XX] RECENT FERNS 301 



with ramental scales or hairs : the remains of old leaves may 

 persist as ragged stumps, or, as in Oleandra, Polypodium vulgare 

 and several other species, the leaf may be cut off by the for- 

 mation of an absciss-layer^ leaving a clean-cut peg projecting 

 from the stem. As a rule the branches bear no relation to the 

 leaves and are often given off from the lower part of a petiole, 

 but in a few cases, e.g. in the Hymenophyllaceae, it is noteworthy 

 that true axillary branching is the rule^. In the typical tree- 

 fern the surface resembles that of a Cycadean trunk covered 

 with persistent leaf-bases and a thick mass of roots. Among 

 epiphytic ferns highly modified stems are occasionally met with, 

 as in the Malayan species Polypodium (Lecanopteris) caj-nosum 

 and P. sinuosum'. 



The leaves of ferns are, among the most protean of all plant 

 organs; as Darwin wrote, "the variability of ferns passes all 

 bounds*." The highly compound tri- or quadripinnate leaves 

 of such species as Pteris aquilina, Davallia and other genera 

 stand for the central type of fern frond ; others exhibit a well- 

 marked dichotomy, e.g. Lygodium, Gleichenia, Matonia, etc., a 

 habit in all probability associated with the older rather than 

 with the more modern products of fern evolution. Before 

 attempting to determine specifically fossil fern fronds, it is 

 important to familiarise ourselves with the range of variability 

 among existing species and more especially in leaves of the 

 same plant. A striking example of heteromorphy is illustrated 

 in fig. 233. Reinecke" has figured a plant of Asplenium multi- 

 lineatum in which the segments of the compound fronds assume 

 various forms. In Teratophylluin aculeatum var. inermis Mett., 

 a tropical climbing fern believed by Karsten' to be identical 

 with Acrostichum (Lomariopsis) sorbifolium, — an identification 

 which Goebel' questions, — the fronds which stand free of the 

 stem supporting the climber differ considerably from the 

 translucent and much more delicate filmy leaves pressed against 

 the supporting tree. From this fern alone Fee is said to have 

 created 17 distinct species. In this, as in many other cases, 



1 Baseoke (08). = BoocHr (00). 



3 Yapp (02). * Darwin (03) ii. p. 381. » Eeinecke (97). 



6 Karsten (93) ; Christ (96) ; Bommer (03). ' Goebel (05) p. 847. 



