26o 



THE SPORE-PRODUCING ORGANS 



[CH. 



£porangiate Ferns it is wanting in the Vittarieae, Gymnogrammeae, Polypo- 

 dieae.and Pterideae,but present in the Asplenieae (with ^^'//jr/«;//), and in the 

 Aspidieae (Fig. 257). It is interesting to note that it is absent in Acrostichiini 



Fig. ■255. Ophioglosstivi xmlgatum, L. Portions of sporangia showing the sporo- 

 genous tissue in two stages of disintegration. In A the tapetum {t.), evidently 

 derived from more than a single layer of cells, has formed a plasmodium with 

 many nuclei, which is beginning to penetrate the sporogenous tissue, in which 

 an occasional cell [st.) is seen disorganised. B shows a more advanced state, 

 where the sporogenous cells {sp.) appear in small clusters, or isolated, em- 

 bedded in the tapetal plasmodium (A): 71;' = sporangial wall, (x 100.) 



Fig. 256. A. Spores of Polypodmtn viilgare, L., showing the wedge-shaped, two-sided form of spore 

 from three aspects. B. Spore of Osmunda regalis, L., of tetrahedral form. (After Luerssen. ) 

 (X444.) 



aureuin, a detailed fact supporting its affinity with the Pterideae suggested 

 by Sir W. Hooker 50 years ago. It is absent also in Cystopteris and Onoclea. 

 The perispore thus possesses a certain value for comparison, but confidence 



