276 THE TLANT COVERING OF OCRACOKE ISLAND. 



ADAPTATIONS TO THE MECHANICAL ACTION OF THE WIND AND 

 THE INSTABILITY OP 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. 



IAppia nodiflora, Monniera monniera, Capriola dactylon, and Pas- 

 pedum distichum 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. 1 Species possessing creeping 

 subterranean stems, from which arise subaerial leafy and flowering 

 brunches, are Panicum amarum rninua and Uniola paniculaia, as well 

 as many of the salt-marsh plants, notably Juncusroemerianvs, Typha 

 Jati folia, and Spartina striata, whose strong, creeping rhizomes form a 

 dense sod in the loose mud. In Un iolapaniculata the rootstock is stout 

 and descends obliquely or almost vertically deep into the sand. 

 Physalis viscosa has a long, slender, branching root, which creeps 

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

 originates at intervals erect, leafy and flowering branches. Teucrium 

 nashii possesses Hiickish stolons, which arise in the axils of the scale- 

 like, lowest leaves. 



Other species growing on the sands have prostrate 1 stem branches, 

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

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

 direct ions from t he primary axis as in certain annuals, Diodia teres, />. 

 virginiana, Molhujo vert ic ilia ta, and Euphorbia poly gonifolia, as well 

 as the biennial Oenothera humifusa. This radiant form, 2 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 apparently not well adapted to conditions 

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



The shrubs and trees of tin 1 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, we, 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 paniculata, 

 JuriQUS roemerianus, Quereus virginiana — and the strong thickening 

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



'Sehimper, Indo-Mal. Strand-flora, p. TS. 



- Schimper (Strand- flora, p. S] ) describes this form as occurring in the East Indian 

 strand vegetation. 



