CHAPTER XXXVII. 



GRADATAE. 



THE Ferns so far described, however different in detail, all correspond in 

 producing those sporangia that are in near juxtaposition simultaneously : 

 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. Matonia 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 in a 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 simultaneous 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 (Todea) or cover both surfaces and margins (Osmundd). 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. 



