Fig. 161. Eel grass {Yallisneria)^ a common pondweed plant. The plants are 

 ancliored and the foliage is submerged. The carpel-bearing flowers are carried to 

 the surface on long stalks which allow a variable depth of water. The stamen- 

 bearing flowers remain submerged, as indicated near the lower left corner, the 

 flowers breaking away and rising to the surface, where they float and effect pollina- 

 tinn.— After Keener. 



