184 BENEDICT: GENERA OF THE FERN TRIBE VITTARIEAE 
is very obvious and probably justifies their juxtaposition in a 
systematic arrangement, as in Diel’s treatment of the ferns in 
Engler and Prantl, Die Natiirlichen Pflanzenfamilien. But there 
are also in the tribe Asplenieae similar and almost as obvious re- 
semblances and it is not unlikely that here also some not very 
distant relationship is indicated. 
The presence of clathrate scales in both the Pterideae and 
Asplenieae is further indication of a relationship. The use of 
scale characters in the classification of ferns is amply justified. 
from taxonomic practice and experience (see Christensen, Am. 
Fern Journal 1: 36. 13 F 1911), and it is also justified on a 
priori grounds. Thus, it would seem reasonable to suppose that 
one type of scale may serve the purpose of protection about as 
well as another of the same size, and that if there are differences 
found, these represent not adaptive but orthogenetic tendencies. 
It follows that similarity in scales may usually be attributed to 
similarity in phylogeny. 
The other three tribal characters mentioned are probably more 
distinctive of the Vittarieae than indicative of relationships. 
As characters which appear regularly in the more primitive 
genera of the tribe, there may be mentioned, first, the presence of 
paraphyses, second, the production of the sporangia in grooves. 
Both of these characters appear significant because they are 
all but general for the tribe; but whether they have any value in 
determining relationships may well be questioned, since both 
appear to be so definitely connected with the same function, that 
of protecting the developing sporangia. There is, however, strong 
suggestion of similar indusial developments in some of the As- 
plenieae, Pterideae, and Davallieae. 
A character which is also of almost general occurrence in the 
tribe, but which cannot be considered of value in determining 
relationships with other tribes, is found in the reticulate venation, 
true for all but the three most primitive species. Ferns in general 
are usually believed to have sprung from primitively dichoto- 
mously veined forms and it has been shown that the present tribe 
is probably no exception in that respect, but the venation types 
above the dichotomous stage, i. e., Vittaria, etc., must be recog- 
nized 4s having been evolved independently, no matter if exactly 
