THE PINNA-TRACE IN THE FERNS. 



353 



" from the point where the adaxial arc or the xylem hook joins on to the abaxial 

 curve," and partly " from the abaxial curve itself at the point where it is folded 

 inwards." These are just the points of departure of the pinna-trace in Histiopteris 

 incisa and Leptochilus cuspidatus, but the involution of the trace in Cyathea 

 Brunonis and its folding to the abaxial curve make both strands in it go off extra- 

 marginally. 



Text-Fig. 2. — Leptochilus cuspidatus (Pr.) C. Chr., showing the method of pinna-supply from the leaf-trace. 



These types of pinna-trace cover the variations which are found in the genera 

 examined. Upwards of a hundred and fifty species have been worked through, and 

 the method of vascular supply to all the pinnae noted from base to apex of the leaf. 

 The species were at first chosen at random, but soon a general trend could be observed 

 through the families in phyletic order. And the later species examined were selected 

 because of their positions on phyletic lines. The classification adopted in the 

 accompanying table of the results (p. 354) is that of Diels in Engler and Prantl's 

 NaLiirliche Pflanzenfamilien, a classification which corresponds closely to Bower's 

 grouping into Simplices — Gradatee — Mixtse. 



Starting with the Leptosporangiate Ferns, we have the Osmundacese showing 

 extramarginal supply to the pinna-traces. The length of the gap may vary. It is 



