6 ON GENERA AND SPECIES. 



relative importance assigned to them. For example, while 

 some, as Presl, Fee, Moore, and myself, break up the old 

 Linnean genera, Poly podium, Aspidium, &c., into a greater 

 or lesser number of smaller genera, upon characters derived 

 from differences in their anatomical structure and modes of 

 growth ; others, as Hooker and Mettenius, prefer adhering 

 to the Linnean genera, without greatly altering their 

 characters, and adopting the modern generic names as 

 sectional ones for such divisions as they find themselves 

 compelled to make. 



On reviewing what I have now stated it may naturally 

 be asked, What is a species or genus ? or, by what law of 

 nature can this be determined ? As generally under- 

 stood by naturalists, a species is an organised structure 

 specially created and endowed with an essence or quality 

 peculiar to itself, possessing the power of increase and 

 transmitting its primitive essence and anatomical structure 

 and form without change, to its progeny for successive 

 generations. But the difficulty of defining species becomes 

 evident on taking a general view of the numerous forms 

 which connect one with another. It will then be found be- 

 yond human power to ascertain whether the several grada- 

 tions of allied forms are descendants of primitive specific 

 creations, or are, according to the Darwinian theory of the 

 " origin of species," only deviations from a few primordial 

 creations, endowed with a protean principle which becomes 

 manifest during the lapse of ages, and controlled by the 

 different climatic and local influences under which the 

 progeny of the original have become established, and 

 which now form the flora of the earth. If the latter is 

 admitted to be the case, and we are led to believe that 

 intermediate forms originate during the slow progress of 

 time, then all must be uncertainty, and the number of 



