28o 



PLAGIOGYRIACEAE 



[CH. 



the distal face. Dehiscence is by a lateral slit with a stomium fairly well 

 organised, but not always exact in position, or in the number or size of the 

 cells which determine it. A comparison of the sporangium shows a definite 

 resemblance to that of Dicksonia and some other Gradatae, while a further 

 reference may be made to the more distant Anemia. The resemblance in 

 detail to the sporangium of the Osmundaceae is not close. 

 A BCD 



Fig. 546. Mature sporangia of Plagiogyria eitphlebia Kze. 

 ^= presenting the distal face: ^ = the basal: C — the 

 indurated side of the annulus: Z' = the stomial side. 

 ( X 50.) A dehisces to the left, but C and D dehisce by 

 a right-handed slit, as viewed from the distal face. 

 Compare Fig. 524 of Loxsomopsis. 



The prothalli are of the ordinary Leptosporangiate type, symmetrical in 

 form, and without distinctive hairs or glands. The antheridia are of the type 

 of the Polypodiaceae, with which Anemia and Mohria were grouped by 

 Heim as regards the detail of rupture {Flora, 1896, p. 349). 



Comparison 



The similarity of the stele of the large stock and of the leaf-trace to that 

 of Osmunda has already been noted, and this together with the enlarged 

 leaf base, and the dense covering of the youngest parts by mucilaginous 

 hairs forms a ground of resemblance that cannot be missed. On the other 

 hand, the Schizaeaceae include protostelic, solenostelic and dict)'ostelic 

 types, and all of these states may be seen in the single runner of Plagiogyria. 

 Moreover the deep axillary involutions are a rare peculiarity which is shared 

 with Anemia. These indications are very suggestive. The open venation so 

 usual in primitive Ferns is shared by both Osmundaceae and most Schizaea- 

 ceae, and by the Dicksonieae. But the superficial sorus, without any indusium, 

 points definitely to Todea, rather than to any Schizaeoid or Dicksonioid 

 Ferns, where its origin is marginal. The mixed character of the sorus is a 

 feature of advance seen in none of the Ferns named. In its structure the 

 sporangium compares most nearly with that of Dicksonia, and both of these 

 may be traced in essentials to a Schizaeoid source, such as that of Anemia. 

 The low output of spores (48) is a sign of advance far removed from 



