362 



MR H. C. DAVIE ON 



out still the aporaehial set becomes broken up into two curved portions, and these 

 separate from each other at their tips, so that the pinna-trace now has the outline 

 of the leaf-trace (text-fig. 6, e). The supply to the pinnules goes off from this in just 

 the way in which the pinna-supply leaves the leaf-trace (text-fig. Q,f). But in the 

 pinnule there is no development of any accessory group of tracheides, and the pinnule- 

 trace retains its narrow plate of tracheides throughout its length, giving off the 

 supplies to the secondary pinnules from its margins. 



In Asplenium lucidum, Forst., the supply to the pinna leaves the petiolar trace 

 as a narrow strip of tracheides enclosed in phloem. Just as in Davallia pallida, a 

 group of tracheides soon appears on the aporaehial side of the pinna-stalk, becomes 

 larger, and soon joins the main group of tracheides of the pinna-trace. The triangular 

 set of tracheides thus formed soon splits at the apex of the triangle, and two portions, 

 each like one part of the binary leaf-trace, remain attached to each other by their 



Text- Fig. 6. — Davallia pallida, Mett. Series of diagrams to show the development of the pinna-trace. 



middles. From this pinna-trace the supply to the pinnules is nipped off* marginally. 

 Just as in Davallia pallida, there is no appearance of tracheides in the pinnule-trace 

 in the position of their occurrence in the pinna-trace. 



In Drynaria rigidula the pinna-trace leaves the leaf-trace (PL XXXV. fig. 20) 

 as a narrow plate of tissue, with about twelve tracheides. The tracheides in the centre 

 of the plate are much larger than those at its edges, and as the strand passes out 

 into the pinna these central tracheides rearrange themselves, crowding into a little 

 four-sided group, the small tracheides remaining as narrow strips at the edges of the 

 group. In this condition the vascular strand passes up to the tip of the pinna. 



In Asplenium prasmorsum the margin of the leaf- trace which goes off to the pinna 

 remains as a narrow plate right through the pinna, only extending laterally and 

 nipping off its edges when pinnules have to be supplied. 



This survey of the pinna-trace and its development and elaboration in the Ferns 

 confirms the impression given by an examination of the table on p. 354. There is a 

 gradual rise; of the extramarginal type out of the marginal, and then a lessening of 

 t In- type until in the most advanced Ferns it disappears altogether and the marginal 

 type remains. The comparison of the pinna-traces of the early leaves of various Ferns 



