02 Palni'^r — Fern^ of ilie. Dhnvil Swimp, Virr/iul't. 



southern and northern types. It is a meeting ground where 

 many Austroriparian forms reach their nortliern liniit,while more 

 northern forms either find their lowest or most southern Inibitat, 

 or liave variously changed re[)resentatives. The causes of tliis 

 complex; condition vary a(;cording to tlie re(iuirements of the 

 different s})ecies and the circumstances of their introduction into 

 the area. In a general way it may be stated that species requiring 

 abundance of sunlight and living above the undergrowth are 

 southern, while those intimately associated with the surface of 

 the swamp are of more northern, or of higher-ground derivation. 

 But there are many exceptions. The swamp undoubtedly has 

 been slowly evolved from a salt-water lagoon to its jiresent con- 

 dition; hence all its present life has been introduced from sur- 

 rounding regions. 



Of the ferns Polypod'mm polypodia ides is distinctly Austroripa- 

 rian, here reaching almost its northern limit.* Dryopteris goldie- 

 ana celsa, though related to an Alleghenian form, is quite distinct 

 and is undoubtedly its representative. The woodwardias are 

 coastal-swamp species, and though found well into New England 

 do not occur at an^^ great elevation. The two species of Strulhop- 

 terls are most abundant at higher altitudes and owe their presence 

 here to their swam [> habits and the ability of the plantlets to find 

 a congenial home. They do not fruit abundantly and doubtless 

 before man interfered with the forest were rare. Seven other 

 species, Dryopteris margiaalls, D. nooeboraceasis, D. thelypteris, Poly- 

 sllchum (icrosticholdes, Aspleamin fillxfceinliia, Pteris aquillaa, Oiio- 

 clea senslhUis, are all higher-ground species. With the exception 

 of D. margbialk they are abundant in the general region border- 

 ing the swamp. Botrychiura obliqaum also belongs in the same 

 category and may be common about the swamp. Two other 

 species usually found on higher and (hyer ground, Dryopteris 

 spiiiidosa and Asplenium pltitynearon, are not abundant in the 

 swamp, and the former was noticed but once elsewhere. Both 

 are somewhat changed from the typical form, though [perhaps 

 hardl}'^ sufficiently to warrant se})aration. 



Thus the only species growing on living trees is truly Austro- 

 riparian ; the next is D. goldieana celsa, which occupies a higher 

 habitat in the swamp than any of the others except D. spinidosa, 

 which occurs with it, though not so abundantly, and which 



*I have taken it near Cape Cliarles City, Northainjiton Co., Ya. 



