— io3— 



needing reinforcement. They are reinforced by the vena- 

 tion of Gonioptcris and by a broader border of cartilage 

 in Polypodium afline and other species. The special re- 

 inforcement of the sinuses can serve only as a protection 

 against tearing, but the reinforcement of the margin as 

 a whole is equally a protection against gnawing animals. 

 It is probably of use in this way to many smaller ferns. 

 Cartilaginous borders, if sharp or deflexed, also help to 

 keep the nether surface dry. 



The ready removal of water from the frond is insured 

 and facilitated in various ways. One of these is by a 

 smooth, even waxy, unwettable surface, as in Asplenium 

 phyllitidis. Caudate tips are very familiar structures 

 serving this end. and, of course, acuminate tips in gen- 

 eral are more common and less conspicuous structures 

 of the same kind. The removal of water from an erect 

 fern is brought about in the same way, by an attenuate 

 base, like that of Diptcris and Mcniscium. Essentially 

 like these are plants such as Odontosoria, with cuneate, 

 erect pinnules. Pinnae drawn down at the base instead 

 of attached horizontally will drain in the same way. The 

 reduction of the basicopic half of the pinna has the same 

 effect, the part of the lamina which is removed being 

 that portion which could not readily drain down the 

 rachis. This modification is begun in Asplenium vul- 

 canicutn, carried further in A. tenerum and its relatives 

 and in Polystichum ; farther still in Asplenium resectum, 

 and completed in our dimidiate Lindsayas and Adiantum. 



If detracted pinnae are carried further they become 

 decurrent, forming a wing on the rachis and stipe which 

 serves at once as a drain for water, aside from any 

 value it may have in increasing the leaf area. A broad 

 wing is sometimes convex upward on both sides, effect- 

 ing a depression along the axis, as in Polypodium papil- 

 losum, the pinnae of Pteris longi folia and the whole 

 frond of Polypodium caudiforinc. The fine divisions of 

 Onychium are concave above. Many ferns have verv 



