THE ECOLOGY OF PLANTS. 



451 



the southern end ; (c) a zone of Bur-reed (Sparyanium) also mixed 

 with Water Plantain ; (d) a central patch of Pondweed (Potamogeton 

 natans). 



The Pondweed lies in the centre towards the northern end ; its 

 leaves were large, and with long leaf-stalks, such as occur in deep 



Water Plantain. 



- Water Dropwort. 



Tall Rushea 



Fig. 183. Zones of Vegetation in a Pond. 



water. From this we suspect that the Pondweed occupies the deepest 

 part of the pond. In consequence of the excentric position of the 

 Pondweed, the zones of Bur-reed and Dropwort are narrow at the 

 northern end, but they are sharply defined. Towards the southern 

 end both plants lose their zonal arrangement, and form masses 



