VEGETATION OF THE BAND STRAND. 367 



mucilaginous slime in the cells of the water tissue, which greedily 

 absorbs and tenaciously retains much water. 1 



(/) Presence of a considerable quantity of mineral salts, especially 

 sodium chloride, in solution in the cell sap. It is well known that the 

 rapidity of evaporation from a given liquid surface decreases in pro- 

 portion to the density of the liquid. Consequently a plant organ 

 which holds in its cells more than the ordinary quantity of dissolved 

 mineral substances loses by transpiration less than the ordinary 

 amount of vapor of water. We have here another instance of the 

 fact that while the presence of much salt in the soil is generally 

 regarded as a circumstance wholly adverse to plant life, certain spe- 

 cies are able to use this substance in such a way as to neutralize its 

 own injurious action. 



(j) Development of compact palisade tissue, usually on both sur- 

 faces of the (in such cases) isolateral leaf, in nearly all the species. 



4. Adaptations to exposure to the mechanical action of the wind. 

 The most noteworthy are (a) the prevailing biological form, i. e., the 

 grassdike, which offer little resistance; and (It) 1 he development of 

 considerable mechanical tissue 1 , notably in the grass-like monocotyle- 

 dons, where this sometimes takes the form of strong peripheral groups 

 of stereome (i. e., in the stem and leaves of Juncus roemerianus). 



Specialized modifications for dissemination of the seeds are not 

 numerous in the salt-marsh plants. The glumes of species of Spartina 

 appear to be fitted to some extent to float upon the water, as is the 

 fruit ing calyx of Salicornia, with its spongy thickening. The bristles 

 of Typha, the callus hairs of Phragmites, and the bristly pappus of 

 the Asters, Solidago, and Paccharis, are of course adapted to carriage 

 by the wind. Burs, winged fruits, and edible fruits appear to be 

 almost entirely wanting. 



SAND-STRAND FORM ATIONS. 



In Virginia, as in other parts of the world, the well-marked topo- 

 graphical division known as the sand strand is occupied by a sparse 

 vegetation, in open formation,!, e., the individual plants mostly grow 

 far enough apart to leave much of Uw soil visible among them. For 

 this reason the strand sand contains an unusually small amount of un- 

 derground parts of plants, and is consequently the more easily blown 

 about by the wind. In the Dismal Swamp region this format ion com- 

 prises three rather clearly defined belts. These are: (1) the beach 



1 Compare Volkens. Flora der Agyptisch-Arabischen Wuste. p. 4.'5. 1887. It has 

 been suggested (Uassart, Mem. Soc. Roy. Bot.de Be~gique, 82, pt. 1. pp. 18, 19. 

 1833.) that the frequency of succulent plants among tbe salt-marsb vegetation is 

 due to the fact that such plants obtain most of tneir water, not when the soil is 

 covered with salt water at high tide, but when rain falls during the ebb. If this 

 could be demonstrated, the necessity for tissue adapted to holding water for con- 

 siderable and indefinite periods would be evident. 



