KEY TO FAMILIES xxxi 



(m) Some or all of the leaves sub- 

 merged NAIADACEAE 301 

 (n) Leaves usually aerial, occasion- 

 ally floating 

 r. Flowers in terminal cylindric 



spikes TYPHACEAE 300 



s. Flowers in lateral heads SPARGANIACEAE 301 



n. Leaves netted-veined CALLITRICHACEAE 47 



