484 



RE LA TION TO ENVIRONMENT. 



water even where rainfall is abundant. The same may be said 

 of the sand dunes farther back from the shore. The plants 

 of these areas are then usually xerophytes. Some of the plants 

 accustomed to growing in such localities are American sea-roclcet, 

 seaside spurge, bugseed, sea-blite, sea-purslane, the sand- 

 cherry, dwarf willow, marram-grass, certain species of beard- 

 grass, etc. 3d. Rocky shores or areas. Here lichens and mosses 

 first grow, later to be followed by herbs, grasses, .shrubs, and 

 trees, as deca\ed plant remains accumulate in the rock crevices. 

 4th. Shores oj ponds, or swamp moors. Here the vegetation 

 often takes on a zonal arrangement if the ground gradually 

 slopes to the shore and out into the pond. In Fig, 493 is shown 



FW- 403- 

 Macrnphytes in tliu upptr ZDiie of the photic rep:ion. Ascophvllum and Fucus 

 at low tide. Hunter's Island, New York City. (PhotoRraph by Si. A. Howe.) 



zonal distribution of |)]anls. 'Fhe different kinds of plants are 

 drawn into these zones 1)y the \-ar)iiig amount of ground water 

 in the soil, or the var\-ing deplh of llie water on the margin of 

 the pond as ime jirocceds from the land towards the dcei)er 

 water. ( )n the liorder lines (ir tension lines between the different 

 zones tlie plants are siniggliiig to <)ccii|)v liere groiin<l which is 

 suitable for each adjacent iii(li\i(lual formation. ( )ther edapliic 

 societies are those of marl ponds, alkaline areas, oases in deserts, 



