II. PERMANENCE OP SPECIES. 57 



that several generally aclinitted species can be converted 

 into one species, and that in only thirteen descents one 

 genus can be converted into another genus, not extremely 

 similar. When such a writer and botanist announces 

 such a belief, we are thrown back upon the questions, 

 Whether permanent species exist in nature ? — And how 

 we know them to be such ? — Also, which of the now re- 

 ceived species (if anj') are permanent, — and which of them 

 are thus convertible ? In short, are there any species ? 

 If jEgilops can change into Tritimm, why not Triti- 

 cum into Brachypodium ? — Brachypodmm into Bromus ? 

 — Bromus into Festuca? — Festuca into Poa? — &c. &c. 

 Genera do thus change — in books. Whatever may be 

 the facts in nature, as to the lines of demarcation between 

 species, those between many genera are uncertain and 

 fluctuating in books. There are species whose generic 

 characters are so ill-defined or uncertain, that they are 

 assigned sometimes to one genus, sometimes to another 

 genus, of the couj)lets named above. And the like mu- 

 tual convertibility in botanical arrangements, by changing 

 the generic place of a species, may be found between nu- 

 merous other genera in books. But those books profess 

 to show the truths of nature, and to record human know- 

 ledge of nature. Human knowledge, it is thus seen, 

 cannot trace positive lines of demarcation between genera 

 any more than between orders. In other words, such 

 positive lines of demarcation, though feigned in books, 

 are not discovered in nature. Orders pass into each 

 other by the existence of genera that are assignable to 

 either, at the option of botanists. Genera pass into each 

 other by the existence of species that are assignable to 

 either genus. Species appear to pass into each other by 

 the practice of botanists, who unite and sever them in dif- 

 ferent degrees and numbers. 



V0I-. rv. ^ 



