14 THE FERNS AND 



and, in ferns particularly, many classifiers — chiefly those of the old 

 school — adhere to purely artificial distinctions. These are very 

 useful in drawing up keys to enable a particular fern to he easily 

 9-ecognized, but should not form the basis of our system. 



Suppose we are collecting ferns in the damp forest of one of our 

 West Coast sounds, we find the ground covered with a luxuriant 

 ^growth of kidney-fern {Trichomanes reni/firme), and, on examination 

 of a great number of specimens, we agree that they are all so similar 

 that they must be of one and the same kind. Some have large 

 fronds, others small ; some are on tall stipes, others on short ones ; 

 ;some are nearly black, and have their margins fringed with sori, 

 while others are of a delicate green colour, and are quite smooth on 

 the edge ; yet, despite these and other differences, we have no doubt 

 that the spores of these ferns will only produce other kidney-ferns. 

 Purther, were we to come across exactly similar ferns — varying to 

 the same extent — near Auckland, we should be justified in asserting 

 "that they were of the same kind as those from the "West Coast of the 

 South Island. Now, the whole assemblage of these kidney-ferns, 

 "wherever we may find them, constitutes what we term a species, and 

 we give it two names in accordance with the rule already explained. 

 We should, further, be justified in assuming that if we could trace 

 back these ferns for an indefinite number of generations, we should at 

 last find that they were all descended from one parent plant which 

 •grew at a very remote period either in New Zealand or in some 

 portion of the now submerged land which at one time probably 

 formed a connection between New Zealand and Australia, or some of 

 -the outljring islands to the north of this colony. 



From these considerations, we may define a species as an assem- 

 blage of individuals agreeing so closely that they may be considered 

 to have all descended directly from a common ancestral form. But 

 it is conceivable, that, owing to causes which we are not able to 

 fathom fully, a kidney-fern might be produced differing slightly but 

 persistently from its immediate parent plant, and this difference 

 might be perpetuated and perhaps intensified in succeeding genera- 

 tions. In course of time the differences or variations thus induced 

 might be so perceptible and constant as to justify us in calling the 

 plant a variety, and after a still further lapse of time — if the 

 ■conditions which caused the first variation continued to act, or if 



