28 PACIFIC STATES FLOKAL CONGRESS. 



Many of the ferns of the southwest are really Mexican species which 

 lap over and intermingle with those of more temperate and northern 

 species. Several species of Cheilanthes and Notholamas are found in 

 southern California, Arizona, and New Mexico, but disappear with 

 more or less rapidity as we leave the Mexican border. 



Occasionally patches of these southern species are found at widely; 

 separated localities, often at high altitudes, and their distribution is 

 such as to give rise to the question, Are these species in process of evo- 

 lution or of extinction? 



But the comparatively recent appearance of man on the earth, and 

 the still shorter time during which he has made a study of these sub- 

 jects, is entirely insufficient to enable us to answer the question with 

 any degree of satisfaction. 



One of our Polypodiums (P. Scouleri) has been noted from Marin 

 County, north of San Francisco, which is perhaps its northern limit: 

 next, in San Francisco County, near the ocean; again, on an outlying 

 islet in San Luis Obispo County; and further south, on one of the 

 Channel islands, off Santa Barbara, from where it skips to Guadaloupe 

 Island, off the coast of Mexico. It does not appear to have been found 

 at any distance from the ocean. Is it the remnant of a species which 

 formerly occupied a larger extent of country and is approaching ex- 

 tinction ? or has it been recently evolved, to become, in time, more gen- 

 erally distributed? Or is it a stray, or survival of the fern flora of 

 territory which formerly existed to the westward of the present coast 

 line? All of these theories have been advanced, but which, if any of 

 them, is the correct answer to the question? 



Nephrodium patens, found in Santa Barbara County, is found in 

 Texas and Florida. Several others of our ferns present equally inter- 

 esting illustrations of the peculiarities of distribution. 



Some of our species are restricted to California, and more of th"t" 

 to California and Oregon, and to California and Arizona, but as we 

 go north we find the species of the eastern states overlapping and inter- 

 mingling with the ferns of the Pacific Coast, until we reach a region 

 where the ferns common to Canada and the northern states predom- 

 inate. 



One marked departure from the general rule in relation to the dis- 

 appearance of the Cheilanthes in the north, is shown by Cheilanthes 

 argentea, which is found in, and restricted to, Alaska; Botrychium 

 boreale is another species which is restricted to the same territory. 



The Pacific fern flora represents a portion of the Nearctic realm, 

 a term applied to the portion of North America lying north of Mexico. 

 This realm is divided into live provinces, called Boreal, Medial, Occi- 

 dental, Arizonan, and Austral. Each of these provinces possesses species 



