i6o 



Aspleninms : marinum, tvichomanes } vi-ride, mta-muraria, sept en- 

 trionale, adiantum-nigvum and lanceolatum are distinct species. 

 Also that the Lastreas : filix-mas, dilatata, Montana and rigida 

 are equally distinct. The question of species or variety 

 comes in only when Aspleniums Germanicum and acutum and 

 Lastreas spinulosa cristata, nliginosa, cemula, pseudo-mas and 

 pvopiiiqna come to be considered. It comes in again among 

 the Polystichums, because there is difference of opinion as 

 to whether P. aculeatmn and angulare constitute one species 

 or two. P. lonehitis is generally considered distinct, but 

 there are grounds for doubting whether even this can 

 always be separated from aculeatum. Mr. Rowlands does 

 me the honour of assuming that I have a clear idea as to 

 what I mean by a species as distinct from a variety. 

 Thus directly challenged, I will endeavour to formulate 

 what I, myself, mean by a species. I do this with much 

 diffidence, and without contesting the right of any other 

 person to hold a different opinion. A species then I 

 should consider as an aggregation of individuals, wild in 

 Nature, having a large number of characters in common 

 and resembling each other more than they resemble other 

 individuals. It must be capable of holding its own in the 

 struggle for existence, and must be marked off from other 

 species by characters which can be precisely defined in 

 words. What, then, is a variety ? We must discriminate 

 between " botanical " varieties and varieties in our special 

 fern sense, which latter are generally referred to, if referred 

 to at all, by botanists as " monstrosities." 



Broadly speaking, a variety consists of a number of 

 individuals resembling some particular species in most 

 points, but differing in minor particulars, which, however, 

 are capable of being precisely defined. It must " come 

 true " from seeds or spores in general, although it may 

 sometimes revert to the parent species. It is this latter 

 point which chiefly distinguishes a variety from a species. 



