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 
Fics. 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 Fée* 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 
*Méd. Foky. a6 tc 
t Bot. Zeit. 537. pl. 13. 1854. 
