224 



MATONIACEAE 



[CH. 



uniform: that of the majority is as in GleicJienia, but many have the annulus 

 indined, a consequence probably of crowding. This is seen also in the fossil 

 Laccopterisoi Rhaetic and Jurassic time. The annulus is incomplete, with an ill- 

 defined stomium, while the rupture is by a ragged lateral 

 slit, opened by the straightening ring (Fig. 500). The 

 sorus originates as a smooth upgrowth from the lower 

 surface of the pinnule, opposite to a vein, a consider- 

 able number of cells being involved from the first : 

 no definite mode of segmentation has been recognised 

 (Fig. 501, F^. As development proceeds the margin 

 of the upgrowth extends all round, to form the over- 

 arching indusium (/, i)\ this, undergoing a somewhat 

 regular segmentation by anticlinal walls, curves so as 

 to cover the sporangia that arise below {s, Fig. 501, F^. The indusium thus 

 A B C 



Fig. 500. A sorus of Matonia 

 pectinata from wliich the 

 indusium has been natur- 

 ally shed. (After Seward.) 



D E 



Fig. 501. Matonia pectinata. A, B, C, as well as the central figure, 

 represent mature sporangia in various aspects. F, young sorus: /, i, in- 

 dusium : s, sporangium. £, young sporangium with cap-cell formed : a, its 

 acroscopic, /', its basiscopic side. Z>, sporangium with tapetum doubled. 

 (.^-Cx5o: D-Fy. 200.) 



precedes the appearance of the sporangia, as in many other indusiate Ferns. 



The sporangia originate from single cells which have commonly a square 



base, though it maybe a question whether this is always so. The segmentation 



is by walls inclined to one another: the segments thus produced surround 



a central triangular wedge-shaped cell, from which finally the cap-cell is cut 



off in the usual way {E). 



The further segmentation of the central cell follows the course usual in 



Leptosporangiate Ferns: a double tapetum is formed {D), of which the inner 



