X 



INTRODUCTION. 



into as many as constant characters can be devised for 

 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 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, 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 com- 

 mon 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 called spe- 

 -- ^is in the genus Achillea), which cannot now be re- 

 ferred satisfactorily to any of the wild ones, although pri- 

 marily derived from them. Knowing, then, this tendeno.v 



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Nat 



tained from one primitive species, there appears to be less 

 violence done to her laws by combining too much, than 

 by subdivision, unless where there is an anatomical or 

 physiological distinction. But cultivation may be used 

 for the reduction of species by proving the fertility of 

 hybrids. Linn^us laid it down as a maxim that no 

 hybrid, if the parents were truly distinct species, could 

 produce perfect seed ; or, where the seed so obtained 

 might produce plants, these would die out in the second 

 or third generation. The discovery, then, alluded to un- 

 der Geum rivale, at p. 120.,_that fertile hybrids do exist 

 between it and G. urbanum, and leading to the presump- 

 tion that the parents are mere varieties of one species, 

 although supposed hitherto to be so organically distinct as 

 to be placed by many in two distinct sections,— shows that 

 widely different structures may be exhibited by the same 

 individual. Extensive experiments on this subject by 

 cultivators will tend much to correct our ideas of species. 



