PLATE IV 



a) A semi-permanent pond in Oxfordshire (permanent except in drought years, 

 when it dries up completely). Various successive zones of aquatic and 

 marsh plants lead finally to grazed grassland on the right, and to elm 

 trees on the left. 



{d) Zonation of habitats on the sea-shore at low tide of Norway (Svolvaer), 

 showing gradation from sea to land, through seaweeds [Fuci/s, etc.), 

 drift-line, shingle, rocks, up to pasture or birchwoods. 



