Observations upon some Noteworthy Leaf Variations. 305 



some extent. Thus in Foster's fern, where there is a relatively 

 low vegetative power with the free formation of spores, there is 

 no special tendency to reversion and the form is apparently 

 well fixed. Unfortunately we have no evidence as to the per- 

 petuation of the sport through the medium of spores, since no 

 attempt has yet been made to propagate the variety in that 

 way, and it is therefore impossible to say if the character is so 

 far fixed as to define a new species. In Pierson's fern, where 

 the vegetative powers are relatively in excess, there is a great 

 want of stability with a constant tendency to reversion. This 

 is expressed in the production of normal fronds, as also in the 

 development of fronds showing all degrees of transitional alter- 

 ation, and in the very limited extent to which spores are 

 produced on the modified fronds. Finally, it is altogether 

 probable that in these examples we have instances illustrative 

 of the theory of Mutation as formulated by De Vries, giving 

 us a fairly clear conception of the general conditions under 

 which such mutation may arise ; but the evidence falls short 

 of a complete demonstration with respect to the transmission 

 of characters through the reproductive process, and we are 

 therefore unable as yet, to define either of these ferns as a 

 species, although they may eventually prove to be such when 

 proper experiments are made in the germination of the spores. 



