AFFINITY TO TROPICAL KAIN FORESTS. 435 



acteristic grass of the swamp, Arundinaria macrosperma, is a woody 

 plant. In the more open parts of the swamp herbaceous forms pre- 

 dominate: in the aquatic vegetation, in areas occupied by the Wood- 

 wardia-Sphagnum Association, in the extensive deforested tracts on 

 the periphery of the Dismal, which are chiefly occupied by the Seir- 

 pus-Erianthus Association, and in the very limited areas of Low 

 Marsh bordering Lake Drummond. 



Among herbaceous phanerogams in the depths of this Hygrophile 

 forest annuals are almost, if not entirely, wanting. Few, if any, of 

 the species complete their development in one growing season. Of 

 life forms, the caespitose form is absent, and likewise the rosette 

 form, so common in the pine barrens. The following are common 

 modes of growth in the wooded swamps: l 



1. Stems creeping above ground and rooting at the nodes: In Juncus 

 rerpens, Hydrocotyh umbeUata, Mitchella repens, and the most abun- 

 dant herbaceous grasses, Panicum gibbum, Panicularia brachyphyUa, 

 P. pallida. 



2. Subterranean rootstocks: Saururus, Khexia, Lycopus, many 

 grasses, sedges, ferns, etc. In fact, this modification of the lower 

 portion of the stem occurs in a large majority of the herbaceous 

 species. 



o*. Stolons: Lycopus rubellus, Rhexia mariana, E. virginica, Scu- 

 tellaria lateriflora, Triadenum virgin icum , etc. Here are to be classed 

 the leafy offsets or extravaginal innovations of many of the grasses and 

 sedges. 



Comparatively rare are— 



4. Bulbs: present in Lilium superbum; and conns, in two orchids, 

 Tipularia unifolia and Limodorum tuberosum. 



5. Tubers: On the rootstocks of Apios apios (tuberosa) and of 

 species of Smilux. 



The epiphytic form, which is only sparingly represented here, has 

 already been sufficiently discussed. The only purely parasitic herba- 

 ceous embryophyte observed was Cuscuta gronovii. No purely sapro- 

 phytic flowering plant was detected in the woody swamps, although 

 this life form is probably represented. 



An impressive feature of the Great Dismal Swamp, especially of the 

 typical Black Gum forest, is its ecological affinity to the tropical 

 "rain forests" (Regenwalder), an affinity which appears in a much 

 slighter degree in the systematic relationship of the species. A num- 

 ber of factors which contribute to this resemblance can at once be 

 distinguished. 



1. The general character of the trees, with their arched roots, 

 swollen bases, and straight stems almost devoid of branches to a 

 great height. 



1 Some of the species here enumerated belong properly to marsh associations, and 

 will be mentioned in that connection. 



