68 ASPLENIUM PARVULUM. SMALLER EBONY SPLEENWORT. 



the midrib of each pinna (see Fig. 2) do not commence to fork 

 in our species until about half-way between the midrib and the 

 margin, while in A. cbcnaun the forking begins at a point much 

 nearer the midrib; the second is that the sori or fruit-dots, owing 

 to the manner of forking just described, are placed much nearer 

 the margin in A. parvulitm than in its fellow species, and that 

 they are rounder in the former- than in the latter when mature. 

 The specimen from which our drawing was made was young, 

 and our artist scrupulously followed copy ; but in some mature 

 specimens in herbariums we have seen the sori almost as round 

 as in some Polypodiuins. It is possible, however, that this differ- 

 ence may be due to variation. 



The investigation of the specific difference between these 

 two Aspleniunis will be particularly interesting to the stu- 

 dent, as the question of the limit of species in ferns is excit- 

 ing a good deal of attention just at present. Some time ago 

 there would have been no hesitation in regarding these ferns as 

 distinct species, but since ferns have become objects of careful 

 garden culture, they have been found to vary as widely from 

 parent types as any flowering plant. A very singular fact also, 

 in regard to ferns, is this, that varieties with remarkably divided, 

 cut, or crested fronds, or with fronds which would be called 

 fasciated, or would be looked upon as monstrosities if we were 

 dealing with flowering plants, are reproduced from spores with 

 almost as much regularity as the parent type from which the 

 variety originally sprung. Formerly a variety was regarded as 

 a mere temporary affair. The test of a true species was that 

 "like must produce like," and the validity of a species was con- 

 sidered as established if from seeds or spores plants could be 

 raised which were like their parents. This is now known to 

 be erroneous. Varieties reproduce themselves. 



Explanation of the plate. — i. A complete plant. — 2. Magnified pinna, with the sori 

 ratlicr widely apart than crowded. It is well known that this character varies in all 

 ferns with the fertility. 



