CHAPTER XXXVII. 
GRADATAE. 
Tue Ferns so far described, however different in detail, all correspond in 
producing those sporangia that are in near juxtaposition sémultaneously : 
the sporangia themselves are of large size, with short, usually massive 
stalks. The output of spores per sporangium is commonly in excess of 
that in other Leptosporangiate Ferns. A/atonta is, however, an exception 
to this, having not more than 64 spores: as also in its dehiscence, which 
is lateral, while in all the rest it is ina median plane. But notwithstanding 
these discrepancies, in the fact that the sporangia are simultaneously 
produced, as well as in other features, the Matonineae find their natural 
place with those Ferns which have been styled the Simplices. 
We shall now proceed to types in which the sporangia appear not 
simultaneously, but in basipetal succession: these have been styled the 
Gradatae. In them the position of the sorus may vary, as indeed it does 
in those with simultaneou8 sporangia ; while the Marattiaceae, Gleicheniaceae, 
and Matonineae have superficial sori, the sporangia of the Schizaeaceae 
may be marginal: in the Osmundaceae the sporangia may be on the lower 
surface only (Zodea) or cover both surfaces and margins (Osmunda). So 
also we shall find similar variations of position in the basipetal sori: the 
Loxsomaceae, Hymenophyllaceae, Dicksonieae, and Dennstaedtiinae all have 
marginal sori, while in the Cyatheaceae they are superficial. Such difference 
of position may serve as a useful character separating the tribes, but need 
not in any way vitiate our comparisons. In other words, the method of 
internal arrangement of the sorus is to be estimated as a more important 
character than the exact position which the sorus holds upon the leaf 
which bears it. It will be seen that while the basipetal succession in the 
sorus is taken as the defining character of the Gradatae, other characters 
indicate a higher position, but none with the same distinctness, and in 
many features these Ferns resemble the Simplices. There is reason to 
think, therefore, that they originated from some similar common stock, 
but adopted the basipetal succession of sporangia at a relatively late stage. 
