— 18— 



similar occurrences may have come about. The first and in some 

 ways the most plausible is that the ferns have spread from a com- 

 mon center, the intervening plants dying out meanwhile, leaving 

 these distinct colonies to mark the extent of their range. The 

 second is, that one or more of these distinct localities has been 

 populated from spores blown from another over perhaps thou- 

 sands of miles of country. The most interesting theory, how- 

 ever, is probably the one that gives to these widely separated 

 stations a separate origin. If a certain set of conditions can 

 make Adiantum pedatum in America, why cannot a similar set 

 make the same fern in Japan and do away with any reasoning 

 that attempts to connect the two with a common ancestor ? 



Some slight endorsement is given this latter theory by the 

 attitude of those botanists who refuse to recognize some of these 

 foreign species as identical with ours. This is true regarding our 

 Botrychium ternaturn, upon whose identity with the Japanese 

 species it is likely the last word has not been said.* I have seen 

 specimens labeled Botrychium Virginianum from Japan, which 

 I should hesitate to call identical with our own. That these and 

 others are not exactly like ours may not militate against the fact 

 of their having a common ancestor, but it may against their being 

 the same species at present. It is quite reasonable to suppose 

 that slight variation in the climate and soil of places far apart 

 would in time slightly change these plants were they the same in 

 the beginning, but whether such change has proceeded far enough 

 to warrant the separation of another species is a matter for fur- 

 ther discussion. 



In a paper of this length no attempt can be made to settle 

 any of the questions I have raised. If I have suggested topics 

 for further thought and discussion, or directed the attention of 

 others to these problems of fern distribution, my purpose will 

 have been served. 



N. Y. Botanical Garden, N. Y. City. 



*Since this was written, Dr. Underwood has published a revision of this 

 and related species, and decide.s that there is no true B. ternatum in 

 America. 



