492 TRANSACTIONS OF THE 



the small magnolia or white bay, the red bay, the loblolly bay 

 and the water oak, it has a pyramid at base, resembling a sugar- 

 loaf; a trunk eighteen or twenty feet high, and seven or eight 

 inches in diameter at the surface, is only two or three inches 

 thick a foot from the ground." Climate can have nothing to do 

 with this. 



But it is with the domesticated plants, when supplied with an 

 increased quantity of salts by agricultural processes, that the 

 effect of soil is most clearly shown. Thus, growing on the one 

 side of the fence in the garden of the western settler are full 

 double varieties of flowers, while outside of his enclosure are the 

 wild single congeners; within is the rich carrot and parsnip^ 

 while without are their brethren which have escaped from the do- 

 minion of art, woody, spindle-shaped and poisonous. The poppy 

 of the east in any other soil is worthless for the production of 

 opium. Rhubarb is of value according to the district in which 

 it grew — raised in England, being nearly worthless as a medicine. 

 The market value of tobacco depends on the locality from which 

 it comes, not the latitude in which it was raised; and, finally, 

 there is no such thing on the face of the earth as a flora, either 

 natural or artificial, extending as far as the condition of no varia- 

 tion of climate extends. 



LIMITS OF CAPACITY OF VARIATION. 



We have seen that notwithstanding all these variations in the 

 form of animals and plants, species always remain the same. A 

 mule may be produced by breeding between the ass and the horse. 

 The older naturalists and some of the later ones, inferred from 

 this that a sufficiently extensive practice of crossing different spe- 

 cies would produce new races, and thus essentially change the 

 face of animated nature. But a little more experience has shown 

 us that different species maintain their forms and perpetuate them 

 for natural reasons. The negro of the ancient sculptures exhibits 

 the same characteristics as the negro of our day, and is as easily 

 recognized. Though the mule has existed from the most ancient 

 times, there is no race of mules ; for mules though in limited in- 

 stances, productive with each other, are always more productive 

 with the parent race, and in these cases, after a few generations, 



