392 Benedict: Revision of the genus Vittaria 



but in more critical characters of the scales, texture, and tissues, 

 and especially in the uniform arrangement of the sporangia in 

 indeterminate lines along the outer portions of the veinlets. (See 

 Figs. 1-7, and the plates.) 



The taxonomic revision of Vittaria presents unusual difficulties 

 as compared with other ferns, owing to the fact that although 

 there appear to be a fairly large number of valid species — about 

 forty — the very simple venation pattern allows only a small 

 range of variation in the more evident characters of gross outline 

 and venation, so that these, the characters ordinarily used in 

 differentiating fern species, are not available. Nearly all the 

 species are grass-like in the outline of the leaves, and the problem is 

 thus about the same as would be offered by a genus of grasses if 

 no flowers and fruit were obtainable. In the case of some few 

 species, the differences in size, outline or coloration of the leaves, 

 or in the venation, are sufficiently marked to allow of specific 

 determination, but in general it is necessary to study the plants 

 microscopically and by sectioning the stems and leaves, to arrive 

 at any understanding of the real specific characters. It has been 

 found by this method of study that there are very considerable 

 differences in the outline of the leaf petioles and blades as best 

 shown in cross-section, in the arrangement of the vascular tissues 

 in the stem and petioles, and in the kind of cortical tissue de- 

 veloped. The scales which cover the stems and leaf-bases, al- 

 though of one pattern, often show well-marked differences in cell 

 structure. There may also be important differences in the shape 

 of the spores and paraphyses. 



Some of the differences in these characters have been indicated 

 by one writer or another during the last sixty years or so, but no 

 one has used them consistently or accurately over any number of 

 species. The last and only monographic treatment of the whole 

 genus was that by Fee* who attempted to figure the scales, 

 spores, and paraphyses, as well as the general appearance of the 

 species he recognized. Unfortunately he seems to have been 

 inaccurate. Miillert discovered differences in the scales which 

 seemed to him to justify the description of several new species, but 

 he appears unfortunately to have missed the really important 



* Mem. Foug. 3: 1852. 



t Bot. Zeit. 537. pi. 13. 1854. 



