NO. 24 REMARKABLE NEW FERN FROM PANAMA — MAXON 5 



synonym), in which a close examination shows the apices of per- 

 fect fronds to be not truly determinate, but rather, as in /'. podo- 

 cai'pum, to remain in a nascent state long after the older parts of 

 the frond have reached maturity. 



As to the cause of the development of- the dichotomous form of 

 the pinnae in fronds of P. podociwpuvi, in preference to the simple 

 elongation of its pinnae by the same method of indefinite evolution, 

 no especial explanation need be sought, inasmuch as instances of 

 repeated subdivision of apical growth in ferns are exceedingly com- 

 mon. But it may be mentioned that in the whole series of this 

 species not one of the fronds is subdivided at its apex, and in only 

 one is the rachis forked, the simple division in this instance having 

 been caused by an injury. The repeated subdivision of the fronds 

 occurs invariably in the pinnae. This is only partially accounted 

 for by the greater likelihood of injury to the apex of the frond. 



With respect to relationship, Polypodium podocarpum is clearly 

 allied to P. curvatum, its nearest relatives being perhaps the Andine 

 species P. pilipes Hook.^ and P.pozusoense Baker,'' the former from 

 Peru, the latter from Ecuador. But these are species with deeply 

 pectinate-pinnatifid pinnae, and the former, at least, has simple 

 veins. Both differ from P. podocarpiim very conspicuously in the 

 position of their sori, which are not placed apically upon special 

 teeth or lobes. The position of the sori in P. podocarpum, indeed, 

 demands especial notice, for it is not only apparently new for the 

 genus Polypodium (Eupoly podium), but seems to reverse the usual 

 observed fact that fertility is commonly accompanied by a loss of 

 foliar tissue. The contrary is here true; the pinnae are entire 

 where sterile, and toothed or lobed only where soriferous; there are 

 no sterile lobes on the fertile fronds. Moreover, the apical position 

 of the sori is so pronounced a feature as to suggest strongly the 

 recognition of this species as a distinct generic type. Without a 

 more critical study of its closest allies this hardly appears desirable; 

 but it is dillficult to escape the conviction that, as proven similarly 

 by Mr. Christensen in the case of Dryopteris, the genus Polypodium 

 (restricted to Eupolypodium) is susceptible of division into several 

 well-defined sections, which will be more than "groups of closely 

 related species," in that they may be recognized by definite charac- 

 ters afforded by a study of their minute morphology and their 

 method of growth. 



'Hook. Tc. PI./)/. 221. 1840. *Hook. Ic. V\. pi. 1672. iJ 



