488 BOTANICAL GAZETTE [june 



are subject to occasional dry seasons and frequent deposit of sand. 

 The presence of the mosses soon leads to accumulation of humus 

 over the sandy bottom and initiates the growth of semihydrophytes. 



In the lagoon region is a far more extensive pond area, both 

 as to actual number of ponds and variation in ecological develop- 

 ment, caused by depth and size as well as by age of the individual 

 lagoons. The chance for transfer of mosses from one pond to 

 another is much better; the variation in depth permits the growth 

 both of floating and fixed species, while the greater age has allowed 

 time for accumulation of more humus, which leads to the introduc- 

 tion of still other species, as well as perhaps a more luxuriant 

 growth of all. With these conditions comes the rapid advance of 

 the shrub and forest or prairie successions. In the swamp forest 

 the moss flora becomes increasingly a dominant factor in humus 

 accumulation as the ecological succession advances toward the 

 climax, but begins to decline with the close approach of the beech- 

 maple association. This appears to be a result both of competi- 

 tion with other ground flora and of the smaller supply of available 

 water near the surface. 



Very little work has been done in determining conditions for 

 plant life in the bogs, but from the xerophytic structures of many 

 bog plants, and the shallow root systems of the trees, Cowles 

 concludes that, while moisture is plentiful, the chemical content 

 of the water is such as to have a toxic effect upon the root develop- 

 ment of plants, and to prevent absorption of water to a great 

 extent. In other words, this is a physiologically xerophytic habitat 

 for seed plants. It is not known how far this may influence the 

 development of mosses; that it is not very injurious is proved by 

 the great abundance of some species, such as Sphagnum. On the 

 sedge mat the shade may be considerable when cat-tails are 

 abundant, but the sun's rays reach the ground more directly than 

 irt the forest. The humidity near the ground is probably greater 

 than among the trees, but evaporation at times is also much greater. 

 The mosses occupy the small spaces around the roots of the fen 

 plants and often cling closely to them, forming a packing between 

 the stems, but there are no large masses. In some places there is 

 a luxuriant growth of marsh forget-me-not and other species of 



