w Ferns of the Dismal Swxmp, V'n-</ini<i. 



southern and northern types. It is a meeting ground where 

 many Austro riparian forms reach their northern limit,while more 

 northern forms either find their lowest or most southern habitat, 

 or have variously changed representatives. The causes of this 

 complex condition vary according to the requirements of the 

 different species 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 present con 

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

 rounding regions. 



Of the ferns Polypodium polypodioides is distinctly Austroripa- 

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

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

 and is undoubtedly its representative. The wood ward ias are 

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

 do not occur at any great elevation. The two species of Struthop- 

 teris are most abundant at higher altitudes and owe their presence 

 here to their swamp 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, Dryopterismarginalis, D. noveboracensis, D. thelypteris, Poly- 

 slichum acrostichoides, Asplenium filixfcemma, Pteris aquilina, Oao- 

 clea sensibttiSj are all higher-ground species. With the exception 

 of D. marginalis they are abundant in the general region border 

 ing the swamp. Botrychiurn obliqtium also belongs in the same 

 category and may be common about the swamp. Two other 

 species usually found on higher and dryer ground, Dryopteris 

 spimdosa and Asplenium platyneuron, are not abundant in the 

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

 are somewhat changed from the typical form, though perhaps 

 hardly sufficiently to warrant separation. 



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. spinulosa, 

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



*I have taken it near Cape Charles City, Northampton Co., Va. 



