PROVISIONS FOR CONSERVING WATER. 281 



taken up and described in sj-stematic order. Tables sliowini,^ wlial 

 are believed to be the characters that are most iinportanl from an 

 ecological point of view have been prepared for tlie two <^m-()iii)s of 

 species. For a nnmber of species the material studied was not 

 obtained npon Ocracoke Island, but from simihir situations on the 

 coast of Virginia, and in all such cases tlie source of tlie spefim«Mis 

 used is mentioned. In some cases comparisons are made with rehited 

 species, usually from other formations, in order to make clear the 

 differential characters of the strand species. 



In a great majority of the sand strand plants the leaf is bifacial, 

 the two species of Yucca being the only exceptions noted. In some 

 species this specialization is imperfect, as in Oenothera humifusd. \n 

 other cases the differentiation of the two sides of the leaf is com- 

 plete, as in Quercus virginiana. In most cases the leaf is thick as 

 com]3ared with the same organ in related nonmaritime species. Good 

 examples are the evergreen, leather}^ leaves of Quercus virfjiniana 

 and Ilex romltoria, as well as the leaves of the two grasses, Uniola 

 paniculaia and Panicuin amarum. A stronglj^ thickened cuticle is 

 . an almost invariable character, and this is conspicuously wrinkled in 

 a few species. The lateral walls of the epidermis cells are undulate 

 in four species, viz, the comparatively thin-leaved Cliloris petraea, 

 Teucrium iiasliii, and Phy sails viscosa, and tlie thick-leaved Ilex 

 vomit or la. 



Half of the species have stomata on both leaf surfaces, but in every 

 such case they are especially protected — in the grasses by being sit- 

 uated in furrows; in the species of Yucca by being deeply sunken, 

 and in Physalis, Oenothera, and Croton b}' a covering of hairs. In 

 the wood}^ species they are always on the dorsal or lower surface only, 

 and in Quercus virginiana they are further protected by a hairy cov- 

 ering (as also in the herbaceous Teucrium nashll). 



Hairs form a dense, i)rotective covering on both leaf sui-faecs of 

 Oenothera, Croton, and Physalis, which species have stomata on both 

 surfaces: only on the dorsal surface in Quercus and Teucrium, agree- 

 ing with the i^osition of the stomata on that surface only. In Quercus 

 and Croton the hairs are pluricellular and stellate; in Physalis iIh.n 

 are irregularly branched; in Oenothera and Teucrium they are elon- 

 gated, unbranched, and unicellular. Teucrium also possesses slioi-t, 

 glandular, cai)itate hairs. 



The chloroi3h3dl tissue is homogeneous in the monocotyledons of 

 the sand strand, while in the dicotyledons it is more or less difTereii- 

 tiated into palisade on the ventral side of the leaf and pneumatic 

 tissue on the dorsal side. The palisade is mostly quite compact, but 

 never of more than 3 and usually of only 1 or 2 layers. 



Colorless parenchyma, which probably performs the function of 

 water-storage tissue, occurs in consideral)le quantity only in the 

 grasses and the species of Yucca. 



