350 MR R, C. DAVIE ON 



the pinna-trace, as the leaf-trace is followed up the petiole, is an extension of the 

 mass of tracheides on the adaxial side of the petiole. In Asplenium obtusatum* 

 Forst. (PL XXXIII. fig. l), which may serve as an example of this type, the two masses 

 of xylem are curved in outline, the convex sides of the curves being directed towards 

 each other. The adaxial extremities of these xylem-masses become extended towards 

 the adaxial corners of the petiole. As the pinnae are not inserted exactly opposite to 

 each other, first the extremity of one and then that of the other xylem-mass is separated 

 off from the parent trace. Phloem completely surrounds the xylem in both portions 

 of the leaf-trace, and the marginal tracheides when nipped off are surrounded by a 

 narrow ring of phloem. There are protoxylem elements at the abaxial tips of the 

 leaf-trace and on the adaxial sides, not far from the ends. The pinna-trace has one 

 small protoxylem group on one side at the time of separation. 



As the tracheides at the margin of the leaf-trace strand are separated from the 

 parent strand to supply the pinna-trace, this type of pinna-supply is termed the 

 " marginal " one. 



The marginal type is not always as simple as this, however. In Loxsoma 

 Cunninghami, R. Br. (PI. XXXIII. figs. 5 and 6), the leaf-trace in the base of the petiole 

 is curved in outline. It has a little hook at each extremity. Below the first pinna 

 this trace extends laterally ; the hook is pushed further and further from the centre 

 of the petiole, a widening of the leaf-trace takes place in the antero-posterior 

 direction just back from the hooked extremity (PI. XXXIII. fig. 5) ; this widened 

 region becomes arched like the parent trace, and the arched extremity is nipped off 

 as a pinna-trace (PI. XXXIII. fig. 6). 



This is more complicated than the process in Asplenium obtusatum, the presence 

 of the hooked extremities dictating the complexity. 



In Balantium culcita (L'Herit.) Klf. (PI. XXXIV. fig. 13) the leaf- trace has small 

 terminal hooks. Its outline is at first that of a simple arch with an almost fiat 

 abaxial portion flanked by curves (text-fig. l). As the trace ascends towards the first 

 pinnae it becomes extended towards the adaxial corners of the petiole ; an arching 

 more marked than that of Loxsoma goes on in the extensions, and the pinna-trace 

 departs as a replica of the parent trace, taking with it the original margin. 



The simplest example of the marginal type of supply from a hooked leaf-trace is 

 found in Aneimia hirta (L.) Sw. (PI. XXXIII. fig. 3). Each hook is merely a little 

 group of tracheides placed at right angles to the set composing the side of the leaf- 

 trace. The pinna is supplied from an extension of the extremity in the usual manner. 

 A swelling in the side of the leaf-trace not far from the tip is the breaking-point for the 

 pinna-trace. The new hook of the leaf-trace is the remnant of the dilated portion. 



All four types agree in nipping off the margins of the leaf-traces to supply 

 the pinnae. 



* For the sake of uniformity, the nomenclature throughout this paper is that of the Index Filicum (Chbistenskn, 

 1806). 



