386 THE STORY OF PLANT LIFE 



and is submerged. The stem is slender, regularly 

 but sparingly branched from near the base, with 

 tooth-like wings at intervals. 



The leaves are opposite, linear, strongly spinous, 

 toothed, ternate, with a narrow blade, with rounded 

 entire or sub-entire sheaths. The upper internodes 

 and backs of the leaves may be spinous. 



The plant is dioecious. The flowers are solitary. 

 The male flowers are enclosed in a membranous sac- 

 like spathe, and possess a single anther, terminal on 

 the axis, one- or four-locular, enclosed in two sheath- 

 ing perianths. The female flowers consist of a single 

 ovary with one carpel, which is naked or surrounded 

 by a perianth-like structure. There are three 

 stigmas. The fruit is a drupe, ellipsoid, succulent 

 or ovoid, and narrowed into the short, persistent 

 style. The seed is ovoid. There is a single ovule, 

 anatropous, terminal. There is no endosperm. The 

 embryo is straight. 



In height the plant is 3 to 9 in. It flowers in July 

 and August and is a herbaceous perennial. 



Being a dioecious plant, pollination must be effected 

 by outside agency. This is carried out by the agency 

 of water as in Zostera, but the pollen is not thread- 

 like, but spherical or oblong, as in Zannichellia. 



The fruit, a \ in. long, is dispersed by the agency 

 of water. 



Naias marina. — In Fig. 108 note the opposite 

 spinous leaves with fairly long internodes. 



