Water 



331 



Fig. 14 5. A species of Myriophyllum, an "amphibious" plant, showing differences be- 

 tween leaves grown in water and in air. ( From Fassett. ) 



whereas the submersed ones are much dissected (Fig. 14-5). Potamogeton 

 and similar forms are entirely aquatic but in some species there are 

 both broad floating leaves, exposed on their upper surfaces to the air, and 

 delicate submersed ones. 



Various explanations have been proposed (p. 216) for the differencs 



