THE FOSSIL OSMUNDACE^E. 



471 



9, scl'.). In the more damaged petioles these specialised masses of sclerenchyma are 

 frequently found isolated, owing to the fact that the ring fractures along their sides. 

 In the living Osmundacese the presence of specialised masses in the sclerotic ring is 

 characteristic of two species only — Osmunda Claytoniana and O. ciiinamornea. 

 Osmundites spetsbergensis is the first fossil member of the order in which the same 

 peculiarity has been found. 



The sclerotic strands in the concavity of the leaf-trace appear at a lower level in 

 the petiole than the specialised masses in the sclerotic ring, and consist of the same 

 type of dense sclerenchyma as the latter (fig. 10, scl.). A strand of exactly the 

 same type of sclerenchyma also appears in each of the stipular wings before the level 



Text-fig. 1. — Osmundites spetsbergensis, Nath. Diagrammatic restoration of stipular base. 



of the specialised masses is reached. These strands taper evenly and without inter- 

 ruption from a stout termination near the sclerotic ring towards the margin of the 

 stipule (fig. 11, scl.). Although the stout end lies very near to the sclerotic ring it 

 is never found in actual continuity with it. 



The Leaves. 



In the peat-like material already mentioned numerous fragments of detached 

 petioles are to be found lying about in all directions. The larger of these are about 

 6 mm. in diameter, and contain a perfectly typical C-shaped leaf-trace with deeply 

 incurved ends (fig. 12). The xylem strand is rather slender, being only two or three 

 tracheae thick except at the ends, which are slightly enlarged. All the softer tissues 

 of the leaf-trace are destroyed. The peripheral tissues of the petiole are heavily 

 sclerotic, even the epidermis itself being thick-walled. This sclerotic zone is denser 

 and smaller-celled towards the epidermis. There is also a narrow and somewhat 

 irregular zone of small sclerotic cells in immediate contact with the leaf-trace which 

 arc most numerous on its concave side. The ground tissue occupying the rest of the 

 concavity of the trace consists of large thin-walled cells which have mostly collapsed 

 (fig. 12, par.). 



The smaller petioles have much the same structure as the larger, only the ground 

 tissue becomes more and more thick-walled as the size of the petiole diminishes until 



