[74 CONTRIBUTIONS PROM THE RATIONAL HERBARIUM. 



tan( region, this also with its various forms diverging, it may be, 

 along quite different lines; and to this fast growing "polymorphic 

 species" may have been added a third and a fourth form, each with 

 it- attendant variations. If the herbarium material at hand is con- 

 siderable ami represents forms from a wide geographic range, the 

 chance <d' determining with certainty the Limits of the several species 

 previously merged or confused is, naturally, improved; yet also the 

 greater is the need of study and of a thorough search of literature in 

 applying the names correctly. With only -cant material available 

 a brief diagnosis of a Jamaican or a Martinique plant might be 

 thought to apply well enough to Mexican specimens, in the absence 

 of specimens from the type region, and one name might be made t<» 

 apply to tlit> whole, [f this happened a century ago the reference, 

 whether right or not, may have the weight of monographic "au- 

 thority " of the intervening period, and the present-day writer may 

 l>e confronted with the need of determining the boundaries and re- 

 lation-hip not of one. hut of two. three, or more species, as the case 

 may be. ( )r. the original form having been rare or not much collected 

 since, the name given to this may have become axed definitely upon 

 a single species, but this very different from the original and p<>- 

 sibly from a distant region. On the other hand, the older writer, in 

 the lack of connecting forms since collected in abundance, may have 

 recognized far too many "species." When, finally, the limits of the 

 several allied species have been made out. it may appear that in the 

 case of any or all of these which may have received name-, the nomen- 

 clatorial type, having been determined not by -election but (often of 

 ssity) by mere accident of first discovery, is not truly typical of 

 the species and represents one of the outlying forms. Under these cir- 

 cumstances the nonavailability of a type specimen for comparison or, 



at lea-t. a lack of knowledge a- to it- exact origin, become- a doubly 

 serious handicap. 



it i- not to be supposed that the difficulties mentioned exist in a 

 study of the ferns alone, though it must be admitted that this group 

 in particular has suffered radically diverse treatment at the hands 

 of various students. This ha- resulted naturally from the circum- 

 stances. Fern species, partly by reason of their ready dispersal and 

 their unusual breadth of variation, are commonly supposed to occupy 

 extensive ranges that would at once be discredited for the great 

 majority of phanerogam-. Undoubtedly a very wide distribution 

 is to be ascribed to many tropica] fern-, mamly lowland species, and 

 very many other- in one form or another too close to be separated 

 are known t<. stretch over half a continent: yet marked exceptions 

 OCCUr, a- in the ( yatheaceae. which have been found to be relatively 



local in range and in which, a- might be supposed, definite though 





