9 255 



I give in the accompanying schematic figures an illustration of the most 

 common ways, in whicli the leaves are found to be narrowed. As even a very 

 detailed diagnosis cannot confer a clear idea of the shape of the lamina, I have in 

 the descriptions of the species referred to the schematic figure, with which the 

 species dealt with best agrees. 



A third character, which might be considered to be of some value for a 

 classification of the species into groups, is the rhizome, if erect or creeping. By 

 the term "creeping rhizome" two things, however, may be understood, which must 

 be distinctly distinguished from each other, viz: (1) the long, horizontally creeping, 

 often cord-like rhizome, which bears leaves at greater or shorter intervals, and (2) 

 the short-creeping rhizome, which only bears leaves near its apex, where they 

 are either fasciculated or only have very short intervals between. This latter form 

 of the rhizome is a simple modification of the erect rhizome with fasciculated 

 leaves, often, possibly, caused by the peculiar conditions of the growing-place, as 

 it seems that some species with normally erect rhizome may vary in that direc- 

 tion. On the other hand the long, horizontally creeping rhizome is a peculiarity in 

 some species, which can, therefore, only with difficulty be united with other spe- 

 cies into groups of real relatives, even though they very much resemble species 

 with an erect rhizome in the shape of the lamina. Many of these species with 

 wide-creeping rhizomes show the peculiarity that they have most often a greater or 

 less number of furcate veins, while species with erect or ascendent rhizomes nearly 

 always have simple veins onlj'. Whether this correlation can be explained by the 

 fact that the creeping species generally grow in swampy or boggy ground (compare 

 our D. thelypteris) may be doubted. It is a well-known fact that plants growing in 

 swampy ground very often have j)roportionally large assimilating leaf-surfaces, and 

 in connection herewith a more differentiated development of the veins, which will 

 be reached here most easily by a simple furcation of the veins. 



These creeping species of ferns belong to the group of D. opposita, which 

 like the species related to D. patens is characterized by the veins being normally 

 simple, quite different from the species of the group of D. filix mas with furcate 

 veins in leaves of the equal size and habit; this different development of the veins 

 in these groups is evidently an inherited peculiarity, of which an explanation is 

 quite out of the question. We have before us here, however, a variation within 

 the group of D. opposita, which seems to indicate a connection between the ecology 

 of the species and the development of their veins. A thorough examination of 

 these relations is much to be desired; it might give us an explanation of this corre- 

 lation between creeping rhizome and furcate veins. Here I shall confine myself to 

 state that it is the rule; it has the advantage that one to a certain extent can con- 

 clude from the venation to the shape of rhizome, especially when working with 

 species from Southern Brazil. 



Having thus mentioned those natural characters which can be used in 

 grouping the species, I shall add some words on the characters which can most 



D. K. n.Viilensk, Selsk. Skr. 7 H:ckke, n.iturviileiisk oijiUMlluin Aid IV 4. 34 



