530 



A TEXTBOOK OF BOTANY 



fCH. XIII 



like leaves, and stilt roots. Here belong also the Cat-tails 

 (Typhacece) of our marshes, with erect sword-shaped leaves 



and superposed 

 spikes of stami- 

 nate and pistil- 

 late flowers, of 

 which the slender 

 ovaries with ac- 

 companying hairs 

 form the familiar 

 " tails." 



Order 2. Nai- 

 ad ales (Helo- 

 bi&): Water- 

 weeds. About 

 100 species, near- 

 ly all small herbs 

 growing in wet 

 places, or sub- 

 merged in the 

 manner of true hydrophytes. The simple flowers are chiefly 

 pollinated by wind or water movements, and the seeds are dis- 

 seminated by water currents. 

 They include the Pondweeds 

 (Potamogeton, Fig. 372) most 

 common of the larger water- 

 weeds of fresh waters, the Eel- lodicules 

 grasses, Zostera and Vallisneria 

 (Fig. 196), with the Water Plan- 

 tain (Alisma), and Arrow-head 

 (Sagittaria) of stream margins. 



Order 3. Graminales (Glu- 

 miflorm) : Grasses and Sedges. 

 About 8000 species in a sharply 

 defined group, of uncertain 



Fig. 372 



- Potamogeton crispus; 

 (From Kerner.) 



STERILE FLOWERS 



FLOWERING 

 GLUME 



OUTER GLUMES 



Fig. 373. — A diagram showing 

 the construction of the highly- 

 specialized Grass flower. (From 

 Cavers.) 



