g2 SEA AND LAND 



the sea to the crown wliich lloats at the surface of the water, 

 and llie phmt may have the length of one thousand feet or 

 more. Remarkaljle as is this structure, it is lowly organized, 

 and does not deserve to be compared with our more highly 

 developed land plants, which, in every feature by which we 

 measure superiority, are far above their kindred of the sea. 

 Although the deeper parts of the seas lack vegetation, the 

 shore belt within the depth of a few score feet abounds in 

 such forms, except, indeed, where the bottom is too sandy to 

 afford them foothold. In this littoral zone, besides the host 

 of forms of lowly organization, the ancestors of which have 

 never been, so far as we know% occupants of the land, there 

 are many species which have adapted themselves by curious 

 transformations of structure and habit, so that they have been 

 able to work down from the dry realni into the sea. Along 

 the high tide line we tind sundry species which have overcome 

 the destructive effect which salt water has on the roots of 

 most land plants. Farther down on the marshes other species 

 have extended their experience so that they can live, provided 

 their upper parts are bared at high tide. Yet deeper there 

 are other forms, such as the eelgrass, which can perform all 

 their functions and flourish greatly, though they are altogether 

 within the water. One or two groups of trees, of which the 

 species of mangrove are the most important, have become 

 specially modified, so that they may make head against the 

 sea in embayed waters even where they are miles in width, 

 gradually extending the margins of the forests over the shal- 

 lows to the border of the deep waters. In Florida some 

 hundred thousand acres have thus been won from the sea, and 

 in the more tropical areas the gain of the land which is thus 

 brought about is of yet greater importance. 



