338 COMMON WEEDS 



many barren branches, elliptical floating leaves and 

 narrow lanceolate submerged leaves. The stem of the 

 flower spike is thicker in the upper part than in the 

 lower. The following species have submerged leaves 

 only : 



P. lucens L. is common in deeper ponds, lakes, and 

 canals. The leaves are 4 to 10 inches long, ovate or 

 lanceolate, and translucent. 



P. perfoliatus L. is a smaller species, with round stems 

 and translucent ovate leaves i to 3 inches long, which 

 clasp round the stems. 



P. crispus L. (Fig. 98) has long flattened stems, on 

 which are arranged, usually in two opposite rows, 

 somewhat narrow oblong leaves i to 3 inches long, the 

 margins of which are crisped or wavy. 



P. densus L. has opposite elliptic-lanceolate short 

 leaves, J to i inch long, arranged very closely together 

 in two rows on the brittle stems. It is sometimes a 

 nuisance to growers of watercress. 



P. pusillus L. is a smaller submerged species, with 

 thin stems, and very narrow acute leaves. 



CYPERACE^: 



This order includes a large number of species of 

 plants, many of which are common inhabitants of river- 

 banks, lakes, ditches, and marshy places, and usually 

 spoken of as Rushes and Sedges. One or two only need 

 be mentioned here. 



Bulrush, Club-rush (Scirpus lacustris L.) is often met 

 with in shallow water on the edges of ponds and slow- 

 moving streams. It has an extensive creeping root- 

 stock, tall green stems, usually leafless, 4 to 6 feet high, 

 and \ to | of an inch thick, with a spongy interior. 

 Occasionally in running water flat floating leaves are 



