Marsh Societies 



347 



have been little studied. There is hardly any situation 

 where the fauna is so imperfectly known. 



As compared with the land, fauna and flora of 

 marshes are characterized by a small number of species, 

 and enormous numbers of individuals. In other words, 



Fig. 205. "Tree-swallow pond": a once famous collecting ground in the 

 Renwick marshes at Ithaca. Photo taken in spring after the burning and 

 the freezing and the floods, but before the growth of the season. 



the population is one of small variety but of great den- 

 sity. Such forms as are fitted to maintain themselves 

 where floods and fire alternately run riot find in the rich 

 soil and abundant light and moisture opportunity for a 

 great development. Fire sweeps the surface clear of 

 trees, which would overtop and overshadow the 

 herbage and would create swamp conditions. The 

 ground layer of water-soaked trash prevents the burn- 



