WEEDS OF PONDS, RIVERS, DITCHES 333 



by blocking up canals and streams. River and canal 

 navigation is impeded by its presence, and it seriously 

 interferes with angling in lakes and slow-moving rivers. 



In certain seasons it becomes rampant, spreading its 

 long tangled stems through the water in all directions. 

 For a period of three or four years afterwards it 

 frequently dies down, probably owing to exhaustion of 

 the nutritive materials of the mud and water, and then 

 is only seen as a green carpet on the bed of the lake 

 or stream. (See also p. 327.) 



It is a nutritious green food for horses and cattle 

 when fresh. 



IRIDACE^E 



Flag or Yellow Iris (Iris Pseud-acorns L.). This well- 

 known, handsome plant, with its large yellow flowers, 

 is common in wet ditches and by the margins of 

 streams and lakes where the water is not more than 

 12 to 1 8 inches deep. It has stout, creeping root- 

 stocks on the mud below, and from them are sent up 

 round stems and sword-shaped leaves. The flowers 

 appear usually from June to August. The plant is 

 propagated by means of its rootstock and its flat seeds, 

 which are produced in numbers in large three-celled 

 capsules. 



TYPHACE.E 



Bur-reed (Sparganium ramosum Huds.) is a fre- 

 quent inhabitant of ditches and the banks of ponds 

 and rivers. The erect stems rise to a height of about 

 2 feet, and bear long, narrow leaves (2 to 3 feet long 

 and about J to i inch broad) three-angled at their 

 base. The flowering stem is branched, and the uni- 

 sexual flowers are arranged in round heads, or " burs," 

 about an inch in diameter. 



