252 



THE SPORE-PRODUCING ORGANS 



[CH. 



state. The indurated sclerotic cap of the Osmundaceous sporangium corre- 

 sponds in position though not in detailed structure to that of Senftenbergia 

 from the Carboniferous Period, where the cells appear to be arranged in three 

 to four more or less definite ring-like rows (Fig. 247, A). In Klukia (Jurassic) 

 and Ruffordia (Wealden) the cap is replaced by an apparently simple ring 

 surrounding a distal plate of thinner cells (Fig. 248). Lygodium, which dates 

 back to Cretaceous times, suggests a transition to this simpler state. Here 

 the mechanical ring may consist of more than one row of cells, and extends 

 down the frontal face of the sporangium on either side of the slit ( Fig. 249, y^). 

 But usually in Lygodimn, as in Schizaea and Anemia, it consists of only one 

 row. These comparisons indicate an origin of the single-rowed annulus, 

 which is so constant a feature of the Leptosporangiate Ferns, by simplifica- 



Fig. 247. Senf/enbei-gia {Pccopteris) 

 elegans, Corda. A=z. small piece of 

 a sporophyll. ( x 4.) B—z. sporan- 

 gium. ( X 35.) (After Zeiller, from 

 Engler and Prantl.) 



1 ig. 24S I\ It la , \i I \\ hillips), 

 Raaborski. l-eiuie pinnule of the 

 last order, seen from below. ( x 20.) 

 From the Jurassic of Krakow. 

 (After Raciborski, from Engler and 

 Prantl.) 



tion from a complex ring. Irregular doubling of the ring, which is sometimes 

 seen in Gleichenia, Ceratopteris^Platysoma, Cryptogramnie.Acrostichumaureum 

 and other Leptosporangiate Ferns, even where the annulus is normally single, 

 serves also to bridge the gap between the many-rowed annulus and the 

 simple ring of the Leptosporangiate Ferns. 



Along with the simplification of the annulus goes the enlargement of 

 that disc of thin-walled cells which the ring surrounds. It has been styled 

 the " Platte" by Prantl {Schizaeaceae, p. 17). In Senftenbergia it appears to 

 be absent, though possibly only overlooked owing to faulty preservation. 

 But in the living Schizaeaceae Prantl states that it is always present, 

 though only a single cell represents it in Lygodiiini and Schizaea (Fig. 249, C). 

 In Anemia {D) it consists of some 12 cells forming a distal ox peripheral 

 I'egion of the wall. The thin area between the annulus and the stalk maybe 



