III.] 



NAIADACEM. 



333 



A common annual weed in swamps and rice-fields, with 

 radical, cordate leaves, and erect scapes, bearing one to 

 three loose verticils of small, white, polygamous flowers. 



The lower flowers of the inflorescence are usually female. 

 In the allied S. sagittcefolia^ with arrow-head leaves, the male 

 flowers have numerous stamens. 



Fig. 214. Longitudinal section of 

 achene of A lisma. 



Fig. 215. Embryo of same removed 

 from the seed. 



The Water Plantains represent the Ranunculus Family 

 amongst Monocotyledons, having the pistil nearly or wholly 

 apocarpous, and hypogynous stamens. They differ widely 

 in their embryo, as well as in other points of structure. 



114. Natural Order, Naiadacece. — The Pondweed Family. 



Floating or submerged plants. Perianth o, or four-leaved. 

 Pistil apocarpous. 



Type — Common Pondweed {Potamogeto7i natans). 



An aquatic herb, with floating, opaque, oblong 01 ellip- 



