APETALiE 263 



three species, which are cosmopolitan in range, found 

 in Europe, Asia, Africa, Arctic North America. 



Bentham and Hooker include Ceratophyllum in the 

 Order Callitrichacese. It differs from the Halorag- 

 aceae in possessing no perianth. By Warming the 

 group is placed in the Ranales, a cohort including 

 Ranunculus,* which the Hornworts resemble in habit 

 and foliage, but the floral structure is entirely dissimi- 

 lar, though the several perianth-leaves and one free 

 carpel suggest aflinity with Nymphaeaceae. WilHs 

 remarks that as in highly adapted aquatic plants the 

 position of the group is uncertain. 



There are two British species, of which one is 

 described. 



Being aquatic in habit the Hornworts are limp, 

 submerged plants with a slender stem. The stems 

 are cylindrical, branched, and weak when withdrawn 

 from the water, as in other water-plants, falling over 

 when held erect. The leaves are in whorls, stalkless, 

 and possess no stipules. They are forked, and 

 divided into narrow linear segments. 



The flowers are solitary, borne in the axils, very 

 small. The plant is monoecious. The flowers are 

 enclosed in a persistent involucre with awl-like lobes, 

 eight- to twelve-partite. There is no perianth. In 

 the male flowers the anthers, which are numerous, 

 are close together, and have no filaments, being 

 oblong. The cells, which are linear, are embedded 

 in a fleshy, blunt, toothed connective. The anthers 



* I.e., the heterophyllous and narrow-leaved aquatic species. 



