374 THE STORY OF PLANT LIFE 



broad thick wings. The seeds are erect, with a hooked 

 embryo, shining, not wetted by water. 



In height Arrow-head varies from 6 to i8 in. It 

 flowers from July to September, and is a herbaceous 

 perenniah 



No honey is secreted by the flowers, which, how- 

 ever, have numerous stamens, and are pollen flowers. 

 Being conspicuous they may be much visited by 

 insects, a necessity for monoecious plants. 



As the seeds are not wetted when they fall into 

 the water, they are water-dispersed. 



Adder's Tongue, Water Archer, are the only other 

 names. 



Sagittaria sag itti folia. — The illustration {Fig. 

 104) shows the habitat of the plant , which grows in the 

 reed swamp, or is half -submerged. The sagittate leaves 

 and long petioles are readily discernible. 



87. The Pondweed Group. 

 In the Order Naiadaceas, as defined by Bentham 

 and Hooker, representatives of other orders now 

 recognised are included, as Potamogetonaceae, 

 Naiadacese, Aponogetonacese * (not British), and 

 Juncaginaceae. They make, however, five tribes : 

 Juncaginacese, including Triglochin, Scheuchzeria; 

 Potameae, including Potamogeton and Ruppia; Zanni- 

 chelliese, including Zannichellia; Zostereae, including 

 Zostera ; and Naiadeae, including Naias. A type of 

 each of these tribes is described hereafter. 



* A species has recently been found in Great Britain. 



