348 Annals of the Carnegie Museum. 



promiscuously over much of this area, many of them forming dunes 

 which appear to be fragments of former ridges. Behind the remains 

 of the Pier of 1839 are three steep Populus dunes which are at least 

 thirty feet high, and which now support the Andropogoii dune-forma- 

 tion. On one trip Morchella esailenta was found to bejquite abundant 

 between the clumps of grass on the dunes. 



The Lagoon-Marsh-Thicket- Forest Succession. 



In the discussion of the conditions under which a Populus dune- 

 formation may be instituted, it was stated that in the southeastern 

 portion of the sand-plain, where the lagoons are less exposed to drift- 

 ing sand, there is likely to be no dune-formation, but that the Populus- 

 Salix formation constitutes the initial stage of a marsh-succession. 



The Populus-SaUx Formation. 



Perhaps no distinction should be made between the initial stages of 

 the Populus dune-succession and the Populus-Salix formation of the 

 lagoon-succession. At the very first they appear to be identical, but 

 the environment of the dune changes so rapidly with the growth of 

 the dune, and the Salix plays relatively so unimportant a part in the 

 formation, that it has seemed best to here recognize two formations. 

 By so doing confusion of the two habitats is also avoided. 



In the lagoon succession there is a remarkable gradual interpola- 

 tion of successively later formations, each forming at the time of 

 its appearance an inner ring or zone around the edges of the lagoon 

 (or pond). Thus, in the structure of the lagoon-formations, zonation, 

 and not alternation, as in the Panicum- Artemisia formation, is the 

 usual method of disposition of the component parts. Some ecological 

 workers will probably take exception to the large number of vegeta- 

 tional structures, which we have here given the rank of formations, 

 but the abrupt dissimilarity in the systematic classification and in the 

 structural adaptations of the plants of adjacent zones combine to make 

 the ecotones very distinct, indeed, and, considering the differences in 

 the ecological conditions of the habitat, there appear to be good 

 reasons for the recognition of a considerable number of zoned 

 formations. 



The accumulation of drifting sand about the banks of a lagoon is 

 usually so rapid that in a few years the surface of the soil in the 

 Populus-Salix zone has been brought up to the general level of the sur- 



