360 MR R. C. DAVIE ON 



supply (PL XXXV. fig. 17). The small plate of tracheides in the leaf-trace of this 

 species extends towards the pinna and gives off its margin as the pinna-trace. 



Chrysler has shown that this marginal type is not invariably found in the species 

 of Botrychium. Botrychium virginianum nips off the edges of its leaf-trace prior 

 to supplying its pinnae, but these edges move along the inner faces of the leaf-trace 

 strands and unite with them. The margins of the re-formed leaf-trace strands then 

 pass off to the pinnae. 



These excursions outside of the Leptosporangiate Ferns help us but little in the 

 interpretation of the great majority of forms of pinna-trace supply. The Marattian 

 and Ophioglossean types of pinna-supply are apparently dependent on the special 

 features of leaf-trace in these groups, and must be brought into line with the Filical 

 types rather than employed as a means for their elucidation. 



Two other regions of investigation may be entered before we attempt to make any 

 general statements about the pinna-traces we have examined. There is first the 

 supply to the terminal pinnae. In general this has been found to be marginal. No 

 matter what the outline of the leaf-trace in the lower part of the petiole, it generally 

 becomes reduced to a simple narrow plate of tracheides with adaxial and abaxial 

 strips of phloem lining it in the distal portion of the rachis. Often the supply is 

 marginal to the pinnae situated third or fourth in position below the tip of the leaf. 

 In such pronouncedly extramarginal forms as Histiopteris incisa, Pteris macilenta, 

 and Hypolepis tenuifolia the supply is marginal to the terminal pinnae and to one 

 or two below them. In H. incisa the supply is marginal to the pinna eighth in 

 order from the tip of the leaf. 



In the Cyatheaceae we might expect a retention of a complicated outline for the 

 leaf-trace up to near the tip of the leaf. In Cibotium Schiedei the strand is below 

 the ultimate pinna an ellipse of tracheides, very " thin " on the adaxial side. The 

 pinna is supplied by the departure of the lateral portion of this ellipse. Though the 

 leaf-trace is a closed ellipse, the margins are, of course, on the adaxial side, and this 

 supply is really of the extramarginal type. Exactly the same kind of trace appears 

 below the ultimate pinna in the leaf of Adiantum polyphyllum, where the pinna is 

 supplied after the same fashion. 



In the early stages of the life of a Fern the method of pinna-supply is the 

 marginal one. In the first pinnae in a very early leaf of a plant of Athy7'ium filix 

 fernina the supply came from the edges of a simple plate of tracheides, in exactly 

 the manner seen in most terminal pinnae of mature leaves. In a later leaf the trace 

 was binary and showed a tendency to form hooks at the edges of the two parts. 

 Here the supply to the basal pinnae was again marginal, though not from the extreme 

 tip of the trace. 



In a young plant of one of the Cyatheaceae the supply was marginal in the first 

 leaf, extramarginal in one considerably older (about the eighth). 



In ;i relatively late leaf of a plant of Peranema cyatheoides (about the seventh 



