ZONAL DISTRIBUTION OF PLANTS. 



407 



overhanging willows. On the left, pond-weeds (Potamogeton 

 natans) and the yellow water lily, or spatter-dock (nuphar), 



Fig. 500. 

 Yellow water lily on jutting arm in stream. (Photograph by the author.) 



float their leaves and flowers on the quiet water, while the small 

 yellow flowers of the mud plantain ( Heteranthera graminifolia) 

 glitter in the sunlight. The arrow-leaf (Sagittaria heterophylla, 



