\ 



k 



1907] BINFORD— SPORANGIUM OF LYGODIUM 223 



The orientation of the sporangia is definite; this is a character- 



istic of the lower members of the series. The stalk is shorter and 



■ more massive than any other form above Kaulfussia. The tapetum 



i is derived from the central cell, as in all the leptosporangiate forms; 



but the peculiar enlargement of the ceils of the inner layer is more 

 characteristic of the lower members of the group. The position of the 

 annulus is the one postulated for the lower leptosporangiate ferns. 

 The large irregular sporogenous mass in which there are occasionally 

 sterile cells, and the large number of spores are also characteristic of 

 the lower leptosporangiate ferns. 



The family to which Lygodium belongs has some characteristics 

 which cannot be considered as intermediate in this line of evolution, 

 but belong to this family only. The marginal initial cell of the 



p sporangium, whose early divisions are of the dolabrate type, is not 



* reported for any other ferns. The single sporangium in each sorus, 



the large sporangium and spores, and the indusium, which in cross- 



i section shows the tissue regions of the foliage leaf, are characteristics 



w^hich in nature or degree of development belong only to this special 

 group of ferns. 



In connection with the monangial sorus, Bowers has called atten- 

 tion to the fact that often Gleichenia has only one sporangium in a 

 sorus near the apex of the sporophyll. A comparison made by Zeil- 

 LER^ and emphasized by Bower (he. cii,, p. 43) brings out a close 

 connection between the fossil form Senftenbergia and the Schizaea- 

 ceae, and also connects Senftenbergia with the Osmundaceae by 



I 



r 



I 



( 



means of the fossil form Kidstonia. Senftenbergia is found in lower 

 horizons than most of the marattiaceous ferns, and is the most ancient 

 fern whose sori are well known; these sori are monangial. 



Osmundaceae, Kidstonia, Senftenbergia, and Schizacaceae form a 

 series in the development of the annulus, and, as Bow^R (loc. cit.) has 

 pointed out, the position of the annulus in Gleichenia corresponds in 

 some points to that in the Schizaeaceae. 



J- 



But after all these comparisons are made, the peculiarities men- 

 tioned above are so striking and apparently so well established, and 



3 Studies in the morphology of spore-producing members. IV. Phil. Trans. 

 i^oy. Soc. London B. 192:33, . 



4 Bull. Soc. Bot. France 44:95. 



