INTRODUCTION. 
IX 
second provides us with artificial ox Book species, arising 
from that morbid appetite for novelties which, when 
truly new ones can no longer be detected in any 
country, induces many to separate those previously re- 
ceived and well known whenever tolerably constant 
characters can be devised for the subdivisions. As to 
cultivation, this is an excellent auxiliary, if properly 
applied ; by it we may sometimes in a single year or 
two satisfactorily show that two supposed species are 
one and the same ; but cultivation for many years cannot 
prove them distinct. The more we cultivate a plant, or 
the more it is limited in its wild state to a particular 
climate or place of growth, it frequently happens that 
the more permanency is given to the peculiarities of 
what was originally derived from the same root, or even 
seed-vessel, of another apparently widely different form. 
Hence a rare mountainous plant may frequently be a 
mere alpine permanent state of some common lowland 
species, or a Swedish species the more northern race or 
state of a southern one ; and it is from this cause that 
we see in our gardens so many in cultivation (as in the 
genus Achillea), which cannot now be referred satis- 
factorily to any of the wild ones, although descended 
from them. Knowing, then, this tendency of all natural 
species to exhibit each many permanent forms, there 
appears to be less injury done by combining too much, 
than by subdivision, unless Avhere there is an anatomical, 
physiological, chemical, or economical distinction. On 
the supposition that many species, composed probably of 
numerous individuals, were simultaneously called into 
existence on the third day of the creation, each distinct 
from the other, and destined to remain so, it is reason- 
able to suppose that all their descendants must have 
still a greater resemblance in general appearance, as 
well as in structure and properties, to each other, than 
the aggregate exhibits to any other aggregate of indivi- 
