236 Davie.—Comparative List of Fern Pinna-traces, with 
reinforcement in addition to the marginal supply. In Hypolepis distaus 
(Col.), Hk., the marginal supply appears alone; in H. repens (L.), Pr., 
and H. tenuifolia (Forst.), Bernh., the marginal supply is reinforced. 
The example of P ter is decurrens confirms what has been found in 
species of the genera Dryopteris? Polypodium? and Polystichum? namely, 
that a ‘ reinforcement ’ appears in the pinna-trace where large pinnae are 
present (Fig. 5). There has been no doubt of the interdependence of the 
presence of large pinnae and of the appearance of the reinforcement in 
connexion with leaf-traces composed of several separate vascular strands. 
Fig. 5. Diagrams illustrating the extra-marginal type of pinna-supply, with a ‘ reinforcement’ 
derived from the abaxial curve of the leaf-trace, in Dryopteris grandis (Pr.), C. Chr. 
This has already been shown in Polypodium decurrens , Raddi, 4 and Poly- 
stichum adiantiforme (Forst.), J. Sm. 5 We may now add that, even where 
the leaf-trace is undivided below the first pinnae, the £ reinforcement ’ of the 
part of the pinna-trace derived from the adaxial portion of the leaf-trace is 
connected with the size of the pinnae. 
The occurrence of a * reinforcement ’ is not to be regarded as helping 
to constitute a third type of pinna-supply. The two types of pinna-supply 
already described are fundamentally contrastive; either type may (usually 
where large pinnae appear) be reinforced from the abaxial portion of the 
1 Trans. Roy. Soc. Edin., vol. lii, p. 11. 
4 Ibid., pp. 7, 12. 
2 Ibid., p. 7. 
6 Ibid., p. 10. 
3 Ibid., p. 10. 
