; and hence 

 we find that variations in such particulars wiU lead to certain 

 peculiarities in form, colour, size, and other minor characters, 

 in the young plants. In this manner we have produced what 

 are termed varieties. In some cases such variations are 

 merely transient, and the individuals presenting such peculiari- 

 ties win in time return to their original specific type, or 

 perish altogether ; while ia other instances they are permanent 

 and continue throughout the life of the individual, the whole 

 plant being, as it were, impregnated with the~ particular 

 variations thus impressed upon it, and hence such variations 

 may be perpetuated by the gardener in the operations of 

 Budding, Grafting, &c., as is the case with many of our fruit 

 trees and flowers. But even these varieties are not perma- 



