276 THE PLANT COVERING OF OCRACOKE ISLAND. 



ADAPTATIONS TO THE MECHANICAL ACTION OF THE WIND AND 

 THE INSTABILITY OF THE SOIL. 



A notable characteristic of the vegetation is the prevalence of low 

 forms. Tall stems (more than 1 meter high) among herbaceous species 

 which are not grass-like, are almost wanting. Often the stems creep 

 above or below the surface of the ground and root at intervals. 



Lippia nodiflora, Monniera monniera, Capriola dactylon, and Pr/.s- 

 paliim disfichum have stems creeping upon the surface. These may 

 be regarded as humble representatives of the Pes-caprae form, which 

 is so characteristic of tropical strands.^ Species possessing creeping 

 subterranean stems, from which arise subaerial leaf}^ and flowering 

 branches, are Panicum amarum minus and Uniola p>aniculata, as well 

 as many of the salt-marsh plants, notably Juncus roemerianus, Typlw 

 Jafifolia, and Spartina stricta, whose strong, creeping rhizomes form a 

 dense sod in the loose mud. In Uniola paniculat a the rootstock is stout 

 and descends obliquely or almost vertically deep into the sand. 

 Pliy sails viscosa has a long, slender, branching root, Avhich creeps 

 horizontally often a distance of a meter or more near the surface, and 

 originates at intervals erect, leaf 3^ and flowering branches. Teucriurn 

 nasliii i)ossesses thickish stolons, which arise in the axils of the scale- 

 like, lowest leaves. 



Other species growing on the sands have prostrate stem branches, 

 which do not root after leaving the main axis. These may be long and 

 trailing, as in the woody Rubus trivialis, or short and radiating in all 

 directions from the primary axis as in certain annuals, Diodia teres, D. 

 virginiana, Jlollugo verticillata, and Eupliorhia polygon if olia, as well 

 as the biennial Oenothera humifusa. This radiant form,^ as we may 

 term it, is not so abundant and characteristic here as at other points 

 along the Atlantic coast of the United States. 



The cespitose form is apparentlj^ not well adapted to conditions 

 upon Ocracoke, for it is well developed only in Mulilenhergia filipes. 



The shrubs and trees of the island show the effect of much exposure 

 to high wind in their short gnarled branches and in the often one- 

 sided position of their crown of foliage, the last peculiarity being 

 especially noticeable in the live oak. Here, however, w^e have to do 

 rather with the direct mechanical effect of the wind than with a pro- 

 tective modification. 



As further adaptations against the coast winds, whose destructive- 

 ness to tender vegetation must be greatly increased by the quantity 

 of sand they carry, should be cited the great development of mechan- 

 ical tissue in the leaves of many species — e. g., Uniola panicuUda, 

 Juncus Toemerianus, Quercus virginiana — and the strong thickening 

 of the outer cell walls of, the epidermis, to which is due the hard pol- 



' Schimper, Indo-Mal. Strand-flora, p. 78. 



■' Schimper (Strand-flora, p. 81 ) describes this form as occurring in the East Iiidian 

 strand vegetation. ; t:^'^>. ^ .»^. 



