1888.] H. F. Blanford— ^ List of the Ferns of Simla. 297 



is inseparable from N. prolixum, as also Mr. Clarke suspected ; I learn 

 from Mr. Baker that the original habitat of the type is unknown, and the 

 Simla ferns do not correspond with it very closely. JV. canum is there- 

 fore omitted from my list. 



Lastly, I follow Col. Beddome in separating Folypodium simplex 

 from Pol. lineare. The former is a thin-fronded, eminently perishable 

 fern which shrivels up and disappears with the first breath of the dry 

 northerly wind. The latter is a thick coriaceous fern which simply rolls 

 up its fronds at the end of the rains and waits till the damp air and rain 

 of the following monsoon once more unrolls them and restores their 

 torpid vitality. P. clathratum, Clarke, is a third allied, but quite dis- 

 tinct, species very abundant in Simla. 



There are a few other changes that, as the result of my own ex- 

 perience in the field, I should be inclined to make, but I have refrained 

 in deference to Mr. Clarke's wider knowledge. 



It is much to be desired that botanists should agree to some general 

 rule to regulate specific distinction in dealing with forms so variable and 

 yet presenting so few marked characters as ferns. At present, the prac- 

 tice of different describers is by no means uniform, and that which each 

 follows is generally to be gathered only by inference from the results of 

 his work. The rule which I have formulated for my own guidance is 

 that, when two sets of forms which can readily be distinguished apart 

 occupy the same or contiguous areas (if as far as is known they are not 

 linked by intermediate forms either in these areas or in the interval be- 

 tween them), they should be recognized as distinct species, and such dis- 

 tinction would not be invalidated by the existence of a form possessing 

 intermediate characters in some far distant region. On such grounds 

 I base the separation of Glieilanthes Dalhousice from Cheilanthes farinosa'y 

 and Adiantum EdgewortJiii from A. caudatuTn. 



I attach much importance too to marked differences of habit such as 

 have been noticed above in the case of Folypodium lineare and P. sim- 

 plex (in this case, however, the two forms have a different venation 

 also). And especially when these are accompanied with equally marked 

 differences in the characters of the habitat and the range of elevation of 

 the contrasted forms. Thus Asplenium tenuifrons differs from A. nigri- 

 jpes, not only in the manner of its growth, and the form and texture of 

 the frond, but it is restricted to levels below 7,000 feet and the imme- 

 diate neighbourhood of streams ; whereas A. nigripes grows on well 

 shaded hill slopes, only at elevations above 8,000 feet. In all these cases 

 no intermediate forms are met with. 



The following is a numerical generic siimma)y of the species and 

 varieties enumerated in this list. 

 39 



