PERN ALLIES OP NEW ZEALAND. 15 



other conditions "were superadded — the change at last might be so 

 marked as to entitle the modified plants to rank as a distinct species. 

 Now, though this is no doubt the correct idea of the term " species," 

 it is not by any means always an easy thing to make application of 

 the principle. It is simple enough in the case of such a distinct and 

 well-characterized plant as the kidney-fern, and we can draw up a 

 specific description of these ferns, as they are found in the bush of 

 the "West Coast sounds, which will apply equally well to those 

 gathered in the Auckland district. 



But now let us go into the bush again, and gather a plant of 

 Aspleniwm hulbiferum. Were we to describe its form, it would be 

 found that the description would not apply very closely to another 

 plant, perhaps from the same part of the bush, which yet was near 

 it in most of its features. The first-gathered plant might look at 

 first sight a very difierent plant from the second, but if we were to 

 collect a very large series of somewhat similar plants, and were to 

 find (as we probably should in the example selected) that though the 

 two most diverse of those chosen had very considerable difierences 

 of external form, yet that a complete gradation could be traced 

 through the intermediates, we would stUl be justified in assuming 

 that all were but forms of one very variable species. It is exactly 

 on this point that so many botanists difier in opinion, and it becomes 

 to a great extent a matter of individual judgment to decide what 

 rank is to be assigned to the variation of plants. If I have erred in 

 this respect, it wUl be found to be in the direction of increasing the 

 limits of the respective species so as to include doubtful and varietal 

 forms, rather than in multiplying unnecessarily the number of 

 species already defined. 



"When several species resemble each other so distinctly that 

 their general appearance indicates a relationship, they are grouped 

 together in a genua" (Prantl). But this is seen to be as arbitrary a 

 definition as that of a species, and consequently it happens that 

 botanists disagree very much as to the limits of various genera. 

 Sir W. Hooker and Mr. Baker in the " Synopsis Filicum" give a 

 wide range to the genera, while Mr. J. Smith — author of the 

 " Historia Filicum," and a great authority on Ferns — subdivides 

 the genera to a very great extent. In this respect, again, it will be 

 found that very artificial limitations are frequently put upon the 



