200 



EDGAR NELSON TRANSEAU 



THE LOWER BEACH 



The strand between the summer tidal limits Schimper has 

 designated the "emerging beach." Under another system of 

 classification than the physiographic this would be a capital term 

 for this habitat. The semidiurnal change of the medium sur- 

 rounding the plants, is its most striking characteristic. This 

 change may involve not only sea water and air but also fresh water 

 derived from rain, beach springs, and streams. It also involves 

 certain other factors, alternation of strong and weak light, rapid 

 changes of temperature, variations in the concentration of the 

 medium from zero to the degree where crystallization takes place, 

 and exposure to t^he full action of the waves at some part of everj' 

 cycle. It should also be noted that the time of submergence and 

 emergence vary as we go from the low tide line to the line of the 

 highest tides. • At extreme low tide the plants are subjected to the 

 dangers of evaporation and dessication only at infrequent intervals 

 and for a short time. At the high tide line there is almost con- 

 stant exposure to the atmosphere. Between these two extremes 

 the variation is not regular but depends upon the peculiarities of 

 the tidal flow. All of these influences determine in just what part 

 of the beach a particular plant may be able to maintain itself. 



The lower beach habitats are continuations of those of the sub- 

 merged beach. The portions of the latter which failed to develop 

 the larger algae because of their instability are continued upward 

 into areas of like character, and they are again free of all forms but 

 the microscopic. 



THE EXPOSED LOWER BEACH 



The Rockweed Formation. This is one of the most conscipu- 

 ous features of all northern coasts. Reaching its maximum devel- 

 opment a short distance above low tide, it shades below into the 

 Chondrus Association and the Eel Grass Formation, and abo\'e 

 in protected situations it passes over to the Salt Marsh Formation. 

 Where it occurs on exposed shores near the Sound it extends but 

 a short distance above the low tide line. In the inner harbors on 

 rocks and sea walls it extends well up toward the neap high tide 



