of Mississippi and Louisiana 69 



I 



which grow in this habitat are therefore exposed to the danger of 

 wave action, as well as that of the wind. Their roots are of course 

 in strictly saline conditions. There is little or no movement of the 

 substratum due to the effect of the wind, at least in ordinary times, 

 inasmuch as the sand is compacted by the water of capillarity. 



Here as elsewhere according to the studies of Macmillan, 

 Cowles, Kearney, and others in this country, the beach formation 

 is readily divided into three main zones, namely the lower, middle 

 and upper beaches. As the tides are here quite slight the lower 

 beach is narrow as compared to that in most maritime regions. 

 Vegetation is either entirely absent, or there may be at most a 

 meagre and inconstant algal association. The middle beach (mid- 

 strand) is relatively broad and the physiological conditions are ex- 

 tremely unfavorable on account of the above-mentioned saline soil 

 conditions and on account also of the intense light and heat aggra- 

 vated by the strongly reflecting surface of the sand. The plant 

 covering is very sparse consisting of succulent annuals of the ces- 

 pitose and radiant habit of growth. Two zones are distinguishable, 

 an outer, seaward zone occupied chiefly by cespitose forms such as 

 Dondia linearis, Cakile fasifonnis and Salsola Kali, with the grass 

 tnchrus megacephalus which grows nowhere else. Towards the 

 u pper limit of this zone the radiant form Sesuvium portidacastrum is 

 e ' ou nd, but no such massing of this plant such as was seen by 

 Boergesen and Paulsen in the Danish Anti les has been observed. 

 '-ragrostis secnndaeftora, is also a beach plant and responds to the 

 >gh humidity of the region after the manner of some other grasses 

 \ oa alpma, e. g.) to similar conditions, by becoming strongly pro- 

 rous. The inner, landward zone is characterized by a growth of 

 pomoea Pes-caprae* I. acetosaefolia, Strophostyles /uivola and some- 

 times Canavalia obtusaefolia. These, with the exception of Stropho- 

 *tyles t are preeminently tropical strand plants whose ecological 

 features have been described by Warming, Schimper, and others. 

 AU of these three forms reduced the layer of over-insolation by 

 bringing the leaf's surface into a vertical position, Ipomoea Pes- 

 caprae by folding the leaf at the midrib, /. acetosaefolia by folding 



life 



Stems *,f immature plants 30 meters long, were found. Dr. H. J. Webber tells 

 me (F- E. [..) that he has measured stern- nearly four times this length on the Florida 



coast. 



