HIGHER PLANTS 



straw and swamp milkweeds in the marshes. Like arrow- 

 heads they readily adapt themselves to land life. They are 

 I to 3 feet high, and bear strongly veined leaves with long 

 petioles which grow from the root. The 3-petaled white or 

 pinkish flowers are very small, hardly more conspicuous than 

 their branching stems. 



When seedling water-plantains are set in pots of earth sub- 

 merged in shallow water, and kept growing there for a couple 

 of months, they will develop into typical water plants, with 

 some floating leaves and others which are narrow and ribbony 

 like those of fresh water eel-grass (p. 80). 



Occurrence. — On shores and in shallow water, in muddy 

 ditches and swamps. Blooms July-August. Common 

 throughout the United States. 



Animal associates. — Adult syrphus flies which feed on its 

 pollen (p. 299) are its most frequent visitors. 



Water-weeds and Eel-grass — Hydrocharitacece 



Water-weed, Elodea canadensis. — Elodea, or Philotria 

 (Fig. 65), is a true aquatic, loosely rooted on the bottom or 

 floating free in the water, entirely submerged, and growing 

 so successfully in water that solid beds of it fill many ponds 

 and slow streams. Its branches are crowded with dark green, 

 translucent leaves arranged in whorls of three or more. They 

 have a single, central vein, and are so thin that they become 

 transparent and papery with very little exposure to the air. 

 Stems of Elodea are brittle and whenever broken the frag- 

 ments continue to grow independently, rapidly increasing 

 the number of plants. The flowers are inconspicuous; in 

 one species the female ones are borne on very long stems 

 which reach up to the surface of the water; while the short- 

 stemmed male flowers form low on the same plants but break 

 off and rise to the surface, where they meet the female flowers. 



Elodea is a beautiful water plant but it spreads with amaz- 

 ing rapidity and crowds out other plants. English botanies 



79 



