THE PINNA -TRACE IN THE FERNS. 367 



for the sake of minute comparisons with the living Ferns, these Zygopteridese seem 

 to have possessed four orthostichies of primary pinnse. The pinna-traces which we 

 have mentioned presently divide into two parts each, so that these Ferns must not be 

 examined too critically for prototypes of leaf-trace. But there is at least a constancy 

 in the position of origin of the pinna-trace-bars, as Gordon terms them. They come 

 from the margins of the solid leaf-traces just from the points nearest to the appendages 

 which it is their work to supply. 



Kidston and Gwynne-Vaughan have classified the Zygopteridese according to 

 the presence of a single row of appendages ("pinnse") on each side of the main 

 rachis or of two such rows. 



Those genera already mentioned fall into their second class. The first class, with 

 a single row of appendages on each side of the main rachis, includes Ankyropteris 

 bibractensis, Renault, and Clepsydropsis antiqua, Unger. From the edge of the 

 leaf-trace in Clepsydropsis antiqua the pinna-trace goes off as a closed ring. This 



TEXT-Fro. 8. — Diagrams illustrating the pinna-trace departure in a, Dincuron ptcroidcs, Renault ; 6, EtaplAris Scotti, 

 P. Bertrand ; c, Metaclepsydropsis duplex, Williamson. (After P. Bertrand, and Gwynne-Vaughan and Kidston.) 



type of pinna-trace occurs also in Ankyropteris. Ankyropteris corrugata, Williamson, 

 has biseriate primary pinnse and one plane of symmetry. The leaf-trace has the 

 outline of a double anchor — a modification of the Etapteris-Diplolabis type. The 

 pinna-traces in this Fern leave the edges of the arms of the leaf-trace in very much 

 the same way as those of Diplolabis leave its leaf-trace, but here there is only the one 

 set of pinnse to be supplied from each arm of the leaf-trace, and thus only one half of 

 the leaf- trace arm is concerned in the process. It is just a Diplolabis type with half 

 of the pinna-trace-bar suppressed. This Ankyropteris-tyye is another illustration of 

 the effect of the position of the pinnse relatively to the leaf-trace in affecting the 

 point of departure of the pinna-trace. But the details of the departure of the pinna- 

 trace in Ankyropteris recall the process in such an extramarginal type as Didy- 

 mochlsena truncatula. The full growth of the pinna-trace has not been followed, but 

 the sections of Ankyropteris bibractensis, var. westphalensis, P. Bertrand, which 

 have been studied by Paul Bertrand (text-fig. 9) (Etudes sur la fronde des Zygo- 

 pteridees, Lille, 1909), show the widening out of the tracheides at the part of the leaf- 

 trace which is to supply the pinna, the appearance of a reparatory set (" anneau 

 reparatrice interne") to ensure the continuity of the tissues of the arms of the leaf- 

 trace past the point of pinna-trace departure, and the departure of the pinna-trace 



